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Synthesis of Inorganic Materials by Solvothermal Methods
05 December 2008
A. Trunschke, Department of Inorganic Chemistry,
Fritz Haber Institute, Max Planck Society
Further reading:•
K. Byrappa, M. Yoshimura, Handbook of Hydrothermal Technology, Noyes
Publications, Norwich, NY, 2001.
•
J.-P. Jolivet, Metal Oxide Chemistry and Synthesis –
From Solution to Solid
State, John Wiley & Sons Ltd., Chichester, 2000.
Modern Methods in Heterogeneous Catalysis Research
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2Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Outline
• Introduction
• Experimental
• Parameters governing the solvothermal reaction
• Oxide synthesis in aqueous media
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3Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Introduction
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4Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Synthesis of nanostructured catalysts and catalyst supports
Method advantage disadvantagePrecipitation and coprecipitation
Defect-rich materials
experimentally easy
Homogeneity difficult to achieve
Sol-gel-techniques Homogeneity of the product Carbon-containing impurities from metal precursors
Microemulsions Particle size control High consumption of solvents
Solvothermal synthesis Kinetic control over the phases formed
Predictions difficult
Solid state reactions 100% yield
stoechiometric reactionHighly crystalline products
Most thermodynamically stable phases are obtainedLow surface area, particle size is difficult to control
Flame pyrolysis Particle size control
Chemical vapor deposition
Molten salt synthesis
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5Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
•
Autogeneous pressure:
self developed pressure, not externally applied
•
Mineralizer:
component that helps to dissolve the reactants by forming complexes,
which are more soluble
(e.g. alkali metal hyroxide in silicate synthesis)
Under solvothermal conditions, reactants which are otherwise
difficult to dissolve go into solution under the action of mineralizers
or solvents
Solvothermal methods in inorganic synthesis
Autoclave/Parr
Solvothermal reaction:Any heterogeneous chemical reaction in a closed system, in the presence of a solvent and temperature above the boiling temperature of the solvent used
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6Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Historical development
1845-1900 Mineral synthesis, imitation of natural conditions
1845 K.E. von Schafhäutl Papin's digestor quartz crystals
1848 R. Bunsen thick walled glass tubes Sr, Ba carbonates
1851 H. de Sérnamont glass tubes in autoclaves quartz, carbonates, (steel tubes) sulfates, sulfides, founder of hydrothermal fluorides synthesis in geoscience
1873 K. von Chrustschoff Au lining prevent corrosion
1890 C. Doetler Ag-lined steel tube mineral closed by a screw cap recrystallization and Cu washer
1892 C.J. Bayer invention of the first leaching of Bauxite indutrial hydrothermal with NaOH at process 170-180°C (hydrometallurgy)
Na[Al(OH)4 ] Al(OH)3 + NaOHNa[Fe(OH)4 ] Fe(OH)3 + NaOH
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7Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Historical development
1900-1950 Mineral synthesis, improvements in pT conditions
1914 G.W. Morey standard „Morey-type“ autoclave
J. Am. Chem. Soc.; 1914; 36(2) pp 215 - 230; New Crystalline Silicates of Potassium and Sodium, their Preparation and General Properties.
1943 R. Nacken fundamentals of industrial growth of quartz crystals using seeds
1948 R.M. Barrer synthesis of zeolites
J. Chem. Soc., 1948, 2158 - 2163; Syntheses and Reactions of Mordenite
1949 O.F. Tuttle cold seal and test tube autoclaves
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8Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Historical development
1900-1950 Mineral synthesis, improvements in pT conditions
Work by Milton at the labs of Linde corporation:
Synthesis of zeolite A, zeolite X
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9Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Historical development
1950-today
1950-1960 phase diagrams for natural systems
1960-1980 synthesis of technologigal materials new inorganic compounds without natural analogs or synthesis before discovery
1980-1990 importance of the technique in materials science physical chemistry of hydrothermal solutions
> 1990 diversification of hydrothermal techniques solvothermal synthesis entry of organic chemists physical chemistry of hydrothermal solutions design of new reactors: batch reactors, flow reactors
mazzite
=
ZSM-4
tschernichite
=
zeolite
betamutinaite = ZSM-5
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10Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Field Application Synthesis of different material families
� Oxides, halogenides, chalcogenides � Nitrides, carbides, phosphides � Metallics, intermetallics � Open-framework and hybrid materials
Synthesis of new phases or stabilization of new inorganic compounds with specific structures and properties
� Functionalized materials � Nanostructures (rods, wires, tubes) � Magnetic nanoparticles � Preparation of materials with narrow particle size distribution and homogeneous microstructure (morphology control of transition metal oxides)
Crystal growth and modification
� Synthesis of single crystals of low temperature forms with low density of defects � Decomposition, dissolution, corrosion, etching
New process developments
� Large-scale synthesis � Synthesis of nanoparticles with supercritical fluids � Morphology control with microwave-hydrothermal synthesis
Novel applications of solvothermal synthesis
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11Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Zeolite ZSM-5 (MFI)
