the development of a high throughput reactor for the catalytic screening of three phase reactions

Applied Catalysis A: General 220 (2001) 253–264

The development of a high throughput reactor for the catalyticscreening of three phase reactions

Stuart Thomson1, Christian Hoffmann, Silvia Ruthe, H.-W. Schmidt, Ferdi Schüth∗Max Planck Institut für Kohlenforschung, Kaiser Wilhelm Platz 1, D-45470 Mülheim an der Ruhr, Germany

Received 3 May 2001; received in revised form 27 June 2001; accepted 3 July 2001

Abstract

The design and utilisation of a reactor for the optimisation of multiple heterogeneous catalytic reactions in liquid phase isdescribed. With the ability to screen up to 25 samples simultaneously at a maximum pressure of 50 bar, the reactor is one of thefirst to be designed specifically for what is termed stage II, the optimisation phase, of catalytic high throughput experimentation(HTE). Experiments demonstrating the reliability and reproducibility of the reactor are described, including the use of thereactor to study the catalytic hydrogenation of crotonaldehyde (CrAld) over bimetallic samples based on a commercial 5 wt.%Pt on activated carbon catalyst. Modification of the mono-metallic Pt sample by the impregnation of aqueous metal salts andvarious pre-treatments, resulted in 140 bimetallic catalysts that were used in the hydrogenation study. The changes observedin both selectivity and reactivity of the modified catalysts are described and show, by way of example, how the speed ofcatalyst screening can be increased by at least an order of magnitude. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: High throughput; Three phase; Combinatorial catalysis; Hydrogenation; Crotonaldehyde

1. Introduction

The use of combinatorial chemical methods to ob-tain high value products has been used extensively inthe pharmaceutical industry [1–3], but such method-ologies have been slow to impact on the search for in-organic materials [4–7]. The general approach used incombinatorial chemistry is based on the current under-standing gained from pharmaceutical and biochemicalresearch, and is discussed at length in several articles

∗ Corresponding author. Tel.: +49-208-3062373;fax: +49-208-3062995.E-mail address: [email protected] (F. Schüth).

1 Co-corresponding author. Present address: Materials Division,Building 3, Australian Nuclear Technology and Science Organi-sation (ANSTO), PMB 1, Menai, NSW 2234, Australia.

[1,2,8–10]. However, such an approach can be ratio-nalised in four steps.

1. Conception.2. Library design and creation (defining the optimum

library of samples to be used combinatorially).3. Screening of library samples (the use of high

throughput experimentation (HTE) to synthesiseand characterise the resultant library).

4. The analysis of data (i.e. neural networks computeranalysis or other techniques).

Although this procedure has been used extensivelyby biochemists for homogeneous reactions, the use ofthese processes in heterogeneous systems introducesunique problems. The use of carefully selected librarycompounds is an important step in minimising theresultant number of samples created. However, the

0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.PII: S0926 -860X(01 )00727 -X

254 S. Thomson et al. / Applied Catalysis A: General 220 (2001) 253–264

application of such libraries to heterogeneous catal-ysis is difficult, because the individual and numerousreactions that occur at an atomic level are, at best,poorly defined. In selecting a library, it must be con-sidered that there exist numerous ways of depositingactive phases, modifiers, and promoters onto a sur-face. It follows that the order, method and conditionsused during deposition are all likely to result in cat-alysts with differing properties. Clearly, with such avariety of possible alternatives in synthesising suchcatalysts, the need for HTE to screen such libraries isof paramount importance.

The use of HTE in the search for new catalysts hasbeen underway for several years and is detailed in anumber of articles [9,11–13]. The application of IRthermography to identify and differentiate catalysts bytheir exothermic behaviour was first applied to an ar-ray of 16 samples supported on an alumina disk [14].Since then a number of researchers have used andmodified the method to compare, study, and discoverheterogeneous catalysts with high activities [6,15].Although this technique has the ability of being ableto rapidly screen many samples simultaneously, it islimited by the absence of catalytic selectivity data. Forthis reason Newsam and Schuth termed such screen-ing techniques as stage I or the discovery phase [11].

