fischer-tropsch catalysts: preparation, thermal pretreatment and behavior during catalytic reaction
DESCRIPTION
Fischer-Tropsch Process Themes Competitive Dissociative Adsorption Reducibility of Metal Oxides Feed Stock ofthe Fischer-Tropsch Process Catalytic Partial Oxidation Heats of Reaction Direct vs Indirect Catalytic Partial Oxida.....TRANSCRIPT
Fischer-Tropsch Fischer-Tropsch CatalystsCatalysts
Preparation, Thermal PretreatmentPreparation, Thermal Pretreatmentand Behavior during Catalytic Reactionand Behavior during Catalytic Reaction
Gerard B. HawkinsGerard B. Hawkins
Managing DirectorManaging Director
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Fischer-Tropsch ProcessFischer-Tropsch Process
Reaction of carbon monoxide and hydrogen to Reaction of carbon monoxide and hydrogen to mainly liquid hydrocarbonsmainly liquid hydrocarbons
Invented in Germany during the twenties of the Invented in Germany during the twenties of the former centuryformer century
Cobalt and iron as catalystsCobalt and iron as catalysts Objective : Producing transport fuels out of coalObjective : Producing transport fuels out of coal Competitor : Bergius coal hydrogenation by I.G. Competitor : Bergius coal hydrogenation by I.G.
FarbenFarben
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ThemesThemes
Dissociative adsorption of methane and carbon monoxide Dissociative adsorption of methane and carbon monoxide in competition with surface oxidation (catalytic partial in competition with surface oxidation (catalytic partial oxidation) or hydrogenation (Fischer-Tropsch synthesis)oxidation) or hydrogenation (Fischer-Tropsch synthesis)
Reducibility of metal oxides to metal oxides of lower Reducibility of metal oxides to metal oxides of lower valencyvalency
Different special procedures for producing supported Different special procedures for producing supported catalystscatalysts
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Competitive Dissociative AdsorptionCompetitive Dissociative Adsorption
CH4
H C H H H
2H2
CO O
CO
O O O O O O O O O O O O O O
CH4
CH4
CO2 H2O CH4
CH4
CO2 H2O
Dissociative adsorption of oxygen usually more rapid than dissociative adsorption of methane at temperatures below about 700oC
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Competitive Dissociative AdsorptionCompetitive Dissociative Adsorption
CO
C O H H
H2OOC
O C C C
CO2
C H C C H C H C H C
CnH2n(+2)
Relatively lowhydrogen coverage
Fischer-Tropsch
Relatively highhydrogen coverage
methanation
C H H H C H H H H C H H
CH4
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Reducibility of Metal OxidesReducibility of Metal Oxides
O O O O O O O O O O O O O O
O O O O O O O O O O O O O O O O O O O
Formation of reducedoxide phase
Formation of isolatedoxygen vacancies
CO C(ads) + O(ads) CH4 CO + 2H2
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Feed Stock ofFeed Stock ofthe Fischer-Tropsch Processthe Fischer-Tropsch Process
Feed stock : Initially coalFeed stock : Initially coalC + HC + H22O = CO + HO = CO + H22
Desired HDesired H22/CO ratio 2/CO ratio 2 Carbon monoxide shift conversionCarbon monoxide shift conversion
CO + HCO + H22O = COO = CO22 + H + H22 Presently : Natural gasPresently : Natural gas
Steam-reforming involvesSteam-reforming involvesCHCH44 + H + H22O = CO + 3 HO = CO + 3 H22
HH22/CO ratio too elevated/CO ratio too elevated Therefore (Catalytic) Partial OxidationTherefore (Catalytic) Partial Oxidation
also Autothermal reformingalso Autothermal reforming
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(Catalytic) Partial Oxidation(Catalytic) Partial Oxidation
Pure oxygen required to performPure oxygen required to perform2CH2CH44 + O + O22 = 2CO + 4H = 2CO + 4H22
Desired HDesired H22/CO ratio/CO ratio Extremely good mixing of natural gas and oxygen Extremely good mixing of natural gas and oxygen