Classical applications of synthetic zeolites
• Ion exchangers
• Molecular sieves
• catalysts
Synthesis of microporous alumosilicates
A. K. Cheetham, G. Ferey et al. Angew. Chem. Int. Ed. 38 (1999) 3268-3292.
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12Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
M. I. Kahn, L. M. Meyer, R. C. Haushalter, A. L. Schweitzer, J.Zubieta, J. L. Dye, Chem. Mater. 8 (1996) 43.
Open framework structures of transition metal phosphates
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Experimental
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14Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Autoclaves: batch experiments
Autoclave/Premex
AG
control unit
250°C60 (200) bar
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15Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Autoclaves: flow experiments
A. A. Galkin, V. V. Lunin, Russian Chemical Reviews 74 (1) (2005) 21-35.
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Material properties
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Material properties
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18Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Water in a closed vessel
Pressure inside a sealed vessel as a function of percentage fill and temperature
critical fill 32%
ρcr = 0.32 g/cm3
32% fill
r.t. 374°CA. Rabenau, Angew. Chem. 97 (1985) 1017-1032.
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19Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Other solvents
M. Rajamathi, R. Seshadri,
Current Opinion in Solid State and Materials Science 6 (2002) 337-345.
ω
acentric factor (tabulated)
Tr =T/TC
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20Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Savety
100 cm3
20 000 psi20 000 J≈
Important:
• Maintenance of the autoclave
• Anticipation of the dangers of
hydrothermal experiments
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21Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Savety
• Consider the technical parameters of the autoclave
• Use rupture discs calibrated to burst above a given pressure
• Make provision to vent the live volatiles out in event of rupture
• Use proper shielding (close the fume hood)
• New autoclaves should be heated with distilled water in the vessel several times
•
Once a vessel has contained reduced sulfur, it should not be used for sulfur-free
experiments unless it has been vacuum cleaned while hot, followed by heating in
air at 350°C
• Do not quench the vessel rapidly
•
Undertake precaution to prevent overheating of the furnace resulting from malfunction of the control system
• Hot surfaces! Wear special insulated gloves
• The vessel to be heated must never be filled completely with aqueous solution
•
Calculate the thermal expansion of the aqueous phase and allow at least 20% of
total volume of the vessel for uncertainty or temperature overturn, consider the
formation of gases
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22Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Parameters governing the solvothermal reaction
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23Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Types of hydrothermal reactions
C.S. Cundy, P.A. Cox, Microporous and Mesoporous Materials 82 (2005) 1–78.
Dissolution, precipitation and modification of precipitates, flocculates, gels or colloids under aging or ripening
• Redox reactions
• Hydrolysis
• Thermolysis • Complex formation• Metathesis reactions
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24Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal transformations
For what purpose do we apply hydrothermal conditions?
Metastable, more complex structures are favoured involving smaller enthalpy and entropy changes than standard conditions
Small crystals or amorphous particles Large crystals or amorphous particles
Amorphous material Crystalline material
Crystal 1 Crystal 2
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25Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Main parameters governing the hydrothermal reaction
• Thermodynamic parameters (T, p)• Kinetics• Chemical parameters
• Solvent• Chemical composition of the precursor• Concentration• pH, ionic strength• Complexing agents• Reducing / oxidizing agents• Templates
• Experimental parameters• Volume / wall
ratio• Wall material• Heat exchange• Stirrer speed• Cooling facilities
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26Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Mechanism of oxide formation in hydrothermal synthesis
A
B
R.I. Walton, Chem. Soc. Rev. 31 (2002) 230–238.