Other techniques, such as resonance enhanced mul-tiphoton ionisation (REMPI) [16] and scanning massspectrometry [17], can in theory be used to obtain bothactivity and selectivity data (stage II techniques). How-ever, the conditions used are far removed from con-ventional testing environments. Clearly both stages Iand II screening techniques have a role in HTE, stage Ibeing able to screen catalysts at high speed, and stageII yielding substantially more information withinlonger timeframes.

More sophisticated fixed bed reactor designs haveallowed truly parallel stage II screening of catalyststo be conducted [18,19], however, parallel reactors forstage II screening of three phase reactions in hetero-geneous catalysis have largely been neglected, withcurrent designs based on commercial reactors in par-allel [20]. The main reasons for this are the difficultiesassociated in designing such reactors. The use of ele-vated temperatures and pressures require rigid designand construction. Engineering problems, such as stir-rer design, the purging and introduction of pressurisedgases, and the sealing of the entire system, must all

be overcome. In this study, the focus was to develop astage II test reactor for such reactions. The design ofthe reactor had to be multipurpose, allowing for a widerange of reactions and experimental conditions to beused. Moreover, the reactor had to enable the testingof catalysts in parallel, under or close to, conventionaltesting conditions.

The conception, design, and use of such a reactor aredescribed. As an example, the catalytic hydrogenationof crotonaldehyde (CrAld) (2-butenal) is studied usingbimetallic catalysts based on a commercial 5 wt.% Pton activated carbon catalyst. This reaction was chosenbecause it highlights the benefits of stage II over stageI screening. CrAld, an �–� unsaturated aldehyde, canbe hydrogenated at either the C=C double bond toform butyraldehyde (butanal) or the C=O bond to formcrotylalcohol (butan-1-ol). Kinetic reasons imply apreferential hydrogenation of the C=C bond, but thehydrogenation of the C=O bonds in allylic compoundsproduces products that are valuable intermediates inthe production of perfumes, flavourings and pharma-ceuticals [21]. Therefore, not only is catalytic activityimportant, but so too selectivity, which requires theuse of a screening technique adapted to this problem.

2. Experimental

The bimetallic platinum containing catalysts usedin this study were all synthesised using a commercial5 wt.% Pt on activated carbon samples (Fluka), whichwill be designated as Pt∗. The catalyst was used asreceived, with no pre-treatment prior to metal de-position. Catalyst preparation was automated by theuse of a commercial pipette system (Gilson XL 232)which was used to deliver the metal salt precursorsto pre-weighed Pt∗ catalysts, as described previously[19]. The incipient wetness deposition was performedusing the metal nitrate salts for: Co, Yt, Ni, Pr, Nd,Cr, Ga, Pb, Mn, Ba, Cu, and La, but for Sn, and Vthe salts SnCl2·2H2O, and VSO4 were used, respec-tively. Upon deposition, samples were dried at 50◦C.Two loadings, 3 and 6 wt.% (total catalyst weight),were used in this study. Samples that were to be cal-cined were heated in a furnace at 300◦C for 2 h, thetemperature limited by the activated carbon support.Reduction of samples was performed at either 350 or550◦C in flowing H2 (20% in N2). Reduced samples

S. Thomson et al. / Applied Catalysis A: General 220 (2001) 253–264 255

Fig. 1. Photograph and schematic drawing showing the design of the 25 sample HTE reactor used in this study.

were stored under laboratory conditions until tested.This was normally no longer than 48 h.

All high throughput hydrogenation experimentswere conducted using a reactor manufactured inhouse by the mechanical workshop (Fig. 1). The bot-tom section of the reactor is constructed from a solidbrass block in which 25 wells have been drilled to

allow the insertion of ca. 13 ml stainless steel liners(Fig. 1). The top section of the reactor contains 25hollow stirring rods containing inlets at the top of thesystem to allow for gas to be introduced and expelledfrom the individual reactors. An synchronised inter-connecting cog driven system, which is connected toa central cog, powers the stirrers. This central cog is


magnetically coupled to an electric motor, eliminatingthe need for o-ring seals and allowing high pressuresof up to 50 bar to be achieved. Containing two valvesfor the introduction, removal, and purging of gases,the apparatus is an open system with no sealing ofindividual autoclaves. However, this interconnectionis through small diameter feed-throughs that existsin the top of the stirring rods for the introduction ofgases, limiting the potential cross contamination. Allexperiments performed in this study were conductedat room temperature, however, the cell has the abilityto be used at higher temperatures (≤100◦C). Furtherdetails of the reactor can be obtained by contactingthe authors.