required to prevent formation of sootrequired to prevent formation of soot Formation of explosive mixtures to be preventedFormation of explosive mixtures to be prevented Initial highly exothermic reaction to carbon dioxide Initial highly exothermic reaction to carbon dioxide
and water; subsequent reaction of carbon dioxide and and water; subsequent reaction of carbon dioxide and water with methane to carbon monoxide and hydrogenwater with methane to carbon monoxide and hydrogen
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Heats of ReactionHeats of Reaction
Reaction of methane to COReaction of methane to CO22 and H and H22O very exothermicO very exothermic
Reaction of methane to CO and HReaction of methane to CO and H22 strongly endothermic strongly endothermic Proceeding of homogeneous reaction of methane with carbon dioxide and water limits temperature increaseProceeding of homogeneous reaction of methane with carbon dioxide and water limits temperature increase High temperatures implies high constraints on materialsHigh temperatures implies high constraints on materials
2CH4+4O2 = 2CO2 + 4H2O
-385.5
-385
-384.5
-384
-383.5
-383
-382.5
-382
0 200 400 600 800 1000 1200 1400 1600
Temperature °C
He
at
of
Re
act
ion
(kc
al)
2CH4 + O2 = 2CO + 4H2
-20
-15
-10
-5
0
0 200 400 600 800 1000 1200 1400 1600
Temperature °C
He
at
of
rea
ctio
n (
kca
l)
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Heats of ReactionHeats of Reaction
Reaction of methane with carbon dioxide and of Reaction of methane with carbon dioxide and of methane with steam highly endothermicmethane with steam highly endothermic
CH4 + H2O = CO + 3H2
4849505152535455
0 200 400 600 800 1000 1200 1400
Temperature °C
Hea
t of R
eact
ion
(kca
l)
CH4 + CO2 = 2CO + 2H2
58
59
6061
62
63
0 200 400 600 800 1000 1200 1400
Temperature °C
Hea
t of r
eact
ion
(kca
l)
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(Catalytic) Partial Oxidation(Catalytic) Partial Oxidation Initial highly exothermic reactionInitial highly exothermic reaction
2CH2CH44 + 4O + 4O22 = 2CO = 2CO22 + 4H + 4H22O O Subsequent endothermic reactionsSubsequent endothermic reactions
COCO22 + CH + CH44 = 2CO + 2H = 2CO + 2H22
HH22O + CHO + CH44 = CO + 3H = CO + 3H22 Autothermal reforming : Adding steam and oxygen to Autothermal reforming : Adding steam and oxygen to
methanemethane Catalytic partial oxidation aims at achieving reaction of CHCatalytic partial oxidation aims at achieving reaction of CH44
to CO and Hto CO and H22 at lower temperature levels by promoting the at lower temperature levels by promoting the
reactionreaction2CH2CH44 + O + O22 = 2CO + 4H = 2CO + 4H22
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CO + H2O CO2 + H2
Reaction PathsReaction PathsCatalytic Partial OxidationCatalytic Partial Oxidation
CH4 + O2 CO2 + H2O
CO + H2
CH4
CO + H2
Direct
Indirect
CO shift
Reforming
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Direct vs Indirect Catalytic Partial Direct vs Indirect Catalytic Partial OxidationOxidation
CH4CO+ H2CO2 + H2O
Direct
Indirect
T cat
Axial position
2a
2b
1
1
2b
2a
kJ/mol
1 - 40
2a - 8002b + 200
CH4CO+ H2
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Methane activationMethane activation
Problem : CH4 activation calls for high temperature at which the reactivity of CO and H2
is relatively high
RT 100 350
r ox
idat
ion
H2 CO CH4
T (°C)
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Methane ActivationMethane Activation
METALS (precious)Low oxygen coveragePd,Pt,Ru,(Ni)
OXIDESStrongly bound oxygen Small amount of adsorbed oxygen Small number of (isolated) sites
Y2O3, La2O3, ZrO2, TiO2
CH4
O
CO H2
CHx H
CH4CO H2
O
H
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Precious metal systemsPrecious metal systems
Pt, Pd, Ru, (Ni) T<700°C Indirect CPO
Formation highly active phase for complete oxidation under steady state conditions
