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PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and of developments in their application in industry

VOL. 35 JULY 1991

Contents

Homogeneous Palladium(I1) Mediated Oxidation of Methane

Platinum 1991

Enhanced Oxidation Resistance

Platinum Media for Data Storage

The Platinum Market in 1990

Iridium Oxide Device for Coulombic Titrations

Permeation of Hydrogen through Palladium-Silver Membranes

Protecting Rhodium Catalysts

“Palladium; or, New Silver”

Abstracts

New Patents

NO. 3

126

132

133

134

137

137

138

140

141

152

166

Communications shou2d be addressed to The Editor, Platinum Metals Review

Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE

Homogeneous Palladium(1I) Mediated Oxidation of Methane SELECTIVE FUNCTIONALISATION UNDER MILD CONDITIONS

By Ayusman Sen Department of Chemistry, The Pennsylvania State University, Pennsylvania, U.S.A.

A metal catalysed, electrophilic approach to methane oxidation is discussed. This involves the oxidation of methane to the corresponding methyl ester in trijluomacetic acid; the oxidant is hydrogen peroxide and the catalyst is the palladiumflz) ion. The latter species activates methane by the electrophilic cleavage of a C-H bond, and then acts as a two- electron oxidant towards the resultant metal-bound methyl group. The hydrogen peroxide reoxidises palladium(0) back to palladium(ll).

Methane is the most abundant and the least reactive member of the hydrocarbon family. Thus, the selective functionalisation, preferably catalytic, of methane under mild conditions is one of the most challenging chemical problems, in addition to being of great practical importance. Among the various functionalisation possibilities, oxidative functionalisation is of special interest, since several commercially important organic chemicals (methanol, formaldehyde and formic acid) are nominally related to methane through oxidation steps.

The number of reported methods for the selective, low temperature (at about 100°C or below) functionalisation of methane is very limited indeed. For example, the radical initiated chlorination of methane is very non- selective and invariably leads to multiple chlorinations (1) (chlorination, however, is more specific in the presence of superacids (2)). Among transition metal mediated procedures, the only one that gives good yield involves PtCI,2- catalysed oxidation of methane by PtCl, * - in water at 12OoC, which leads to the formation of equal amounts of methanol and methyl chloride (3).

The oxidative functionalisation of methane through direct reaction with molecular oxygen in homogeneous media at low to moderate

temperatures is not a practical procedure for two principal reasons. The interaction of triplet oxygen with a singlet organic molecule is associated with a high activation energy barrier due to the requirement of a “spin-flip”. In addition, the auto-oxidation of alkanes is usually a chain reaction and is very non-specific in nature (4). In view of the above problems, it is attractive to consider metal mediated pathways for the oxidative functionalisation of methane. One role of the metal would be to stabilise unstable organic intermediates by binding to them. Specifx reaction pathways may be promoted in this manner.

Three basic modes of interaction of a metal with methane may be envisaged. The first involves the metal as a le- oxidant as shown in Equations (i) and (ii), (5).

MN++CH,-H * M(N-l)++CH,- + H+ (i)

MN+=O+CH,-H M(N-’)+-OH+CH,* (ii)

Sometimes, as shown in Equation (ii), an auxiliary ligand on the metal may assist in the le- oxidation step, as is observed with the enzyme cytochrome P,,, (6, 7) and, perhaps, methane mono-oxygenases (8). Unfortunately, the methyl radical thus generated will participate in a multitude of reaction pathways. Only when severe steric restraints are present, as in an enzyme pocket, is any degree of

Platinum Metals Rev,, 1991, 35, (3), 126-132 126

specificity expected. In addition to the problem of reaction specificity, le- oxidation of methane is particularly unfavourable from a thermodynamic standpoint (see Table I) and, therefore, the generation of methyl radicals requires the use of rather strong oxidants and/or high temperatures (9).

The two common modes of interaction of a metal with methane that do not lead to the formation of radicals are oxidative addition, Equa- tion (iii), and electrophilic displacement, Equation (iv). In recent years, Bergman, Graham and others have demonstrated that methane can participate in oxidative addition reactions (10).

MN+ + CHI-H + MN+-CH,- + H+ (iv)

However, a problem associated with this reaction is that the relative weakness of the metal-carbon bond often makes the oxidative addition step thermodynamically unfavourable (11). A common way to circumvent this problem is to generate a high-energy, co- ordinatively unsaturated species (usually by photochemical means) which then reacts, with the CH,-H bond in a “downhill” process. Un- fortunately, the presence of the highly reactive metal species precludes the simultaneous presence of most oxidising reagents capable of functionalising the bound methyl group in the oxidative addition product. Thus, it is difficult to construct a “one pot” catalytic procedure for the oxidative functionalisation of methane that is based on Equation (iii).

The electrophilic displacement (heterolytic cleavage) pathway, Equation (iv) (3, 12, 13), is generally more favourable than the corresponding oxidative addition reaction for two reasons (11). First, the low reactivity of methane vis-A- vis most metal compounds is due, at least in part, to the absence of low-lying unoccupied orbitals. Hence, the transition state often involves the promotion of electrons into antibonding orbitals. Accordingly, the reactivity of methane is expected to be highest towards species having low-lying unoccupied orbitals, - that is to elec-

trophiles. Second, the electrophilic displacement reaction is not as severely limited as is oxidative addition by the thermodynamic constraint associated with the weakness of the M-C bonds, since the driving force for processes such as Equation (iv) can be favourably influenced by the stabilisation of the leaving group, H+. For example, it has been shown that the analogous heterolytic cleavage of H, by metal ions such as Cu2+, Ag+ and Hg2+ is favoured by the presence of bases which serve to stabilise the released H+ ion (14). Moreover, the recent reports of the addition of CH, across a Zr = NR bond may be an example of base assisted heterolytic cleavage of an alkane C-H bond (1 5).

Our general scheme for oxidative functionalisation of methane is outlined in Equation (v) and is based on an initial electrophilic displacement step (12(a), (b)). The 2e- oxidant could be the metal itself or a separate reagent.

MN+ + CH,-H = MN+-CHl- + H+

(v)

Meox Ox = 2e- oxidant, Me,,, = cmidised organic product

If the metal acts both as the electrophile and oxidant, then the above scheme may be modified in the following way, Equation (vi). The overall reaction is shown in Equation (vii). If the final reduced metal species

M” + CHI-H + MN+-CH,- + H +

Nu: - (vi)

I I I f ‘ I

I

L _ _ _ _ _ _ - M(N-2)+ +CHl-Nu + H+

1 [Ox1

0x=2e- oxidant, Nu:- =nucleophile

M“ + CH,-H + H-Nu +

M(N-2)+ + CHI-Nu + 2H+ (vii)

can be reoxidised back (either chemically or electrochemically) then a catalytic cycle would ensue. Note that the steps involved in Equations (v) and (vi) are not totally unprecedented since Shilov and others have reported the following

Platinum Metals Rev., 1991, 35, (3) 127

Table I

Redox Potentials of Hydrocarbons for the RH R - + H' +e Process in Aqueous Solutions (pH = 0) (5a)

(Differences in R . and RH Solvation Energies are Neglected)

RH

CHa C2H6

C3H8 C3H8 i~o-C.Hlo C6H12

C6H6

RH

ROH

CH30H C,H50H n-C3 H, OH i-C 3 H OH t-C, H 9 OH C6HiiOH C6H50H

CH.3

C3H8 C3H8 iso-C,H,O

C2H6

C6H6

C6H5CH3

C6H12

R

CH3

n-C3H7

tert-C,Hg

C 2 H 5

is0 -C H

C 6 H 5

C6H5CH2

C 6 H 1 7

E, volts

-2.25 -1.99 - 1.99 - 1 '84 -1.78 -2.48 - 1.44 - 1.85

reaction sequence, Equation (viii) (3a). A comparison of Tables I and I1 also indicates that the 2e- oxidation of methane is significantly more favourable than the corresponding le- oxida- tion process.

PtCI, + R-H * CIPt-R + H++CI-

PtCI,'- (viii) 1 2Ptc1,- + R - a

In the context of the reaction scheme depicted in Equation (vi), the Pd(I1) ion is a particularly attractive choice for two reasons. First, as we and others have shown (16), the Pd(I1) ion is a strong electrophile. For example, Pd(I1) was found to activate olefins and small

ring compounds through an initial electrophilic cleavage of the C-C *-bond or a C-C a-bond, respectively, Equation (ix). In addition, as Table I11 illustrates (17), the electron affinity of Pd(I1) is comparable to that of the traditional main-group Lewis acids.

> C = C < + P d z + * > C - C < - I +

n n

I +

Pd + (ix)

>C-C< + Pdz+ e >C C < -

Pd +

The second advantage in using Pd(I1) is that it is a good 2e- oxidant (avoiding the formation

Table II

Redox Potentials of Hydrocarbons for the RH + H,O 4 ROH + 2e + 2 H+ Process (5a)

E, volts

-0.59 -0.48 -0.44 -0.37 -0.31 -0.30 -0.20


Table 111

Promotion Energies and Electron Affinities for Selected Metal Ions (17)

ion I Promotion energy*,ev

1 . 6 2 . 4 3 . 0 5 3 .39 8 .25 9 .94

17 .1 16 .6 1 2 . 8

*ndx- ndx-'(n + l l p '

of radicals). For example, the Pd(I1) mediated 2e- oxidation of olefins and arenes is well-known (18). In addition, Pd metal can be readily oxidised back to Pd(I1) using several different co-oxidants, such as Cu(I1) + 0, and RONO, and this forms the basis of several practical Pd(II) catalysed oxidation processes, such as, the Wacker process and the Pd(I1) catalysed oxalate synthesis (19).

In our own work we chose to focus on the reactivity of the Pd(I1) ion based on the arguments presented above (12). The initial problem involved the choice of the proper complex and the solvent, and Pd(I1) in CF,CO,H was chosen for the following reasons: the CF,CO,- ion is a relatively poor base and M- O,CCF, bonds are known to be quite labile (20). Therefore, the Pd(I1) species present in the above system is expected to be labile and highly electrophilic. In this context, it is noteworthy that the electrophilic metallation of arenes by Tl(O,CCF,), occurs readily under mild conditions, while the corresponding acetate derivative is unreactive (21). Also of note is the observation of facile electrophilic cleavage of the allylic C-H bonds of olefins by Pd(O,CCF,), in CF,CO,H (22).

When CH, (at 800 psi) was heated in the presence of Pd(O,CMe), in CF,CO,H at 80°C, a yield of approximately 60 per cent of CF,CO, Me together with precipitated Pd metal was observed, Equation (x) (12(a), (b)).

Electron affinity, eV

7 .31 7 . 9 5

18.56 19 .42 7 . 7 2 7 . 5 9

17 .96 1 6 . 9 18 .75

No deuterium incorporation into CF, CO, Me was observed when Pd(O,CCH,), was replaced by Pd(02aD3)2Y

CF,CO,H CH, + Pd(O,CMe), -

8OoC

CF,CO,Me + Pd(0) (x)

indicating that the MeC0,- group did not participate in the product formation through a decarboxylation step. Since the ester can be hydrolysed to the corresponding alcohol, the overall reaction can be written as follows:

CH, + Pd2+ + H , O + CH,-OH + Pd(0) + 2H+ (xi)

Further information concerning the mechanism of the Pd(I1) oxidation of hydrocarbons was obtained through the study of arene oxidations (12(a), (b)) which were also performed at 80°C using Pd(O,CMe), in CF,CO,H. Under these conditions, the monotri- fluoroacetoxylation of 1 equivalent of p- dimethoxybenzene proceeded to completion in 1 hour. Furthermore, comparative experiments indicated the following relative oxidation rates: p-dimethoxybenzene (l), p-xylene (0. l), toluene (0.02) and benzene (0). For pxylene and toluene, attack on the ring rather than the benzylic position accounted for over 97 per cent and over 90 per cent, respectively, of the monotdluoroacetate esters obtained. The two conclusions that can be drawn from our

Platinum Metah Rev., 1991, 35, (3) 129

observations on Pd(I1) oxidations (12(a), (b)) are that (a) radical pathways are not involved, since the weak benzylic C-H bonds were not at- tacked to any significant extent and (b) the enhanced rate of oxidation with electron-rich arenes is consistent with an electrophilic displacement pathway, as shown in Equations (iv) and (vi). The latter conclusion was further supported by the observation that the trifluoroacetoxylation of anisole proceeded to yield para and ortho products in a 3: 1 ratio with almost no meta isomer formed.

In order to make the oxidation of methane catalytic in Pd(II), it is necesssry to have a co- oxidant that is capable of reoxidising the Pd(0) formed at the end of the stoichiometric oxidation step, see Equation (vi). Hydrogen peroxide is one such co-oxidant. Thus, peroxytduoro- acetic acid, generated from H,O, and (CF,CO),O, was found to oxidise methane specifically to CF,CO,Me, with the Pd(I1) ion acting as the catalyst, see Figure l(12c). The reaction shown in Equation (xi) can therefore be rewritten as follows:

WII), (CF3CO),O CH, + H,O,

9OoC CH,-OH + H,O (XU)

The purpose of having an excess of trifluoroacetic anhydride is to remove the water generated, thereby preventing the hydrolysis of the ester to the more easily oxidised methanol. Ready further oxidation (eventually to CO , and H,O) of the primary products is a persistent problem in the area of selective oxidation of alkanes. As is evident from Figure 1, our strategy works to a certain extent; however, at long reaction times, further oxidation of CF, CO, CH, does occur. Significantly, this latter oxidation step is also catalysed by Pd(I1) since CF,CO,CH, was found to be stable in the reaction mixture in the absence of the metal.

The following observations seem to indicate that an electrophilic, rather than radical, mechanism also operates for the catalytic oxidation of methane. The oxidation of cis and trans 1,2-dimethylcyclohexane to the corresponding

Platinum Metals Rev . , 1991, 35, (3)

a i o 20 4 0 60 TIME, hours

Fig. 1 The yield of methyl tduoroacetate is shown versus time, at a temperature of 9OoC, methane pressure 900 psi and 1.8 mi of (CF,CO),O o 2 mmol 30% H,O, o 2 mmol 30% H,O, + 0.15 mmol

Pd(OzCC 2 H , ) 2

X 2 mmol 309’0 H,O, + 0.15 mmol Pd black

tertiary alcohols by peroxytrifluoroacetic acid was previously shown to proceed by complete retention of configuration (23). The addition of the Pd(I1) ion to the system does not appear to alter the mechanism since, when p-xylene was used as the substrate, the ratio of esters derived from the attack on the ring versus the benzylic position was >100:1. Therefore, a radical pathway is not involved since the weak benzylic C-H bonds were not broken.

Since the catalytic cycle presumably com- bines the reaction shown in Equation (x), with a step involving the reoxidation of Pd(0) 10 Pd(I1) by peroxytrifluoroacetic acid, it should be possible to initiate the catalytic cycle starting with Pd(0). The addition of “palladium black” to peroxytrifluomacetic acid did result in an enhanced yield of CF , CO CH, ; nevertheless, the effect was much less than that observed with Pd(O,CC,H,),, as shown in Figure 1. This observation does not necessarily rule out the above catalytic cycle since, in several catalytic oxidations involving the Pd(II)/(O)/(II) cycle, it has been observed that once Pd(0) is allowed to aggregate, it cannot be easily reoxidised to Pd(I1) (24).

An alternative explanation for the catalytic

130

effect of the Pd(I1) ion encompasses attack by an incipient OH+ ion and proceeds through the following transition state (25). Under this scenario, the

Pd(I1) ion promotes the reaction by co- ordination to the a-oxygen atom, thereby further polarising the 0-0 bond (26). Other metal ions should also have a similar effect. The substitution of Pd(O,CC,H,), by either Pb(O,CCH,),, Fe(O,CCH,), or

Co(0, C-CF ,) , however, (27) resulted in a yield of CF,CO,CH, that is either similar to, or only marginally higher, than that observed with peroxytrifluoroacetic acid alone.

In conclusion, the selective transition metal catalysed, oxidation of methane through an electrophilic pathway under mild conditions has been demonstrated.

Note that the electrophilic oxidation of methane in superacid media is known (28). In the latter case, the methanol formed is pro- tected from further oxidation by protonation to the methyloxonium ion.

Acknowledgment Our work was funded by a grant fiom the National

Science Foundation (CHE-8906587). We thank Johnson Matthey, Inc. for a generous loan of palladium salts.

References J. March, “Advanced Organk Chemistry”, 9 (a) J. H. hnsford, Caral. Today, 1990, 6, 235; Wiley, New York, 1985, p. 620 and references (b) G. H. Hutchings, M. S. Scurrell and J. R. theteir. Woodhouse, Chem. SOC. Rev., 1989, 18, 251; (c) G. Olah, Ace. Chem. Res., 1987, 20, 422 G. H. HutChings, J. R. W c d h ~ ~ s e and M. S . (a) A. E. shilOv, ~ ~ ~ ~ ~ i ~of Saturated Scumell, 3. Chem. SOC., Faraday Trans. I, 1989,

85, 2507; Also see, Catal. Today, 1989, 4 Hydrocarbons by Transition Metal Compounds”, Reidel, Dordrecht, 1984, Chapter V; (b) L. A. 10 Leading references: (a) T. T. Wenzel and R. G. Kushch, V. V. Lavrushko, Yu. S. Misharin, A. Bergman, 3. Am. Chem. Soc., 1986, 108, 4856; P. Moravskii and A. E. Shilov, Nom. 3. Chim., (b) C. K. Ghosh and W. A. Graham, 3. Am. 1983,7, 729; (c) Yu. V. Geletii and A. E. Shilov, Chem. SOC., 1987,109, 4726; (c) M. Hackett and Kinet. Katal., 1983, 24, 486 G. M. Whitesides,J. Am. Chem. Soc., 1988,110, Review: (a) N. M. E-ud, E. T. &&ov and 2. K. bs, “Lquid-mase %&tion of

1449; (4 T. G. p. Harper, R. s. Shinomoto, M- A. D e b g and T. c. flood, 3. h. Chem. sot.,

Hydrocarbons”, Plenum, New York, 1967; (b) N. M. Emanuel. G. E. ZaikovandZ. K. Maizus .

19883 110, 7915 11 J. Halpern, Inow. Chim. Acra, 1985, 100, 41

“Oxidation of Organic Compounds”, Pergamon; New York, 1984 Reviews: (a) op. cit, (Ref. 3a), Chapter IV; (b) R. A. Sheldon and J. K. Kochi, “Metal-Catalyzed Oxidation of Organic Compounds”, Academic, New York, 1981 Reviews: (a) J. T. Groves, 3. Chem. Ed., 1985, 62, 928; (b) F. P. Guegerich and T. L. Mac- donald, Ace. Chem. Res., 1984, 17, 9 Leading references for related oxidative functionalisation of alkanes by metalloporphyrins: (a) B. Meunier, Bull. SOC. Chim Fr., 1986, 4, 578; (b) D. Mansuy, Pure Appl. Chem., 1987,59,759; (c) C. L. Hill, Adv. Oxygenaced hcess . , 1988, 1, 1: (d) C. L. Hill. “Activation and Functionaliza-

. . - . - 12 (a) E. Gretz, T. F. Oliver and A. Sen, 3. Am.

Chem. SOC., 1987, 109, 8109; (b) A. Sen, E. Gretz, T. F. Oliver and Z. Jiang, New 3. Chem., 1989, 13, 755; (c) L.-C. Kao, A. C. Hutson and A. Sen, 3. Am. Chem. SOC., 1991, 113, 700

13 References for the related “four-centre” electrophilic activation of methane by early transition, lanthanide and actinide metal complexes: (a) M. E. Thompson, S. M. Baxter, A. R. Bulls, B. J. Burger, M. C. Nolan, B. D. Santasiero, W. P. Schaefer and J. E. Bercaw, 3. Am. Chem. Soc., 1987, 109, 203; (b) P. L. Watson, 3. Am. Chem. SOC., 1983, 105, 6491; (c) C. M. Fendrick and T. J. Marks, 3. Am. Chem. SOC., 1984, 106, 2214

tion of Alkanes’;, John Wdey, New York, 1989 14 (a) B. R. James, “Homogeneous Hydmgena- Reviews: (a) C. T. Hou, “Methylotrophs: tion”, Wdq, New York, 1977; (b) J. Halpern, Microbiology, Biochemistry and Genetics”, CRC Press, Boca Raton, 1984; (b) C. T. Hou, 15 (a) P. J. Walsh, F. J. Hollander and R. G. Bwtechnol. Genet. Eng. Rev., 1986, 4, 145; Bergman, 3. Am. Chem. Soc., 1988, 110, 8729; Mechanism: (c) J. Green and €3. Dalton, 3. Bwl. (b) C. C. Cummins, S. M. Baxter and P. T. Chem., 1989, 264, 17698 Wolczanski, 3. Am Chem. SOC., 1988, 110, 8731

Annu. Rev. Phys. Chem., 1965, 16, 103


1 J. March, “Advanced Organk Chemistry”, Wiley, New York, 1985, p. 620 and references theteir.

2 G. Olah, Acc. G e m . Res., 1987, 20, 422 3 (a) A. E. Shilov, “Activation of Saturated

Hydrocarbons by Transition Metal Compounds”, Reidel, Dordrecht, 1984, Chapter V, (b) L. A. Kushch, V. V. Lavrushko, Yu. S. Misharin, A. P. Moravskii and A. E. Shilov, Now. 3. Chim., 1983,7,729; (c) Yu. V. Geletii and A. E. Shilov, Kinet. Katal., 1983, 24, 486

4 Review: (a) N. M. Emanuel, E. T. Denisov and 2. K. Maizus, “Liquid-Phase Oxidation of Hydrocarbons”, Plenum, New York, 1967; (b) N. M. Emanuel, G. E. ZaikovandZ. K. Maizus , “Oxidation of Organic Compounds”, Pergamon, New York, 1984

5 Reviews: (a) op. cit, (Ref. 3a), Chapter IV; (b) R. A. Sheldon and J. K. Kochi, “Metal-Catalyzed Oxidation of Organic Compounds”, Academic, New York, 1981

6 Reviews: (a) J. T. Groves, J. Chem. Ed., 1985, 62, 928; (b) F. P. Guegerich and T. L. Mac- donald, Acc. Chem. Res., 1984, 17, 9

7 Leading references for related oxidative functionalisation of alkanes by metalloporphyrins: (a) B. Meunier, Bull. SOC. Chim Fr., 1986, 4, 578; (b) D. Mansuy, Pure Appl. Qlem., 1987,59,759; (c) C. L. Hill, Adv. Oxygenaced k e s s . , 1988, 1, 1; (d) C. L. Hill, “Activation and Functionaliza- tion of Alkanes”, John Wdey, New York, 1989

8 Reviews: (a) C. T. Hou, “Methylotrophs: Microbiology, Biochemistry and Genetics”, CRC Press, Boca Raton, 1984; (b) C. T. Hou, Bwtechnol. Genet. Eng. Rev., 1986, 4, 145; Mechanism: (c) J. Green and €3. Dalton, 3. Bwl. Chem., 1989, 264, 17698

16 A. Sen, Acc. Chem. Res., 1988, 21, 421 and

17 R. S. Nyhdm, Proc. Chem SOC., 1961, 273 18 Review: (a) P. M. Henry, “Palladium Catalyzed

Oxidation of Hydrocarbons”, D. Reidel, Dordrecht, 1980; (b) R. F. Heck, “Palladium Reagents in Organic Synthesis”, Academic, New York, 1985

19 Specific examples: (a) op. cit., (Ref. 18); (b) A. Montreux and F. Petit, “Industrial Applications of Homogeneous Catalysis”, Reidel, Dordrecht, 1988; (c) F. J. Waller,J. Mol. oltal., 1985,31,123

20 Review: C. D. Garner and B. Hughes, Adv. In- 0%. Chem. Radwchem., 1975, 17, 1

21 A. McKillop and E. C. Taylor in “Comprehen- sive Organomaallic Chemistry”, ed. G. Wilkin- son, F. G. A. Stone and D. W. Abel, Pergamon, New York, 1982, Vol. 7, p. 499

22 B. M. Troa and P. J. Metzner, J. Am. Chem.

references therein 23 G. A. Hamilton, J. R. Giacin, T. M. Hellman, M.

E. Snook and J. W. Weller, Ann. N . Y. Acad. Sci., 1973, 212, 4

24 H. S. Kesling, A C S Symp. Ser., 1987, 328, 77 25 N. C. Deno, E. J . Jedziniak, L. A. Messer, M.

D. Meyer, S. G. Stroud and E. S. Tomezsko, Tetrahedron, 1977, 33, 2503

26 Effect of Lewis acids on arene oxidation by peroxytrifluoroacetic acid: H. Hart, Acc. Chem. Res., 1971,4, 337

27 The oxidation of methane at elevated temperatures ( - 18OOC) by Co(O,CCF,), generated in situ has been reported: M. N. Vargaftik, I. P. Stolarov and I. I. Moiseev, J . Chem. SOC., Chem. Commun., 1990, 1049. However, this reagent appears to display little activity under the milder conditions that we have employed

28 G. A. Olah, N. Yoneda and D. G. Parker,J. Am. SOC., 1980, 102, 3572 Chem. SOC., 1976, 98, 483, 5261

Platinum 199 1 During 1990 the supply of platinum to

the Western World increased to 3.73 million ounces, while demand rose by 5.5 per cent to a record 3.66 million ounces, due to increased usage for automobile emission control catalysts, by the chemical and petroleum industries, and for the p r e duction of jewellery. These are just a few of the many facts contained in “Platinum 1991”, a 64 p g e comprehensive review of the platinum industry recently published by Johnson Matthey.

Sales of platinum and palladium by the U.S.S.R. increased by 27 and 12 per cent, respectively, compared to the previous year. Almost 20 per cent of platinum and Over half the palladium supply comes from that country, although it is not known what part of the shipments represents current mine production and what was withdrawn from stock.

Demand for rhodium rose by 20 per cent during 1990, the increase being due entire ly to purchases by the car manufacturers, and included some inventory building. Supply did not match demand, and a significant price increase resulted. On the South African Bushveld Igneous Complex, the source of almost 75 per cent of the Western World’s supply of platinum, the p1atinum:rhodium ratio in the generally

mined Merensky reef is 19:1, but in the UG2 seam it is 6: 1 , thus more rhodium will become available as mining of the latter increases.

There are indications that fuel cells may become the next major application for platinum. In fuel cells, platinum catalyst coatings on the electrodes promote the combination of hydrogen and oxygen ions and thus the generation of electricity. h r - ing 1990 Toshiba and Fuji Electric in Japan, and International Fuel Cells in the U.S.A. decided to start the commercial production of fuel cell electricity generators. It it predicted that their com- mercialisation will make a significant im- pact on the demand for platinum, as the versatility of fuel cells for producing “clean” power becomes more widely ap- preciated, and as economies of scale reduce manufacturing costs.

Readers of Platinum Metals Review who do not have access to this survey and who believe that they would benefit from a better understanding of the platinum market, and many of the factors that influence it, are invited to request a free copy of “Platinum 1991” from the author: Mr. Jeremy S. Coombes, Johnson Matthey P.L.C., New Garden House, 78 Hatton Garden, London EClN 8JP, England.