For the HTE hydrogenation of CrAld, catalysts werepre-weighed (15 mg) into 23 stainless steel liners andusing the automated pipette system, 0.5 ml of H2O(distilled), 4.9 ml of the methanol solvent (Fluka GCgrade), and 0.5 ml of CrAld (Fluka, purity >99.5%,cis: 25 trans) were added. Water was added becauseit has recently been established that this increases therate of CrAld consumption in similar bimetallic sys-tem supported on SiO2 [22]. The remaining two lin-ers were used as control samples, one filled only withmethanol, the other with all three reagents. The linerswere then transferred to the reactor and sealed. Thereactor was flushed with argon followed by hydrogen,filled to a pressure of 25 bar, and left to equilibrate.The pressure was again set to 25 bar and stirring ini-tiated. For conventional three phase testing, commer-cial reactors (Roth, model 1) were filled with 45 mgof catalysts, 14.7 ml of methanol, 1.5 ml of H2O, and1.5 ml of CrAld using the same reagents and condi-tions listed above.

Analyses of the reaction products was performedby halting the reaction after 2 h and taking aliquotsfrom each reactor using the automated Gilson pipetterobot. A standard isopropanol–methanol mixture wasadded to each sample and diluted with diethylether.Upon completion, the liners were returned to the ves-sel, purged with argon and hydrogen, and reacted for afurther 3 h at 25 bar. The reaction was again halted andGC samples obtained. All samples were analysed byGC using a Hewlett-Packard 5890 with an automaticcarousel, FID detector, and equipped with a 30 m DBWAX capillary column. Due to limitations in the abil-ity of this column to separate the cis and trans forms ofCrAld, analysis of the conformers was not attempted.

3. Results and discussion

3.1. Commissioning of the reactor

Prior to using the reactor for catalyst screening,experiments were performed to determine; the levelof gaseous exchange, the reproducibility of individualcatalytic reactions, and the experimental conditionsneeded to ensure mass transport limitations wouldnot prevail. As stated previously, the reactor designis such that the individual systems are not sealed andtherefore, the possibility of gaseous product exchangeexists. To determine the level of such exchange, ex-periments were conducted using 24 liners filled with4.9 ml of methanol and 1 ml of CrAld. In the centre ofthe reactor, an experimental blank (a single liner con-taining only methanol) was placed. The reactor wassealed, filled with 25 bar of nitrogen, and mechani-cally stirred for 16 h. Analyses of the blank liquids byGC detected <3.6% of CrAld. Clearly, this level ofcross contamination is low and bearing in mind thereaction times used in this study (5 h), are unlikely tohave any great effect on the outcome of reactor test-ing. Nonetheless, all reactions performed in this studycontained a blank sample to continually monitor thislevel of exchange. In all cases the most prevalentimpurity was CrAld, found at concentrations ca. 1%.Other impurities, butyraldehyde (BuAld), crotylalco-hol (CrOH) and butanol (BuOH) were found at totalconcentrations of less than 0.5%.

To determine the effect of mass transfer and ensurethat this did not prevail as rate limiting, a standardreaction mixture (0.5 ml of H2O, 4.9 ml of methanol,and 0.5 ml of CrAld) was added to varying weights ofa commercial 5 wt.% palladium on activated carboncatalyst (Fluka) reduced at 350◦C prior to use. Theresults obtained from reactions conducted at roomtemperature and at 25 bar of H2, showed that masstransport limitations prevailed at catalyst weightsgreater than 20 mg. However, from the results ob-tained for the Pt∗ catalyst (reduced at 350◦C) rununder the same conditions, it was determined thatmass transport limitation occurred at weights greaterthan 30 mg (Fig. 2). Because the platinum system isknown to be the basis for more selective catalysts, itwas chosen as the preferred catalyst. The amount ofcatalyst used in testing the bimetallic catalysts (15 mg)was chosen to allow for increases in activity due to


Fig. 2. Graph of CrAld consumption versus catalyst weight for the reduced (group D) Pt∗ catalyst, which shows the onset of mass transportlimitation above catalyst weights of 30 mg.

various treatments and modifiers, and to minimise thequantity of catalyst used. The effect of internal masstransfer limitations is difficult to assess, since the tex-tural parameters were not systematically varied. Allcatalysts tested in the present study, however, werebased on the same parent catalyst, so that a possibleinfluence of internal mass transfer limitations shouldbe fairly similar for all samples.