CH4 + O2 CO2 + H2O CO + H2
Oxidation Reforming
”Oxidic” phase Metallic phase
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Precious metals : PdPrecious metals : Pd
0
0.5
1
1.5
2
50 150 250 350 450 550 650
T (°C)
pX
(%
)
CO
H2
CH4
O2
CO2
300 mg 0.5 wt% Pd/SiO2 CH4/O2/Ar 1 / 0.5 / 98.5 ml/min
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Influence of Oxidizing / Reducing Influence of Oxidizing / Reducing ConditionsConditions
Highly active but unstable reduced system
0
0.4
0.8
1.2
1.6
2
Time
p X
(%
)
CH4
O2
CO
CO2
O2 H2 pulse
0.5% Ru/TiO2 diluted with quartz2% CH4 1% O2 in Ar
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Catalytic Partial Oxidation of Catalytic Partial Oxidation of MethaneMethane
1 vol% CH4 0.5 vol% O2 in argon 100 ml(stp)/min
Mn oxideon alumina
850 K
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Catalytic Partial Oxidation on Precious Catalytic Partial Oxidation on Precious Metals (Nickel)Metals (Nickel)
Oxidation to carbon dioxide and water Oxidation to carbon dioxide and water Subsequent reaction of remaining methane Subsequent reaction of remaining methane
with carbon dioxide and water to carbon with carbon dioxide and water to carbon monoxide and hydrogenmonoxide and hydrogen
Catalyst bed not uniform being oxidized at Catalyst bed not uniform being oxidized at entrance and reduced at exitentrance and reduced at exit
Catalyst system not stable against deactivation Catalyst system not stable against deactivation by oxidationby oxidation
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Trade Time for TemperatureTrade Time for Temperature
Catalytic partial oxidation at temperatures above Catalytic partial oxidation at temperatures above 11001100ooCC
High rate of reaction; no problem in keeping the High rate of reaction; no problem in keeping the surface of the precious metal reducedsurface of the precious metal reduced
Also reaction of methane with carbon dioxide and Also reaction of methane with carbon dioxide and water proceeding rapidlywater proceeding rapidly
Problem to prevent deposition of carbon on Problem to prevent deposition of carbon on precious metal particlesprecious metal particles
Demands on materials at such elevated Demands on materials at such elevated temperaturestemperatures
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Catalytic Partial Oxidation on OxidesCatalytic Partial Oxidation on Oxides
OXIDES
Strongly bound oxygen Small amount of adsorbed oxygen Small number of (isolated) sites
TiO2, ZrO ZrO22, Y2O3, La2O3
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Catalytic Partial Oxidation on ZrOCatalytic Partial Oxidation on ZrO22
0
20
40
60
80
100
450 550 650 750 850T (°C)
%
XCH
S H
S CO
ZrO2 1% CH4 0.5% O2 100 ml/min 500 mg
4
2
Conversion CH4
Selectivity to H2
Selectivity to CO
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Effect of Residence TimeEffect of Residence Time
0
20
40
60
80
100
0 2 4 6 8 10
Methane conversion (%)
sele
ctiv
ity
(%)
2% CH4, 1 % O2 in Ar T=550°C30000 < GHSV < 150000 (Nl/l)hr-1
ZrO2 Gimex
ZrO2 Daiichi
CO
H2
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Oxidation of HOxidation of H22 and CO on ZrO and CO on ZrO22
0
20
40
60
80
100
300 400 500 600 700T (°C)
Co
nv
ers
ion
(%
)
500 mg catalyst 1% CO / H2 , 1% O2 in HeCO oxidation
CH4 oxidationH2 oxidation
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Experimental Results on ZrOExperimental Results on ZrO22
ZrO2
Inactive reforming catalystLow activity CO-shift Low activity H2 and CO oxidation
Primary reaction:
CH4 CO + H2 + H2O
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Survey Different Metal OxidesSurvey Different Metal Oxides
0
20
40
60
80
100
%
X CH
S CO
S H
S C
2% CH4 1% O2 100 ml/min T=600°C
TiO2 ZrO2 Y2O3 La2O3
4
22