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27Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal conditions
• Strength of acids and bases is changed
•
Condensation of metal cations is linked
to the their acid-base characteristics
•
Forced hydrolysis of cations
(thermohydrolysis)
•
Modification of the chemistry of cations
in solution
• Coordination of cations with unusual symmetry
The kinetics of solid transformation in suspensions are accelerated
The properties of the solvent are significantly influenced by T and p
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28Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Water as a polar protic solvent
The high polarity of water is responsible for solvation of metal ions
•
Solvation of cations: Water has Lewis base character due to the electrons in
the 3a1
MO (nucleophilic interaction with Lewis acids)• Solvation of anions: Electrophilic interaction by formation of hydrogen bonds
B.E.= 20-40 kJ mol-1
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29Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Schematic phase diagram of water
~ 6 mbartriple point
critical point
liquid
solidsuper- heated vapour
supercritical fluid
T
vapour
~ 0°C
p Gibb‘s phase ruleF = N - P + 2N number of componentsP phases
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30Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Characteristics of water under different conditions
•
The characteristics of supercritical water are intermediate between those of
liquid and gas
• Physico-chemical properties change continuously
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31Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Density
Infinite compressibility of water in the near critical region -
Density variations over a wide range by only slightly varying
T and
p
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32Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Viscosity
Ki
decreases as T increases (ΔR
H<0)
298 K: up to 100 molecules in one cluster673 K: 50% of hydrogen bonds broken
Under supercritical conditions the clusters have chain structure
• Viscosity of water decreases with increasing temperature• Mobility of dissolved species increases• Viscosity changes in presence of ions: H-bonds are broken by K+, NH4+, NO3-, ClO4-
•
Weakly polarizing ions ([NR4
]+, R=CH3
, C2
H5
,…) are incorporated within the solvent
-
formation of polyhedral cages
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33Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
ε<15 nonpolar solventε>15 polar solvent
•
The dielectric constant of water decreases with increasing temperature and
increases as pressure increases
•
The solvation is affected: Under supercritical conditions water molecules
cannot sufficiently screen ions -
electrolytes form ion pairs
Dielectric constant
macroscopic property
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34Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Ionic product
•
The ionic product of water
strongly increases with
temperature
•
sub-critical water is a rich source
of H+
and OH-
•
supercritical water shows
properties of an ionic liquid at
very high p and T
Ke
= aH+
ÿ
aOH-
=
1.00 ÿ
10-14
at
T=298 K
pH=7
= 74 ÿ
10-14
at
T=373 K
pH=6.07
2 H2
O
F
H3
O+solv.
+ OH-solv.
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35Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Redox potential
A. Rabenau, Angew. Chem. 97 (1985) 1017-1032.
MnO4-
+ 8 H+
+ 5 e-
F
Mn2+
+ 4 H2
O
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36Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Other parameters
•
In concentrated solutions the critical temperature is higher –
below 800°C
no differentiation between sub-
and supercritical conditions possible
• Additives to control the oxidation state•
Hydrolysis of metal acetates, formates, and oxalates involves CO
formation, CO is more soluble in water under hydrothermal conditions
• Hydrocarbon ligands favour the formation of reduced nanoparticles
• Oxidazing agents: H2
O2
, HClO4
, HNO3
, Cl2
, Br2
, O2
•
Formation of specific structures or morphology by addition of complexing
agents, structure directing agents and templates
Tetramethylammonium cations occluded into the sodalite cage
G.J. de A.A. Soler-Illia, C. Sanchez, B. Lebeau, J. Patarin, Chem. Rev. 102 (2002) 4093.
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Oxide synthesis in aqueous media
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38Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Mechanism of oxide formation in hydrothermal synthesis
A
B
R.I. Walton, Chem. Soc. Rev. 31 (2002) 230–238.