The reproducibility of the cell was tested using thePt∗ catalyst (reduced at 350◦C). Twenty-three wellswere filled with the same quantity (30 mg) of the Pt∗catalyst, the remaining two reactor wells were filledwith methanol only and the methanol, CrAld and watermixture, respectively. This was done to monitorgaseous exchange and background hydrogenation.The observed background hydrogenation was negli-gible, typically being in the order ca. 1–2%. The re-producibility of the individual reactors containing thePt catalyst was observed to have a standard deviation(conversion) of less than ±4%.

Fig. 3 details the results obtained from a bimetalliccatalyst containing 3 wt.% Co synthesised using thePt∗ catalyst. The results from 13 sequential reactorpositions are compared to results obtained using two100 ml total volume commercial single sample threephase reactors. For conventional testing, the quantityof reagents was scaled by a factor of three. In per-forming this test, the catalyst was synthesised in bulkprior to testing ensuring the consistency of sample

composition. The results not only demonstrate thereproducibility of the combinatorial reactor, but alsoshow the consistency of the results with conventionaltesting techniques. The activity of samples measuredin the conventional reactors were about 10% fasterand exhibited a somewhat higher selectivity towardsCrOH, but these deviations seem to be acceptable con-sidering the higher throughput that can be achieved.These results are consistent with those obtained fromanother direct comparisons between high throughputand conventional reactor results for both 3 wt.% Baand 3 wt.% Yt on Pt∗ sample which were calcinedat 300◦C prior to testing. The results of this test areshown in Fig. 4.

3.2. Crotonaldehyde hydrogenation

The hydrogenation of CrAld results in the forma-tion of several products and intermediates detailed inFig. 5. The major products from such reactions arethe liquid phase products: BuAld, CrOH, and BuOH.During the formation of these compounds the interme-diates crotonaldehydedimethylacetal, and to a lesserextent butyraldehydedimethylacetal, were observed.However, these intermediates were generally found tobe less than 5% of the total products and each wereadded to the CrAld and BuAld totals, respectively. Ina recent paper by Englisch et al., the use of methanolin CrAld hydrogenation reactions over SiO2 based


Fig. 3. Graph detailing the reproducibility of the reactor (marked A) and showing a comparison of results from the commercial single shotreactors (marked B).

Fig. 4. A comparison of results after 2 h of reaction time from the high throughput reactor (HT) and conventional catalytic testing (c).The catalysts used were 3% Yt on Pt∗ and 3% Ba on Pt∗ which were calcined at 300◦C prior to testing.


Fig. 5. Possible reaction pathways for the hydrogenation of CrAld.

bimetallic Pt containing catalysts, was found to sig-nificantly increase the formation of side products toca. 29% [22]. However, in this study the typical levelsof side products was found to be generally <5%, andthis may be due to activated carbon being used as asupport, reducing acid catalysed reactions.

Samples synthesised by impregnation underwentseveral different treatments before catalytic testing.Table 1 details the treatments applied to both the 3and 6 wt.% impregnated catalysts and the nomencla-ture used throughout this paper. Prior to hydrogena-tion reactions, some samples were calcined in air at300◦C. An examination of the mono-metallic precur-sor (Pt∗) by N2 adsorption showed no change in themeasured microporous volumes of 0.23 cm3 g−1 priorto calcination and after calcination. However, someweight loss, attributed to the both particulate loss and

Table 1Nomenclature used for sample treatments

Group Treatment

A Calcined at 300◦C for 2 hB Group A + reduction in H2 at 350◦C for 2 hC Group A + reduction in H2 at 550◦C for 2 hD Reduced in H2 at 350◦C without calcinationE Reduced in H2 at 350◦C without calcination

combustion of the carbon, was observed and calcu-lated to be no greater than 8 wt.%.