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Orders of the Reaction with respect Orders of the Reaction with respect to Oxygen and Methaneto Oxygen and Methane
Reaction orders : PdReaction orders : Pd OO22 0.1 - 0.20.1 - 0.2
CHCH44 0.8 - 1.10.8 - 1.1• Reduction of surface rate-determiningReduction of surface rate-determining
Oxides : High orders of reaction with Oxides : High orders of reaction with respect to oxygenrespect to oxygen• Re-oxidation of surface rate-determiningRe-oxidation of surface rate-determining
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Orders of the Reaction with Respect to Orders of the Reaction with Respect to Oxygen of Metal OxidesOxygen of Metal Oxides
0
0.2
0.4
0.6
0.8
1
TiO2 ZrO2 Y2O3 La2O3
CH4
O2
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Discussion OxidesDiscussion OxidesTiOTiO22,, ZrOZrO22,Y,Y22OO33,La,La22OO33
Low activity High selectivity High reaction order O2
Low number of (isolated) sites
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Catalytic Partial OxidationCatalytic Partial Oxidationon Metals on Metals
Precious metals Pd, Pt, Ru, (Ni) steady state
conditions T<700°C “Oxidic” phase highly active in complete
combustion
Indirect formation of Syngas
CH4
CO 2 + H2O
CO + H2
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Catalytic Partial OxidationCatalytic Partial Oxidationon Oxides on Oxides
ZrO2, TiO2 : CO , H2 (H2O) primary
products
Y2O3, La2O3 : CO , H2 (H2O) primary
products
C2 - products : formation of CH3-species
CH4
CO + H2 + H2O
C2H6 + H2O
CHx
CH3
Direct formation of Syngas
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Fischer-Tropsch SynthesisFischer-Tropsch Synthesis
Reaction : CO + 2HReaction : CO + 2H22 ‘CH ‘CH22’ + H’ + H22OO
Undesired reactions CO + 3HUndesired reactions CO + 3H22 CH CH44 + H + H22O, carbon deposition O, carbon deposition
on supported metal particles, and carbon monoxide shift on supported metal particles, and carbon monoxide shift conversionconversion• Higher hydrogen pressure promotes formation of methaneHigher hydrogen pressure promotes formation of methane
Highly undesired : Growth of carbon nanofibersHighly undesired : Growth of carbon nanofibers• Mechanically very strong carbon fibers plug reactor and Mechanically very strong carbon fibers plug reactor and
can even pierce reactor wallcan even pierce reactor wall• With bubble column reactor and suspended catalyst With bubble column reactor and suspended catalyst
bodies growth of carbon nanofibers less disastrousbodies growth of carbon nanofibers less disastrous
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Carbon Fibers Grown in Catalyst Carbon Fibers Grown in Catalyst BedBed
Scanningelectron-
micrograph
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Carbon FibersCarbon Fibers
Transmission electronmicrograph
Thick and thin carbon fibers have grown from this catalyst
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Nickel Particle at End of Carbon Nickel Particle at End of Carbon FiberFiber
Transmissionelectron micrograph
Carbon fibers grown from silica-supported nickel particlesNickel particle present at end ofcarbon fiber
90 nm
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Catalysts forCatalysts forFischer-Tropsch SynthesisFischer-Tropsch Synthesis
Required :Required :• Dissociation of carbon monoxideDissociation of carbon monoxide
Ability to react to metal carbide(s)Ability to react to metal carbide(s)• Removal of adsorbed oxygen by reaction to either carbon Removal of adsorbed oxygen by reaction to either carbon
dioxide or waterdioxide or water• Limited availability of adsorbed hydrogenLimited availability of adsorbed hydrogen
Considerable extent of reduction of supported precursor to Considerable extent of reduction of supported precursor to metal particlesmetal particles
Oxidation by water resulting from the Fischer-Tropsch reaction Oxidation by water resulting from the Fischer-Tropsch reaction to be consideredto be considered