Platinum Metals Rev. , 1991, 35, (3) 132

Enhanced Oxidation Resistance ROLE OF PALLADIUM IN REFRACTORY METAL ALLOYS

The refractory metals, tungsten and molybdenum, and their alloys possess excellent mechanical properties at elevated temperatures, but their propensity to rapid oxidation has precluded their industrial application. The addition of small amounts of palladium to chromium-containing tungsten alloys is known to enhance considerably their oxidation resistance ( 1 -3), but there is little agreement on the mechanism involved.

Recently a substantial investigation on tungsten-chromium-palladium and tungsten- molybdenum-chromium-palladium alloys has been carried out at the Pennsylvania State University in order to clarify the oxidation mechanism and to characterise the oxidation behaviour in the temperature range 1000 to 125OOC. The influence of palladium coatings was also studied (4, 5).

Alloys of tungsten containing 9 to 29 weight per cent chromium and 1 weight per cent palladium, and similar alloys in which half the tungsten was substituted by molybdenum, were prepared by activated sintering of powder metallurgy compacts (6).

Cyclic oxidation tests showed unusual behaviour in that the oxidation resistance increased with increasing temperature. Isother- mal oxidation curves were m m t h with relatively little localised breakdown of the protective oxide scale. In general the tungsten- molybdenum-chromium-palladium alloys were more resistant. Microstructural examination showed the formation of a protective chromium oxide, 0, 0,, scale with a chromium-depleted alloy layer adjacent to the scale interface.

The role of palladium is to facilitate the rapid formation of these protective Cr,O, scales. Palladium, segregated at grain boundaries, acts as a channel for the outward diffusion of chromium to the surface and, possibly, as a barrier to the inward diffusion of oxygen.

Further studies on (45-55) per cent molybdenum-(35-45) per cent tungsten-9 per

cent chromium-1 per cent palladium alloys have shown the beneficial effect of a 7 gn elec- troplated palladium coating. Uncoated alloys oxidised at 1000°C showed sudden failure due to the breakdown of the protective Cr, 0, scale and the formation of volatile oxides of tungsten and molybdenum. Palladium coated alloys had smooth kinetic curves and a low oxidation rate. At a temperature of 120O0C, both the coated and uncoated alloys show excellent oxidation behaviour.

The observation of enhanced oxidation resistance in tungsten-chromium-palladium and also tungsten-molybdenumchromium- palladium alloys, through the promotion by palladium of chromium diffusion to the surface, is entirely consistent with other work reviewed here earlier (6). The platinum group metals, especially palladium, have been shown to improve the sintering and secondary recrystallisation behaviour of tungsten and molybdenum, by enhancing diffusion at grain surfaces and boundaries, sites where the platinum group metals segregate preferentially.

Interestingly, research at Johnson Matthey has shown that platinum group metals- particularly platinum- as alloying additions in cast nickel-based alloys promotes enhanced oxidation and hot corrosion resistance (7) under both isothermal and cyclic conditions.

C.W.C.

Reference8

1 D. S. Evans, “High Temperature Materials,” 6th

2 T. Itogaki and R. Yoda, Trans. Res. Inst. Met.

3 Y. Muramatsu and T. Takeda, Trans. Res. Inst.

4 B.-D. Lee and G. Simkovich, 3. Less-Common

5 D.-B. Lee and G. Simkovich, 3. Less-Common

6 C. W. Corti, Phtinum Metals Rev., 1986,30, (4),

7 C. W. Grti, D. R. Coupland and G. L. Selman,

plansee Seminar, Reutte, 1%8, p.42

up.), 1975, 17, 1

Met. (Jpn.), 1982, 24, 15

Met., 1990, 163, (l), 51

Met., 1991, 169, (l), 19

184

Platinum Metals Rev., 1980, 24, (l), 2

Platinum Metals Rev., 1991, 35, (3), 133 133

Platinum Media for Data Storage REPORT FROM MAGNETO-OPTIC RECORDING SYMPOSIUM

The first international conference dedicated entirely to magneto-optic recording, MORIS’91, Magneto-Optic Recording International Sym- posium, was held in Tokyo, Japan, from 16th to 19th April 1991. The scope of the conference covered a broad range of topics, including current and potential magneto-optic materials, their processing and properties, and the physics and technology of magneto-optic recording. Rare earth alloys are currently used as first generation magneto-optic materials, but platinumlcobalt and palladiumlcobalt multilayered thin films shotv great promise forfuture use as second generation media. A selection of the papers presented are reviewed here.

The first magnetic storage devices were used in computers about thirty-eight years ago, the most important of these devices being the magnetic disk. The evolution of this magnetic disk technology was outlined in a paper given by Y. Miura of Fujitsu Laboratories Ltd., Kanagawa, Japan. The technology of magnetic disks is sti l l being developed and improved, but ultimately it will be limited by the fact that, to increase the storage density, the flying height of the writelread head above the disk must be extremely low (0.2 pm), and hence the disks must remain fured within the computer. For magneto-optic recording, the optical writehead head is relatively distant from the disk (1.5 mm), and so the disk is removable. This has the advantage of increased security and ease of data transfer between systems.

The other main advantage of optical based systems is their increased storage density. The amount of data which can be stored on a disk depends on the size of each “bit” of information. In magnetic and magneto-optic recording, this is the size of the magnetic domains “written” on the disk surface. In magnetic recording, the magnetic moments of the domains are horizontal, and their size depends on how close the writehead head is to the surface. In a magneto-optic disk, however, the domains are vertical and can, therefore, be more closely packed. Their size is controlled by the area covered by a laser beam focused onto the sur-

face. The size of this area is governed by the wavelength of the laser: the shorter the wavelength the smaller the area.

The first generation magneto-optic materials to reach the market are amorphous rare earthhransition metal alloys, for example, TbFeCo- and GdTbFe-based compounds. These materials have good magneto-optic properties at the wavelengths of commercially available solid state lasers, that is around 820 nm. In an invited talk on the challenges for future magneto-optic materials, P. F. Carcia from Du Pont Company, Wilmington, U.S.A., and W. B. &per and H. W. van Kesteren, Philips Research Laboratories, Eindhoven, The Netherlands, discussed the role of metal multilayers for shorter wavelength recording. By changing the optical wavelength of the writehad laser from 820 nm to 410 nm, the density of stored information can be increased by about a factor of four. Substantial progress has been made recently in generating shorter wavelength, blue laser light by frequency doubling techniques using non-linear optics. However, the Kerr rotation, which is used to read the stored data, is small in the blue region of the optical spectrum for the me earth/transition alloys currently in use; reducing from 0.27O at 800 nm to 0.14O at 400 nm.

The spectral dependence of platinumkobalt and palladidcobalt multilayers shows an increase in Kerr rotation at the shorter

Platinum Metals Rev., 1991, 35, (3), 134-137 134

wavelengths: 0.20° at 800 nm increasing to 0.35O at 400 nm for multilayers of 9A Pt/4A Co. This strongly indicates that these materials could become the second generation magneto- optic media. This effect at shorter wavelengths is enhanced by increasing the cobalt content in the multilayaed structure. However, with a greater thickness of cobalt, the perpendicular magnetic anisotropy which controls the vertical nature of the domains, becomes less pronounc- ed. Also, the Curie temperature of the film is increased with increasing cobalt concentration. This would necessitate using a higher laser power to switch the domains during the writing process. One consequence of this is the reduction of signal to noise ratio with repeated write/read/erase cycles, due to heating in the multilayers. Cobalt-rich multilayers suffer more than a 6 dB loss in signal to noise ratio after fewer than 10' cycles, whereas a more platinum-rich multilayer suffers no loss after more than 20,000 cycles. The challenge, therefore, is to produce a media with a reduced Curie temperature while maintaining the Kerr rotation.

Work on high density recording on platinum/cobalt multilayers, using a blue laser was also presented by S. Sumi, K. Tanase, Y. Fuchigami and K. Torazawa of Sanyo Electric Co. Ltd., Gifu, and S. Tsunashima and S. Uchiyama of Nagoya University, Japan. Struc- tures with 18 double layers of 13A W4A CO were magnetron sputtered onto silicon nitride and tested using an argon laser with a wavelength of 458 nm. The film had a Curie temperature of 300OC (the writing temperature of rare earth based media is approximately 200OC) and the Kerr rotation was 0.67O. Stable magnetic domains as small as 0.2 pm could be sustained on the film. The magnetic and recor- dmg characteristics of these multilayers make them very attractive for high density recording.

There are many factors to be considered when optimising a multilayered structure for magneto-optic recording. In order to reduce the vast amount of experimental work required in such a task, computer modelling is often used to predict some of the characteristics of a poten-

tial magneto-optic film. This topic was considered by several speakers. Not only are the mathematical equations used in the model important, but it is also necessary to understand the optical, magnetic and magneto-optic properties of the constituent layers. The model can then be validated by comparison between the predicted results and the properties of a multilayered stack.

Work in this field formed the basis of a paper presented by J. W. Stuart of Johnson Matthey, on work by R Carey, D. M. Newman, P. A. G. Sandoval and B. W. J. Thomas of Coventry Polytechnic, and P. J. Grundy and E. T. M. Lacey of Salford University, U.K. The aim of this work was to measure the properties of thin films and multilayers in order to use the ap- propriate material parameters in a model of multilayered structures. Structures with 8A w ~ A CO, with total thicknesses ranging from 11 to 44 nm, were prepared by DC sputtering onto glass substrates. Measurements were made over a wavelength range of 500 to 800 nm.

The saturation magnetisation of the films containing cobalt were measured with a vibrating sample magnetometer and showed a linear dependence of magnetisation with total thickness of cobalt as expected.

The optical and magnetooptic properties of the multilayered films had superior properties to those of the single films of equivalent thickness, showing the advantageous effect of the multilayered structure. The optical properties of the multilayers and of single layers of platinum and cobalt showed interesting results for the thinner samples. Above 20 nm thickness, the optical constants n and k (the real and imaginary parts of the refractive index) were fairly constant but were reduced in the thinner films. Comparing the multilayered films with the single films, a 10 double layered stack containing a total of 3 nm of cobalt had much larger optical constants (n = 2.2 and k = 4.3) than the 3 nm single layer of cobalt (n = 0.5 and k = 2.0). Similar results were obtained from the magneto-optic measurements.

It must be noted that the calculations used for these results treated the multilayered structure

Platinum Metals REV., 1991, 35, (3) 135

as a homogeneous film. The next stage of this work will be to use the properties of the in- dividual layers in the calculations. However, it can be seen from these results that the measurements on the very thin layers would not give a satisfactory answer. Neither is it reasonable to expect that the properties of the bulk materials could be used to predict those of very thin layered structures. In order to resolve these questions, this work is continuing at Coventry Polytechnic and at the Johnson Matthey Technology Centre.

Computer modelling was described in a paper by T. W. McDaniel of IBM, San Jose, U.S.A., and W. A. McGahan and J. A. Woollam of the University of Nebraska, U.S.A. They compared the properties of three magneto-optic materials over a 300 to 800 nm wavelength range: a 15 x (lOA PtI3A Co) platinum/cobalt multilayer, TbFeCo and BiDy-substituted FeGa-garnet. At 800 nm the Kerr rotations for the platinum/cobalt, TbFeCo and garnet were 0.165O, 0.209O and 0.128O, respectively. However, at the lower wavelengths platinumkobalt had superior properties, although no figures were given. Garnets also look promising at lower wavelengths if the noise due to grain size can be eliminated. This model did not include the thermal response of the media and was not confirmed with experimental data.

The properties of the substrate used to support the recording film must be taken into account when considering the ease of manufacture and the effect on the properties of the film itself. J. G. Barnes, J. M. Bradshaw and I. Molyneux of Pilkington, Lathom, U.K., discussed the properties of glass, polycar- bonate, polyolefine and aluminium. One of the main advantages of glass is its high service temperature of 400°C, compared with 130°C for the polymers. This, together with its low thermal expansion (95 x 10-’/°C) and low absorption Properties, make it attractive for use in data storage. However, it is more than twice as heavy as the polymer substrates and requires a more complex manufacturing process. Pilk- ington are currently developing a direct

pressing technique for the bulk manufacture of pre-grooved glass disks.

The condition of the substrate during processing will also have an effect on the final recording media. S. Shiomi, T. Miyauchi and M. Masuda of Mie University, Tsu, and S. Yahagi of Daido Steel, Nagoya, Japan, presented a poster on the effect of substrate heating on the perpendicular magnetic anisotropy of platinumkobalt multilayered films. For a multilayered structure of 30 x (lOA PtI3A Co) deposited onto glass, the anisotropy was maximised when the substrate was heated to 130OC. By comparing the bulk and interface anisotropies it was concluded that moderate substrate heating makes the interface between the layers sharper.

The effect of applying an electric bias to the substrate during the deposition process was discussed by H. Tanimoto, M. Nawate, S. Honda and T. Kusuda of Hiroshima Universi- ty, Japan. Platinumkobalt multilayers were sputter deposited onto water-cooled glass substrates, with an applied bias ranging from 0 to - 70 V. The application of a bias had little effect on the saturation magnetisation and perpendicular magnetic anisotropy but the coercivity of the multilayers reduced substantially; from 1.2 kOe with no bias to 60 Oe when -30 V was applied. From X-ray diffraction analysis it was concluded that a small bias promoted sharper interfaces between the in- dividual layers. However, alloying at the interface was induced at the higher bias fields. Transmission electron microscopy studies showed a columnar structure in films produced with no bias, which becomes vague and disap- pears in films produced with increasing bias. Domain patterns, studied using the Bitter method (a 0.1 pm magnetic colloid on the sample surface), confirmed these observations.

In conclusion, this was a very interesting conference which covered a wide range of topics which cannot all be considered in the scope of this article. As summarised by Y. Aoki of Sony, Atsugi, Japan, magneto-optic media have a large role to play in the data storage industry of the future. Magneto-optic media are currently


available with over 150,000 units (using 5.25 inch disks) having been sold worldwide; 50 per cent in U.S.A., 35 per cent in Japan and 15 per cent in Europe. It is expected that 3.5 inch disks will be introduced within the next year

Magnetic disks and solid state memories may still be used for fast data processing in main- frame computers but magneto-optic storage is expected to replace the floppy and hard disks in personal computers and microcomputers by

with over 200,000 units in use by 1992. 2000. J.W.S.

The Platinum Market in 1990 The Platinum Yearbook 1991 BY B. H. NATHAN, Woodhead pUblishing/Metal Bulletin, Cambridge, 1991, 153 pages, ISBN 1-85573-045-6, l95.00

The Platinum Yearbook sets out to provide a reference to events in the markets for platinum group metals during 1990. It contains a description of the evolution and operation of the metals markets, prefaced by a concise history of the platinum metals, from the earliest decorative applications of platinum to the isolation of the other five platinum group elements during the nineteenth century, and on to the growth of their major modern applications.

As the managing director of Ayrton Metals, one of the longest established platinum dealers in London, Brian Nathan is well qualified to review the features of the platinum markets of the world and to explain the basic practice of dealing in the platinum group metals. His account of how the markets work is comprehensi- ble, and avoids entangling the reader in the deeper complexities of trading strategems.

Indeed, the principal value of the book lies in its description of the mechanics of the London and the New York markets, its clarification of some of the mystique which surrounds traders, their colloquialisms, and its discussion of the techniques of trading such as ‘‘stops’’, options,

-

charts and arbitrage, which do so much to influence the pattern of platinum metals prices in the short term.

Half of the book is devoted to an extensive review of monthly developments in the markets for the platinum metals, including the economic, political and fundamental supply and demand factors which were of influence during 1990. Access to key events and features described in the text is simplified by a comprehensive and well planned index, while the review is supported by records of the daily movements of platinum and palladium prices in London and New York. The provision of statistics to compare the trading activities in the New York and Tokyo futum markets might be of use in future editions.

As the first in what is intended to be an annual series, the Platinum Yearbook sets out an attractive stall of information. Junior dealers and commentators on the platinum group metals should therefore find it a helpful guide to dealing in the platinum group metals and a useful source for details of price changes during the year 1990. J.S.C.

Iridium Oxide Device for Coulombic Titrations When determining the acidity or basicity of a

solution by coulombic titrations, an actuator electrode is positioned close to the pH sensitive gate of an ion sensitive field effect transistor. The ISFET acts as the indicator electrode to establish the equivalence p i n t in the titration. However, in this system, the operating potentials of the actuator electrode are such that any other redox couple in the solution, or any chloride ions present, will interfere.

Now, however, an all iridium oxide sensor- actuator system has been proposed by researchers at the University of Twente, The Netherlands, and tested for such titrations (W. Olthuis, J. C. Van Kerkhof, P. Bergveld,

M. Bos and W. E. Van Der Linden, Sens. Actuators By 1991, 4, (1&2), 151-156). Since the reversible redox reaction at an iridium oxide electrode functions at a favourable potential, it is suitable for use as the actuator electrode, with a pH sensitive iridium oxide sensor determining the equivalence point. Such a system eliminates interference from any chloride ions present. The preparation of this system is reported to be easier than the preparation of conventional ISFET-based devices.

The authors go on to describe a new current- pulse method of producing iridium oxide where the growth parameters are independent of the pH of the growth solution.


Permeation of Hydrogen through Palladium- Silver Membranes STRAIN-GRADIENT-INDUCED “UPHILL EFFECTS”

By F. A. Lewis and X. Q. Tong.

and R. V. Bucur

School of Chemistry, The Queen’s University of Belfast

Chemistry Institute, University of Uppsala, Sweden

The hydrogen content gradients that occur during hydrogen permeation through palladium-silver membranes produce complementary strain gradients of lattice expansion, which induce opposing Gorshy Effect components of DifSusion Flux. A body of observations of related “uphill effects” and allied d i f i swn phenomena have recently been studied, using sheet and tube membranes; these phenomena have been correlated with hydrogen pressure-hydrogen content relationships of the Pd,AgZsH, system.

The suitability of employing palladium-silver alloys, of composition Pd77Ag21 and Pd,,Ag,, , as diffusion membranes for hydrogen permeation (1 , 2) is related to the high solubility of hydrogen in these alloy compositions, which is accompanied by high hydrogen diffusion coefficient values and is also linked to the resistance of the alloys to deformation during cycles of absorption and desorption of hydrogen (3).

Particular advantages of these two alloy compositions, in regard to these factors, are centred around the forms of their corresponding equilibrium hydrogen pressure-hydrogen content relationships (p-n). At temperatures near 25OC these relationships are of critical- or super critical- type forms, with reference to structure damag- ing (Y -fl phase transitions and allied hysteretic effects (3 -5).

Associated with these considerations, substantial data on various experimental parameters have become available for the Pd-Ag-H system (4, 5). These have included estimations of hydrogen diffusion coefficients, both as functions of temperature and of hydrogen content (3 - 6).

One frequently employed means of deriving hydrogen diffusion coefficients has been by

“breakthrough technique” analyses of the time dependence of hydrogen permeation fluxes (3 -6). Recently such derivations have, however, been shown to be temporarily complicated by the possibility of “uphill” processes related to Gor- sky Effect responses to strain gradients developed by lattice-expanding hydrogen interstitials (7). Preliminary outlines of a substantial series of studies of “uphill effects”, carried out with membranes of Pd,,Ag,, alloys in the form of both sheet and tube, have been reported quite recently (8 - lo).

In addition to having a technological significance (1 , 2), the form of the p-n isotherms of the Pd 77 Ag,, H, system at temperatures near to 25OC (illustrated in Figure 1) provides certain experimental advantages from the view point of the recent studies of “uphill effects” (8 - 11). For instance, the p-n isotherm at 25°Ccovers a con- veniently wide range of hydrogen contents, n, (where n = WM, the atomic ratio of hydrogen to metal atoms) for equilibrium hydrogen pressures p < 1 atm (6,8 - lo), for example, with p = 1 atm at point Z in Figure 1 (i), n - 0.42. A practical advantage of a tubular form of membrane, Figure 1 (ii), is that in addition to

* Visiting student: Department of Materials Science and Engineering, Tsinghua University, Beijing, P.R. China


A

P

1

I- 6 4‘ I - 6 4

Fig. 1 Diagrammatic representations of forms of: (i) the isotherm of equiliirium hydrogen pressure @) versus hydrogen content (n), where n = HIM, for the Pd77Ag23 alloy at 25OC, (ii) a tubular membrane, (i) time dependences of changes in the internal hydrogen gas pressures, following (a) electrolytic cathodisation or (b) modisation of the membrane outer s d a c e at times denoted by A, and (iv) corresponding “wd bendings” and Concentration profiles (of hydrogen content n; horizontal broken lines represent at points A in (iii)) within the membrane wall at times indicated by points Y and Y’ in (iii)

possibilities of use as a bi-electrode, it has proved to be sensitively reliable - with respect to “leakage problems” associated with interstitial hydrogen expansive effects (1 - 10) - for accurately measuring changes in hydrogen gas pressures at inner surfaces. The tubular form of membrane has also been important for obtaining allied complementary measurements of actual changes of internal volume by a water displacement technique (12).

Analyses of “Uphill Effects” The essential characteristics d “uphill effects”

are shown in Figure 1 (iii). Thus when a quasi- static hydrogen pressure is established within the tube, corresponding (for surfices having high catalytic activity) to a hydrogen content both on the surface a d throughout the tube wall as given by the p-n isotherm in Figure 1 (i), the re- introduction of hydrogen to the outer surface, for example at point A in F i r e 1 (iii(a)), will produce an initial ‘‘uphill” decrease of internal hydrogen pressure - or, in alternative experiments of a more electrochemical type, an equivalent increase of the internal surface electrode potential. The alternative procedure of

removal of hydrogen from the outer surface (point A in Figure (iii(b)) self-consistently produces the converse effect, namely an increase in the internal gas pressure or a decrease in the internal surface electrode potentials (12).

The magnitudes of “uphill effects” - as defm- ed with reference to the maximum ‘‘uphill” decrease (or converse increase) Ap, of the internal tube pressure indicated by points Y and Y* in Figure 1 (iii) and of their associated influences on “breakthrough time” parameters, and subsequently derived values on the hydrogen diffusion coefficient - have now been investigated for a series of initial hydrogen contents, no, in both Pd,,Ag,, (8-11) and Pd,,Pt,, (12) membranes.

From these studies sound evidence has been obtained that hydrogen permeation, Ja, through membranes of wall thickness 6 can be described by an outline relation of the form

J& = -D{grad n-f(n,, grad c)} (9

indicative of the combined influences of a generally expected Fickian concentration gradient term, represented by grad n, and a second term representing an opposing Go* Effect flux - involving strain gradients, grad E , produced


by the expansion effects of the hydrogen interstitials, and initial concentrations, n,, , of the interstitials in the wall. More pictorial representations of the influences of these factors at an intermediate stage (points Y and Y* in Figure 1 (iii)) of both increasing and decreasing pressure “uphill effects” are shown in Figure 1 (iv). Here, for a section of tube wall with an initial hydrogen content, no, hrther entry of hydrogen into the outer surface has been represented as producing an outward distortion of the tube wall, compon- ding to a developing strain gradient, represented by grad E . This strain gradient has produced a Gorsky Effect transfero of hydmgen away fro inner regions of the wall of a magnitude propor- tional to no - with a reduction corresponding to Ap of the hydrogen chemical potential and, effectively, a simultaneous equilibration of hydrogen gas pressure within the tube. In complementary studies of permeation rate alterations - resulting from medhanically p d u c e d strain gradient responses to pressure changes at the outer sulface, involving either hydrogen or any other gas likely to be encountenxl in technological working conditions - self-consistently clear evidence has now been obtained (10) that the corresponding Gorsky Effect hydrogen transfer in this case supplements the normally expected concentration gradient directed hydrogen flux.

From combined academic and technological standpoints, these studies of hydmgen permeation would now seem to represent particularly clear demonstrations of Gorsky E f k t operation. As a consequence of the good opportunities provided through the p-n-T data to obtain quite accurate estimates of the hydrogen contents of both wall substrates and suitably activated surfaces, there has been good progress (13) in matching experimental permeation r a ~ with quantitatively more precise forms of Equation (i) and analogous relationships.

Acknowledgements The loan of palladium-silver alloys by Johnson

Matthey, in bath sheet and tubular form, is most gratefully acknowledged. Thanks are also due to Queen’s University for providing visiting research grants to R.V.B and X.Q.T.

References 1 G. J. Grasshoff, C. E. Pilkington and C. W. Corti,

2 J. E. Philpott, Platinum Me& Rev., 1985,29, (11,

3 R. V. Bucur and F. A. Lewis, Scr. Metall. M a w . ,

4 E. Wick, H. Brodowsky and H. Ziichner, Top.

Platinum Metals Rev., 1983, 27, (4), 157

12

1990, 24, 2071

Appl. Phys., 1978, 29, 73 5

6 7

8

9

10

11

12

13

F. A. Lewis, Platinum Metals Rev., 1982, 26, (3), 121; Pure Appl. Chem., 1990, 62, ( l l ) , 2091 A. Kiissner, Z . Naturfotsch. A , I%, 21, (4), 515 F. A. Lewis, K. Kandasamy and B. Baranowski, Platinum M m l s Rev., 1988,32, ( l) , 22 K. Kandasamy, F. A. Lewis and X. Q. Tong, Pmc. 4th Im. caf: Hydmgen Effects on Materials Behavior, ed. N. R. Moody and A. W. Thompson, Metallurgical Soc., AIME, \Kturendale, PA 1990, p.249 X. Q. Tong and F. A. Lewis, Aoc. 8th World Hydmgen Energy Conf: , ed. T. N. kiroglu and €? K. Takahashi, Pergamon, New York, 1990, p. 1175 X. Q. Tong and E A. Lewis, 3. Les-Comma Met., 1991, 169, 157 F. A.-Lewi and X. Q. Tong, 3. h-Common Met., in press K. Kandasamy, F. A. Lewis, J. P. Magennis, S. G. M c k and X Q. Tong, 2. n y s . Chem. New Folge, in press K. Kandasamy, Vignanam 3. Sci. Univ. 3 a f f n , 1989, 3 , 25; and to be published

Protecting Rhodium Catalysts An understanding of the relationship bet-

ween the chemistry and structure of rhodium surfaces with their catalytic performance has already been gained from extensive surface spectroscopic investigations. Now, researchers at the University of Pittsburgh, Pennsylvania, have studied the protection of rhodium supported catalysts by potassium functionalisation, in connection with their performance in syngas- related industrial reactions and in automobile exhaust gas converters (M. I. Zaki, T. H. Ball- inger and J. T. Yates, J. Phys. Chem., 1991,

They found that the exchange functionalisation of isolated aluminium-hydroxide groups of the alumina support by potassium carbonate modifier produced aluminium+xygen potassium groups which stabilise the rhodiwdalumina catalysts against rhodium(1) formation.

The functionalisation could thus produce an effective practical method for the protection of environmental rhodium catalysts against loss of catalytic activity due to rhodium(0) degradation.

95, (lo), 4028-4033).