The introduction of a second metallic phase can re-sult in the modification of the catalytic activity of Pt∗catalysts. Two models have be used to explain the ef-fect of the introduced metal in increasing the selec-tivity to CrOH [23]. The first relates to the increasedelectron density produced from alloying of platinumwith the second metal, that results in preferential in-teraction with the polar C=O bond. The second is de-scribed in terms of Lewis acidity, at or near active sites,that accept the lone pair electrons from the oxygen onthe C=O group and therefore lowering the strength ofthe bond and facilitating its subsequent hydrogenation.

Tables 2 and 3 detail the catalysts with the high-est selectivity to CrOH, with respect to the differentpre-treatments used. However, because data was col-lected at 2 and 5 h periods, the individual catalystselectivity will be biased by conversion effects. It isexpected that catalysts with increased activity will ex-hibit a predilection to total hydrogenation (the forma-tion of BuOH), and therefore direct comparisons willfavour the less active catalysts. Nevertheless, it is rea-sonable to assume that small differences in CrAld con-sumption are unlikely to have a significant affect onselectivity. This assumption is confirmed from a com-parison of individual reactions at 2 and 5 h timeframes


Table 2Results from the hydrogenation of CrAld, at reaction times of 2 and 5 h, using 6% Me modified Pt∗ catalystsa

Catalyst Group CrAld consumed (%) Selectivity (%)

BuAld BuOH CrOH

t = 2 h6% Mn on Pt A 10 33 3 646% Nd on Pt C 21 32 6 626% Nd on Pt B 33 33 8 596% Mn on Pt B 6 40 2 586% Cr on Pt C 39 39 5 566% Ba on Pt A 54 36 10 546% Ga on Pt D 10 38 8 546% Yt on Pt B 63 33 14 53

t = 5 h6% Mn on Pt A 27 28 4 686% Nd on Pt C 46 33 8 596% Nd on Pt B 87 22 20 586% Mn on Pt B 21 35 3 626% Cr on Pt C 88 29 18 536% Ba on Pt A 93 24 24 526% Ga on Pt D 26 40 9 516% Yt on Pt B 92 6 90 4

a The best eight catalysts are shown in order of their selectivity to CrOH.

Table 3Results from the hydrogenation of CrAld, at reaction times of 2 and 5 h, using 3% Me modified Pt∗ catalystsa

Catalyst Group CrAld consumed (%) Selectivity (%)

BuAld BuOH CrOH

t = 2 h3% Co on Pt D 28 44 6 503% Ga on Pt B 20 41 9 503% Nd on Pt B 19 50 8 423% Co on Pt B 23 54 6 403% Yt on Pt D 32 46 14 403% Pr on Pt C 15 53 9 383% Pr on Pt A 8 56 7 373% Ga on Pt C 7 60 6 34

t = 5 h3% Co on Pt D 61 38 10 523% Ga on Pt B 42 39 12 493% Nd on Pt B 40 44 9 473% Co on Pt B 43 52 7 413% Yt on Pt D 83 35 40 253% Pr on Pt C 35 51 9 403% Pr on Pt A 17 50 7 433% Ga on Pt C 16 60 6 34

a The best eight catalysts are shown in order of their selectivity to CrOH.


Table 4Results from the mono-metallic commercial samples with respectto pre-treatment conditions used

Catalyst Group CrAldconsumed(%)

Selectivity (%)

BuAld BuOH CrOH

t = 2 hPt∗ A 12 81 11 8Pt∗ B 20 79 9 12Pt∗ C 34 58 13 28Pt∗ D 39 72 16 12Pt∗ E 26 66 14 20

t = 5 hPt∗ A 42 75 14 11Pt∗ B 62 73 13 14Pt∗ C 65 57 18 25Pt∗ D 74 69 19 12Pt∗ E 43 69 15 16

where nearly all reactions show similar selectivitiesas long as CrAld consumption levels are below 85%.Furthermore, the overall goal of obtaining both moreactive and selective catalysts enables catalysts to besuccessfully screened prior to conventional testing.