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Catalysts forCatalysts forFischer-Tropsch SynthesisFischer-Tropsch Synthesis
Iron, cobalt and nickel able to react to metal carbidesIron, cobalt and nickel able to react to metal carbides Dissociation of carbon monoxide on iron and cobalt not Dissociation of carbon monoxide on iron and cobalt not
strongly surface-sensitivestrongly surface-sensitive Dissociation of carbon monoxide on nickel surface-Dissociation of carbon monoxide on nickel surface-
sensitivesensitive Selectivity to methane therefore on iron and cobalt lower Selectivity to methane therefore on iron and cobalt lower
than on nickelthan on nickel Supported iron and cobalt precursor difficult to reduceSupported iron and cobalt precursor difficult to reduce
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Catalysts forCatalysts forFischer-Tropsch SynthesisFischer-Tropsch Synthesis
Dissociation of carbon monoxide not on most stable Dissociation of carbon monoxide not on most stable Ni(111) surfaceNi(111) surface• Hydrogen from Ni(111) surface migrates toward Hydrogen from Ni(111) surface migrates toward
carbon atoms resulting from dissociation of carbon carbon atoms resulting from dissociation of carbon monoxide on other crystallographic surfacesmonoxide on other crystallographic surfaces
• Abundance of hydrogen leads to undesired Abundance of hydrogen leads to undesired reaction to methanereaction to methane
• Nickel therefore high selectivity to methaneNickel therefore high selectivity to methane H H H
H H H
HH
HH
CC C
C
C
C
C
C
C
C C
C
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Promoted Nickel CatalystsPromoted Nickel Catalysts
Assisted dissociation of carbon monoxide at Assisted dissociation of carbon monoxide at edge of nickel particles by supportedge of nickel particles by support
Comparison of silica-supported nickel and Comparison of silica-supported nickel and titania-supported nickeltitania-supported nickel
Titania support reducible to lower valent Titania support reducible to lower valent metal oxidemetal oxide
Application of nickel on support by Application of nickel on support by deposition-precipitationdeposition-precipitation
Titania
COOC
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Preparation of SupportedPreparation of SupportedNickel CatalystsNickel Catalysts
Injection of nickel nitrate into suspension of Injection of nickel nitrate into suspension of silica or titania supportsilica or titania support
Maintaining pH at constant level of 9 by Maintaining pH at constant level of 9 by simultaneous injection of ammoniasimultaneous injection of ammonia
Suspension of finely divided supports in water Suspension of finely divided supports in water After separation from the liquid, washed and After separation from the liquid, washed and
dried in vacuum at room temperaturedried in vacuum at room temperature Shaped and subsequently calcined at 573 K Shaped and subsequently calcined at 573 K
for 3 hoursfor 3 hours
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Mean Size of Nickel Oxide ParticlesMean Size of Nickel Oxide Particles
Assessment of mean size of nickel oxide particles in Assessment of mean size of nickel oxide particles in calcined catalysts by evaluation of XPS resultscalcined catalysts by evaluation of XPS results
Catalyst Mean Particle Sizenm
2Ni/TiO2 1.2 5Ni/TiO2 1.810Ni/TiO2 1.920Ni/TiO2 4.9
2Ni/SiO2 2.510Ni/SiO2 5.720Ni/SiO2 10.6
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Temperature-Programmed Reduction of Temperature-Programmed Reduction of Silica-Supported Nickel CatalystsSilica-Supported Nickel Catalysts
Initial peak due toreduction of
non-stoichiometricoxygen NiO1+x
20 wt.% Ni
10 wt.% Ni
2 wt.% Ni
Second peak :Reduction of NiO
Third peak :Reduction nickel