Platinum Metalr Rev., 1991, 35, (3) 140

by the expansion effects of the hydrogen interstitials, and initial concentrations, n,, , of the interstitials in the wall. More pictorial representations of the influences of these factors at an intermediate stage (points Y and Y* in Figure 1 (iii)) of both increasing and decreasing pressure “uphill effects” are shown in Figure 1 (iv). Here, for a section of tube wall with an initial hydrogen content, no, hrther entry of hydrogen into the outer surface has been represented as producing an outward distortion of the tube wall, compon- ding to a developing strain gradient, represented by grad E . This strain gradient has produced a Gorsky Effect &a of hydmgen away from the inner regions of the wall of a magnitude propor- tional to no - with a reduction corresponding to Ap of the hydrogen chemical potential and, effectively, a simultaneous equilibration of hydrogen gas pressure within the tube. In complementary studies of permeation rate alterations - resulting from medhanically p d u c e d strain gradient responses to pressure changes at the outer sulface, involving either hydrogen or any other gas likely to be encountenxl in technological working conditions - self-consistently clear evidence has now been obtained (10) that the corresponding Gorsky Effect hydrogen transfer in this case supplements the normally expected concentration gradient directed hydrogen flux.

“Palladium; or, New Silver” NO STRANGER TO SCIENTIFIC CONTROVERSY

By Ian E. Cottington Johnson Matthey, Hatton Garden

The recent surge of interest in palladium, an element whose history has not been aflorded the same coverage in this Journal as that given to platinum, has prompted this account of the discovery and preliminary investigation of this important member of the platinum group of metals. The first written reports about palladium resulted in controversy, confusion and embarrassment; its inclusion in jewellery in the early twentieth century, and more especially some recent claims concerning palladium electrodes, had similar eflects. A number of the people who contributed in various ways to the introduction of this metal to the scientific community in the early nineteenth century are also considered, briefly.

In April 1803 a small advertising leaflet listing some properties of what was claimed to be a new metal called palladium or new silver, was distributed anonymously to a number of scientists in London; it announced that the metal was available only from Mr. Forster of Soho. [Adolariusl Jacob Forster (1739-1806), a dealer in minerals, was abroad at the time so prospec- tive purchasers had to approach his wife, Elizabeth, for samples of the metal. However, when William Nicholson, editor of the Journul of Natural Philosophy, Chemistry and the Arts, sought to establish who had supplied the palladium, Mrs. Forster maintained that she did not know the name of the “genteel young man who gave her the metal for sale”. Nicholson reprinted in his journal the information given on the leaflet (l), but, not surprisingly, the unusual way in which this new element had been brought to the attention of the scientific community, aroused the suspicions of at least some of the first people to hear about it.

Prominent among the sceptics was the chemist Richard Chenevix who, having read on the 29th April what was claimed in the leaflet, formed the opinion that it was a piece of deception. He therefore obtained and made a prelimhaq investigation of a sample of the “new metal”, and finding that its characteristics did not resemble

those of any known metal, refumed to Forster’s shop at N0.26 Gerrard Street and purchased all the remaining stock (2). Having carried out a considerable number of hurried experiments

In April 1803, this l ede t was distributed to a number of people in London, advertising a new noble metal which muld be obtained only from a shop in Soho, owned by Jacob Forster, a collec- tor and dealer in minerale. The cost worked out at about one shill ing a grain, this being approximately six times the price of gold at that time

Platinum MeraLr Rev., 1991, 35, (3), 141-151 141

Richard Chenevix 1774 - 1830

This noted chemist was a native of Ireland, although of French extraction. Hie fvst English language paper was published in 1801, the year in which he was elected a Fellow of the Royal Society. He lived in France on a number of occa- sione, and nine of hie chemical memoira were published in that country. Apparently Chenerix enjoyed arguments, which perhaps explains his persistence during the palladium controversy. In later life he emgaged in literary pursuits

“He sent in his memir to the Royal Society, and two evenings were spent in the reading of it” (3, this being on 12th and 19th M a y 1803. At this time Chenevix was already an established analytical chemist, and a Fellow of the Royal Society with some 16 scientific papers and a text- book on chemical nomenclature to his credit. He had travelled widely on the continent of Europe where he had met some of the leading scientists of the day. Clearly, he was not content to accept without question all of the claims made by other scientists, for he had already engaged in a number of arguments about scientific mat- ters, and made no secret of the fact that he believ- ed palladium to be a hoax. In fact, erroneous announcements of the discovery of new elements were not unusual during the nineteenth century.

The investigations carried out by Chenevix showed that the specific gravity of the samples varied from piece to piece, between about 10.97 and 11.48, but that their other properties were as described on the sales leaflet. None the less he doubted the elemental nature of the samples, and was convinced that palladium was only an alloy of platinum. He formed the opinion that the element most able to mask the true properties of platinum, while hiding its own, was mercury. He therefore turned his attention from analysis to synthesis, and set out to reproduce the supposed alloy. As a result of his work he soon claimed that he had “formed palladium by the immediate union of platina and mercury”, and went on to “describe the means by which I have attempted to produce it, whether they failed, or were attended with success.” (4) During one of his experiments he produced a fused button, calculated to consist of about two parts of platinum and one of mercury, which “was not to be distinguished from palladium.” (5)

For another experiment he enlisted the help of Mr. W. H. Pepys who used his powerful galvanic battery to heat a platinum wire partly immersed in mercuy, but although the wire was brought close to its melting point the two elements did not combine to form palladium (6). Conversely, when Humphry Davy used the galvanic batteries at the Royal Institution to ignite a strip of bought palladium no mercury was detected, even though the metal “burned with a very vivid light . . .” (7).

Despite such set-backs Chenevix was convinced that he had produced palladium, and that it was not a new element. In a comment, however, which is every bit as pertinent now as it was when he wrote it nearly two centuries ago (8), he reminded his fellow scientists that although it was dangerous to accept new claims without the most careful examination,

“The philosopher, indeed, will feel no humiliation in being forced to correct or to extend his knowledge; and will not altcgether disbeiieve a fact, because he can adduce no parallel instance, or because it is not in unison with his received opinion. Such conduct would be raising an unsur- mountable barrier against the progress of science:”

Further on in the paper, when referring to his


William Hyde Wollaeton 1766- 1828

During the course of a brilliant career, Wollaston made a number of fundamental discoveries in several branches of science. Generally regarded as the outstanding @we in the history of platitnun, he WM the first to refme the metal on a commercial scale, and it was during his investigations that he discovered the new element which he named palladium. To prevent others learning of the direction, and the progress, of his work be chose to establish hie priority to palladium by the anonymoue sale of samples through the Forster’s shop. He also discovered rhodium, which he announced in the more d way, by a paper presented to the Royal Society

own palladium investigations, he emphasised: “The general importance of the principle, and the extensive influence it is likely to have upon chemistry, demand that it should be treated by multiplied mearches. The experiments that can elucidate it are of the most delicate nature, and require particular care; for they do not always suc- ceed, unless performed under the most favourable circumstances.” (9)

The purchase of the total remaining stock of palladium by Chenevix must have restricted the opportunity for others to conduct their own analysis. But on May 4th, only five days after fmt learning of the new metal, he sent one of the notices and a little piece of the palladium he had purchased to the distinguished French chemist Nicholas Louis Vauquelin (1763 - 1829) for examination. Vauquelin checked the properties against the claims made in the notice and found them to be correct. He was unable to detect either platinum or mercury in the sample; also he found that the addition of sal am-

moniac to a solution of platinum and mercury gave a copious precipitate but this did not occur when it was added to a solution of palladium. To his report the editors added a footnote which reads, in translation, “all this must give rise to doubt.” (10)

Notable scientists in Germany who contributed sigdkantly to our knowledge of the platinum group metals, but who failed in their attempts to synthesise palladium from platinum and mercury in the ways described by Chenevk, included the analysts Valentin Rose and A. F. Gehlen, the distinguished chemist M. H. Klaproth and Professor J. B. Trommsdorff of Erfurt. Thus, Chenevk’s work failed to pass what was then, and st i l l remains, the most critical of tests; it could not be confiied by the independent investigations of his peers.

Another Fellow of the Royal Society who attempted to synthesise palladium was William Hyde Wollaston, but it will be shown later that

Platinum Meialr Rev., 1991, 35, (3) 143

he could not be considered an independent investigator. Wollaston’s notebooks record that in addition to conducting trials with platinum and mercury, he also investigated platinum and iron, and was satisfEd that palladium could not be manufactured from these components (1 1).

Perhaps surprisingly, Chenevix does not seem to have been deterred by the fact that such eminent scientists were unable to repeat his results. His work was widely reported, and “the artiticial synthesis of palladium by one or mom of his methods became a popular pursuit throughout Europe.” (12) He later reported that no more than four out of one thousand attempts to synthesise palladium had been (supposedly) suc- cessful; but this only minfo~ed Chenevix’s belief that perseverance would be required to discover the secret of its formation (13).

A Reward Offered for Producing Palladium Artiticially

A second intriguing notice concerning palladium appeared in London in early 1804, when Nicholson published an anonymous letter, dated December 16th, 1803, which had been sent

to him (14). This offered a reward of a 0 to anyone who, in the presence of three chemical assessors, could produce palladium artificially. Having established that the handwriting was the same as that on the previous communication, and also that the a0 had been deposited with Mrs. Forster as claimed in the letter, Nicholson selected two Fellows of the Royal Society, Charles Hatchett and Edward Howard to serve with him as adjudicators. No doubt hoping for a journalistic scoop, Nicholson expressed the hope that “the commission will enable me to present to my readers an account of whatever may be the result of th is public invitation. ” (1 5) As far as is known, the services of these eminent men were not required, and the money was later retrieved.

The next major event in this fascinating saga, and a lost opportunity to set the records straight, occurred on 24th June 1804 when Wollaston read to the Royal Society a paper entitled “On a new Metal, found in crude Platina” in which he set out to prove the existence and to examine the properties of a previously unknown metal which he had named Rhodium (16). In the paper he

William Nicholson 1753- 1815

Born in London, Nicholson bad a varied career in India and Europe. Commercial agent, scientist, inventor, patent agent and publisher, in 1797 he started the Journal of Natural Phihophy, Chemistry, and the Arts. His contribution to the story of palladium was as a mmmunicator; he was one of the people to receive the ledlet announc- ing the availability of palladium, and reprinted it in the next issue of his popular j o d . He was later asked, again anonymously, to select three chemiete to ovemee attempts to produce palladium from other materide, a challenge which he publicked in hie j o d . He also reprinted information on palladium from both English and foreign language joumnla


In a section devoted to scientiiic news, and headed “Reward of Twenty Pounds for the Artificial Production of Palladium” Nicholeon’s Journal of Naaual Philosophy, Chemistry, and the Arts carried Wohton’e eecond anonymous communication, this time offering 220 to anyone who could make twenty grains of palladium before an audience of three chemiete selected by Nicholson

stated that, as a result of his scientific study of a solution of native platina in aqua regia, he was convinced that:

“the metallic substance which was last year offered for sale by the name of Palladium, is contained (though in very small proportion) in the ore of platina. ”

and that considering the difficulties in trying to synthesise palladium or to separate it into other metals,

“I think we must class it with those bodies which we have most reason to consider as simple metals.’’

In a postscript to a paper written in Freyberg dated June 3rd 1804, and read to the Royal Society on January loth 1805, Chenevix records that Wollaston had mentioned to him more than a year earlier that “He has found that palladium is contained in very small quantities in crude platina.” (18) Chenevix observed that the fact that palladium could be found in nature did not settle whether it was an element or an alloy. Fur- thermore, he claimed that the process to which platina was subjected before it arrived in Europe would be sufficient to account for the presence in it of a small amount of palladium.

In the next month Nicholson received a letter from Wollaston, dated February 23rd 1805, in which Wollaston admitted that he was the author

(17)

of the first anonymous communication concerning palladium, which he had discovered, and thanked Nicholson for the candour with which he had communicated the information about palladium that had been passed to him (19). With the mystery explained, the matter moved towards a conclusion when on 4th July 1805 Wollaston read to the Royal Society his paper “On the Discovery of Palladium; with Observations on other Substances found with Platina”, in which he gave an account of the way he had detected, and subsequently obtained, palladium (20). This paper should have finished the contro-

versy once and for all, but apparently this was not the case. As late as 1809 Joseph Cloud (1770-1845) of the Philadelphia Mint, pre- fmed an account of experiments he had made on a discoloured ingot of gold received from Brazil in 1807, with the words:

“Notwithstanding the numerous experiments that have been made by several eminent chemists, on a metallic substance, discovered by Doctor Wollaston, in combination with crude platinum, and by him called palladium; there still remains much doubt with respect to the existence of such a simple substance.” (21)

Having again noted that palladium was found in combination with crude platinum, Cloud claimed “It has beem my fortune, however, to obtain it from a different source;.. .” this being


the Brazilian gold. By the end of his experiments he was convinced the palladium was genuine, and that it had occurred in nature alloyed with gold “without the presence of platinum, or any other metal”. This final comment may have been in- correct, however.

Of course, if Wollaston had first announced his discovery of palladium to the Royal Society, or had published an account of his work in a respected journal, then much controversy would have been avoided. While his conduct may appear strange, the explanation that he gave for his most curious behaviour is entirely plausible. His reason for not disclosing where palladium was found being “that I might make some advantage of it, as I have a right to do.” (14)

As has been admirably narrated in this Journal previously, Wollaston and his friend Smithson Tennant formed a working partnership in 1800 to engage in various chemically-based enterprises (22, 23,24), including the scientific investigation of platinum and its preparation for commercial use. Their partnership was kept a secret, and when Wollaston eventually developed a way of producing malleable platinum the method was also closely guarded. Indeed, details of the process were only published in late 1828, when Wollaston knew that he was close to death, seven or eight years after the business had ceas- ed. Initial expenditure was considerable, not only for the purchase of crude platinum but also for chemicals and apparatus, and it was to be five years before annual revenue exceeded expenditure and another four years before the platinum enterprise began to show an overall profit.

During the refining of platinum Wollaston undertook an investigation of the portion of the platina that was soluble in aqua regia, while Tennant concentrated on the black insoluble residues. As a consequence, Tennant isolated osmium and iridium, while Wollaston discovered first palladium and then rhodium. He estimated that the palladium amounted to about one part in two hundred of platinum, so under the circumstances it was quite understandable that he did not want to be diverted from his platinum activities to investigate in detail the properties of th is new, but apparently exceedingly scarce

element. At that stage he did not want to publicise his work on platinum, neither did he wish to forgo any scientific recognition or commercial advantage that might eventually result from a more detailed examination of the materials. Aware that chemists on the European continent were actively and successfully engaged in the investigation of platina, and, perhaps, suspecting that their efforts would lead them to the new elements, Wollaston wished to establish his priority but without disclosing his identity. The latter constraint severely limited his ability to accomplish the former; for example, the editors of the Philosophical Transactions of the Royal Society did not publish papers from anonymous sources. The notice and the offer of palladium for sale through Mrs. Forster enabl- ed Wollaston to achieve his purpose, but accor- ding to Sir Joseph Banks, President of the Royal Society, Wollaston’s reputation in the scientific community was damaged by the episode (25).

Banks had become involved in the controversy in an unfortunate way. The Royal Society presents the Copley Medal annually to the scientist who is judged to have published the most important results on some aspect of natural history, and in late 1803 Chenevk was a smng contender for the next award. Wollaston was aware of the situation, possibly because he had received the medal the previous year. Therefore in an unsuc- cessful attempt to save the Royal Society from embarrassment when it eventually became known that Qenevix’s synthesis and investigation of palladium was largely wrong, Wollaston admitted his discovery of palladium to the President. The situation was clearly difficult for Banks, as Wollaston asked him not to disclose the secret. In fact, Wollaston’s information was disregarded and Chenevix received the medal (26).

In the end, Wollaston made no significant financial gain from his discovery and sale of palladium; indeed, it appears that 97 per cent of the palladium he separated h m the crude platina was sti l l available at the time of his death in 1828 (27). During the early years palladium sales were held back by the fact that most potential applications for it could be satisfied equally well by


Percival Norton Johnson 1792-1866

After being apprenticed to his father, the assayer John Johnson, Pereival started his own business on 1st January, 1817. Mov- ing to Hatton Garden in 1822, his business in assaying and refining the precious metals and producing vitreous colours grew rapidly. Johnson was also active in the mining and smelting of the silver-lead ores found in Devon and Cornwall. He was one of the founders of the Chemical Society, and was elected a Fellow of the Royal Society in April 1846

platinum, which was more readily available, and cheaper. Some of the palladium was used alloyed with gold, producing a white alloy upon which Edward Troughton engraved the graduation scales of asmonomical and navigational instruments. Other scientific instrument makers including Dolland and Jean Nicolas Fortin followed the lead of Troughton (28,29) but the demand was not large and Wollaston gave most of his unused palladium to the Royal Society (30). It was to be many years before a fuller understanding of the properties of palladium, and a significantly lower price, led to the identification of applications for which it could be used advantageously.

Much more important and interesting information regarding Wollaston’s early work with palladium is contained in his notebooks (23). For example, an entry for 3rd August 1802 referred to the new metal as “palladium” and he later wrote that it had been namd after the planet that had been discovered nearly at the same time by Dr. Olbers (20); the minor planet Pallas being discovered on the 28th March 1802 by the German astmnomer Heinrich W. Olbers. Another entry relates to the determination of the

specific gravity of a binary alloy of lead and C, and on the facing page a note records

“the upper part of the opposite page was written July 1802. I believe the C meant Ceresium a name which I once thought of giving to Palladium.”

(a res , the first and largest asteroid to be discovered was sighted by Giuseppi Piazzi on 1st January 1801 , an observation which was confirmed in 1802). Data in another of Wollaston’s notebooks suggest that he had left nearly 1350 grains (2.8 troy ounces) of palladium with Mrs. Forster, and that by the time the account was closed in May 1805 only 420 grains had been sold, of which 332 grains had been purchased by Chenevix in April and May 1803 (31).

Percival Norton Johnson Several years later, in July 1812 the

Philosophical Magazine carried a paper by Percival Norton Johnson, described as an assayer of metals, reporting that although pure platinum is not affected by nitric acid, if it is alloyed with gold and silver it then becomes soluble in that acid (32). It is not clear whether Johnson thought this was an original observation; we now know that is was the basis of a technique


used earlier in Spanish South America to separate platinum from gold, and it was certainly known in Paris in the late 1770s. Be that as it may, appended to the paper was a note of considerable interest and significance. In this Johnson and his father reported that some gold arriving from Brazil contained so much palladium that the colour was changed, and that coins made fiom it were suspected as being counterfeits.

In due course Peruval Norton Johnson moved to Hatton Garden and built up the business that was to become Johnson Matthey. But before this happened, Johnson was contracted to refine the gold brought into London by the Imperial Brazilian Mining Association. This Association had been formed in December 1824 to mine at Gong0 Soco, in the Brazilian province of Minas Geraes, some 180 miles north of Rio de Janeiro. As had been reported previously by Wollaston, the gold contained a signifcant amount of palladium, both as particles of native palladium and alloyed with the gold. In the latter, the palladium content varied from, perhaps, one or two up to a maximum of 8.2 per cent. Prior to 1832 the gold was brought to London in the form of crude bars cast at the Government Mint at Sabara, but these contained varying amounts of iron, palladium and tellurium. As a result the bars were discoloured and some were brittle; the latter, being rejected by the Bank of England’s smelters, were unsaleable (33). On the other hand, the non-brittle bars were refined at the Royal Mint but the process resulted in the loss of all the palladium. After 1832, however, the export of gold from Brazil in the form of powder was permitted, and by this time Johnson had

“discovered the means of separating from the gold all the metals in combination with it, and which consist of silver, platina, palladium, rhodium and iridium.. ..palladium is a metal but little known, and is found to be most valuable in the construction of astronomical, nautical and experimental instruments, being perfectly free from all oxydation, and quite malleable, and will no doubt increase in value as its d e n t qualities become more generally understood.” (34)

Indeed, his success in refining this difficult gold, which contained tellurium in addition to

palladium, “led eventually to the full recognition of his fm as refinem and their appointment as Assayers to the Bank of England.” (35) More immediately, as a result of his scientific investigations and his accumulated technical skills, Johnson was able to add significant value to the ore imported by the Imperial Brazilian Mining Association.

As Wollaston had found, applications for the recovered palladium did not develop rapidly. In July 1823, Aim2 Puymaurin, then Deputy Direc- tor of the Paris Mint, wrote a paper detailing the properties of palladium, as determined by Jean Robert Breant, one of the assayers at the mint. He had undertaken the refining of 1000 kilogrammes of Spanish platina fiom which he had recovered some 900 grammes of palladium. Brhnt used part of this palladium to strike a medal which he presented to Louis XVIII of France; then in 1824 when King Charles X suc- ceeded his brother, Br6ant presented him with an ornate cup consisting of a palladium bowl mounted on a silver base (36).

In an attempt to identify further industrial applications, Johnson also sought to promote a greater awareness of palladium by making suitable presentations. For example, in 1826 a massive ceremonial chain made of palladium was presented to King George IV (37). The promo- tional exercise lasted at least until 1845, when Johnson presented to the Geological Society sufficient palladium to make their prestigious Wollaston Medal for several years. In time such early uses as for the scales of scientific and astronomical instruments, reflectors for lighthouses, analytical weights, jewellery, and for dental purposes, were supplemented by medical and electrical contact applications, and uses based upon the remarkable ability of palladium to absorb vast amounts of hydrogen.

The latter property was discovered by Thomas Graham (1805 - 1869) who, after studying the behaviour of hydrogen when exposed to heated platinum, found that palladium could absorb up to six hundred times its own volume of hydrogen (38). He also investigated the absorption of hydrogen by silver-palladium alloys, made by George Matthey, a property which finds major


industrial application for the production of ultra- pure hydrogen (39). The topic continues to interest academic investigators - as evidenced by the preceeding scientific paper by F. A. Lewis, X. Q. Tong and R. V. Bucur, and a number of Abstracts of the current literature, in this issue of Platinum Metals Review.

The Platinum-Palladium Jewellery Debate

Although platinum had been used by the in- habitants of South America for the fabrication of ornaments in pre-Hispanic times (40), until the start of the twentieth century the platinum metals were little used for the manufacture of jewellery on a large scale. As a result there was no necessity to indicate the composition of a platinum article, in the way that the minimum purity of a gold or silver item is defined by the carat or sterling mark stamped on it. With the use of platinum for jewellery increasing from about 1906, however, opportunities for deception arose. The problem was worst in the United

States of America, where, by the early 1 9 2 0 ~ ~ four or five times as much platinum was being used for jewellery as in the whole of Europe. As a result, the New York State Stamping Act of 1920 included a section dealing with the composition of platinum jewellery which reads, in Part,

" The standard is 925/1000 fine which not only includes the platinum metal alone, but also the other metals in the platinum group, and if tests are made all the metals in this family group of platinum may be included".

Similar legislation was passed in the states of Illinois and New Jersey.

Although most U.S. platinum jewellery was manufactured in these three states, it became apparent that Federal Law would be required. Ex- perience of how the state regulations had worked in practice indicated that, for a variety of reasons, modifications would have to be incorporated when drafting the Federal Law. Concern arose over the relative cost of the other platinum group metals that were added to pure platinum to


In about 1819 Jean Robert Br4ant (1775-1850), an assayer at the Paris Mint, undertook to refine 1000 kilogrammes of platina which had been sold by the government in Spain. Having taken advice from Nicolas Louis Vauquelin, an eminent ehemist and analyst and the recipient of a piece of the palladium purchased by Chenevix, Br6ant extracted from the platina about 900 grammes of palladium. From this he made the bowls of two decorative cups, the larger being presented to King Charles X and now preserved in the Trianon at Versailles. Brkant also made a number of palladium medals, one of which was presented to Louis XVIII m 1823; another, illustrated here at actual size, was struck to commemorate the opening of the Museum of the DCpartment des Monnaies et M6daiUes in 1833 by King Louis Philippe I and Queen Mane Am6lie

impart a particular property. The most controversial point was whether palladium additions should be dowed, because at that time it was substantially cheaper than platinum. The course of the American discussion up to late 1924 was thoroughly documented by Charles Engelhard in hisbook “The Platinum-Palladium controversy” (41). To this compilation of documents he added comments, based upon his vast experience of the platinum and jewellery industries. In the United Kingdom it was only in 1975 that platinum jewellery was first given a hallmark to indicate that analysis had established that the object contained a minimum of 95 per cent platinum (42).

A Newer Controversy More recently, palladium has again featured

in a major scientific controversy when, on 23rd March 1989, Professors Martin Fleischmann and Stanley Pons claimed that they had achieved controlled nuclear fusion by the electrolysis of deuterium in a simple electrochemical cell, using a palladium cathode and a platinum anode, in the presence of lithium deuteroxide. Most unusually, the announcement was made at a press conference organised by the University of Utah, where the research was being carried out. Immediately, the news was reported widely in the daily and weekly newspapers (43), in the scientific press and elsewhere (44). The major phenomena reported were the production of excess heat and tritium. It has been suggested that as large amounts of deuterium enter the palladium lattice structure the nuclei fuse together, generating heat; while the formation of tritium could be an indication of nuclear reaction.

Both the timing and the manner of this first announcement appear to have been dictated by the suspicion that other scientists worlung on so- called “cold-fusion” were about to publish the results of their work. Not surprisingly, with a perceived opportunity to harness the excess heat for electric power generation or even to power road vehicles, commercial considerations appeared to assume paramount importance. In some ways repeating the excitement that had

followed the early paper by menevix, it was soon reported that “retired professors, cranks and housewives are joining the m e to reproduce the controversial ‘test-tube’ fusion experiment announced last week . , ,” (45).

A frenzy of world-wide activity followed the origmal claim by Fleischmann and Pons, and for a time the views of participating scientists and research establishments were, perhaps, determined largely by their success or failure to instan- taneously reproduce the results announced in 1989. This polarisation was apparent in the at- titudes of some providers of research funding, and possibly even some scientific publishers. There were also reports that the wider scientific debate could be Mered by the possibility of litigation! It is however fair to say that the debate continues, largely between sceptical nuclear physics and revolutionary electrochemists (46). Perhaps in April 2003, two hundred years after Wollaston’s leaflet was first distributed in London, it may be possible to consider more fully the significance of these reports of the use of palladium electrodes for “cold fusion”.

Palladium-Based Autocatalysts The market for platinum has been upset twice

in recent times as car manufacturers have announced that they were planning to install emission control catalysts which did not require platinum in some of their vehicles. The first time was by the Ford Motor Company of the U.S.A. who, on December 14th 1988, reported that it had “developed a catalyst that is just as effective as platinum in meeting stringent exhaust emission standards . . .” (47); this was generally assumed to contain palladium (48). More recently, on May 30th of this year the Nissan Motor Company of Japan announced that it had developed a new palladium catalyst for remov- ing noxious materials from car exhausts (49). The following day, however, Nissan cautioned that “There are several questions about the feasibility of the new converter which have not been answered.” (50) On the same day as the initial Nissan announcement, Ford was reported to have said that it planned to expand further its use of palladium-only catalyst technology in its

Platinum Metals Rev., 1991, 35, (3) 1so

catalytic converters (51). Clearly an objective assessment of the role of palladium in automobile emission control catalysts is another aspect of the remarkable story of pauadium that should be left until the next century.

Current Demand In conclusion, it is interesting to note that not-

withstanding the early controversial history of palladium and the more recent surges in excit- ment associated with the metal, demand for palladium in 1990 amounted to 3.425 million ounces (52); major uses being in the- electrical and

electronics industries, for dental alloys, as a component of emission control and chemical process catalysts, and for jewellery.