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Dissolution -
solvation
Solvation
+
-
[M(OH2 )6 ]2+ M= Mg, Ca, Cd, Hg, Pb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
[M(OH2 )8 ]2+ M= Sr
[M(OH2 )6 ]3+ M= Al, V, Cr, Mn, Fe
Ions with a charge higher than three undergo hydrolysis
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Cations in aqueous solutions: Hydrolysis
[M(OH2)]z+ [M(OH)](z-1)+ + Haq [M-O](z-2)+ + 2 Haq
H2O H2O
pH<7, z ≤
4 pH>7, z ≤
4 z > 4aquo hydroxo oxo
Acid-base properties of coordinated water molecules
[CrO4 ]2-
[CrO3 (OH)] -
[Cr (OH2 )6 ] 3+ [Cr(OH)3 (OH2 )3 ]
[Cr(OH)4 (OH2 )2 ]-
[VO2 (OH2 )4 ]+ Small cations of high formal charge (z>4) form π
bonds (V:r=0.54Å)[VO(OH2 )5 ]2+
B.L. Cushing et al., Chem. Rev. 104 (2004) 3893-3946.
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41Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Ti(IV) hydrolysis constants derived from rutile solubility
measurements made from 100 to 300°C
Kevin G. Knauss *, Michael J. Dibley, William L. Bourcier, Henry F. Shaw Applied Geochemistry 16 (2001) 1115-1128.
Solubility of TiO2 under hydrothermal conditions
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42Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Ti(IV) hydrolysis constants derived from rutile solubility
measurements made from 100 to 300°C
Kevin G. Knauss *, Michael J. Dibley, William L. Bourcier, Henry F. Shaw Applied Geochemistry 16 (2001) 1115-1128.
Solubility of TiO2 under hydrothermal conditions
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43Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Polycondensation in aqueous solution
Addition of a base to an aquo complex (polycations)
[Al(OH2
)6
]3+
+ 3 OH-
→
Al(OH)3
+ 6 H2
O
13
[Al(OH2
)6
]3+
+ 32 OH-
→ [Al13
O4
(OH)24
(OH2
)12
]7+
+ 70 H2
O
Addition of an acid to an oxo complex (polyanions)
[SiO2
(OH2
)2
]2-
+ 2 H+
→
SiO2
+ 2 H2
O
4 [SiO2
(OH2
)2
]2-
+ 4 H+
→
[Si4
O12
]4-
+ 4 H2
O
Transition metal ions often change the coordination
12 [WO4
]2-
+ 18 H3
O+
→
[H2
W12
O40
]6-
+ 26 H2
O
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44Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Polycondensation in aqueous solution
precursor
[M-O] - + H3O+ M-OH + H2O [M-OH2]+ + HO-
Initiation (hydroxylation)
Initiation → Propagation
→ Termination
Propagation (nucleophilic addition/substitution)
M-OH + M-OH2 M-OH-M + H2O OlationOligomeric species: PolycationsReaction leading to a hydroxy bridge
M-OH + M-OH M O
H
M OH M-O-M + H2O OxolationOligomeric species: PolyanionsReaction leading to an oxo bridgeTermination
• Condensation of cationic or anionic hydroxylated complexes limited• The formation of a solid requires the presence of zero-charge complexes
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45Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal zeolite synthesis
C.S. Cundy, P.A. Cox Microporous and Mesoporous Materials 82 (2005) 1-78.
Experimental procedure1. Mixing amorphous
reactants containing Si and Al in a
basic medium
2. Heating (often) above 100
°C in a sealed
autoclave.
3. Isolation of the crystalline
zeolite product
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46Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal zeolite synthesis
Amorphous material
Dissolved species
Elements of local order
Periodic structure
nucleation
crystal growthdissolution of amorphous phase
Crystalline product
Associated solvated cations act as coordination centers
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47Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal zeolite synthesis
C.S. Cundy, P.A. Cox / Microporous and Mesoporous Materials 82 (2005) 1-78.
Matching between ZSM-18 and
the triquat template molecule used in ist synthesis
Templates• „space fillers“• Structure directing agents• True templates
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48Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Transition metal ions in aqueous solution
2[VO4
]3-
+ 2H+
→ [V2
O7
]4-
+ H2
O
4[VO4
]3-
+ 8H+
→ [V4
O12
]4-
+ 4H2
O
10[VO4
]3-
+ 25H+
→ [HV10
O28
]5-
+
12H2
O
[H2
V10
O28
]4-
+ 14H3
O+
+ 18H2
O → 10 [VO2
(H2
O)4
]+
[VO(OH)3
(OH2
)2
][VO2
(OH)(OH2
)3
]
V2 O5 precursorIn diluted solution:
vanadic cation
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49Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal synthesis of vanadium oxide
S.A. Corr, et al., Chem. Mater. 20 (2008) 6396-6404.