containingclay mineral
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Temperature-Programmed Reduction of Temperature-Programmed Reduction of Titania-Supported Nickel CatalystsTitania-Supported Nickel Catalysts
Initial peak due toreduction of
non-stoichiometricoxygen NiO1+x
Reduction ofNiO second peak
Reduction ofnickel titanate
final peak
Extent of reductionof nickel
110 % indicatingreduction of titania
5 wt.%
20 wt.% Ni/TiO2
10 wt.% Ni/TiO2
2 wt.%
50 mg samples5 K/min from300 to 1123 K
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Infra-Red Spectra of Carbon Monoxide Infra-Red Spectra of Carbon Monoxide Adsorbed on Nickel CatalystsAdsorbed on Nickel Catalysts
Catalysts reduced at 673 K
Adsorption of CO on reduced sites on TiO2
absorption band around 2180 cm-1
Note higher absorption with 2 wt.% Ni/TiO2
which indicates induced reduction at the edgeof nickel particles
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CO Hydrogenation at 525 K onCO Hydrogenation at 525 K onSilica-Supported Nickel CatalystsSilica-Supported Nickel Catalysts
Catalysts reduced at 673 K20 wt.% Ni/SiO2
reduced at temperaturesindicated
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Selectivities of Fischer-Tropsch Selectivities of Fischer-Tropsch Synthesis on Ni/SiOSynthesis on Ni/SiO22 Catalysts Catalysts
Catalyst Reduction CO2(%) CH4(%) C2(%) C3+(%)
Temperature°C
2Ni/SiO2 673 0 87 4 9
10Ni/SiO2 673 2 90 5 3
20Ni/SiO2 673 2 90 5 3
20Ni/SiO2 573 7 85 5 3
20Ni/SiO2 673 2 90 5 3
20Ni/SiO2 773 3 90 5 2
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CO Hydrogenation at 525 K onCO Hydrogenation at 525 K onTitania-Supported Nickel CatalystsTitania-Supported Nickel Catalysts
H2/CO = 2for reaction toCH4 required
H2/CO = 3
Catalyst Reduction CO2(%) CH4(%) C2(%) C3+(%)
Temperature°C
20Ni/TiO2 573 21 78 1 0
20Ni/TiO2 673 20 80 0 0
20Ni/TiO2 773 3 54 13 30
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Comparison T.P.R. and Activity at 525 K of Comparison T.P.R. and Activity at 525 K of Ni/TiONi/TiO22 Catalysts Catalysts
20 wt.% Ni/SiO2
reduced at temperaturesindicated
Temperature-Programmed Reduction (T.P.R.) ofNi/SiO2 catalysts. Ni content (wt.%) indicated atT.P.R. curves
50 mg samples5 K/min from300 to 1123 K
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Comparison T.P.R. and Activity at 525 Comparison T.P.R. and Activity at 525 K of Ni/TiOK of Ni/TiO22 Catalysts Catalysts
20 wt.% Ni/TiO2
reduced at temperaturesindicated
Temperature-Programmed Reduction (T.P.R.) ofNi/TiO2 catalysts. Ni content (wt.%) indicated atT.P.R. curves
50 mg samples5 K/min from300 to 1123 K
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CO Hydrogenation at 525 K onCO Hydrogenation at 525 K onTitania-Supported Nickel CatalystsTitania-Supported Nickel Catalysts
CO conversion at 525 Kof Ni/TiO2 catalysts of
different nickel loadingsreduced at 673 K
Reaction to C3+ at 525 K
of Ni/TiO2 catalysts ofdifferent nickel loadings
reduced at 673 K
CO conversion at 525 Kof 2 wt.% Ni/TiO2 catalystreduced at the differenttemperatures indicated
in the figure
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CO Hydrogenation at 525 K onCO Hydrogenation at 525 K onTitania-Supported Nickel CatalystsTitania-Supported Nickel Catalysts
Catalyst Reduction CO2(%) CH4(%) C2(%) C3+(%)
Temperature°C
2Ni/TiO2 673 5 37 16 42
5Ni/TiO2 673 6 53 13 28
10Ni/TiO2 673 6 59 12 23
20Ni/TiO2 673 20 80 0 0
2Ni/TiO2 573 4 35 14 47
2Ni/TiO2 673 5 37 16 42
2Ni/TiO2 773 5 34 14 47
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Magnetization ofMagnetization ofTitania-Supported Nickel CatalystsTitania-Supported Nickel Catalysts
Measured after reduction at 673 Kduring exposure to H2/CO = 2
at 525 KDrop in magnetization 31 % with20Ni/TiO2 and no less than 70 %
with 2Ni/TiO2
Measured after reduction at 673 Kand Fischer-Tropsch synthesis