Acknowledgements This account has been compiled from information

given in the relevant sections of “A History of Platinum and its Allied Metals” with additional material glean- ed mainly from the references therein. In particular it owes much to the referenced papers by Professor M. C. Usselman. The illustration of the leaflet an- nouncing the sale of palladium is reproduced by courtesy of the Syndics of Cambridge University Library, the portraits of Chenevix and Nicholson by courtesy of the National Portrait Gallery, London.

References

1 W. Nicholson, 3. Nut. Phil. Chem. Arts,

2 R. Chenevix, Phil. Trans., (London.), 1803,93,291 3 T. E. Thorpe, “Essays in Historical Chemistry”,

4 Op.cit., (Ref.2), 299 5 Ibid., 300 6 Ibid., 303 7 Ibid., 306 8 Ibid., 308 9 Ibid., 313

(Nicholson), 1803,5, 136-139

Macmillan, London, 1902, p.560

10 N. L. Vauquelin, Ann. Chim., 1803, 46, 337 11 M. C. Usselman, Ann. Sci., 1978, 35, 565-567

13 R. Chenevix, Phil. Trans., (London), 1805,95,112 14 3. Nut. Phil. Chem Arts, (Nichoh), 1804,7,75 15 Ibid., 159 16 W. H. Wollaston, mil. Tmns., (Lmdon), 1804,94,

17 Ibid., 430 18 Op.cit., (Ref.l3), 130 19 W. H. Wollaston, 3. Nut. Phil. Chem. Arts,

20 W. H. Woliaston, Phil. Trans., (London, 1805,95,

21 J. Cloud, Trans. Am. Phil. SOC., 1809, 6, 407 22 D. McDonald, Plahinmr Metals Rev., 1966,10, (4),

23 M. C. Usselman, Platinum Metals Rev., 1978,22,

24 M. C. Usselman, Platinum Metals Rev., 1989,33,

25 @ A t . , (Ref.ll), 576 26 Ibid., 568 27 B. I. Kronberg, L. L. Coatsworth and M. C.

12 Ibid., 560-561

419

(Nicholson), 1805, 10, 204-205

316330

101-106

(3), 100-106

(3), 129-136

Usselman, Ambix, 1981, 28, 32 28 Ibid., 26-27 29 J. A. Chaldecott, Platinum Metals Rev., 1987,31,

(2), 91-100

30 M. C. Usselman, Private Communication, June 199 1. The plladium gift is recorded in the Royal Society minutes for 11th December 1828

31 @ A t . , (Ref.27), 25 32 P. N. Johnson, Phil. Mag., 1812,40, (171), 3-4 33 D. McDonald, “Percival Norton Johnson”,

34 Ibid., p.48 35 “A Brief History Of The Partners & Directors Of

Johnson, Matthey And Company”, published privately

36 D. McDonald and L. B. Hunt, “A History of Platinum and its Allied Metals”, Johnson Matthey, London, 1982, pp. 191-192

Johnson Matthey, London, 1951, p.43

37 Ibid., pp. 197-198 38 Ibid., p.266 39 G. J. Grashoff, C.E. Pilkington and C.W. Corti,

Platinum Metals Rev., 1983, 27, (4), 157 40 D. A. Scott and W. Bray, Platinum Metals Rev.,

1980, 24, (4), 147 41 C. Engelhard, “The Platinum-Palladium

Controversy”, Baker & Co., Newark, New Jersey, 1924

42 Platinum Metals Rev., 1975, 19, (2), 63 43 C. Cookson, Financial Times, 23rd March 1989,l

44 Platinum Metals Rev., 1989, 33, (2), 54; see also

45 R. Highfield, Daily Telegraph, 1st April 1989, 3 46 For example: F. Close, New Scientist, 19 January

1991, 129, (1752), 46-50; J. Bockris, ibid., 50-53 47 News release from the Ford Motor Company,

Pittsburgh, December 14th, 1988 48 F. J. Smith, “Platinum 1989”, Johnson Matthey,

London, 1989, p.30 49 Reuters, Tokyo, May 30th 1991 50 News agency report, May 31st 1991 51 Financial Times, 4th June 1991, 28 52 J. S. Coombes, “Platinum 1991”, Johnson

Matthey, London, 1991, pp.10-11, pp.49-55

and 26

G.A.H., ibid., (3), 114-116

Platinurn Metals Rev., 1991, 35, (3) 151

ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Scanning Tunneling Microscopy of the Annealing of a Thin Platinum Film on Highly Oriented Pyrolytic Graphite X. CHuAN ZHOU and E. GULARI, Acta ctyst., 1991,

Scanning tunneling microscopy was used to study morphological changes in a thin Pt film deposited on highly oriented pyrolytic graphite (HOPG) during annealing. In air the film could be imaged with a vertical resolution of 0.5A and a lateral resolution of 20A. After annealing below 573 K surface morphology changed only slightly; at 573-873 K the originally uniformly distributed “rolling hills” of Pt coagulated into larger lumps. Above 873 K Pt crystal facets started to form on the surface. At 1123 Kmuch of the surface turned into well defined F’t crystal facets. Above 1123 K the Pt f h started to crack and formed scattered crystals on the HOFG surface. The crystabed Pt was preferentially oriented with the (1 11) plane parallel to the substrate graphite (0001) basal plane, indicating epitaxy of the Pt overlayer with the graphite substrate underneath.

Kinetic Studies of the Chemical Vapor Deposition of Platinum

S. ROY and P. A. YOUNG, Chem Muter., 1991, 3, (2),

The chemical vapour deposition (CVD) of Pt was monitored by FTIR and UV spectroscopies using cis-[PtMe,(MeNC),l as precursor in order to examine the effects of H, and UV irradiation, which can enhance CVD. Pt deposition in a 2 cm pathlength UV cell under UV irradiation at <300 MI occurred on a pyrex target. Irradiation at longer wavelengths gave negligible deposition. The effect of H, in a 10 cm pathlength pyrex cell was to accelerate the reaction.

Hydrogen, Hydrogen SuKde and Hydrocarbon Coadsorption on Pt( l l1) and Pt(l10): Selective Formation of

A47, (l), 17-21

B. MXON, P. R. NORTON, E. C. OU, R. J. PUDDEPHATT,

222-224

Alkylthiols D. VASSILAKIS, C.-M. PRADIER, Y. BERTHIER and J. OUDAR, Appl. surf. Sci., 1991, 47, (3), 273-280 The simultaneous adsorption of diolefme, H, and H, S on Pt single a y s t a l s forms mercaptan and alkanes. The nature, amount and temperature of desorption of these p d u c t s depend on the size and configuration of the diolefme and on the structure of the surface. Mechanisms are proposed to explain the observed surface reactions. Some compounds are selectively produced when H, S reacts firstly with the diolefme; this occurs with C,H, on (111) and (110) orientations, and with C,H, on Pt(ll0).

Magneto-Optical Kerr Effect and Perpen- dicular Magnetic Anisotropy of Evaporated and Sputtered Co/Pt Multilayer Structures

McDANIEL and H. Do, 3. Appl. Phys., 1991, 69, (7),

Thin and ultrathin Co/Pt multilayered structures were prepared on glass substrates by electron-beam evaporation at room temperature and by sputtering at various substrate temperatures and sputtering pressures. Perpendicular magnetic anisotropy was found in samples with Co/Pt bilayer thicknesses near 3 &lo A and total thicknesses of the layer stack of (300 A. The effects of sputtering parameters, such as pressure and substrate temperature, on the magneto-optical Kerr effect were studied.

Perpendicular Magnetic Anisotropy in PtlFe Multilayers

and M. HASHIMOTO, 3. Appl. Phys., 1991, 69, (S),

Perpendicular magnetic anisotropy and related magnetic properties in Pt/Fe multilayers were investigated. Pt/Fe com sitionally modulated f h s (CMFs) with - an 18w”pt layer and Fe layer <5A become perpendicularly magnetised films. Surface magnetic anisotropy (KJ was 0.46 erg/cmz and volume anisotropy (K.,) was - -2 x 10’ erg/cm3 at room temperature. The K, is almost equivalent to that of Pt/Co CMFs and increases with decreasing temperature. The absolute value of K., is much larger than that of the Pt/Co s stem. The effective

changes from positive to negative at T - 200 K with decreasing temperature.

Permanent Magnetic Properties in Fe-Pt- Nb System Alloys

P. HE, W. A. MCCAHAN, J. A. WOOLLAM, F. SEQUEDA, T.

402 1-428

T. KATAYAMA, Y. SUZUKI, Y. MSHIEURA, T. SUGMOTO

Part IIB, 5658-5660

magnetic anisotropy of IFe(4.7 x )/Pt(18.5A)Im CMF

K. WATANABE, 3. 3m. h t . Met., 1990, 54, (11), 1284- 1290 Magnetic properties and temperature dependence of Fe-Pt-Nb ternary alloys were investigated by various techniques. Permanent magnetic properties were obtained by water-quenching from the 7-phase region and tempering at -850-900 K in the phase region. A Fe-39.5 at.%Pt-0.75 at.%Nb alloy exhibits the maximum energy product of 167 kJ/m3, with a residual flux density of 1.05 T and a coercivity of 398 kA/m. These properties are superior to those of basic binary Fe-Pt. The Fe-Pt-Nb composition range is wider than that of Fe-Pt, so the heat-treatments can be easily controlled, and the reproducibility of the magnetic properties can be improved. Fe-38Pt-1Nb has excellent rectangular hysteresis loops at 400 and 290 K with stable thermal properties.


Amorphous Phase Formation in an As- Deposited Platinum-GaAs Interface D.-H. KO and R. SINCLAIR, Appl. Phys. Lett., 1991,58,

A thin amorphous intermixed layer at the Pt-GaAs interface in as-deposited Pt/GaAs and Si/Pt/GaAs samples has been investigated by various techniques. The intermixed layer forms below the native oxide of the GaAs substrate and consists of the elements: Pt, Ga and As. It is suggested that this layer forms during the deposition process of the Pt.

High Temperature Reactions between Sic and Platinum T. C. CHOU, 3. Muter. sci., 1991, 26, (5 ) , 1412-1420 Solid state reactions between Sic and Pt were performed at 900-11OO0C. In the reaction zones, alternating layers of Pt, Si and C, and Pt,Si and C were formed at 900 and looO°C, respectively. Both the Pt,Si and R,Si phases were stable at respective temperatures, but annealings at ll0OoC produced alternating layers of mixed Pt silicides and C. The formation of Pt silicides gave rise to interfacial melting between Sic and Pt and Sic decomposed into C and Si at all the temperatures. The Si reacted with Pt and formed Pt silicides, while the carbon formed clusters and was unrective.

Solid State Reactions of Sic with Co, Ni, and Pt T. c . CHOU, A. JOSHI and J. W A D S W O R ~ , 7. Muter. Res., 1991, 6, (4), 796-809 Solid state reactions between Sic ceramics and Pt, Ni and Co were studied at 800-1200OC for various times under He or vacuum. The WSiC reactions at 900, 1000 and ll0OoC were very similar to each other; interfacial melting was observed and Pt,Si, Pt,Si and a mixture of Pt silicides, respectively, were formed upon annealing. C precipitation behaviour, annealing conditions, diffusion phenomena and major reaction products for diffusion couples are given. A CPFZ(C precipitation free zone) was generated in Ni/SiC and &/Sic but not in Pt/SiC. While a CPZ(carbon precipitated zone) was formed in all the systems, both M-CPZ(modulated) and R-CPZ(random) were noted in the Pt and Ni systems, but only a R-CPZ in the Co system.

Magnetic-Field-Induced Strong Diamagnetic Transition in the Quasi-One- Dimensional Halogen-Bridged Platinum Complex [Pt(en) I[Pt(en) 212 I(Cl0,) (Where en Represents Ethylenediamine) M. HARuKI and P. WACHTER, Phys. Rev. B, 1991,43,

DC magnetisation measurements on the quasi-one- dimensional halogen-bridged Pt title complex show a magnetic-field induced strong diamagnetic transition at fields above 20 kOe. The diamagnetic signals are as large as 3.5-72% of complete diamagnetism and show large fluctuations. The transition temperature to pararnagnetkm is at - 180 K.

(17), 1851-1853

(7), 6273-6276

Interfacial Reactions between Palladium Thin Films and InP D. G . IVEY, L. ZHANG and P. JIAN, 3. Mazer. sci., Muter. Elecnm, 1991, 2 , (l), 21-27 The reaction between a thin layer of Pd( = 100 nm) and an InP substrate was studied at annealing temperatures of 250-45OOC for up to 30 s, which are typical annealing conditions encountered during contact fabrication. Pd reacted readily with InP forming an amorphous ternary phase which later transformed to crystalline Pd,InP on annealing. Pd,InP had an ordered cubic structure, and mkrotwins, 2-3 atomic layers thick, were identified in the ternary phase and these formed along the (110) and (1 10) planes.

Comparative Study on Phase Formation in AI-Pd Thin Film by Ion Beam Mixing and Thermal Annealing - R. Y. LEE, J. H. PARK and c. N. WHANG, 3. Muter. sci., 1991, 26, (3), 721-725 Ion beam mixing and/or thermal annealing were con- ducted to study the phase formation and dissociation in Al-Pd thin films prepared by sequential evaporation. The intermetallic compounds formed by ion mixing with Ar+ were found to be Al3PdZ and AlPd at a dose of 1.5 x 10l6 Ar+/cm2. Thermal annealing after t h i s radiation gave two new phases of All Pd and Al,Pd, in addition to AllPd2 and AlPd. For an as- annealed sample without Ar+ bombardment, the observed phases are Al, Pd, Al Pd 2 and AlPd.

Retardation of Grain Boundary Reactions in Ag-Pd-Cu AUoys by Additions of Small Amounts of Other Elements I. KAWASHIMA, Y. ARAI<I and H. OHNO, 3. Muter. Sci.,

The grain boundary reactions in Ag-ZS%Pd-lO%Cu (mass%) with 1% of Al, Co, Sn, G or In were studied. Addition of Sn and G retarded grain boundary reactions. Grain interior reactions were ac- celerated with Q, Sn and In additions, with G being the most effective. The activation energies for the grain interior and grain boundary reactions were 192-1% and 144-208 kJ/mol, respectively. Addi- tions retarded the growth but not the nucleation at the grain boundary.

Mechanical-Strain-Induced Influences on Hydrogen Diffkion within Pd,,Ag2, AUoy Membranes x. Q. TONG and P. A. LEWIS, 3. Less-Common Met.,

Sudden changes in H z gas pressure on the upstream side of tubular membranes of Pd7,AgZl and Pd,, Pt ,, alloys are known to produce complementary changes of H pressure an the downstream side; this has been attributed to “elastic dynamic” or “mechanically induced memory” effects. Further experiments show that such effects could be associated with combinations of Gorsky effect and self-strain-induced diffusion-elastic effect migrations of H interstitials in the walls of the membranes.

1991, 26, (4), 1113-1118

1991, 169, (l), 157-165

Platinum Metals Rev . , 1991, 35, (3) 153

Hydrogen Permeable Palladium-Silver Alloy Membrane Supported on Porous Ceramics S. UEMNA, T. MATSUDA and E. KIKUCHI, J . Membrane Sci., 1991, 56, (3), 315-325 The H permeability and selectivity of a composite membrane consisting of misable Pd-Ag alloy film supported on the outer surface of a porous alumina cylinder were investigated. The membrane had much higher flux than commercially obtained Pd-based membranes for H separation. The high H flux was due to the thinness of the f h and its high H solubility. H embrittlement was suppressed by alloying the thin Pd film with Ag, and 100% H selectivity was retained even at relatively low temperatures.

On the Origin of a Lattice Expansion in Palladium and Pd-Au Vapour Deposits on Variaus Substrates c. KUHRT and R. ANTON, Thin Solid Films, 1991, 198,

Vapour deposits of'Pd and Pd-Au alloy particles and films were produced under UHV or in high vacuum, with and without the admission of H,O, on amorphous fdms of C and SiO, and single crystal surfaces of NaCl and KBr. In all cases lattice expansions of up to 2.6% were measured, depending on the condition of degassing of the substrate and on the residual gas composition during deposition, especially with respect to water vapour. Lattice expansion correlated with the presence of H on or in the substrate materials, as detected by SIMS.

Mechanical Behavior of Nanocrystalline Cu and Pd

Muter. Res., 1991, 6, (3, 1012-1027 Bulk mechanical properties of nanocrystalline Pd and Cu samples, consolidated from powders prepared by inert gas condensation, were measured. Average grain sizes were 3-50 nm and mean lattice strains ranged from 0.02-3%. Densities rang from 97-72% of that of a coarse-grained standard. Microhardness exceeds that of annealed, coarse-grained samples by a factor of 2-5, despite indications that sample porosity reduces hardness values below the ultimate value. Uniaxial tensile strength is also high.

The Palladium-Rich P&Ho(Er) Systems Y. SAKAMOTO, K. TAKA0 and Y. NAGAOKA, J. Muter.

Pd-Ho and Pd-Er alloys containing 10-21.0 at.% Ho(Er) prepared by arc-melting in Ar and heat treated to - 1193 K for 10 min followed by quenching in iced H,O were studied by various metallographic, spectroscopic and electrical resistance measurements. It is concluded that the magnitude of the order-disorder transition temperature, T,, for the reaction a-Pd + L1,-type Pd,RE (or W,RE where RE is Ce, Sm or Eu)=Pd,RE of the Pd-RE alloys is due to the magnitude of the metallic radius of the rare-earth metals.

(1-2), 301-315

G . W. NIEMAN, J. R. WEERTMAN and R. W. SIEGEL, J.

S C ~ . , Lett., 1991, 10, (6), 341-344

A Contribution to Coupled Reduction of Rare Earth Oxides with Pd and H,

and R. FERRO, z. Metallkd., 1991, 82, (3), 169-173 Stoichiometry and structural types of Pd-rare earth alloys are presented. Results from reacting Gd,O,- Pd mixtures with H , are reported. For alloys containing up to 20 at.% Gd the reduction was nearly complete and Pd-rich Gd-Pd alloys were obtained. For Pd solid solutions containing up to - 12 at.% Gd nearly single-phase samples of composition close to the nominal ones were obtained. For 10-22 at.% Gd when two solid phases, Pd and GdP,, are stable at temperatures over 537OC, twephase alloys not too far from the nominal ones of eutectic appearance were obtained.

Kinetic and Thermodynamic Investiga- tion of Hydrogen Absorption by Ternary LaNi Al and LaNi A1-Pd Alloys M. v. SUSIC and Y. M. SOLONIN, Int. J. Hydrogen

Differential scanning calorimetry and X-ray analysis of H, absorption by ternary LaNi,Al and a LaNi,Al- Pd alloy containing 4 % Pd showed that in a flowing H, atmosphere H absorption by the fmt alloy took place exothermally at about 150 and 45OOC. The alloys containing Pd behaved similarly with absorption facilitated by the presence of Pd, and the formation of a new phase with a phase transition at 150°C was observed.

Mechanical Alloying of the Pd-Si System. Investigation of the Early and Late Mill- ing Stages

V. CONTARDI, R. MARAZZA, G. RAMBALDI, G. ZANICCHI

Emrgt, 1991, 16, (4), 271-276

M. MAGINI, N . BASILI, N . BURGIO, G . ENNAS, S. MARTELLI, F. PADELLA, E. PARADISO and P . SUSINI, Muter. Sci. Eng., 1991, A134, 1406-1409 Four Pd-Si compositions: Pd,.,Si, Pd,Si, Pd,Si and Pd , Si, have been processed by mechanical alloying. After the early milling stages, consisting of very fine fragmentation of the Si particles into a Pd matrix, the Pd Si, Pd, Si and Pd, Si can nucleate intermetallic Pd , Si, depending on the milling conditions and/or the milling apparatus. Further milling seems to promote amorphisation, probably starting from the previously formed Pd , Si compound.

Standard Molar Enthalpies of Formation of Me,Ge, (Me Zr, Nb, Mo), MeGe (Me

Ru, Rh, Pd) and PdlGe by High- Temperature Calorimetry W.-G. JUNG and 0. J . KLEPPA, J. Less-Common Met.,

The standard enthalpies of formation of the above 4d transition-metal germanides were determined using a high-temperature calorimeter at 1473+2 K. Liquid (Ni + Ge) alloys were used as solvents in the solute- solvent drop experiments, and values were obtained for Zr,Ge, and I%,&,. Values of -56.9e1.4 kJ/mol for RUG, - 113.8k2.1 kJ/mol for RhGe and -92.921.5 kJ/mol for PdGe were obtained.

1991, 169, (l), 93-103


Hydrazine Decomposition on a Clean Rhodium Surface: A Temperature Pro- grammed Reaction Spectroscopy Study J. PRASAD and J. L. GLAND, hngmuir, 1991, 7, (4), 722-726 The adsorption, desorption and decomposition of N,H, on a Rh foil surface was studied as a function of its coverage by temperature programmed reaction spectroscopy. The gas-phase products observed depend markedly on the initial hydrazine coverage. At low coverage only H, and N2 desorb from the surface, but at near monolayer Coverage H,, NH,, N, and diimide are observed. Simultanmus desorption of N2 and NH, at 220 K for high coverages suggests the direct decomposition of hydrazine N,H,- N, +H(ad) and N,H,+H(ad)-NH,. Diimide formation was observed over a wide range of N,H, coverages above 220K

Dissociation of Nitric Oxide and Reaction with Hydrogen on Rh(l11) and Various Stepped Rh(ll1) Surfaces

Surf. Sci., 1991, 246, (1-3), 135-140 The reaction between NO and H, was studied on Rh(ll1) and stepped surfaces: Rh(331), Rh(211) and Rh(321) by scanning field emission probe-hole microscopy. Reaction start-up temperature strongly depends on NO coverage, and is sensitive to surface structure. At low NO coverage the reaction starts by 240 K on Rh(321), and at a much higher temperature on Rh(211) and Rh(ll1). On Rh(321) characteristic features of both (100) and (1 11) steps are observed.

Infrared Spectroscopy at High Pressure. Interaction of N 2 with Rh/Al,O, at Am- bient Temperature

WORLEY, 3. Am. Chem. Soc., 1991, 113, (8),

A new high-pressure infrared cell reactor capable of variable temperature operation was used to study the interaction of N, with Rh/Al, 0, catalyst fdms in the pressure regime 1 x to 9000 Tom at 298 K. The results were in good agreements with those previously obtained for similar catalysts at low temperatures and pressures. Infrared bands for chemisorbed and physisorbed N, species were detected and assigned.

Solidifcation of Copper-Rhodium Alloy Single Crptal~

R. M. WOLF, J. W. BAKKER and B. E. NIEUWENHUYS,

J. P. WEY, H. D. BURKElT, W. C. NEELY and S. D.

2919-2922

M. P. DELPLANCKE, M. JARDINIER-OFFERGELD and F. BOUILLON, Mater. Chem. Phys., 1991, 27, (3), 225 -2 33 The preparation of Cu-Rh alloy single crystals by the vertical Bridgman method is described. Dendritic structures are formed during the solidification process of 1.5, 4, 8.75 and 15 at.%Rh alloys. Various methods are used to characterise the solute distribution. Formation conditions and the thermal stability of the structures are also discussed.

Ditrusion of Ir-Dimers on Ir(l10) Sur- faces by Atomic-Exchange and Atomic- Hopping Mechanisms T. T. TSONG and c.-L. CHEN, Surf. Sci., 1991, 246,

On the Ir(ll0) surface, single Ir adatoms and Ir- dimers can diffuse along, as well as across, the 1101 surface channels. The across-channel diffusion most probably occurs by an atomicexchange mechanism. The visited-site-lattice for Ir and Ir, is the (1 x 1) net of the substrate lattice. Atomic jumps are concluded to extend only to the nearest-neighbour sites. For single Ir-adatoms, a s i o n across the channels is easier than along the channels. For Ir-dimers the along-channel diffusion is easier. The energies needed for single Ir-atoms and I r - h e r s to hop along the channel and to displace across the channel by atomic exchanges are derived. The binding energy of the dimer is 1. 10+0. 11 eV.

Structure and Magnetic Properties of FeRuGaSi Multilayer Thin Film

(1-3), 13-24

T. M. JAGIELINSKI, A. M. ZELTSER and C. F. BRUCKER, J. Appl. Phys., 1991, 69, (8), Part IIB, 5628-5630 The structure and magnetic properties of FeRuCaSi thin films used in VHF (150 MHz) recording heads have been studied. The best soft magnetic properties of coercivity (0.2-0.3 Oe), permeability (2000 at 1 MHz and 400-500 at 150 MHz), and magnetostric- tion (<W6), were obtained after annealing at 450-50O0C. This magnetic behaviour is attributed to the phase transformations and the increase in the grain size of the films occurring during annealing.

Phase Equilibria in the RuO -Bi 0 Xu0 System

Len., 1991, 10, (2), 69-70 Studies of interactions between CuO and the conductive phases RuOz or Bi,Ru,O, in thick-fdm resistors have been performed and the ternary phase diagram of the Ru0,-Bi,O,-CuO system is presented. The phase equilibria indicate reactions between the conductive Bi,Ru,O, phase in thick-fh resistor material and the CuO, which was added as a temperature coefficient of resistivity modifier, with CuO being incorporated into the pyochlore crystal structure, resulting in the Bi, - ,C~Ru,O, solid solution. When RuO, was the conductive component, CuO did not react with it.

Growth and Characterization of RuSe, Single Crystals

Mazer. Res. E d . , 1991, 126, (l), 11-17 Single crystals of RuSe,, up to 10 x 8 x 6 mm’, were grown by an oscillating chemical vapour transport method using ICI, as the transport agent. Optimum conditions for the growth of large single crystals are given. Crystal stoichiomeuy is discussed, and electrical resistivity and Hall effect measurement indicate n-type semiconducting properties.

S. BERNlK, M. HROVAT and D. KOLAR, J. Mater. sci.,

J.4. SHEU, Y.-S.SHIH, S.4. LIN and Y . 4 . HUANG,


CHEMICAL COMPOUNDS Crystal Growth and Properties of R2Ba2CuPt08 (R = Ho, Er, Y), R2 Ba Cu, PtO ,,, and Ba, CuPt O9

and T. FUKUDA, 3. Cyst. Growth, 1991, 109, (1-4),

Three new Pt complex oxides have been identified as products of the CuO-flux growth of R-Ba-Cu-0 (R = Ho, Er, Y) superconducting oxides in Pt crucibles. These oxides are formed under normal atmospheric conditions and a growth mechanism for the compounds involving incorporation of Pt from the crucible is proposed. The crystal structure of R,Ba,CuPtO, has been determined. The T-1” temperature dependence of the conductivity is explained by a -Cu~+-O~--Pt‘+-O~- conduction chain model. The magnetic susceptibility measurements reveal an antiferromagnetic interaction of spins Ho”, El’+, and Cuz+.

High-Nuclearity Platinum-Osmium Alloy Cluster Complexes. Synthesis and Structural Characterizations of Pt 0 s 6 - (CO) 2 2 (COD) and Pt, a 6 (CO) 21 (COD) 2

R. D. ADAMS, J.C. LII and w. wu, Inorg. Chem., 1991,

The fmt example of a possible series of new high- nuclearity Pt-0s carbonyl cluster complexes having structures based upon alternating layers of Pt and 0 s are reported. The clusters were formed when Pt,0s3(CO),,,(COD),, where COD is 1,s-cyclo- octadiene, was refluxed under N, for 30 min.