Scroll-like morphology of the products of the two- day hydrothermal treatment of dodecylamine-intercalated V2 O5
Ch. V. Subba Reddy et al., Journal of the Electrochemical Society, 155 (2008) A599-A602.
Vanadium oxide nanorods for Li-ion battery applications by template-free hydrothermal synthesis at 180°C/15 d
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50Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Transition metal ions in aqueous solution
HTS, 110°C, molybdic acid solution
F. Harb et al., Solid Statc lonics 32/33 (1989) 84-90.
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51Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Hydrothermal synthesis of MoV oxide
10~20 nm
BET surface area#6142: 69.21m2/g#6274: 79.41m2/g
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52Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Synthesis of M1 (MoVTeNb mixed oxide)
Raman UV-vis SEM-EDX
(NH4 )6 Mo7 O24 ·4 H2 O
Te(OH)6 Ammonium niobium oxalate
slurry
VOSO4
Mo, V Mo, V, Te
b=26.6 Å
a=21.1 ÅV= 300 mlTeflon
Phase formation by dissolution-precipitation mechanism
Mo and MoV clusters:A. Müller, S. Roy,Coordination Chemistry Reviews 245 (2003) 153–166.
[TeMo6
O24
]6-
[Mo7
O24
]6-
Te(OH)6
MoVTeNb
Starting suspension: inhomogeneous slurry that contains an amorphous solid
[SO4
]2-
[NH4
]+
[C2
O4
]2-
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53Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Synthesis of M1 (MoVTeNb mixed oxide)
0
20
40
60
80
100
448423403
phas
e co
mpo
sitio
n [%
]
T [K]
M1 M2 Mo5O14
V0.95Mo0.97O5
383
• T = 383-448K• tsynt.
= 96h• inert gas = N2
V= 300 mlteflon
Variation of the synthesis temperature at t=96h
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54Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Synthesis of M1 (MoVTeNb mixed oxide)
10 20 30 40 50 60
♦
∗
∗
♦
Inte
nsity
[a. u
.]
∗ ∗
∗
∗∗
∗
∗•
•
2θ
•
∗
929
•
∗
∗
∗
2445
3298
• 3777
∗ ∗
3961
3791
2431
∗
3648
*
M1●
(NH4
)8
(V19
O41
(OH)9
)(H2
O)11
[ICSD 063213]♦
(NH4
)6
Mo8
O27
·4H2
O
[ICSD 2017] M5
O14 TeMo5
O16 V0.95
Mo0.97
O5(M=Mo,V,Nb)
0 20 40 60 80 100
M1
M2
M2
M2
M2
M2
M2
M2
M1
M1
M1
M1
M1
M1
M1
phases
after
crystallization / %XRD of amorphous precursor after hydrothermal synthesis
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55Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Reaction of solid oxides with superheated steam
O. Glemser, U. Stöcker, H.G. Wendlandt, Ber. Bunsenges. 70 (1966) 1129.
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56Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Synthesis of MoVTeNb oxide
0 400 800 1200 1600 200002468
101214161820
Cou
nts
(a.u
.)
Length (nm)0 100 200 300 400 500 600 700 800
05
101520253035404550
Cou
nts
(a.u
.)
Width (nm)
0 400 800 1200 1600 200002468
101214161820
Cou
nts
(a.u
.)
Length (nm)0 100 200 300 400 500 600 700 800
0
10
20
30
40
50
Cou
nts
(a.u
.)