The results obtained for the mono-metallic Pt∗ cat-alysts are detailed in Table 4. Selectivity of the Pt∗catalysts was observed to increase with increasing re-duction temperature, while calcination of the catalystprior to reduction (group C) resulted in a slight in-crease in selectivity of the samples reduced at 550◦C,when compared to the same sample reduced at 550◦C(group E) without calcination. Samples reduced at350◦C (groups B and D) had a similar predilection toCrOH. This increased selectivity has been observedbefore in gas phase reactions of CrAld over Pt onTiO2 catalysts [24]. However, the authors reasonedthe change in selectivity was an effect of Pt–TiO2 in-terface sites, created during higher temperature treat-ments, that selectively reacted with the C=O bond.Carbon being a more inert support, is unlikely to re-sult in such interactions. Although the oxidation ofcarbon supports has been studied and shown to affectboth the activity and selectivity of Pt containing car-bon catalysts [25], the fact that in this study a differ-ence is only evident at higher temperatures, suggeststhermal effects are responsible for such changes.

The Pt∗ catalyst with the highest activity was ob-tained for the group D sample (reduced at 350◦C only),

while a calcination step prior to reduction resulted ina decreased activity. Both groups C and E samplesshowed similar activities. The fact that the activities ofthe groups C and E samples was lower than that of thegroup D Pt∗ sample, coupled with the increased selec-tivity of the groups C and E samples to CrOH, suggeststhe different thermal treatment results in changes tothe Pt clusters resulting in the modified activity. Suchchanges are consistent with an increase in Pt particlesize resulting in a higher fraction of Pt(1 1 1) facesaccessible to CrAld [26], which Delbecq and Sautethave proposed modifies the activity and selectivity ofthe Pt active sites [27,28].

The introduction of a second metallic phase to thePt∗ catalyst resulted in some interesting effects. For the3 wt.% samples, those catalyst found to be most selec-tive to CrOH were Co, Ga and the rare earth metals Yt,Pr and La. Naturally, the pre-treatment calcination ofthe materials also modified the selectivity and activityof the catalyst, but overall these bimetallic compositesconsistently showed higher selectivities to CrOH thanthose of the corresponding Pt∗ catalysts (Fig. 6). Asdiscussed above, since the activities of the differentcatalysts are somewhat different, the data given in thefigure are biased by different conversions. Anyway, thegeneral trends observed from the figure are still valid.For all the experiments shown, the full product dis-tribution was analysed. However, presenting the fulldata set would go beyond the scope of this paper.

Englisch et al. have previously demonstrated thehigh selectivity of Ga–Pt and Co–Pt composite ma-terials, supported on SiO2, to CrOH in liquid phasereactions [23]. However, the results obtained in thisstudy for the La–Pt composite materials differ to thoseof the latter study in that lower activities and slightlyhigher selectivities to CrOH were observed for thiscatalyst. Whether this is a factor of the increasedLa:Pt ratio used in this study (0.84 compared to 0.25)or an effect of the support is not known. The loadingused in our study is already very high compared toliterature data and for some compositions, probablyis beyond the optimum.

Of particular interest is the inactive and unselec-tive nature of the Sn–Pt composite materials, whichare known to be highly selective to CrOH [23,29,30].Coloma et al. observed that the selectivity of theCrAld system to CrOH is dependent on the ratio ofSn:Pt on carbon supported systems, passing through


Fig. 6. Selectivity of 3% bimetallic Pt∗ catalysts to CrOH after a reaction period of 2 h.

a maximum at 0.8 [29]. The fact that the atomic ratioof Sn:Pt for the 3 wt.% samples is >1.2, is consistentwith the low selectivity of the catalyst.

The most active catalyst was the Ni–Pt composite,but the selectivity to CrOH was low, preferring to hy-drogenate the C=C bond to form BuAld. Once mostof the CrAld had been consumed (≥85%), the majorproduct was BuOH, indicating the BuAld hydrogena-tion was occurring. These results are consistent withprevious studies of Ni–Pt composites supported onSiO2, which demonstrated a high affinity for the hy-drogenation of the C=C bonds of CrAld [31]. Morerecent gas phase studies have revealed that Ni de-posited on ordered graphite nanofibres results in CrOHselective catalysts, but this phenomenon is clearly as-sociated with the properties of the support rather thanthe active metal species [32]. It must be noted thatthe large increase in activity observed for this catalystis likely to result in mass transport limitations forthis system.