The Synthesis of Os3Pt Clusters. X-ray Crystal Structure of Os,Pt(CO) I I (PPh3)2 D. H. FARRAR, R. R. GUKATHASAN and J. A. L~NNISS, Inorg. Chim. Acra, 1991, 179, (2), 271-274 The reaction of 0s,(CO),,(NCMe) (1) with sources of PtL, gave new clusters 0s,Pt(CO),,L, as major products, where L is PPh, or PBu,Ph. Each 0s-Pt edge was bridged by a carbonyl ligand, while the remaining nine carbonyl ligands were terminally bound to 0s atoms. The minor products from the reaction of (1) and PtL, were phosphine-substituted derivatives of Os,(CO),, and the raft clusters 0s,(CO),, -,(NCMe), with n = 1, 2. Crystal structures of the products are given.

Syntheses and Crystal Structures of [Pd9As8 (PPh,) D. FENSKE and c. PERSAU, z. Anorg. Allg. Chem., 1991, 593, (2), 61-68 A new cluster [Pd,As,(PPh,),l which was prepared by reaction of [PdCI,@Ph,),l with As(SiMe,), was characterised by X-ray crystal structure analysis. The cluster molecule has four [Pd,(PPh,),l units bridged by As, units with a further Pd atom being located in the centre of the cluster. The reaction of [PdCl,(PPh,),l with Sb(SiMe,), yielded [Pd,Sb,(PPh,),l which has a b.c.c. Pd,-cluster.

Y. SAITO, T. SHISHIDO, N. TOYOTA, K. UKEI, T. SASAKI

426-43 1

30, (lo), 2257-2258

and [I’d9 Sb 6(PPh3)

Structural, Magnetic, and Charge Transport Properties of Bis[(5,10,15,20- Tetrameth ylporph yrinato)Palladium(II)l Perrhenate, [Pd(tmp)l [ReO, 1 E. M. MCGHEE, B. M. HOFFMAN and J . A. IBERS, Znorg. Chem., 1991, 30, (9), 2162-2165 Electrochemical oxidation was used to produce the new molecular conductor [Pd(tmp)l ,[ReO, 1, which is composed of partially oxidised Pd(tmp) cations stacked metal-over-metal and surrounded by chains of ReO, anions. Single crystal room temperature conductivity along the needle axis averages 30/Q cm, and can be fitted to an expression that describes a semiconductor with temperature-dependent carrier mobility, and is comparable with that of the best Pt- spine conductors, despite the interplanar separation being -3.38 hi, compared to that for Pt-Pt of 2.95 hi. This conductor is isostructural with [Ni(tmp)l ,[ReO,l and LCu(tmp)l ,[ReO,I.

Ring Migration Reactions of (C5Mes)Rh(PMe3)H2. Evidence for q 3 Slippage and Metal-to-Ring Hydride Migration w. D. JONES, v. L. KUYKENDALL and A. D. SELMECZY, Orgamtallics, 1991, 10, ( 3 , 1577-1586 The reactions of (C,Me,)Rh(PR,)H, (PR, =PMe,, PMe,Ph, PMePh,, PPh,) with D, gas occurred quickly at 25OC, leading to the stepwise exchange of H for D. Kinetic studies showed a second-order reaction mechanism involving Rh and D. (C,Me,)Rh(PMe,)H, also reacted with PMe, at 4OoC to yield C,Me,H and HRh(PMe,), in a reaction displaying bimolecular kinetics. Isotope effect studies showed no rate difference with the dideuteride Rh complex.

Synthesis and Reactivity of Rhodium(I) Complexes of the Type Rh(G

E. KwASKOWSKA-CHEC and A. M. TRZECIAK, Transinim Met. Chem., 1991, 16, (2), 212-214 The carbonyl ligands in the Rh’ complexes Rh(L-L)(CO), (L-L is anthranilate (AA) or N-phenylanthranilate (FA) ions) were replaced by P(OPh), to form the mono- or disubstituted products. Under Ar at [P(OPh),lfiRhl)4 the ortho-metdated Rh’ complex Rh[P(OPh) I - [P(OC,H,)(OPh),l was formed. The Rh(AA)(CO), complex was used as a catalyst precursor in hydroformylation of olefms.

Reaction of Ru(q-RC5 H4)C1(PPh3)2 with Carbon Dieulfide

Coord. Chem., 1991, 22, (4), 255-258 The reaction ofCS, with Ru(q-C,H,)Cl(PPh,), produced [Ru(q-C,H,)(CS,)(PPh,),l+ by two different routes. Results suggest that the formation of the CS, derivatives is related to the partial dissociation of the Ru-CI bond, which increases with the basicity of the phosphine attached to the metal.

L)(CO)[P(OPh) 3 1 and Rh(GL)[P(OPh) 3 1 2

A. GUTIERREZ-ALONSO and L. BALLESTER REVENTOS, 3.


ELECTROC HEMISTRY Electrocatalytic Properties of Ultrafine Platinum Particles for Oxidation of Methanol and Formic Acid in Aqueous Solutions

and Y. TAKASU, Electrochim. Acta, 1991, 36, (5/6),

The effect of size of ultrafime Pt particles prepared by vacuum evaporation onto a glassy C rod, on the electrochemical oxidation of MeOH and HCOOH acid was examined by cyclic voltamwtry. The specific activity for the oxidation of MeOH decreased by decreasing the Pt particle size, whereas that of the HCOOH acid increased as the particle size decreased.

XPS Analysis of Amorphous Ni-Nb-Sn-Pt Alloy Catalysts for Electro-Oxidation of Formaldehyde

Sci. Eng., 1991, A134, 1070-1073 Amorphous Ni-40Nb-xSn-(3-x)F't alloy ribbons were prepared and used for the electrmxidation of HCHO after surface activation by HF. Maximum activity was observed at - 0.4 at.%Sn. X P S revealed that the surface layer was rich in Pt and deficient in Ni, but that the surface concentration decreased continuously with increasing Sn content.

Electrochemical Properties of Ultra-Fine Palladium Particles for Adsorption and Absorption of Hydrogen in an Aqueous HClO, Solution

K. YAHIKOZAWA, Y. FUJII, Y. MATSUDA, K. NISHIMURA

973-978

A. KAWASHIMA, K. ASAMI and K. HASHIMOTO, Maoter.

N. TATEISHI, K. YAHIKOZAWA, K. NISHIMURA, M. SUZUKI, Y. IWANAGA, M. WATANABE, E. ENAMI, Y.

(7), 1235-1240 MATSUDA and Y. T ~ U , Electrochim. Acta, 1991,36,

Ultra-fine Pd particles were prepared by vacuum evaporation onto a plane of glassy C (GC) rod. Their diameters were estimated to be 2-10 nm by SEM. Properties of Pd/GC electrodes in H adsorption and absorption were characterised by cyclic voltammetry. Adsorption strength of H species on the Pd particles of Pd/GC did not depend on the particle size, whereas amounts of the adsorbed H species and the absorbed ones into the Pd particles were dependent.

Electrochemical Hydrogen lnsertion into Palladium and Palladium-Nickel Thin Films

tmchim. Acta, 1991, 36, (7), 1203-1208 A generator-detector mode with the rotating ring- disk electrode was used to determine the difference between Pd and Pt electrode behaviour and the origin of the larger overpotentials at Pd-H evolving cathodes. The use of thin f h (1-10 pm) Pd disk electrodes has allowed full H or D charging of the metal phase in short times. This electrode system enables measurements of the H uptake in PdH, f h s to be made, with PdH,.,, being the maximum.

J. M. ROSAMILIA, J. A. ABYS and B. MILLER, Elec-

The Role of the Electrolyte Anion in Anodic Dissolution of the Pd(100) Surface T. SOLOMUN, J. Electroanal. Chem. InteflaCial Elec- tmchem., 1991, 302, (1 and 2), 31-46 Electrodissolution of Pd during its electro-oxidation in H,SO, was studied by XPS, LEED, cyclic voltammetry and IR spectroscopy. At the beginning of the surface electro-oxidation reaction Pd species, showing a rather large shift of the (34 core levels (2.5 eV towards the high binding-energy site), were elec- trogenerated at the surface in H,SO,, but not in HCIO, electrolyte. Their concentration was directly related to the anion surface concentration. A surface complex of the type PdO(HS0,) acted as a precursor in the formation of highly soluble PdSO, . Adsorption Properties of an Iridium Oxide Electrode: A Thermodynamic Approach 0. A. PETRII and A. VITIN'SH, Elektdhimiya, 1991, 27, (4), 461-476 Adsorption properties of electrodes made of thermally prepared IrOx, deposited on Ti layers were studied by potentiometric titration during isoelectric conditions in 0.1 M KNO, . A strong dependence of the acid-oxidation properties of the IrO,/Ti electrode on the stoichiometry of the active oxidation surface, characterised by the value of the e lec tde potential at the determined pH of the solution, was observed.

Characterization of DSA-Type Oxygen Evolving Electrodes. Choice of Base Metal

HINDEN, T h e m h i m . Acta, 1991, 176, 31-47 The effect of the base metals: Ti, Ta, Zr, Nb and some of their alloys, on the performance of Ir02- Ta 0 coated DSA-type 0 -evolving electrodes was investigated. The thermal behaviour and 0 affinity sequence of the metals in relation to the electrode preparation procedure were determined ther- mogravimetrically . The chemical and electrochemical stability of the base metal was directly related, through the wear mechanism, to the savice life of the electrode, measured in 30% Hz SO, at 8OoC and 750 mA/crnZ. Ta-based electrodes have the longest service life of 1700 h, compared to 120 h for Ti-based electrodes.

Morphological and Microstructural Study of the TinrO, -Ta 0 Electrode: Effect of the Preparation Temperature

Electrochim. Acta, 1991, 36, (5/6), 991-998 Morphological and structural examinations of dimen- sionally stable electrode coatings (Ir02-Taz0,) (70:30 mol %) show that at moderate fumg tempexatures, - 55OOC, separation of phases occurs with the formation of agglomerates of I r 0 2 crystals and amorphous Ta,O,. At -750OC both crystalline IrO, and Ta,O, are present.

G. P. VERCESI, J. ROLEWIW, C. COMNINELLIS and J.

G. P . VERCESI, J.-Y. W I N and C. COMNINELLIS,


Reaction between [(TPP)Ru(CO)l'- and Methyl Iodide. Evidence for Formation of a Ruthenium(I1) Carbonyl Methylated Tetraphenylchlorin Derivative

WISH, Inorg. Chem., 1991, 30, (8), 1957-1960 This study provides the first example for elec- trogeneration of a methylated chlorin. The reaction between [(TPP)Ru(CO)l'-, where TPP is the dia- nion of tetraphenylporphyrin, and CH,I differs from that of reduced Co, Fe, and Rh porphyrins because a stable o-bonded CHI derivative is not formed.

Y. J. DENG, X. H. MU, P. TAGLIATESTA and K. M.

PHOTOCONVERSION Photocatalytic Dehydrogenation of Pen- tane in the Presence of RhCl(CO)(PR,), (R = CH,, iso-C,H, and n-C,H9)

CHIKOVA, E. A. GRIGORYAN, A. 0. BORISOV and v. D. MAKHAEV, Kinet. Katal., 1991, 32, (2), 473-477 Studies of the effect of the nature of phosphine ligands on the activity and selectivity of the process during dehydrogenation of p t a n e solutions in the presence of RhCI(CO)(PR,), (R = CHI, iso-C,H, and n-C, H,) were performed in the IR spectra region on >270nm light exposure.

Tris(2,2 '-bipyridine) Ruthenium(I1) Complex by Viologens m Anionic Micellar and Polyelectrolyte Solutions: Variation with Alkyl Chain of Viologens J. w. PARK, M. Y. SUK and B.-T. AHN, Bull. Korean Chem. Soc., 1990, 11, (6), 552-557 Luminescence quenching reactions of photoexcited tris(2,2 '-bipyridine) Ru(I1) complex cation, Ru(bpy) + , by dialkylviologens were studied in Na dodecyl sulphate (SDS), poly(styrenesu1phonate) (PSS) and poly(vinylsu1phonate) (WS) solutions. The relative quenching rate varies widely with the microheterogeneous media used. The highest quenching rate was observed for methyldodecylviologen in homogeneous aqueous medium, dibenzylviologen in SDS and PVS and dimethylviologen in PSS.

Preparation and Photochemical Charac- teristics of the Copolymer Pendant Tris(2,2 '-bipyridine)Ruthenium-Mercury [Ru(bpy), ,+.Hg2C16 Complex R. RAMARAJ, A. K I M and M. KANEKO, J. Photochem. Photobwl. A: Chem., 1991, 56, (2-3), 287-293 The title Ru-Hg copolymer pendant complex was prepared and characterised by IR, visible absorption and emission spectroscopies and emission decay measurements. The solubility and excited state lifetime both in DMF solution and the film state were quite different from those of the low molecular Ru- Hg complex reported before. The emission from the excited ply-Ru-Hg was much longer than that from the poly-Ru in DMF solution.

N. K. KHANNANOV, E. A. KOCHETKOVA, G. N. MEN-

Luminescence Quenching of

APPARATUS AND TECHNIQUE Preparation of an Oxygen Sensor Com- posed of Tightly Stacked Membranel- ElectrodelElectrolyte K. KATAKURA, A. NOMA, z. OGUMI and z. TAKEHARA, Denki Kugaku, 1991, 58, (12), 1184-1189 An amperometric 0 sensor operating at room temperature was constructed using a porous Pt cathode on Nafion and perfluoropolymer as the 0 transport limiting membrane, which was directly bound on the cathode by plasma polymerisation. The 0 reduction current increased with increasing 0 concentration, from 0 to 30 ppm. A microsized 0 sensor can be prepared in principle.

Kinetics of Oxygen Interaction with PtKeO, Sensors: Application of a New Pressure Modulation Spectroscopy A. DUBBE, H. D. WIEMHOFER, K. D. SCHIERBAUM and w. G ~ P E L , Sens. Actuators B, 1991,4, (1 & 2), 23-28 A new method for characterisation of the dynamic response of the electrode potential upon sinusoidal 0, partial-pressure variations, and its powerful application was demonstrated in a study of the kinetics of different Pt electrodes on GO-doped GO, elec- trolytes. Surface diffusion effects play a major part in the overall kinetics of the 0, response of their microstructures. Gradients of the 0 , surface concentration were analysed in an independent spectroscopic study on CeO, samples with Pt contacts.

A Laser Power Detector Built Up by Ap- plication of Thick-Film Technology J. NICOLICS and w. S M ~ A N A , Sens. Actuators A , 1991,

A structure for a laser power detector using thick-film technology was developed. The incident laser radiation caused a heat flow in a metal plate where the resultant temperature differences, detected by thick- fdm Pt sensor elements, acted as a measure of the laser power. The sensitivity of the sensor was calculated and experimentally determined. The indicated laser power was independent of the radial in- tensity distribution of the laser beam.

Schottky-Barrier and Conductivity Gas Sensors Based upon PdISnO, and PtiTiO, K. D. SCHIERBAUM, u. K. KIRNER, J . F. GEIGER and w . &PEL, Sens. Actuators B, 1991, 4, (1& 2), 87-94 Electronic conductivity, mixed conductivity and Schottky-barrier sensors based on SnO, and TiO, modified by Pt and Pd metals can be used to detect CO, CH,, H , and 0, gases. Sensor response signals result from changes in surface and bulk conduc- tivities or in Schottky-barrier heights, which are measured using different geometric arrangements of Pt or Pd metal contacts. Studies showed that reliable sensor properties can only be achieved either by forming stable metal/oxide interfaces or by adjusting a stable dopant distribution.

25, (1-3), 235-239


HETEROGENEOUS CATALYSIS Hydrogenation of Olefms on Platinum c.-M. PRADIER and Y. BERTHIER, 3. Catal., 1991,129,

The hydrogenation of buta-1,3-diene and isoprene was studied on three Pt planes. The reaction for buta- diene was structure sensitive, with an increase in the turnover frequency by a factor of 5 from the denser to the rougher planes: Pt(111)<Pt(100)<Pt(110). There is a remarkable correlation between variations of the reaction orders and changes in the selectivity. The surface works as a bi-functional catalyst: hydrogenation and exchange seem not to occur upon the same kind of sites. The catalytic surfaces works with a HC layer present, not identical on the three studied surfaces.

Hydrocracking and Isomerization of n- Octane and 2,2 ,.l-Trimethylpentane over a Platinum/Alumina-Pillared Clay c . DOBLIN, J . F. MATHEWS and T. w. TURNEY, Appl.

The hydrocracking and isomerisation of n-octane and 2,2,4trimethylpentane (TMP) over an AlzO,- pillared clay (A-PILC), containing 0.16% Pt were studied in a microreactor at atmospheric pressure, at 175-325OC and weight hourly space velocity of 0.48-7.5h. The Pt/A-PILC catalyst underwent an initial stabilisation period of -30 h, resulting in changes in the physical structure of the catalyst. The catalyst showed ideal hydrocracking behaviour for nC, giving high isomerisation yields, with a maximum isomer yield of 64% at 80% conversion. For hydrocracking 2,2,4-TMP, the major reaction was A type &scission giving a product with >96% isobutane at all conversions.

Platinum-Tin Complexing and Its Ap- plication to Catalysis

Catalysts for the dehydrogenation of long chain alkanes were prepared by impregnating a y-Al,O, support with a [PtCl,(SncI,),l2 - complex using H,PtCl, and SnCl, solutions in an acidic medium. The catalytic performance of the catalyst prepared by the complex method was remarkably improved compared to the Pt-Sn dehydrogenation catalyst prepared by non-complex methods.

Infrared Study of CO Adsorption on Pt- Rh/A12 0 Catalysts

Faraday Trans., 1991, 87, (9), 1479-1483 Studies of CO adsorption on Pt/Al,O,, Rh/Al,O, and Pt-Rh/Al,O,, at 303-573 K were performed by FTIR spectroxopy. Catalysts containing Rh were precalcined at either 673 K or 873 K before reduction in H, and exposure to CO. The intensities of IR bands due to gem-dicarbonyl and linear carbonyl species were a function of both the precalcination temperature and the temperature of contact with CO.

(2), 356-367

Catal., 1991, 70, (2), 197-212

L. Y. JIN, Apfd. catd., 1991, 72, (I), 33-38

J. A. ANDERSON and C. H. ROCHESTER, J. Chem. SOC.,

Improved Higher Alcohols Selectivity in Syngas Reaction (CO + H2) over Platinum Deposited on Rare Earth Ox- ides of the Fluorite Structure J. EL FALLAH, F. LE NORMAND, s. BOUJANA and A. KIENNEMANN, Eur. 3. Solid Stnte Inorg. Chem., 1991,

The effect of rare earth oxide as support on the reactivity of Pt in syngas conversions was tested. A chain growth process, giving up to C, alcohols is observed on Pt deposited on rare earth oxides of the fluorite type(CeO,,Pr,O,,,Tb,O,).Thisremarkableselec- tivity is explained by the creation of anionic vacancies at the interface of the metallic particle and the support, similar to that previously reported for Pd. On such catalytic sites both the dissociation of the CO molecule and the chain growth process occurs. F'raseodymia gives the most effective support for improved higher alcohol formation.

Hydrogenation of Acetylene over Various Group ,VnI Metals: Effect of Particle Size and Carbonaceous Deposits A. J. DEN HARTOG, M. DENG, F. JONGERIUS and v.

Supported Pt, Pd, Rh and Ir catalysts were studied for the hydrogenation of CzH2 and the effect of the particle size on this reaction was established. Rh and Ir show effects that can most probably be explained by the influence of the particle size on the intermediate of direct hydrogenation to C,H, while for Pt and Pd the effect of deposition of carbonaceous layers prevails.

Gas-Phase Hydrogenation of Styrenes by Transfer over Pd/AlPO, Catalysts

MARINAS and M. E. SEMPERE, React. Kinet. catal. Lett., 1991, 43, (11, 1-6 The hydrogenation of styrene and a-methylstyrene over Pd/AlPO,, using cyclohexene as donor is reported. The catalysts were activated in the pulse reactor and retained H, which was subsequently used to reduce the olefm. The amount of ethylbenzene produced from the styrene can be accounted for by H transferred by cyclohexene and H stored over the catalyst surface during treatment with cyclohexene, intended to reduce the impregnating metal salt.

Kinetics of Liquid-Phase Hydrogenation of Hexene-1 on Palladium Sulphide Catalyst L. v. SHALIMOVA, A. D. BERENTS, s. v. wwv and 0. v. CHEBAEVA, Kinet. Katal., 1991, 32, (I), 55-59 Studies of the kinetic dependence of hexene-1 hydrogenation in benzene solution in the liquid phase in a flow system over a Pd sulphide/Al,O, catalyst were performed at 50-150°C and HI pressure of 5 MPa. Intermediate adsorption stages were calculated and an equation for the rate of change of the concentrations of basic components was obtained.

28, Suppl., 433-436

PoNEc, J. Mol. Catal., 1990, 60, (l), 99-108

M. A. ARAhiENDfA, V. BORAU, C. JIMkNEZ, 1. M.


A New Palladium-Catalyzed Coupling Reaction of Vinyl and Allylic Triflates with Pyrimidine Nucleoeides

Vinyl trifluoromethane sulphonates (triflates) form Pd intermediates which react with pyrimidine nucleosides to yield C-5 alkyl substituted nucleosides, after hydrogenation of the vinyk coupling products with H, and Pd/C in MeOH under mild conditions. The reaction is a general one since mono-, disubstituted and cyclic vinylic triflates give high yields of the corresponding C-5 alkyl-substituted nucleoside.

Oxidation State of the Surface of Palladium in the Catalytic Combustion of Hydrogen M. G. JONES, T. G. NEVELL, R. J. EWEN and c. L. HONEYBOURNE, Appl. Catal., 1991, 70, (2), 277-286 The activity of supported Pd catalysts for the oxidation of H, was studied at 80-500°C using a microcalorimetric technique and XPS. The reaction involved a surface layer of 0, , and was inhibited by adsorbed H,O. Palladium(I1) oxide was formed on the surface of metallic Pd under 0, at 45OOC. Heating in H, at 25OOC reduced this surface layer and produced deactivated catalyst but the activity was subsequently restored by exposure to 0,.

Methylcyclopentane Conversion Catalysis by Zeolite Encaged Palladium Clusters and Palladium-Proton Adducts

M. E. HASAN, Can. 3. Chem., 1991,69, (2), 198-200

X. BAI and W. M. H. SACHTLER, 3. Caul., 1991, 129, (l), 121-129 The conversion of methylcyclopentane (MCP) was studied over the prototype catalysts HY, Pd/HY, PdNaHY and proton-free Pd/NaY. Ring opening of MCP to hexane isomers was catalysed by Pd, clusters, but ring enlargement (RE) of MCP to cyclohexane and benzene required metal sites and protons. The RE of MCP was catalysed by the “electrondeficient” [Pd,HI + adducts more effectively than by separate metal and acid sites. The catalysts containing Pd and protons in the same zeolite cavity, were dramatically more active for RE than a mixture of HY and proton-free PdNaY.

Direct and Indirect Promotion of PdN and CaZ + Ions x. BAI, z. ZHANG and w. M. H. SACHTLER, Appl. Catal., 1991, 72, (l), 165-178 Studies of Pd in Nay or Cay zeolites tested as catalysts for HC conversion reactions showed that the pre-exchanged Caz + cations in Y zeolite increase the concentration of [Pd,HI+ adducts and subsequently improve the rate and stability of the catalyst for ring enlargement, while decreasing the ring opening rate of methylcyclopentane. The results suggest a direct interaction of the charge compensating ions (Ca’ + or Na+) with Pd particles and an indirect effect viz. by affecting the concentration of electron-deficient Pd- proton-adducts.

Liquid-Phase Oxidation of Propylene on Supported Palladium Mono- and Bimetallic Catalysts in Acetic Acid

A. I. BORONIN and E. M. MOROZ, Kinet. Katal., 1991,

Studies of the oxidation of propylene and propylene glycol and their acetates in acetic acid solutions, in HNO, were performed in the presence of heterogeneous Pd, Pd-Pt and Pd-Rh catalysts deposited on C, SO, and TiO, supports. The Pd-Pt catalysts were found to be most resistant to deactivation in the presence of reactive S. One of the reasons for deactivation of the catalysts was the formation of cyanide metal complexes on the support surfaces.

Effect of Promoters on the Catalytic Ac- tivity of Rh,(CO),2/TiOz for CO Hydrogenation Y. CHEN, J. DU, Y. CHEN and z. DU, 3. Fuel Chem. Technol., 1991, 19, (l), 1-7 The activities for CO hydrogenation in a continuous flow microreactor of promoted Rh catalysts were in the order Rh, N-TiO, >Rh, /Ti0 , >Rh, /Mg-TiO, . On the Rh,N-TiO, catalyst CO was completely converted to CH, at 200OC, while for CO hydrogenation at various H,:CO ratios on Rh,/Mg-TiO,, CO, was always present in the product. Catalyst dispersions were determined by H,-0, titrations. A high H:M ratio occurred for Rh,(CO),,N,O,-TiO,, which was caused by the low temperature reduction of V,O, catalysed by metallic Rh. The H:Rh ratio was in the same order as their activities. Only a twin CO band without linear or bridged CO was found during temperature programmed adsorption and desorption of co. HCN Synthesis from NH, and CH, on Rh and Ir M. P. s u k ~ z and D. G. L~FFLER, React. Kinet. catal. Lett., 1991, 43, (l), 195-199 The synthesis of hydrocyanic acid from CH, and NH, on Rh and Ir wires was studied at temperatures between 1200 and 1500 K, at a pressure of one atmosphere. Activation energies and pre-exponential factors are reported.

The Effect of CeO Support upon Activity and Selectivity of Ru and Co Fischer Tropsch Catalysts

M. WINTERBOTTOM, Eur. J. solid state Inorg. Chem., 1991, 28, (2), 453-456 5% Ru and Co catalysts supported on G O , were prepared by impregnation and characterised by TPR. Their catalytic activities and selectivities were tested in H, and CO reactions and compared with a Ru/SiO, catalyst in the range 1-9 atm and 260OC. RdSiO, and Co/SiO, catalysts gave CH, only at 1 atm and 70% CH, at 9 atm, while Ru/GO, and Co/CeO, gave significantly smaller quantities (20-80%) of CH, over the same pressure range.

A. V. KARANDIN, E. V. GUSEVSXAYA, V. A. LIKHOLOBOV,

32, (2), 367-374

A. F. Y. AL-SHAMhtARY, I. T. CAGA, A. Y. TATA and J.

Platinum MetaE Rev., 1991, 35, (3) 160

HOMOGENEOUS CATALYSIS Substitution of Halogen in Vinylbromide and Reduction of Vinylhalogenides to Ethylene in the Syetem PtO-NaI- HClO4-H 2 0 S. A. MITCHENKO, V. V. ZAMASHCHIKOV and A. A. SHUBIN, Kinet. Katal., 1991, 32, (2), 343-345 Studies of the kinetics of the NaI (2.5 M)- HClO4(O-2.5 M)-H20 system at 8OoC catalysed by Pt(I1) (0.004-0.06 M) showed the substitution of B by iodine in vinylbromide (RBr). When tHCl0,I > 0, parallel substitution of RBr occurred by reduction to ethylene, and in acid solutions the formed vinyliodide also reacted with Pt(II) yielding ethylene. A phase mechanism is provided which includes oxidative addition of vinylhalogenide to Pt(I1) with the intermediate formation of a-vinyl Pt(IV) complexes.