Width (nm)
Hydrothermal synthesis under mild conditions
Hydrothermal synthesis in superheated water vapour
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57Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Synthesis under supercritical conditions
• Precipitation•
Rapid expansion of supercritical
solutions (RESS)
•
Rapid expansion of a supercritical
solution into a liquid solvent
(RESOLV)
•
Supercritical anti-solvent
precipitation (SAS)
• Supercritical solvothermal synthesis
• Supercritical drying
Methods for the preparation of nanoparticles• Particles with one dimension smaller than 200-100 nm• Surface properties become relevant with respect to volume properties
triple point
liquid
solid
critical
point
T
vapour
P
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58Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Other solvents
Reducing T and p
Catalyst Fluid T / K p / MPa Phase composition
MoVTeNbOx H2
O 773 20 M1
MoVTeNbOx CO2 573 6 M1
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59Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Microwave assisted hydrothermal synthesis
Domestic and laboratory microwave ovens:ν= 2.45 GHz (λ
º
12.2 cm)ν = 915 MHz (λ
º
32.7 cm)
A. S. Vanetsev, Yu.D. Tretyakov, Russ. Chem. Rev. 76 (2007) 397-413.
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60Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Interaction of microwave radiation with matter
1. Electronic and ionic conductivity•
Insulators are transparent•
Conducting materials reflect the microwave radiation (destroy the magnetron by overheating)
2. Dielectric permittivity and dielectric loss factor (absorption capacity)•
The substances should contain mobile dipoles (high dipole moment) or ionic conductivity•
The more efficiently the sample absorbs, the smaller is the volume that can be heated•
Dielectric properties depend on temperature3. Heat conductivity to avoid „hot spots“
G. A. Tompsett et al., ChemPhysChem 7 (2006) 296 – 319.
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61Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Microwave assisted hydrothermal synthesis
• High rates of phase formation•
Processes in the microwave field
caused by possible acceleration of
nucleation due to „non-thermal“
effects
Hydrothermal Synthesis of ZnBi2
O6
N. Kumada et al., Materials Research Bulletin, 33 (1998) 1411–1414.
M1 synthesis by a factor of ca. 10 faster
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62Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Sonochemical/hydrothermal synthesis
Cavitation
–
the formation, growth, and implosion of bubblesGeneration of high amount of energy (formation of radicals)
Combined with hydrothermal synthesis• Acceleration of crystallization
• Increase in the content of thermodynamically stable phases
• Initiation of redox reactions
D. G. Shchukin, H. Möhwald, Phys. Chem. Chem. Phys. 8 (2006) 3496 –
3506.
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63Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
In-situ methods to understand crystallization
Synchrotron X-ray radiationHigh intensityGood time resolution (ms)EDXRD: Big autoclavesAngular dispersive XRD: Quartz tubes
Neutron diffractionlow intensity of neutron sources limits time resolutionLarge samples –
real autoclaves
(Ti-Zr alloy)
A schematic of the cell used for in-situ energy dispersive synchrotron X-ray powder diffraction studies at the SRS, Daresbury
Laboratory. A three-elementdetector system is used for efficient detection of the EDXRD patterns.
P. Norby, Current Opinion in Colloid & Interface Science 11 (2006) 118–125.
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64Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
In-situ methods to understand crystallization
P. Norby, Current Opinion in Colloid & Interface Science 11 (2006) 118–125.
ULM-n oxyfluorinated phosphates
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65Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
In-situ methods
Investigation of mesoscopic structures
Particle size distributionParticle shapeParticle interaction
Crystallinity
Raman spectroscopyFTIR spectroscopy in non-aqueous mediumUV-vis spectroscopy
G.A. Tompsett et al., ChemPhysChem 7 (2006) 296 – 319
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66Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Summary
Application of hydrothermal synthesis in catalyst preparation• Stabilization of metastable phases
• Growth of single crystals
• Synthesis of inorganic materials with high-(phase-)purity
• Synthesis of nanostructuted catalysts
Parameters•
By varying the synthesis conditions (T,p,c, ...) it is possible to vary
the particle size and change the morphology
• Increase in time and concentration increases the particle size
•
Decrease of particle size to a certain critical size causes
preferred formation of the phases with higher symmetry of the
crystal lattice
• In complex systems predictions are difficult
• In situ studies of synthesis help to approach better understanding
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67Modern Methods in Heterogeneous Catalysis Research; 05/12/2008; Solvothermal synthesis; A. Trunschke
Acknowledgements
Thank
you
for
your
attention!
Thanks to Almudena Celaya Sanfiz, Yury Kolenko, Wei Zhang,
Gisela Weinberg, Zirong Tang, Frank Girgsdies and Edith Kitzelmann for
synthesis, SEM and XRD of the examples