The addition of both vanadium and lead to the Pt∗catalysts resulted in a large drop in activity comparedto that of the Pt∗ sample, and this is consistent withPb–Pt and V–Pt composites supported on SiO2 [23].This effect is probably due to the preferential sitingof both lead and vanadium on the Pt sites, effectivelypoisoning the catalyst.

For the 6 wt.% samples, the introduced metals thatresulted in the best CrOH selective catalysts were onceagain Ga, Co, Mn, and the rare earth metals Yt, Pr and

La. Nonetheless, the loading of excessive amounts ofthe secondary metals resulted in some interesting re-sults. In particular, the deposition of larger amounts ofthe secondary metal resulted in more active catalysts,with those most selective to CrOH being in groupsA–C, all of which were calcined in oxygen. Again the6% Sn–Pt∗ catalyst showed similar properties to thatof the 3% sample, with moderate activity for the groupA sample and little activity in the others.

Of the metals used, most of the oxides producedwill result in the formation of Lewis acid sites, whichprimarily will interact with the C=O bond making itmore susceptible to hydrogenation. It must be noted,that the high activity of many of these catalyst resultedin ca. 100% conversion over the 5 h reaction period.This resulted in many of the catalyst producing highquantities of BuOH.

The group A Ba–Pt composite showed both highcatalytic activity and selectivity for CrOH. As the3 wt.% loaded samples did not exhibit a similar trend,it is likely that the extra oxide material that forms uponcalcination is most likely to be responsible for the in-creased catalytic activity. The role of barium in thisstudy is unclear and warrants further study.

4. Conclusions

Experiments conducted in this study demonstratethe potential of a new HTE technique for liquid


phase catalytic systems. The ability to obtain quan-titative data attaining to both catalyst selectivity andactivity in timeframes one to two orders of magni-tude shorter than conventional catalyst testing, willdrastically decrease the times needed for catalyticdiscovery. The high throughput reactor has the advan-tage of being able to incorporate an array of sampleswithout the duplication of expensive pressure gauges,valves, and fittings. Results obtained from the cellhave been shown to yield reproducible data with astandard deviation (activity) of ±4%, and are consis-tent with results from commercial single sample reac-tors. The latter is an important fact if such results areto be extrapolated to conventional catalytic systems.The multiple reactor is limited by gaseous diffusioneffects that can occur due to reactor being an the opensystem design. Therefore, there is a trade off betweenthe simplicity of design versus the inability to usehigh shear stirring systems that would accommodategreater sample weights and more active catalyticsystems. However, this may be of little consequencefor the reaction investigated, due to the inability ofmany highly active catalysts in selectively producingCrOH.

Modifications to the stirring system, such as the useof high shear stirring devices and the individual seal-ing of the 25 reactors to prevent both gaseous andliquid exchange between reactors would enable morereactive samples to be probed and have the advantageof enabling the hydrogen consumption of individualreactors to be monitored. This would allow more de-tailed kinetic studies to be performed. With this inmind we have built and are currently commissioninga second prototype reactor which will fulfil these re-quirements. In addition, the reactor will allow on-lineintroduction of reagents or sampling during the cat-alytic runs at pressures exceeding 100 bar and tem-peratures up to 473 K. However, in terms of quicklyscreening samples and obtaining both selectivity andreactivity data, the HTE reactor used in this studyis adequate for many catalytic samples. Many reac-tions, such as oxidation or homogeneously catalysedreactions, impose less stringent requirements on thereactor set-up and can be run advantageously in thesystem described here. Furthermore, while not beingable to replace conventional catalytic testing, HTEmethods will drastically reduce the time needed forcatalyst discovery.

Acknowledgements

In addition to the basic funding provided by theMax Planck Society this work was supported by theGerman Federal Ministry for Education and Research(BMBF) under Contract No. 02 D 0068 A2 and isgratefully acknowledged.

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