’ H-NMR-Study of Deuterium Exchange in Styrene under the Conditions of Hydrocarboxylation Catalysed by Palladium Complexes YU. G. NOSKOV, N. A. NOVIKOV, M. I. TEREKHOVA and E. s. PETROV, Kinet. Katal., 1991, 32, (2), 331-335 A study of the hydrocarboxylation of styrene catalysed by PdCI,(Ph,P), at 1 10°C and CO pressure of 2.0 MPa by the deuterium exchange method showed that terminal protons of unreacted substrate were noticeably substituted by D, but that proton exchange in the a-position of phenyl groups was not observed. When the pressure was decreased and SnCl, was added, proton exchange occurred in both C atoms of the vinyl styrene group.

Homogeneous Catalytic Hydrogenation of Alkenes by Zero-Valent Palladium Complexes of cis-Fiued Dinitrogen Ligands R. VAN ASSELT and C. J. ELSEVIER, 3. MOl. Catd., 1991, 65, (3), L13-Ll9 Zero-valent Pd complexes (DIAN)Pd(olefm) containing a cis-fmed dinitrogen ligand (DIAN) (N,N’-diaryl-diiminmenaphthene) are active as catalysts in the homogeneous hydrogenation of various unsaturated substrates. The title hydrogenation can be performed under mild conditions (THF, 2OoC and 1-1.5 bar of H, pressure). This results in complete conversion of various substituted alkenes to the corresponding alkanes.

Palladium-Catalyzed Coupling Reactione of Trifluoroacetimidoyl Iodides with Olefins and 1-Alkynes K. ~ A M A and H. WATANABE, Tmahedtim Lett.,

Pd-catalysed coupling of trifluoroacetimidoyl iodides with olefins and also 1-alkpes produced vifluoromethylated a, &unsaturated imines which were transformed into N heterocycles bearing CF , - group. N-aryl vifluoroacetimidoyl iodides underwent smooth palladation with Pd , (dba) , .CHU 3 .

1991, 32, (ll), 1459-1462

Palladium Catalysed Tandem Cyclieation- Anion Capture Processes Initiated by Alkyl- and ?r-Allyl-Palladium Species R. GRIGG, s. SUKIRTHALINGAM and v. SRIDHARAN, Tetrahedron Len., 1991, 32, (22), 2545-2548 Palladium catalysed tandem cyclisation-anion capture processes initiated by oxidative addition of benzylic or allylic halides or acetates to Pd(0) occurred regio- and stereo-specifically in good yield. The benzylic halide reacted with Na tetraphenylborate in the presence of Pd(0) to yield 69 % of the organic species. Examples of “anion” capture involving formate (H-), and organo- Sn, -Zn and -B species are described.

Palladium-Catalyzed @-Vinylation of Vinyl Acetate with En01 Triflates. An Entry to 1 -Acetoxy-1 , 3-Dienes P. G. CIATTINI, E. MORERA and G. ORTAR, Tetrahedron

Reaction of enol viflates with vinyl acetate in the presence of Pd(0Ac) , catalyst produced 1-acetoxy-1, 3-dienes as the major products in 40-79% isolated yields. Formation of the 8-vinylated product was si@icantly favoured. The results showed that steric effects prevail over electronic factors in these organo- Pd reactions, in contrast to the corresponding reactions with enol ethers where electronic factors predominate.

Synthesie of Carboxylic and Phosphonic a-Amino Acids Using Palladium Allylic Alkylation

Lett., 1991, 32, (12), 1579-1582

J. P. GENET, S. JUGE, I. BESNIER, J. UZIEL, D. FERROUD, N. KARDOS, S. ACHI, J. RUIZ-MONIES and S.

78 1-786 THoRIMBERT, Bull. sot. Chim. Fr., 1990, 12, (6),

Schiff bases derived h m glycine and alanine esters were alkylated in the presence of Pd catalysts under neutral or basic conditions using dylic carbonates, esters or halides. Asymmetric Pd allylic alkylation of the benzophenone imine glycine methyl ester using Pd(OAc), + (+)DIOP was achieved with up to 70% ee. After hydrolysis, several functionalised a- aminoacids-enzyme inhibitors-were obtained.

Cationic PaUadium(II)-Diphosphine Com- plexes as Catalysts for the Carbonylation of Alkenes to Ketones

Chem. Soc., Chem. Commun., 1991, (6), 421-423 Cationic Pd complexes of the type [(dppp)Pd (solvent),ltXI,, where X = a non or weakly co-ordinating anion and dppp = 1,3-bis(diphenylphosphino)propane, are active catalysts for the carbonylation to ketones, for the selective formation of E-1,5-diphenylpent-l-en-3-one from styrene. In the presence of water and depending on the acidity conditions dimerisation to the much less catalytically active [(dppp)Pd(p-OH),Pd(dppp)IX, takes place, the structure of which has been determined by X-ray crystallography.

C. PISANO, G. CONSIGLIO, A. SIRONf and M. MORET, 3.


New Highly Water-Soluble Surfactants Stabilize Colloidal Rhodium(0) Suspen- sions Useful in Biphasic Catalysis

Catal., 1991, 65, (3), L35-L40 New highly water-soluble uisulphonated surfactants C H ,, and C ,H efficiently stabilise suspensions of colloidal (20-301) ~ ( 0 ) particles. These novel protective-colloid agents provide the means to perform catalytic hydrogenations of alkenes without cosolvents in real biphasic liquid-liquid conditions, and to recycle the aqueous colloidal suspensions after decantation.

Selective Catalytic Reduction of Aromatic Nitro Compounds Using CO and Water with Highly Active Rhodium-Phosphine Chelate Complexes

Caul., 1991, 65, (3), L5-L7 The reduction of aromatic nitro compounds, such as nitrobenzene, nitroanilines, chloronitrobenzenes, etc., was found to proceed at significant rates with remarkably high nitro-group selectivities under extremely mild reaction conditions of room temperature, and atmospheric CO pressure, using Rh phosphine chelate complexes. The reduction was complete in the case of pnitroaniline. 1-Nitro- anthraquinone was also converted to l-amino- anthraquinone with extremely high selectivity.

Homogeneous Catalytic Asymmetric Hydrogenolysis of Sodium Epoxysuc- ciuate: the First Example of Asymmetric Hydrogenolysis of an Epoxide A. s. c. CHAN and J. P. COLEMAN, 3. Chem. SOC.,

The fmt example of the asymmetric catalytic hydrogenolysis of an epoxide, Na epoxysuccinate, is discussed in which the chiral product is formed via a critical bond-brraking process using Rh catalysts containing chiral phosphine ligands. The enantioselec- tivity of the catalyst system was found to be independent of the H, pressure, and the reaction rate is faster under higher H, pressure, while the enan- Uoselectivity is lower at higher reaction temperatures.

Regioselective Rhodium-Catalysed Hydroformylation of Olefins: Efficient Synthesis of Ethyl 2-Formylpropanoate from Ethyl Acrylate D. NEIESECKER and R. &u, N m J . Chem., 1991, 15,

Ethyl acrylate hydroformylation was performed using in situ generated catalysts from tRh(CO),ClI, and a phosphole or phosphanorbornadiene at 40°C and 20 bar syngas pressure and was compared to the Rh/1,4bis(diphenylphosphino)butane system. The hydroformylation of ethyl acrylate was brought about under mild reaction conditions by a Rh- monophosphane system. The phosphanorborna- dienes were superior ligands for this reaction.

C. LARPENT, F. BRISE-LE ME" and H. PATIN, 3. MOl.

K. NOMURA, M. ISHINO and M. M A M A , 3. MOl.

Chem. C a m n . , 1991, (9, 535-536

(4), 279-281

Rhodium(III) Biphasic and Phase- Transfer-Catalyzed Hydrogenolysis of Chloroarenes under Exceptionally Mild Conditions v. v. GRUSHIN and H. ALPER, & g a m u ~ ~ i c s , 1991,

The Rh(II1) complexes L,Rh(H)Cl, tL = tricyclohexylphosphine or triisopropylphosphinel were excellent catalysts for the hydrogenolysis of chloroarenes. The reaction proceeded under biphasic (40% NaOH, PhCH,) conditions, or giving higher product yields, under phase-transfer conditions, using benzyltriethylammonium chloride as the quaternary ammonium salt. The reaction occurred under mild conditions.

Catalytic Tail-to-Tail Dimerization of Methyl Acrylate Using Rh(IIQ Catalysts M. BROOKHART and s. SABO-ETIENNE, 3. Am. Chem.

Cp*(P(OMe),)Rh(C,H,)(H)+(l) (where Cp* is C,Me,) catalysed ethylene dimerisation and further treatment of (1) with methyl acrylate (MA) resulted in initial formation of Cp*(P(OMe),)Rh(CH,CH,- CO,Me)+ followed by slow tail-to-tail dimerisation of MA. A much more reactive catalyst was prepared when Cp*(C, H,)RhCH, CH, CH, -pH+ (2) was used in which P(OMe), was replaced by a labile ethylene ligand. A long-lived catalyst system could be generated by adding neat MA to (2) under 1 atm of H, . Total turnover numbers of up to 1.3 x 10' were achieved with > 99% conversion of MA.

Rhodium(II) Perfluorobutyrate Catalyzed Hydrosilylation of 1-Alkynes. Trans Ad- dition and Rearrangement to AUylsilanes

CLAYTON and J. LIN, organometa&cs, 1991, 10, (5 ) ,

Hydrosilylation of 1-alkynes catalysed by Rh(I1) periluorobutyrate or chloroplatinic acid formed either allylsilaws or vinylsilanes in moderate to high isolated yields, dependent on the mode of addition of reactants. The duality of these transformations depended on co-ordination of the organosilane or akyne with the transition-metal catalyst.

Hydrosilylation of Phenylacetylene via an Oe(SiEt , ) (q2 -H2) Intermediate Catalyzed by OsHCl(C0) (FPr ,)

Organometallics, 1991, 10, (2), 462-466 The five-co-ordinated hydrido carbonyl complex OsHCI(CO)(F'Pr,), catalysed the addition of triethylsilane to phenylacetylene. Trans- and cis- F'hHC=CH(SiEt,) were selectively obtained in high yields depending on the reaction conditions. Although the +yl compound Os((El- HC=CHPh)Cl(CO) (P'Pr,), was the main species under hydrosilylation conditions, the d o n proceeded via the silyl eydrogen intermediate

10, (5 ) , 1620-1622

SOC., 1991, 113, (7), 2777-2779

M. P. DOYLE, K. G. HIGH, C. L. NESLONEY, T. W.

1225-1226

M. A. ESTERIELAS, L. A. OR0 and C. VALERO,

Os(SEt3)CI (11 '-Hd(co)(PPr3) 2.


Ruthenium-Catalysed Aerobic Oxidation of Alcohols via Multistep Electron Transfer

3. Chem. Soc., Chem. Commun., 1991, (7), 473-475 The aerobic oxidation of primary alcohols occurs under mild conditions at 2OoC in air via a triple catalytic system of RuCl(0Ac) (PPh,) ,-hydro- quinone-Co(salophen) (PPh,) [H,salophen = N, N'-bis(salicylidene)-o-phenylenediaminel. The present multistep electron transfer system leads to a very mild aerobic process which can be run under a reduced partial pressure of O,(air).

Formaldehyde and Formates as Sources of Synthesis Gas via Ruthenium- Catalyzed Decomposition Reactions

Mol. Catal., 1991, 64, (3), 337-347 Paraformaldehyde can be decomposed into mostly CO and H, with a Ru phosphine catalytic system, and with the s a m catalyst HCOOH is fully decarbox- ylated into CO, and H,. The best chemical systems for the generation of CO/H2 mixtures are aqueous methyl formate solutions. Ru , (CO) I I - tricyclohexylphosphine decarbonylated methyl formate, and simultaneously catalysed the water gas shift reaction. The catalytic species is [HRu , (CO) ,I I - formed by the reaction of Ru , (CO) with phosphine and water. The present precess can be applied to hydrogenation and to hydrocarbonylation reactions.

Selective Reduction of Dimethyl Oxalate by Ruthenium Carbonyl Carboxylates in Homogeneous Phase. Part IS'

PIACENTI, 3. Mol. Catal., 1991, 64, (3), 257-267 Ethylene glycol can be selectively obtained from dhethyl oxalate by hydrogenation in homogeneous phase in the presence of Ru,(CO),(CH,COO),- (PPr,),. In order to avoid decomposing the substrate the hydrogenation must be performed at 120°C to completely convert the oxalic diester and then at 18OOC to hydrogenate the intermediate methyl glycolate.

Catalytic Carbonylation of Acetone Oxime at Bisoximatodiruthenium Complexes: A Simple Access to Anhydrous Acetonine. Isolation and Molecular Structure of [Ru~(CO),(M~~CNO)~(M~~CNOH)I M. LANGE", n. SMIECKLI-EVANS and G. sfh- FINK, Hdv. Chim. A m , 1991, 74, (3), 549-553 Acetone oxime reacted with CO in the presence of catalytic amounts of [Ru,(CO),(Me,CNO),- (Me,CNOH),l (1) to yield 2,3,4,5,-tetrahydro- 2,2,4,4,6-pentamethylpyrimidine (acetonine), CO , and NH , . The reaction may proceed via carbonylation of Me,C=NOH to the unstable intermediate Me, C = N - OCHO which undergoes decarboxylation to give the corresponding imine Me,C=NH.

J.-E.BdiCKVALL, R. L. CHOWDHURY and U. KARLSON,

G. JENNER, E. M. NAHME and S. LIB-KONRATH, 3.

U. MATl'EOLI, G. MENCHI, M. BIANCHI and P.

Ruthenium Complex-Catalysed Highly Selective Codimerisation of Acetylenes and Alkenes T.-A. MITSUDO, s.-w. ZHANG, M. NAGAO and T. WATANABE, 3. Chem. SOC., Chem. Conmnm., 1991,

2,CDienes were prepared in high yields with high regioselectivity by the codimerisation of acetylenes and alkenes in the presence of a catalytic amount of Ru(cod)(cot), where cod is cycloocta-1,5-diene and cot is cycloocta-1,3,5-triene, at 80OC. The best yield was obtained in pyridine, while in triethylamine, toluene and tri-n-butylamine as solvents, the yields were low.

Reactivity and Catalytic Activity of [RuBr2(Me2SO),l

Chim. Acza, 1991, 179, (l), 17-23 [RuBr,(Me,SO),l was used as precursor for the synthesis of many Ru(1I) complexes containing bromide ion and other ligands. The complexes synthesised were of the types: [RuBr,L,l (L=PPh,; L, =phen or bpy), [RuBr,(Me,SO),L,l (L=py, hPh3; L z =phen, bpy or o-phenylenediamine), etc. [RuBr , (Me SO) , 1 was used as a catalyst for the oxidation of PPh, by 0,.

(8), 598-599

B. C. PAUL, U. C. S A R h U and R. K. PODDAR, h r g .

FUEL CELLS A Methanol Fuel Cell Having a Molybdenum-Modified Platinum-SPE Membrane Electrode H. NAKAJIMA,~. Chem. Technol. Bwtechnol., 1991,50,

Studies of the modiflition of a methanol fuel cell made of a Pt-solid polymer electrolyte composite (Pt- SPE) with Mo showed that adsorption of Mo species on Pt enhances catalytic activity for MeOH oxidation both at F't and Pt-SPE electrodes. The treatment with Mo increased the cell voltage by 100-200 mV at a current density lower than 2 mA per apparent unit area. MeOH permeated through the SPE membrane and reduced stability of the fuel cell.

(4), 555-561

CORROSION PROTECTION Alloys Cathodically Modified with Noble Metals J. H. POTGIETER, 3. Appl. Electmchem., 1991,21, (6), 47 1-482 Cathodic alloying platinum group metal additives to Cr greatly increases the corrosion resistance of Cr in non-oxidising acid environments. The corrosion resistance of Fe-Cr stainless steels was significantly increased by addition of <0.5% of platinum group metals. When Mo and platinum p u p metals occurred together in the alloy, a synergistic beneficial effect was exerted on the corrosion mistance. AUoyiug of stainless steels with Pd leads to a significant increase in the corrosion resistance of the steels.


CHEMICAL TECHNOLOGY ELECTRICAL AND ELECTRONIC ENGINEERING New Methods of Uranium0 Production

Using a Pt-Loaded . Gas-Diffusion Electrode M. SHIBATA and N. FURWA, 3. Appl. Electrochem.,

A local-cell mode and a fuel-cell mode are proposed as new methods for the production of uranous nitrate. In the local-cell mode the cell consists of a Pt loaded gas diffusion electrode and a system of circulation for uranyl nitrate solution and H gas, although H gas is required instead of the power source. H gas is the more economical method if it is easily obtained. In the fuel-cell mode the reduction can take place at a Pt gauze cathode in the catholyte, above the gas diffusion electrode. Uranyl ions are spontaneously reduced to 250-300 gldm' U(1V) using these methods and electrical energy is obtained by the fuel-cell mode.

Water Gas Shift Reaction Assisted by a Palladium Membrane Reactor

Eng. Chem. Res., 1991, 30, (3), 585-589 The water gas shift reaction was operated at 673 K in a double tubular type membrane reactor, the inner tube of which was Pd membrane of thickness 20 pm, supported on a porous glass cylinder. The membrane reactor gave higher levels of CO conversion beyond the equilibrium attainable in a closed system, resulting from a shift of thermodynamic equilibrium toward the product side, caused by the selective and rapid removal of H from the reaction system. The amount of steam needed to achieve reasonable levels of conversion could be reduced, and from computer simulation, the high reaction efficiency attained by this membrane reactor is credited to the thinness of the Pd fdm.

1991, 21, (3), 226-230

S. UEMIYA, N. SATO, H. ANDO and E. KIKUCHI, Id.

GLASS TECHNOLOGY Heterogeneous Platinum Nucleation and Crystallization of a Heavy-Metal Fluoride Glass

Am. Ceram. Soc., 1991, 74, (4), 788-796 The effect of controlled heterogeneous nucleation by Pt on the crystallisation of a ZrF,-BaF,-LaF,-AlF,- NaF glass was studied, using various levels of Pt doping introduced into the glass by a combination of PtCl, doping and melting-atmosphere variation. The effect of doping levels and melting conditions on the incorporation of Pt and the subsequent nucleation of crystals was studied by optical microscopy, SEM, DSC and XRD. Increased Pt in the glass increased the number of nucleation sites for the growth of p- ZrF,-BaF, crystals. The crystallisation of this glass changed from surface controlled to bulk controlled with an increased number of nuclei. An accurate ap- proximation of the number of nuclei in the glass was also found.

J. M. JEWELL, J. JAGANATHAN and I. D. AGGARWAL, 7.

Conduction Mechanism in PtSi/Si Schottky Diodes M. WITTMER, Phys. Rev. B, 1991, 43, (5), 4385-4395 The conduction mechanism in PtSi/Si Schottky diodes was studied over temperatures 80-300 K. Above 100 K the forward current-voltage (IN) characteristic of the diodes is highly ideal and obeys the thermionic-emission theory, including image- force lowering of the barrier. Some diodes show a deviation from this behaviour, due to carrier recom- bination in the depletion region. Carrier recombina- tion is also responsible for the soft behaviour of the reverse I N characteristic. The temperature dependence of the barrier height and the bias- independent position of the quasi-Fermi-level at the interface are associated with a high density of interface states. The activation energy for current transport at low temperatures suggests that these states are due to substitutional Pt atoms on the Si.

The Effect of Sintering Temperature on the Barrier Height of pType PtSi Schottky Diodes V. W. L. CHIN, S. M. NEWBERY, J. W. V. STOREY and U. THEDEN, AUt. 3. Phys., 1991, 44, (I), 67-72 The effect of sintering temperature on the barrier height of p-type <100> PtSi Schottky diodes was studied by various means. The diodes sintered in a furnace under foaming gas at 35OOC for 40 min had a barrier height of 0.235 eV, which is lower than diodes sintered at 475OC for an additional 20 minutes (0.290 eV). For IR detection a low barrier height and high IR responsivity are necessary. Thus sintering by the first method is preferable, giving a cutoff wavelength of 5.3 pm at a reverse bias of 2 V, and a Schottky emission coefficient of -0.5 eV-".

Ultraviolet, Visible, and Infrared Response of PtSi Schottky-Barrier Detec- tors Operated in the Front-Illuminated Mode C. K. CHEN, B. NECHAY and B.-Y. TSAUR, IEEE Trans. Electron Devices, 1991, 38, (9, 1094-1103 The quantum efficiency of PtSi Schottky barrier detectors was measured as a function of wavelength, from 0.23-7 pm. For front-illuminated PtSilp-Si devices at low temperatures, quantum efficiencies of 40-70% are obtained for the UV and visible regions with little loss of the IR photoresponse that is obtained for operation in the conventional back- illumination mode. At room temperatures for front- illumination the quantum efficiencies are - the same in the UV and visible regions, but the IR response decreases abruptly beyond the Si absorption edge. Calculated quantum efficiencies in the UV and visible regions agree well with measured efficiencies. The temporal response of front-illuminated PtSilp-Si was fast enough for operation at video frame rates.

Platinum Metak Rev., 1991, 35, (3) 164

Wear Reliabiliiy of Gold-Flashed Palladium vs. Hard Gold on a High-speed Digital Connector System

Plat. Surf. Finish., 1991, 78, (3), 5743 The wear characteristics of Au-flashed Pd and hard Au terminals in high-speed digital connector systems were evaluatedafter 60, 125, 250, 375, 500 and 1000 insertion and withdrawal cycles for thicknesses in the range 1.25 to 2.5 pm. Contact areas and wear tracks were examined by various techniques. The location, size, shape and depth of wear tracks were quantitatively examined and compared.

Thermal Stability of Pd-In Ohmic Con- tacts to n-GaAs Formed by Scanned Elec- tron Beam and Rapid Thermal Annealing

Lett., 1991, 27, (2), 149-151 Thermally stable and low resistance Pd-In ohmic contacts to n-GaAs were formed using scanned electron beam (SEB) and rapid thermal annealing (RTA). A specific contact resistance e, of - Q cm2 was obtained using both techniques with the SEB annealed contacts exhibiting a superior surface morphology. High temperature ageing of the contacts showed that the SEB annealed contacts were more stable than RTA contacts, as displayed by an increase in their respective e, values, a factor of - 5 for SEB annealed contacts, against an increase by a factor of -8 for RTA contacts after 25 h of ageing.

Thermally Stable and Nonspiking Pd/Sb(Mn) Ohmic Contact to p-GaAs

E. J. KUDRAK, J. A. ABYS, I . KADIJA and J. J . MAISANO,

K. PRASAD, L. FARAONE aiid A. G. NASSIBIAN, Electron.

C. C. HAN, X. Z. WANG, S. S. LAU, R. M. POTEMSKI, M. A. TISCHLER and T. F. KUECH, Appl. PbS. Lett., 1991, 58, (15), 1617-1619 A thermally stable, nonspiking Pd/Sb(Mn) ohmic contact to p-GaAs was developed based on the solid- phase regrowth mechanism. The contact metallisa- tion consisted of a layered structure of Pd(250 i)/Sb(100 A)/Mn(lO A)/Pd(250 A)/p-GaAs. Rapid thermal annealing of the contact at 50OOC for 10 s yielded contact resistivities of - 2 x 10W6 cm’ and 4 x lo-’ Q cm’ on substrates doped to 2.5 x IO1*/cm3 and 4 x 1019/cm3, respectively.

Temperature Cycling Effec9s between Sn/Pb Solder and Thick Film Pd/Ag Con- ductor Metallization B.-S. ~ I O U , K. c. LIU, J.-G. DUH and P. s. PALANISAMY, IEEE Trans. Components, Hybrids, Manuf Technol., 1991, 14, (l), 233-237 Thermal cycling effects on the solder joint between thick f im mixed Pd/Ag conductor and Sn/Pb solder are investigated. Microstructural evolution of the interfacial morphology, elemental and phase distribution are probed by electron microscopy and XRD. Microstructural analysis reveals the formation of intermetallic compounds: Pd Sn, Pd, Sn, Pd Sn ,, PdSn, Pd,Pb, Ag,Snand Ag,Sn after thermal cycles from -55 to +125OC.

Contact Resistance Characteristics of Noble Metal Alloys for Connector Contacts s. UMEMURA, K . 4 . YASUDA and T. AOKI, IEEE Trans. Componenrs, Hybrids, Manuf Technol.. 1991,14, ( I ) ,

Contact resistance characteristics, corrosion characteristics and the degradation mechanism for Pd, Ag, Au and Ni containing binary and ternary alloys were investigated to find useful lower cost noble metal alloy for connector contacts. The test conductor contacts are clad inlays mated with each other, clad inlays mated with hard gold plating and clad inlays with hard gold flash mated with inlays of the same material. Air mixed with SO,, NO,, Cl, or H,S were the test gases. The following alloys are listed in order of increasing contact resistance: Au- Ag, Ag-Pd, Au-Ag-Pd, Au-Pd and Pd-Ni. The domi- nant corrosion products causing an increase in contact resistance were the chlorides in Pd alloys.

A Study of the Discharge Phenomena of Rhodium-Plated Contact Reed Switches T. KOBAYASHI, K. HINOHARA and C. KAWAKITA, IEEE Trans. Componenrs, Hybrids, Manuf Technol., 1991, 14, (l), 20-22 The discharge phenomena of high breakdown voltage reed switches, such as the pressurised reed switch and vacuum reed switch, and the discharge phenomena of general purpose reed switches, with respect to their basic mechanism and reactions were studied. Rh- plated reed switches with contacts treated with high temperature 0 for surface deactivation were used in the study. lXe contacts were analysed after discharge, and it was found that the N cation and 0 anion serve as carriers in the discharge for the pressurised reed switch and general purpose reed switch, and a nitride is formed on the cathode and oxidation increases on the anode. In the vacuum reed switch, the 0 anion triggers the discharge as a carrier, and oxidation increases on the anode.

181-186

MEDICAL USES Screening of a Stable Cholesterol Ox- idase for the Fabrication of Microbiosen- sor of Cholesterol by the Embodiment of Cholesterol Oxidase and a Platinized Platinum Electrode

IKARIYAMA, Denki Kagaku, 1990, 58, (12),

Microbiosensors for cholesterol of diameter 100 pm were fabricated by direct imbilisation of cholesterol oxidases from different sources on a platinised Pt electrode. The response current of the cholesterol senwr decreased gradually at +0.6 V (vs. Ag/AgCl), however, reproducible, stable responses were obtained at +0.5 V. The response of the microbiosensor for cholesterol determination was very rapid, the response time being 20 s. This sensor detects cholesterol contents of 1.3-52 pM.

S. YAMAUCHI, M. YAOITA, R. NAGAI, Y. YOSHIDA and Y.

1 103- 1106


NEW PATENTS METALS AND ALLOYS Platinum-Cobalt-Boron Alloy for Permanent Magnets VANDERBILT UNIV. World Appl. 90/13,134A A magnetic PtCoB alloy contains 12-14 at.% B and Pt and Co in amounts to give a Pt:Co atomic ratio of 0.90-1.1, and is prepared by rapid solidification of a homogeneous melt of the alloy to form a casting, and heat treating to improve its magnetic microstructure and increase coercivity. The alloy is used for permanent magnets, especially where large energy products, corrosion resistance and fracture toughness are required.

Palladium Alloys with Oxidation Resistant Surface Coating JOHNSON M A ~ Y P.L.C. U. S. Patent 4,960,647 Pd metal or Pd alloys, preferably 30% Pd-70% Ag, are treated by wetting the surface with 0.5-10 wt.% boric acid, and heating at 25-150OC b r 4-5 hours to produce a ceramic-like surface which is resistant to oxidation. The treated metal or alloy is specifically claimed for use between layers of dielectric as a capacitor.

Palladium Material Containing Boron for Welded Pipes TANAKA KIKINZOKU KOGYO

Japanese Appl. 2/205,638 A Pd based material containing B is manufactured by melting B rich Pd or F'd alloy together with B poor Pd or Pd alloy in vacuum. Oxidation of B during the manufacture of the material is mostly avoided, and Pd alloys containing B at high precision can be produced. The Pd material is used for welded pipes of H, purifiers.

Platinum Alloy Spring for Ornamental Use TANAKA KIKINZOKU KOCYO

Japanese Appl. 21250,946 A Pt alloy spring consisting of 84-96 wt.% Pt, 1-10 wt.% Ga and 0.5-10 wt.% Cu is made by brazing the components, followed by heat treatingat 400-600°C. The spring is used for tiepins and clip form brooches.

Production of a Fine-Grained Alloy Powder TANAKA KIKINZOKU KOGYO

Japanese Appl. 21254,101 A fine-grained alloy powder is produced by thermal treatment at 300-60O0C of a fine-grained composite powder of Ag with Pt or Pd, in a fused alkaline salt such as NaOH, to alloy the composite powder. A fine-grained alloy powder is produced which has high reliability for use in pastes and solders.

Magneto-Resistive Alloy Containing Rhodium and Palladium URALS UNIV. Russian Patent 1,534,082 An alloy having a magneto-resistive effect up to 7.5 times higher than that of the known alloy contains 57.7-64.3 wt.% Rh, 1.4-8.1 wt.% Pd and balance Fe, and is produced in an arc furnace. The alloys have an increased magneto-resistive effect and an ex- tended range of working temperatures.

ELECTROCHEMISTRY Deuterium-Lithium Cold Fusion Energy Cell DREXLER TECHN. CORP. World Appl. 90/13,897A An energy conversion cell includes heavy water and an electrolyte containing 6-LiOD, electrodes, and an ion accumulator having a D ion and Li ion permeable surface layer, preferably of Pd or F'd alloy, which allows ion-ion combination. The apparatus separates the electrolysis and ion accumulation processes, and by applying a variable voltage local ion flow can be changed, which can trigger the fusion process.

Modified Palladium Cathode for Cold Fusion Type Electrochemical Process JOHNSON t u n m y P.L.C. World Appl. 90/15,415A A heat generating electrochemical process of the cold fusion type may be obtained by electrolysis of D,O using a modified Pd cathode. Pd of grain size 10-40 pm is modified by combination with rare earths, Y, Sc, Ce, Gd, Li enriched with Li-6, or Ag, and may have a coating which is a modified surface region of Pd black or a PdIAg alloy. When the compositions are loaded with deuterium cold fusion can occur, producing heat, neutrons and/or tritium.

Electrolytic Production of Ozone SASAKURA KIKAI SEIS. Japanese Appl. 21259,090 Ozone production by water electrolysis using a cation-exchange resin of a peduorosulphonic acid type uses a cathode of porous Ni or Ni alloy steel coated on one side with Pt. Zero-gap electrolysis is carried out by contacting the Pt electrode surface with the cathode side of the cation exchange membrane, while pressurising.

Platinum Cathode for Electrolytic Polymerisation TOYOBO K.K. Japanese Appl. 21263,825 Conductive polymers are produced by oxidative electrolytic polymerisation of monomers using a Pt cathode and a NESA glass anode. The conductive polymers have excellent stability and high conductivity in the doped state, and am used as conductive materials, electrode materials and display materials.


Electrodes for Chlorine Production TDK COW. Japanese Appl. 21263,989 An electrode for chlorine production is produced by coating an elecuoconductive base with a solution of Ir, Pt and Ta compounds, and heating in an oxidising atmosphere to give a coating layer consisting of 4-80 mol% Ir as Ir oxide, 1-20 mol% Pt, and 50-20 mol% Ta as Ta oxide. The electrodes are used for high efficiency electrolysis of dilute brines such as sea water to produce chlorine, useful for producing hypochlorous acid.

Platinum and Gold Electrodes for Electrolytic Ozone Generator ODs. K.K. Japanese Appl. 2/270,981 An electrolytic ozone generator has a solid electrolytic membrane with a porous Pt electrode laminated to the anodic surface and a Au electrode attached to the other side, with the electrodes having DC potentials of negative and positive polarity. Highly effkient ozone generation is achieved.

Oxygen Generating Anode with Palladium and Iridium Layers DAIS0 CO. LTD. Japanese Appl. 2/282,490 An 0 , generating anode consists of an elecuoconductive metal base, an intermediate coating layer of 85-95 mol% of an oxide of at least one of Ti, Ta, Sn, Nb and Zr, and 5-15 mol% Pd oxide, and a catalytic surface coating layer of 20-70 mol% of an oxide of at least one of Ti, Ta, Sn, Nb and Zr, and 30-80 mol% Ir oxide. The insoluble anodes are used in electrolytic processes with 0, generation, particularly for elec- troplating Sn, Zn and Cr.

Composite Material for Surface Coatings

European Appl. 401,611A A composite material consists of 0.01-75 wt.% of hard particles of carbides of V, Nb, Mo, W and/or others, dispersed in a matrix based on a metal-G-Al- Y type alloy with 5-15 wt.% Pt and/or Rh as the alloying element. The composite has high temperature stability at 600-1100°C, good wear and corrosion resistance, and is used for surface coatings produced by build-up welding or spraying.

Catalytically Active Coatings for Hydrogen Cyanide Production DEGUSSA A.G. European Appl. 407,809A Catalytic coatings containing AlN and Pt metal($ are produced on moulded Al oxide products by wetting with a suspension of a Pt metal and Al at a Pt metal:Al atom ratio of 0.001-1, evaporating, heating slowly to 100O-135O0C under N, andlor NH,, and optionally activating. The process is simpler and safer, and enables different thicknesses to be produced with a single coating process.

H. C. STARCK, BERLIN G.m. b.H.

Selective Electroless Plating on a Non- Conductive Substrate UEMURA KOGYO K.K. Japanese Appl. 21240,271 An activating agent for forming a metal Pd nucleus on W, Mo or Cu contains a water soluble Pd salt, an inorganic acid, and a water soluble compound of one or more of Pb, Tl, Bi and Sb. Selective electroless plating involves forming conductor patterns of W, Mo or Cu on the non-conductive substrate, dipping in Pd activating agent solution, forming a metal Pd

water ~ l ~ ~ ~ ~ l ~ ~ i ~ Anode with Reduced Potential

nucleus selectively on the patterns, and electroless plating on the patterns.

MOSC. POWER INST. Russian Patent 1,564,202 An anode is prepared by sequentially applying layers of Ir and Pd of equal thickness onto a substrate, heating at 300-40O0C for 4 hours, then chemically dissolving the Pd in boiling HNO 1. In an example an anode had 0.15 pm thick layers of Ir and Pd on a porous Ti substrate before dissolving the Pd. Using the anode, the power requirement for water electrolysis is reduced by reducing the anode potential.

ELECTRODEPOSITION AND SURFACE COATINGS

Palladium Catalyst for Electroless Plating NIPPON PAINT K.K. European Appl. 392,2356 Plating a metallic deposit between functional pattern lines on a plastic or glass plate involves forming a cured film containing a Pd catalyst for electroless plating on the substrate, forming functional pattern lines, and electroless plating. The Pd catalyst is prepared by reducing Pd chloride with stannous chloride in the presence of an acid.

Noble Metal Coated Electroconductive Particles MATSUSHITA ELEC. IND. K.K.

Japanese Appl. 2/243,768 Electroconductive particles are prepared by activating the surfaces of electmconductive composite oxide particles with a Pd-colloid, and coating directly with noble metal in an electroless plating bath. The composite oxide has one or more solid solution system compositions, such as La, -,Sr,CoO,, where x=0.1-0.8. The particles are used for an electrode material and have excellent conductivity.

Platinum Plating for Electrochemical Devices MITSUBI~HI DENKI K.K. Japanese Appl. 21247,386 Pt plating is effected using an electroless plating bath containing a Pt nitro- and/or nitroamhe complex, and a hydroxylamine salt as a stabilising agent, followed by heating in an acidic solution and rinsing in water. The plating process is used for material for electrochemical devices.


Water Electrolysis Anode with Reduced Potential MOSC. POWER INST. Russian Patent 1,564,202 An anode is prepared by sequentially applying layers of Ir and Pd of equal thickness onto a substrate, heating at 300-40O0C for 4 hours, then chemically dissolving the Pd in boiling HNO 1. In an example an anode had 0.15 pm thick layers of Ir and Pd on a porous Ti substrate before dissolving the Pd. Using the anode, the power requirement for water electrolysis is reduced by reducing the anode potential.

Electrochemical Nuclear Fusion Reaction

European Appls. 392,324-25A Apparatus used for an electrochemical nuclear fusion reaction has a pressurised reaction vessel containing a solution of heavy water and a metal salt, in which are two electrodes of Au and Pd, connected to a DC voltage source. The apparaNS also includes a shield plate and heat exchangers. The reaction is optionally controlled by a pulsed DC voltage, and gives a high pressure and means of producing heat energy.

Platinum Resistance Thermometer Compensated for Non-Linearity NORAPP J.H. ANDRESEN World Appl. 90113,009A A Pt resistance thermometer has a Pt resistor and a reference resistor which are fed by equal, constant DC currents, with the voltage difference across them sensed by an ampmier. The amplifier output generates a current which is used to compensate for thermometer non-linearity, by this simple process.

SEMICONDUCTOR ENERGY LAB.

Determination of the Alcohol Content of Beer CRISP INSTR. LTD. World Appl. 90113,026A Measuring the alcohol content of aqueous solutions, particularly beers and other alcoholic beverages, involves passing gas thmugh the solution, and determining the alcohol content of the resulting vapour with a sensor. The alcohol sensor includes two heated Pt wires, one of which is coated with a catalyst. The simple apparatus can give accurate and reliable results in a short time, using a small sample.

Hydrogen Gas Sensor

A sensor for monitoring H, concentration in gases has a thick f h solid electrolyte body printed on a substrate, a printed thick frlm detector electrode of Pt, Pt oxide, Pd or Pd oxide with the surface to be exposed to the gas on the electrolyte body surface, a printed thick f h reference electrode of Na-W bronze, and an insulating material. The sensor can be made cheaply, has a short response time for H, and a low cross-sensitivity to other gases.

BAlTELLE MEMORIAL INST. u. s. Patent 4,976,991

Temperature-Humidity Sensor TANAKA KMINZOKU KOGYO

Japanese Appl. 21228,546 A ceramic base plate has a temperature measuring Pt resistor on one face, and a Pt or Au comb electrode on the other with a humidity sensitive element formed over it. The Pt resistor and comb electrode have 250 and 100 pm line widths, respectively, spacings of 250 and 100 pm, and 1.0 pm thickness. The temperature and humidity of a location in a wide or narrow space can be measured simultaneously.

TANAKA KIKINZOKU KOGYO Japanese Appl. 21258,170

A Pt based member reinforced by dispersed oxide has a hot forge-welded reinforced band at the butt welded joint, which is highly hammered at the centre but only lightly hammered at both ends. This provides a Pt based member such as a large crucible for melting glass; enforced at the welding joint without causing grain coarsening. In an example a Pt member with 0.1 wt.% of dispersed ZrO, grains, and a reinforced band showed improved creep fracture strength.

Platinum Electrode for Hydrogen Peroxide Detector TOSHIBA K.K. Japanese Appl. 2/259,556 A hydrogen peroxide detector consists of a sealed pressure resistant vessel containing a Pt electrode and a stainless steel electrode, and an instrument to measure the potential difference between them, for measurement at high temperature and pressure. The sample solution can be measured directly.

Semiconductor Gas Sensor Used as an Alarm Device

A gas sensor has a substrate such as Al,O,, an internal layer of 0.2-0.6 wt.% Pt catalyst on Sn oxide, and an outer layer on the internal layer of 1.0-2.4 wt.% Pt catalyst on Sn oxide, and includes electrodes and a heater. The gas sensor is used as an alarm device for gas leakage, does not give an error signal due to alcohol, and gives constant resistance.

FUJI ELECTRIC MFG. K.K. Japanese Appl. 21263,145

Electrochemical Element for Oxygen Sensors

An electrochemical element consists of a solid electrolyte, a measuring electrode exposed to sample gas and containing as catalyst a Pt group metal and a metal oxide hexaluminate, and a reference electrode exposed to standard gas. Sintering of the measuring electrode at high temperatures is suppressed, and high surface area, activity and gas permeability are maintained, providing 0, sensors of good response and durability.

NGK INSULATORS K.K. Japanese Appl. 21276,957

Sensor to Detect Ruthenium Tetraoxide Concentration HITACHI K.K. Japanese Appl. 21293,644 A sensor to detect Ru tetraoxide has sample and reference quartz oscillators with an organic membrane of polyethylene or rubber on the electrode surface. The Ru teuaoxide is reduced to Ru dioxide and deposited on the organic membrane, where the weight increase changes oscillator frequency. The concentration of Ru tetraoxide can be detected on the spot with high sensitivity especially in HNO , .


APPARATUS AND TECHNIQUE

Electrochemical Nuclear Fusion Reaction

European Appls. 392,324-25A SEMICONDUCTOR ENERGY LAB.

Oxide-Dispersed Platinum Based Member TANAKA KIKINZOKU KOGYO

Japanese Appl. 21258,170

Dissolved Ozone Detector with Platinum Anode ODs K.K. Japanese Appl. 21298,858 A sensor for detecting dissolved ozone consists of a Ag(Q) cathode coated with a F type cation exchange membrane, a Pt or Au anode, and a device to detect the electromotive force between the cathode and anode. The dissolved ozone detector is simple, has a quick response time, allows continuous reading of the ozone concentration, is small, and is useful for measurement of the ozone water in a bio clean room.

Catalyst Sample Preparation for Electron Microscopy

A Pd catalyst is prepared for electron microscopy by milling in a ball vibro-mill to powder form with a dispersion of 80-l2OAy then suspending in a neutral liquid such as water, applying to a Cu lattice carrier, and drying. This preparation involves less work as it is not necessary to apply layers to a substrate, and the sample gives more information as an image is formed of the separate powder particles at the surface.

MEDICINE MICROBIOL. Russian Patent 1,553,879

Platinum Wire Catalyst Used in Detection of Harmful Gases HETEROGENEOUS CATALYSIS SIEMENS A.G. Gennan Appl. 4,007,375 A gas stream is passed over a catalyst such as a directly heated Pt wire before reaching a heated sensor for detecting harmful gases such as chloroform, acetone or trichloroethylene vapours. The catalytic reaction, for example at 1000°C, may be aided by an additive in the gas stream, and produces the target compound or an identifiable compound fraction.

Photometric Determination of Rhodium COLLOID CHEM. WATER Russian Patent 1,536,309 Analysis of Rh in natural or industrial materials is made possible by complexing with 0.002M C(2-pyridylazo) resorcinol in an 8-15% solution of a water soluble aliphatic alcohol in acetate buffer at pH 5.7, followed by warming and measuring the optical density at 520 nm. The method is rapid, taking only 20 minutes to hrm the complex, and has high sensitivity, allowing determination of 0.03 mglml Rh.

Potentiometric Determination of Rhodium without Interference LAW. UNIV. Russian Patent 1,545,154 Determination of Rh involves complex formation with tetraethylammonium Cnitrobenzol- dithi-boxylate, and standard potentiometry at 455 nm. The analysis is 3 4 times faster then before as the sample does not need degrading, sensitivity is higher - 0.001 &ml of Rh can be determined, and selectivity is improved, with interference from the Pt group metals being prevented. The method can be used for natural or industrial samples and wastes.

Qualitative Determination of Ortho- Nitroaniline LENINGRAD LENSOVET TECH.

Rhodium Catalyst for Improved Hydrogenation of Aromatic Amines AIR PRODUCTS & CHEM. INC.

European Appl. 392,435A Hydrogenation of aromatic d e s to the ring hydrogenated equivalents is by contact with H, in the presence of a novel catalyst consisting of Rh supported on Ti0 chemically bonded with SiO, , T i 0 , or ZrO, , or ZrO, bonded with SiO, or Al, 0,. A low H, partial pressure can be used, such as 700-1500 psig. The catalyst has good attrition resistance, does not have to be alkali-moderated, and gives the product with high selectivity and reaction rates.

Platinum-Palladium-Ceria Catalyst for Exhaust Gas Treatment ENGELHARD COW. Eumpean Appl. 393,612A A catalyst composition consists of a carrier having a bulk ceria support, with dispersed Pt and Pd present at a Pt:Pd wt. ratio of 5O:l-150, and a binder. The catalyst may be used with a second catalyst composition effective for reduction of NO,, and is used as an oxidation catalyst andor a three-way catalyst.

Exhaust Purification Catalyst with Effective Nitrogen Oxides Removal TOYOTA CHUO KENKYUS European Appl. 396,085A An exhaust purification catalyst consists of a porous support, preferably a silicoalumiuophosphate with pores >3 A in diameter, supporting as base metal Cu, C, Co or Fey and Pt, Pd or Rh. The catalyst is used to purify high temperature internal combustion engine exhaust gases from fuel/& mixtures having excess 02, has high heat resistance and durability, and is particularly effective for removal of NO,.

Russian Patent 1,550,387 Ortho-nitroaniline present in solutions is detected by introducing a sample into an acetone solution containing 0.6-1 mg/ml bisctriphenylphosphhe) car-

Preparation of Fluoroalkyl Vinyl C O ~ P O ~ ~ DAIKIN -. LTD. European Appl. 396,974A

bony1 hydroxo Rh, and observing the appearance of a red-orange coloration over 20-30 min if it is present. The method shows increased dectivity, giving best results at 2-5 mg/ml ortho-nitroanihe. Oxida- tion products do not interfere with the results.

A fluoroalkyl vinyl compound is prepared by reacting a fluoroalkyl vinyl halide with H, in the presence of water and a catalyst of Pd supported on activated C. The process requires no strict controls of reaction conditions and gives high yield of the compounds.

Platinum Metak Rev., 1991, 35, ( 3 ) 169

Diesel Exhaust -cation Catalyst NIPPON SHOKUBAI KAGAKU European Appl. 397,411A The catalyst consists of 3-300 gA of refractory inorganic oxide, 2-200 gA of an oxide of at least one of Pr, Nd and Sm, 0.1-10 gA (total) of Pt and/or Rh and optionally Pd, preferably Pd and Rh, and 0.1-3 gA of an oxide of at least one of Cu, Ag, Zn, K and Na, deposited on a 3-dimensiod structure. The catalyst is used to remove carbonaceous fine particles, hydrocarbons and CO from diesel exhaust gases, and has good long term stability at 400OC or above.

Three-Way Catalysts Containing Noble Metal and Uranium INST. FMNCAIS DU PETROLE

European Appl. 399,892A A catalyst has a support with a porous layer containing 0.1-20% of at least one of Pt, Pd, Rh, Ru, Ir or a mixture, 5049.7% of inorganic refractory oxide@), 0.1-25% of uranium oxide(s), and 0.1-35% of metal oxide(s). The catalysts are used for the conversion of CO, hydrocarbons and NO, in exhaust gases from petrol or diesel engines; having enhanced initial activity and stability above 800OC.

Platinum-Iron Catalyst for Carbon Monoxide Oxidation PHILLIPS PETROLEUM co. European Appl. 402,899A An oxidation catalyst contains Pt metal and Fe oxide and/or metallic Fe supported on Al , 0 and/or Mg aluminate. During preparation the impregnated support is reduced, treated with liquid acid, and reduced again. The catalyst can be used at -50 to 400°C and 0.1-2000 psia for oxidation of CO to CO, in the presence of 0,, and is used in breathing masks, exhaust purifcation, tobacco products, CO, lasers, and to prepare labelled CO,.

Catalyst for Steam Reforming Hydrocarbons IDEMITSU KOSAN CO. LTD. European Appl. 406,896A A reforming catalyst consists of 0.01-5 wt.% Rh and/or Ru, 0.1-10 wt.% CO and/or Mn as promoter, 0.01-2.5 wt.% K and/or Baas further promoter (op- tional), on a carrier of ZrO, optionally stabilised with an oxide of Y, M g or Ce. The carrier has a specified pore size distribution, which gives the catalyst high activity and long life.

Modified Alumjna Support for Reforming Catalyst EXXON RES. & ENG. CO. European Appl. 407,117A A reforming catalyst consists of 0.01-2 wt.% Pt, 0-2 wt.% Ir, 0-2 wt.% Reandmaycontain 0.5-1.5 wt.% Cl, on a modified Al, 0 support containing not more than 5000 wt. ppm of a modifier consisting of 100-200 wt. ppm Si and 100-3000 wt. ppm Ca or Mg. Use of the modified support increases reformate yield, suppresses metal and acid site cracking and increases aromatisation activity and selectivity.

Oxidation Catalyst of Platinum Coated with Tin TANAKA KIKINZOKU KOGYO

European Appl. 408,528A An oxidation catalyst consists of Pt, Pd, Rh or Ir preferably in the form of metal black, surface coated with 10-90 wt.% Sn, and may be prepared by elec- trodepositing Sn on the surface of the metal black from a solution of Sn sulphate in H,SO,. The catalyst is used to decompose CO, formalin or HCHO in 0,, at ambient-150°C, and is used in air cleaners.

Isomerisation of Alcohols to Ketones HENKEL RES. COW. World Appl. 90/12,859A Isomerising an olefinically unsaturated secondary alcohol in which the double bond and OH group are separated only by methylene groups involves heating to 200-300°C in the presence of a fully hydrogenated Pd catalyst, 5% Pd/C and sulphided 5% Pd/C and passing H, through the reaction mixture to produce a saturated ketone. The alcohol is converted to the ketone with only minor amounts of saturated hydroxy- and unsaturated keto-compounds as im- purities.

Catalyst for Decomposition of Organohalogen Compounds ALLIED-SIGNAL INC. World Appl. 90/13,352A A catalyst for treating a gas stream containing organohalogen compounds consists of TiO,, VO,, WO, and at least one of Pt, Pd and Rh, with the VO, and noble metal uniformly dispersed on the Ti02. The gas stream is contacted with the catalyst at 200-5OO0C in the presence of H, 0. The new process enables reduced temperature catalytic removal of at least 99% of hydrocarbons and organohalogen compounds from waste gases, over a longer time.

Lower Temperature Preparation of Lactones GAF. CHEM. COW. World Appl. 90/14,344A A method for preparing lactones from 1,4 and 1,5 aliphatic saturated diols involves reaction with a chemical oxidising agent and 0.001-2 wt.% of a Ru containing catalyst such as Ru oxide or Ru/C, at -20 to 100°C, preferably ambient temperature.

Automotive Exhaust Catalyst with Improved Thermal Stability ALLIED-SIGNAL. INC.

U.S. Patents 4,868,149 and 4,960,574 Catalysts for treating automotive exhaust consist of a honeycomb carrier, with a layer of high surface area Al,O containing dispersed: 3-22 wt.% La oxide as <25 Rcrystallites 5-50 wt.% Ce oxide, 0.1-9 wt.% Pd oxide as <25 8, crystallites, and 0.01-4 wt.% Rh oxide. This Pd/Rh catalyst has comparable or better activity than the prior art Pt/Rh catalyst, especially for hydrocarbon and NOx removal, both when fresh and after thermal durability testing.


Diesel Exhaust W c a t i o n Catalyst NIPPON SHOKUBAI KAGAKU European Appl. 397,411A The catalyst consists of 3-300 gA of refractory inorganic oxide, 2-200 gA of an oxide of at least one of Pr, Nd and Sm, 0.1-10 gA (total) of Pt and/or Rh and optionally Pd, preferably Pd and Rh, and 0.1-3 gA of an oxide of at least one of Cu, Ag, Zn, K and Nay deposited on a 3-dimensiod structure. The catalyst is used to remove carbonaceous fine particles, hydrocarbons and CO from diesel exhaust gases, and has good long tern stability at 400OC or above.

Platinum Catalyst for Hydrocarbon Dehydrogenation UOP U.S. Patents 4,880,764 and 4,973,779 Hydrocarbon conversion catalysts consist of Pt (op- tional), a uniformly impregnated Group IA andlor IIA metal component, a surface impregnated Ir and/or 0s component, and a Group IVA metal component, on a refractory oxide support. A preferred catalyst may contain 0.1-2.0 wt.% Pt, 0.1-5.0 wt.% Li, 0.1-2.0 wt.% Ir and 0.1-5.0 wt.% Sn on an Al,O, support. The catalysts are used for dehydrogenation of 2-30C alkanes, cycloalkanes, alkenes, and so on, and have high activity.

Ruthenium Oxide Catalyst for Double Bond Isomerisation SHELL OIL co. US. Patent 4,962,267 Isomerisation of an olefin feedstock of mainly 4-30C a-olefins to corresponding internal olefms, at 80-25OOC and 0.1-1000 psia pressure, uses a catalyst consisting of a rAl,O, support, 0.5-5 wt.% Ru present as Ru oxide and 0.2-2.5 wt.% alkali metal present as alkali metal oxide, with the weight of alkali metal 0.1-3 times that of Ru.

Catalyst Compositions for Naphtha Reforming EXXON RES. & ENG. CO. U.S. Pm62?ltS 4,966,682

and 4,966,878-80 and 4,968,408 A naphtha feed is reformed in the presence of H, using a catalyst consisting of (a) selected combinations of: up to 2 wt.% Rh, 0.01-2 wt.% Ir which may have >50% crystallinity, 0-2 wt.% Re, 0-2 wt.% Sn, and 0-3.5 wt.% halide; (b) 0.01-2 wt.% Pt; and (c) balance Al, 0, modified with Si and alkaline earth metal($. Using the modifed support gives improved reformate yield, while metal and acid site craclung are suppressed.

Iridium Catalyst Preparation of Alkoxylate Tertiary Amines ETHYL COW. U.S. Patent 4,967,005 An alkoxylate tertiary amine is prepared by reaction of an oxyakylated alcohol with a secondary amine at elevated temperature, in the presence of an amination catalyst consisting of Ir metal dispersed in an inert support with added H , . The process is carried out at ambient pressure, and gives high yields.

Selective Catalytic Conversion of Cyanohydrins to Aldehydes ALLIED-SIGNAL INC. U.S. Patent 4,970,302 A cyanohydrin is selectively converted to the corresponding aldehyde by contacting an aqueous acidic cyanohydrin solution with a catalyst of zerovalent Pd dispersed on a porous solid organic polymeric resin, at 10-85OC and 10-2000 psi H,. The nitrile group is hydrogenated to an imine, which is separated and then hydrolysed to an aldehyde.

Regeneration of Noble Metal Hydrodechlorination Catalysts

Pt, Pd, Rh, Ir andlor Ru catalysts optionally supported on C, Al 0 s, fluorided Al , 0 s, AlF, andlor CaF, are regenerated by contact at above 200OC, for more than 15 minutes, with an atmosphere containing a fluorohalo(hydro)carbon but fxee of air andlor 0,, and H,. The catalyst is used for fluorohalo(hydro)carbon hydrodechlorination, and the deactivated catalyst can be regenerated to the equivalent of fresh catalyst activity.

DU PONT DE NEMOURS CO. U.S. PaZe?22 4,980,324

Selective Production of Lower Aliphatic Alcohols TEXACO INC. U.S. Patent 4,980,380 Lower aliphatic alcohols are prepared by reaction of CO and H, using a catalyst containing Rh, Co and Mo, a combination of K and Rb, preferably at equal atomic ratio and 0.01-0). 1 moles (total)/lOOg catalyst, 1-100 ppm Cl, and a support. The catalyst is selective, does not result in substantial hydrocarbon production, and gives a product containing 2-6C alcohols and CH OH, used as a blendmg component for hydrocarbon motor fuels.

Resin Film Catalyst for Ethylene Oxidation CHISSO cow. Japanese Appl. 21222,725 Ethylene generated by fruits and vegetables makes them over ripe, but can be removed using a catalyst consisting of a SiO1-Al,Os carrier supporting 0.01-2.0 wt.% Pd and 0.1-5.0 wt.% of one or more of V, Mn and Ti. A resin f h containing 0.01-1.0 wt.% of the catalyst is used to decompose absorbed ethylene by oxidation at room temperature, and is able to absorb large amounts of ethylene.

Waste Gas Pdication Catalyst Contain- ing Cerium and Palladium Oxides

A waste gas purification catalyst is prepared by coating a support with a sluny containing activated Al,O, powder coated with Ce and Pd oxides. In an example, a cordierite monolithic support was wash- coated with slurry, and fued to give a 150 gA Al, 0,, coating. A car exhaust purification catalyst is produced with improved durability and catalytic activity.

TOYOTA JIDOSH.4 K.K. Japanese ApPl. 2037,643

Selective Platinum Hydrogenation Catalyst JAF'AN TOBACCO & SALT PUB.

Japanese Appl. 21241,546 A new hydrogenation catalyst for aliphatic compounds having C C double bonds consists of a Pt- loaded SiO, coupled with alkylsilyl. In an example, a catalyst was prepared from 3.0 g of dimethyl- octadecylsilyl chloride and 3.0 g of 0.5% Pt on SiO,, after stirring for 3 days.


Catalyst for Partial Oxidation of Alcohols

Japanese Appl. 2/25 1,244 A new catalyst used for partial oxidation of alcohols in the presence of air consists of a gas diffusible support, with a catalyst layer containing C powders loaded with Pt fm particles poisoned with S and a binder. The catalyst can convert alcohols to the corresponding carboxylic acids with higher efficiency.

TANAKA KIKINZOKU KOGYO

Catalysts for Methanol Reforming MITSUBISHI HEAVY IND. K.K.

Japanese Appl. 21252,602 Catalysts consisting of pt and/or Pd on supports containing oxides of alkaline earth elements and rare earth elements are used in the reforming of CH , OH to produce H,-containing gases. In an example a catalyst consisting of Pt on a support of MgO, La, 0, and Al,O, in the ratio of 70:20:10 was used. H,- containing gases can be produced stably for a long time by reacting CH , OH and 0, -containing gases at low temperatures.

Improved Preparation of Dih y droxyquaterphenyl WNKO ~ T S U KAGA Japanese Appl. 2/255,634 4,4Dihydroxyquaterphenyl is prepared by the dehalogenating and dimerising of 4-hydroxy-Chalogenobiphenyls at 50-20O0C, for 1-12 h, in an inert organic polar solvent, in the presence of - for example - NaOH, and a catalyst of 0.1-20 wt.% Pd on a carrier. The products are useful as raw materials for liquid crystal compounds and synthetic rubber modifiers, and can be prepared in high yields with high purity.

Nitrogen Oxides Decomposition Using an Iridium Catalyst OSAKA GAS K.K. Japanese Appl. 21258,061 Apparatus for combustion has a part for decomposing NO, which contains a catalyst consisting of 2-50 wt.% Ir, 0-20 wt.% Cu, 30-90 wt.% Al,O,, and 0-20 wt.% Y-zeolite. The apparatus prevents air pollution by enabling NO, in combustion gas or air to be decomposed, at a lower temperature, without supplying a reducer, which gives low investment and running costs, and easy maintenance.

Noble Metal Catalyst for Decomposition of Nitrogen Oxides BABCOCK-HITACHI K.K. Japanese Appl. 2/258,063 A NOx decomposition catalyst consists of at least one of Pt, Pd, Rh, Ir, Ru, or Re, a composite oxide containing rare earth elements, Ba, Sr, Ca and Co, or a composite oxide containing Bi, Ba, Sr, Ca and Co. The catalyst is used to decompose NOx in exhaust gases h m combustion apparatus such as a boiler or car, and can be used at a lower temperature such as 400-80O0C, compared with a conventional catalyst.

Ruthenium Catalyst for Ammonia Synthesis

A catalyst with high activity for synthesising NH, is easily produced by supporting a Ru compound containing no chlorine, such as Ru nitrate, on N , O , or MgO , , evacuating and/or reducing under H to give a metallic Ru catalyst, and supporting on a nitrate of Rb, Cs or K. The catalyst does not contain chlorine so poisoning by chlorine is inhibited, and it has resistance to poisoning by CO which allows use of reactant gases containing CO.

SHIN NENSHO SHISUTE Japanese Appl. 2/258,066

Waste Gas Purification Catalyst with Separated Catalytic Metals NISSAN MOTOR K.K. Japanese Appl. 21265,646 A waste gas purification catalyst consists of a substrate with a frst layer of active Al,O, containing Pt and/or Pd, a second oxide layer of rare earth element oxide or ZrO, , and a third layer containing Rh. Loweriug of the catalytic activity at high temperature is controlled by using the three layer structure which prevents a solid solution of Rh with N , O , forming on heating, and by the co-catalytic effect of the rare earth element oxide.

Ruthenium Catalyst for Hydrogenation of Carbonyl Compounds to Alcohols M ~ U B I S H I USEI cow. Japanese Appl. 2/273,635 Carbonyl compounds are hydrogenated to the corresponding alcohols at 15-15OoC, under ordinary pressure 100 kg/cm * in the presence of a Ru catalyst. The catalyst is prepared by supporting Ru halides, preferably Ru chloride, on SiO, gel, treating with alkali to fix the Ru halides, reducing, washing and drying. The catalyst is stable and active for a long time, and gives alcohols selectively and in high yield.

Methanol Reforming Catalyst KANSAI NETSU KAGAKU Japanese Appl. 2/277,546 A reforming catalyst consists of 2-25 wt.% Ni or Co, 0.5-15 wt.Oh Ce oxide or L a oxide, and 0.01-2 wt.% Rh and Ru, loaded on a sepiolite support. It is used to reform CH,OH to a gas containing H, and CO, which is used as a high calorific fuel gas for com- bustors, fuel cells or organic synthesis. Side reactions are suppressed, and the catalyst has higher selectivity for CO and H,, higher activity at 250-40O0C, and longer operating life.

Preparation of High Purity Isopropanol

Japanese Appl. 21279,643 Isopropanol is prepared by catalytic hydrogenation of acetone over a catalyst of 0.01-5 wt.% Ru on an inorganic carrier, in a fixed catalyst bed, while maintaining the concentration of isopmpanol in the reaction system above 50 wt.%. High purity isopropanol is prepared without by-products.

MITSUBISHI PETROCH. K.K.


Dual-Phase Catalytic Hydrogenation of Nitrobenzene to Prepare Aniline SUMITOMO CHEM. IND. K.K.

Japanese Appl. 21279,657 A controlled reaction to prepare aniline of high purity is by liquid phase hydrogenation of nitrobenzene at 18O-24O0C, at 0.05-10% in aniline, in the presence of a supported Pd or Pd-Pt catalyst, followed by gaseous phase hydrogenation of nitrobenzene in a composition of aniline, water and H,, over a fmed Cu-G catalyst, at 150-250OC.

Palladium Catalyst for Dehalogenation Process SOC. ATOCHEM. French Appl. 2,645,531 A hydrogenation process for dehalogenation of o-halo-carboxylic acids or esters by H, is carried out in the presence of a Group VIII metal, especially 0.3-1% Pd on C, and S or S compounds, especially S , C I , or CS,. The process is specifically claimed for purification of monochloroacetic acid containing dichloroacetic acid.

Cross-Coupling Metal Organic Compounds and Halogen Compounds MERCK PATENT G.m.b.a. Germun Appl. 3,930,663 Metal organyls are crosssoupled with halo compounds or perfluoroakyl sdphonates by reacting a known organometallic compound with the relevant substituted ethylidene, optionally in the presence of a metal alcoholate and using a transition metal catalyst of Pd, optionally supported. The relatively mild and stereaselective process gives good yields of the products, which are used as precursors of liquid crystalline materials.

Processing Pyrolytic Gas Line Fractions B. A. GRIGOROWCH Russian Patent 1,541,238 Hydrocarbon hydrogenation uses an alumino-Pd catalyst and H 2 at 8O-18O0C, with partial recircula- tion of hydrogenation products to mix with the raw material. Part of fraction C9 is additionally hydrogenated using an alumino-Pd catalyst at 200-35OoC, and then recirculated for extraction of fraction C6-a. The method is used for processing liquid products of hydrocarbon pyrolysis.

HOMOGENEOUS CATALYSIS

Platinum Catalyst for Preparation of Silane Anti-Clouding Agents SHIN-ETSU CHEM. co. European Appl. 392,509A New 3-(2-0xo-l-pymlidhyl)-propyl silane compounds are prepared by hydrosilylation of 1-allyl-2-0x0-pyrrolidine with a hydrogen silane in the presence of a Pt catalyst. The products are used as anti-clouding agents for treating a variety of surfaces, or as effective coupling agents, etc.

Preparation of Adipic Acid from Lactones DU PONT DE NEMOURS CO. Eumpean Appl. 395,038A Adipic acid is prepared by reaction of at least one lactone-for example a-ethylpmpiolactone-with CO and water at 190-250°C and 100-2000 psi, in the presence of a homogeneous Rh catalyst and at least one promoter selected from an iodide or bromide.

Preparation of Unsaturated Acids NONE-POULENC CHIMI.

European Appls. 395,545-46A New methods for the preparation of hexene-dioic acids or /3, y-unsaturated acids involve reaction at raised temperature and pressure of (a) a disubstituted butene containing alkoxy groups, for example 1,4-diacetoxybut-2-ene, or (b) an allylic alcohol, for example 2-butene-l,4diol or l-butene-3,4-diol; with CO and optionally water, in the presence of a Pd based catalyst and a quaternary onium chloride of N or P. High yields of 1,6-hex-3-ene-dioic acid can be obtained, which can be hydrogenated to adipic acid.

Preparation of Dihydrophenanthrene- Carboxylic Acid Eaters AGENCY OF IND. SCI. TECH.

Eumpean Appl. 397,41812 New 9,10-dihydrophenanthrene-2,7-dicarboxylic acid diesters and 7-bromo-9,10-dihydrophenanthrene-2- carboxylic acid esters are prepared by reacting 2,7-dibromo-9,10-dihydrophenanthrene with CO and alcohol, using a Pd-phosphine catalyst. The products are used as intermediates for drugs, agricultural chemicals and heat-resistant or liquid crystal polymers.

Cross-Linked Siloxane Copolymer for Optical Use AMERICAN TEL. & TELEG. CO.

Eumpean Appl. 398,573A A siloxane copolymer is cross-linked with a cross- linking agent in the presence of a Pt catalyst, which is preferably a chloroplatinic acid-cyclovinylmethyl- siloxane complex, used in amounts of 1-20 parts per million. The silicone polymers are used as encap- sulating agents, surface protective agents, or to index match optical components to other optical devices, and show good optical quality, physical and chemical properties.

Preparation of Substituted Urea Compounds NKK cow. Eumpean Appl. 400,299A N,N-disubstituted urea compounds are produced in good yield by reacting a primary aromatic amine, an aromatic nitro compound and CO in the presence of a halogen-free Rh compound andlor Ru compound as catalyst, and a solvent. The solvent stabilises the catalyst and enables recovery as a solution for re-use, and increases catalyst activity.


Palladium Complex Catalyst for Preparation of Ibuprofen HOECHST CELANESE European Appl. 400,892A Ibuprofen, a well known anti-inflammatory agent, is prepared by carbonyktion of I-(4’-isobutylphenyl) ethanol with CO at 10°C or above and at least 500 psig, in an acidic aqueous medium, in the presence of hydrogen ions, halide ions, and a Pd compound com- plexed with at least one monodentate phosphine ligand as catalyst. In this process the catalyst can be precipitated from the reaction products in pure form, and recycled.

Preparation of Polycyclic Aromatic and Aromatic Vinyl Compounds MITSUBISHI USEI c o w . European Appl. 405,389A A polycyclic aromatic compound or an aromatic vinyl compound is produced by couplug an aromatic sulphinic acid with an aromatic halogen compound or a vinyl halogen compound using a catalyst containing Pt, Pd (preferred), Rh, Ir, 0 s or Ru, and preferably 0.01-25 mol of an organophosphorus ligand per mol of catalyst. The products are obtained in high yield and with high selectivity, and are useful industrial starting materials.

New Preparation of Pseudo-Ionone RHGNE-POULENC SANTE European Appl. 406,065A A new preparation of pseudo-ionone is by oxidative decarboxylation of new ally1 fl-ketoesters such as ally1 (2-acetyl-5,9-dimethyldeca-4,8-diene)-oate, in a solvent, in the presence of a catalyst. A Pd based catalyst such as Pd(OAc), is used, optionally with a ligand such as triphenylphosphine. Pseudo-ionone is an intermediate in the synthesis of vitamin A.

Heat Curable Organopolysiloxane Composition SHIN-ETSU C m . co. European Appl. 410,697A An organopolysiloxane composition consists of an organopolysiloxane, an organohydrogenpolysiloxane, and a Pt catalyst present at 0.1-100 ppm of the fmt component. The products are heat curable to form silicone gels used in the electronic or electrical industries as potting or sealing materials. They have reduced discoloration due to thermal deterioration compared to compounds in use.

Palladium Catalyst for Preparation of 3-Keto-1-Alcohols NIPPON ZEON K.K. Japanese Appl. 2/240,040 A 3-keto-1-alcohol is prepared from an ally1 type or propargyl type ester of a fl-keto-carboxylic acid having a carbonyl group, by subjecting to an intramolecular aldol reaction in the presence of a Pd compound catalyst. In an example the catalyst consisted of Pd acetate and triphenyl phosphine. The product can be p r e p a d in high yield, and with high selectivity for the intramolecular reaction.

Heat Curable Polymer Blend HITACHI CABLE K.K. Japanese Appl. 21242,839 A heat curable polymer blend is produced by com- poundmg 50-95 wt.% of chloro-sulphonated polyethylene and 50-5 wt.% of a mixture of silicone compounds in the presence of a Pt compound, and cross-linking to make a network structure. The blend composition shows increased heat resistance without decreasing the tensile or tear strength, and is used as a wire coat or cable sheath, hose, or a sheet.

Preparation of High Purity Monosilanes TONEN COW. Japanese Appl. 21267,111 Monosilanes are prepared by disproportionation of arylhydrosilanes in the presence of Rh and/or Ru or their compounds as catalyst. High purity monosilanes can be obtained under mild conditions, at low cost. In an example, Rh,(CO),, was used to catalyse the disproportionation of phenylsilane.

Palladium Catalyst for Preparation of Vinyl Dioxolanes MITSUBISHI PETROCH. K.K.

Japanese Appl. 21282,382 4-Vinyl- lY3-dioxolanes are prepared by reaction of diene monoxides with excess ketones in the presence of 0.001 -1 mol-fold for a Pd catalyst, preferably zerovalent Pd compounds, for example tetrakis- (triphenylphosphine) Pd. The product is useful as a monomer to prepare a 1,3-dioxolane ring having (co)polymer(s), reactive towards acids and/or bases.

Palladium Compound Used in Cyclisation of Organic Acids TEIJIN K.K. Japanese Appl. 21286,647 3,5-Dihydroxy-2-methyIenecyclohexylidene acetic acid esters are produced by cyclising 5,7-dihydroxy-8-nonen-2-ynoic acids at O-10OoC, in an organic solvent, using a Pd compound at 0.001-1 equivalents of the acid. This provides a new in- dustrially applicable process using readily available starting materials but not highly toxic or explosive raw materials, giving products useful as intermediates for the A ring of active type vitamins D3.

CHEMICAL TECHNOLOGY

Sintered Compact for Prevention of Rusting in Water Pipes T. MIYANOO Japanese Appl. 21232,385 An aqueous solution is passed through a sintered compact made by moulding a mixnw of TiO, fmes as n-type semiconductor, Pt-black and SiO, fines, to prevent rust in steel piping for water supply. Alter- natively the mixture may be applied on a solid body and fmd. This method is for preventing rusting of the steel piping without any effect on the taste of the water, and using no supplementary chemicals.


ELECTRICAL AND ELECTRONIC Platinum Composite Wire for Corona ENGINEERING Discharge Electrode

TANAKA KIKINZOKU KOGYO

Sintering Control Additive Containing Rhodium and Iridium ENGELHARD COW. European Appl. 394,037A An additive consisting of Rh andor Ir metallo organic resinates is used at 0.1-10 wt.% to control the sintering rate of Ag or mixed AgPd internal electrode materials, in the manufacture of multilayer ceramic capacitors. The preferred resinates are Rh 2-ethylhexoate and Ir trichloride-tris-di-n- butylsulphide. The additive slows the electrode material sinteriag rate to match that of the dielectric.

New Electrically Conductive Ruthenates W.C. HERAEUS c.m.b.a. Eumpean Appl. 395,799A Novel electrically conductive pyrochlore-related oxides (ruthenates) contain Pb, Bi, Ru, Cu andor Ag, and Cay Sr and/or Ba, and are useful for production of thick film resistance elements. The elements have an extremely small difference between their hot (25-125OC) and cold ( - 5 5 to 2 5 O C ) temperature coefficients of resistance, and have low hot and cold temperature coefficient values.

Thick Film Thermistor Compositions Containing Ruthenium Pyrochlores D U PONT DE NEMOURS CO.

U.S. Patents 4,906,406 and 4,961,999 Thick f h thermistor compositions are an admixture of finely divided particles of: 5-60 wt.% of a Ru- based pyrochlore, and 40-95 wt.% of a borosilicate glass or glass h r e with viscosity 10-10,OOO poises on fVing at 700-1000°C. These components are dispersed in an organic medium, printed on a substrate, and fired. The novel thick film thermistor compositions have high positive temperature coefficient of resistance over a wide temperature range.

Electrodes Used in Moisture Sensors for Windscreen Wipers

A conductive pattern is formed on a glass windshield with electrodes consisting of a conductive oxide in glass matrix. The pattern is silk screen printed on to a windshield h m an ink containing 5-20 wt.% RuOl , 40-70 wt.% glass frit and 25-40 wt.% organic vehicle, and then dried and heated to fuse to the screen during shaping.

Compound Superconductor with Platinum Intermediate Layer TOSHIBA K.K. Japanese Appl. 21201,819 A compound superconductor is made by melting an oxide superconductor or precursor mixture and applying the melt to a matrix having a Pt or Pt alloy layer at least on the surface, or vice versa, followed by crystallising the melt to form oxide superconductors.

DELCO ELECTRONICS GORP. U.S. Patent 4,970,122

Japanese Appl. 21217,450 A composite Pt wire is prepared by plating Pt on a W or Mo wire, extension to f d wire diameter, heat treating at 600-800°C, and tension-annealing at 500-60O0C. The thickness of the Pt or Pt alloy layer is homogeneous, with no pin holes, and the wire has uniform corona discharge. The Pt composite wire is used for a corona discharge electde, with M- ticipated long life, reliability, and high performance.

Improved Magnetic Recording Medium MATSUSHITA ELEC. IND. K.K.

Japanese Appl. 2/235,2 15 A magnetic recording medium consists of a Co group alloy perpendicular magnetic film formed on a particle shaped base, having an undercoat layer made of Pt, Pd or Rh. The medium is applied to magnetic tape, and has an impmved running life at suitable play back power and C/N ratio, at high density recording domain.

Contact Point Material with Excellent Wear Resistance NRUKAWA EL~~TRIc co. Japanese Appl. 2/259,086 A contact point material has a coating layer of at least one electroconductive ceramic of Ti nitride, Ti boride and Zr boride formed on at least part of the surface of a Cu or Cu alloy base, with a thin layer of at least one of Pt, Pd, Au and their alloys on the coating layer. The material is for use at weak currents, providing excellent wear resistance, corrosion resistance and heat resistance.

Optical Recording Medium with Protecting Layer MITSUI PETROCHEM. IND. K.K.

yapanese Appk. 2/260,253 and 21261,822 A photo- or optical recording medium consists of a base plate, a protecting layer containing Si, N, optionally 0 and one or more of Pt, Pd, Rh, Ir, Ru, Au, Ag, Ni, Cu, Tc and others, and a recording layer which may contain om or more 3d transition metals, an anti-corrosive metal such as Pt, Pd, Ti or Zr, and rare earth elements. The refractive index is preferably >1.7, and the extinction coefficient is <0.1. The protecting layer is free from cracking, and prevents oxidation or corrosion of the recording membrane.

Soft Magnetic Thin Film Containing Ruthenium

A soft magnetic thin film contains Fey over 0-5 at.% of at least one of Coy Ni and Ru, and over 0-5 at.% of N. The thin film is used for the core material of magnetic heads having high satmation magnetic flux density and low coercive force.

FUJI PHOTO FILM K.K. Japanese AHl. 2/262,307

Platinum Metak Rev., 1991, 35, (3) 175

Heat Resistant Silicone Gel for Sealing Integrated Circuits SHINETSU CHEM. IND. K.K. Japanese Appl. 21269,771 A silicone gel consists of an organopolysiloxane, an organohydrogenpolysiloxane, a zero valent Pt compound at 0.1-100 ppm of F’t to the total of the silox- anes, and 150 ppm or less of OH bonded to Si atoms to the total of the other components. The gel has low elasticity, good electrical properties, heat and low temperature resistance, stain resistance and moisture resistance, and is used for sealing (hybrid) I&.

Ink for Forming Thin Fihn Resistor Device MATSUSHITA ELEC. IND. K.K.

Japanese Appl. 21301,101 An ink used to form a thin fdm resistor consists of a Ru compound, a solvent, 5-60 wt.% of a Ru oxide with mean particle diameter 50-1000 & and a metal or metal oxide (may be Co, but not Ru) with the same particle diameter. The ink is coated on a substrate, dried, heated and fued to form a rigid resistor fh.

Material Containing Ruthenium for Electrical Resistors W.C. HERAEUS c.m.b.H. Gennan Appl. 3,941,283 A material mixture used for elecuical resistors preferably consists of 5-90 wt.% of Cu and Ru oxides, and 10-95 wt.% glass f i t . The oxides consist of CaCu Ru, 0 ,z andlor LaCu Ru, 0 The material mixture is used for the production of temperature dependent resistance layers in temperature sensors, and has a high coefficient of resistance.

Thermoelectric Transducer MITSUBISHI METAL K.K. Gennan Appl. 4,017,776 In a doped n-conducting Fe silicide used as a thermoelectric transducer, part of the Fe is replaced by Pt, Pd andlor Ni, and optionally part by Co. The product has excellent energy conversion properties, especially a large Seebeck coefficient and low specific resistance, and is useful as a thermoelectric generator or cooler, and for various heat sensors.

MEDICAL USES

Platinum Complexes with Anti-Tumour Activity DANA-FARBER CANCER European Appl. 392,662A Complexes of K tetrachloroplatinate with nitroaromatic-azoic-do dyes, preferably the nuclear dye “Fast Black”, are used to delay tumour growth in mammals, and in enhancing the kiUing of tumour cells by radiation therapy andlor hyperther- mia. The complex can be administered by per- cutaneous iniection in solution. at a dose of 50-600

Palladium Alloy Foil for Dental Crowns D.C. DIMMER U.S. Patent 4,980,124 A dental restoration is made by forming a malleable Pd alloy foil to the shape of a tooth, applying a par- ticulate alloy coating to the external surface of the foil, sintering to bond the alloy to the foil and give a crush resistant unitary copying, and applying a porcelain veneer. The technique is used to prepare dental crowns, uses less noble metal, and elimates the need for waxing, casting and machining.

New Tetraplatinum Complexes for Anti- Tumour Drugs TSUMURA & CO. Japanese Appl. 21258,789 A new Pt complex showing an anti-tumour effect against mouse leukaemia cell P-388 is used in an anti- tumour drug. The acute toxicity (LD50) is 200 mgkg, and the drug can be administered by common dosage forms, at a daily oral dose of 1-600 mg for an adult, divided over several times.

Cancer Treatment Drug Containing Platinum Complex and Iodinated Oil SUMITOMO SEIYAKU K.K. Japanese Appl. 21290,813 An anti-cancer drug composition contains an oil- soluble Pt(I1) complex and an iodinated oil. For preparation, iodinated oil and its fatty acid esters are used, such as olive oil, peanut oil, lanolin, and so on. The Pt(I1) complex dissolved in iodinated oil was shown to reduce tumour size in rats transplanted with sarcoma 180, when injected into the tail artery.

New Platinum Complex with Anti- Tumour Activity TORAY IND. INC. Japanese Appl. 21295,993 A new Pt(I1) complex for treating malignant tumours consists of dichloro-( 1,2-diaminocyclohexane) Pt(1I) and 18-0-glycyrrhetic acid, and an anti-tumour remedy is obtained by reaction of these components. The remedy can be given orally or parentedy in various forms, at a daily dose of 0.01-50 mgkg, and preferably contains 0.005-60 wt.% of the effective component. The remedy has potent anti-tumour activity with only weak toxicity.

Fixing Tissue Sections Using an Osmium Solution PHYSIOLOGY INST. Russiun Patent 1,528,435 More efficient detection of Ca ions in the s t r u c ~ of neurons involves furing sections of the tissue in a 1 : 1 mixture of OsO, solution and 2% K pyroantimonate solution, for 5 min. Subsequent treatment with alcohol, alcohol-acetone, acetone, acetone-araldite, and araldite, thermostating and electron microscopy complete the process.

mgkg body’ weight, preferably given a few hours before exposure when used with radiation or heat.

The New Patents abstracts have been prepared from material published by Derwent Publications Limited.

Phtinun Metals Rev., 1991, 35, (3) 176

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