at 525 K during temperature-programmed hydrogenation in
2 % hydrogen in heliumHeating rate 2 K/min
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Temperature-Programmed Hydrogenation Temperature-Programmed Hydrogenation of Nickel Carbidesof Nickel Carbides
20 wt.% Ni/TiO2 catalyst reducedat 673 and 773 K
Measured after Fischer-Tropsch synthesis at 525 KHeating rate 5 K/min
Surface carbide is hydrogenated atrelatively low temperatures
Transport of carbon to the metal surfacecalls for elevated temperatures
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Nickel (Surface) CarbideNickel (Surface) Carbide
CC C C C
C
CCCC C
CCC C
C CC C CC
Surface carbide leading to methaneMagnetization only slightly decreasedHydrogenation of surface carbon atrelatively low temperatures
Bulk carbide leading to higherhydrocarbons. Magnetization stronglydecreased. Hydrogenation of carbon atmore elevated temperatures due totransport of carbon through metal
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Schematic Description of Silica-Schematic Description of Silica-Supported Nickel CatalystsSupported Nickel Catalysts
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Schematic Description of Titania-Schematic Description of Titania-Supported Nickel CatalystsSupported Nickel Catalysts
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Conclusions about Fischer-Tropsch Conclusions about Fischer-Tropsch on Nickelon Nickel
Promotion of dissociative adsorption of Promotion of dissociative adsorption of carbon monoxide required for synthesis of carbon monoxide required for synthesis of higher hydrocarbonshigher hydrocarbons
Promotion by reducible support, which is not Promotion by reducible support, which is not reduced to metal, but to oxygen acceptorreduced to metal, but to oxygen acceptor
Reaction to bulk carbide goes together with Reaction to bulk carbide goes together with Fischer-Tropsch synthesis to higher Fischer-Tropsch synthesis to higher hydrocarbonshydrocarbons
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Preparation of Supported Cobalt Catalysts by Preparation of Supported Cobalt Catalysts by Impregnation and DryingImpregnation and Drying
Alumina Alumina AA22STST g-alumina g-aluminapore volume 0.48 ml/g, surface area 110 mpore volume 0.48 ml/g, surface area 110 m22/g /g employed as supportemployed as support
Impregnation withImpregnation with• Solution of cobalt nitrateSolution of cobalt nitrate• Solution of cobalt EDTA complexSolution of cobalt EDTA complex• Solution of cobalt ammonium citrateSolution of cobalt ammonium citrate
Catalyst according to Exxon patent as reference Catalyst according to Exxon patent as reference catalyst 10Co1Ce/TiOcatalyst 10Co1Ce/TiO22
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Shape of Drop dried on GlassShape of Drop dried on Glass
Drop of solution of copper(II) nitrate dried on microscope glass slide
Note preferential build up of crystallites at the rim of the drop
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Shape of Drop dried on GlassShape of Drop dried on Glass
Drop of solution of copper(II) citrate dried on microscope glass slideNote absence of large crystallites
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Mean Particle Size of Supported Cobalt Mean Particle Size of Supported Cobalt Oxide by XPSOxide by XPS
CatalystCatalyst Mean particle size Mean particle size (nm)(nm)
2.5Co/Al2.5Co/Al22OO33 nitrate nitrate 7.37.3
2.5Co/Al2.5Co/Al22OO3 3 citratecitrate 1.71.7
2.5 Co/Al2.5 Co/Al22OO3 3 EDTAEDTA 0.70.7
5 Co/Al 5 Co/Al22OO3 3 nitratenitrate 15.5 15.5
5 Co/Al 5 Co/Al22OO3 3 citratecitrate 3.93.9
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Estimation of Reducibility by Measurement Estimation of Reducibility by Measurement of the Magnetizationof the Magnetization
Reducibilitydepends on size ofcobalt oxide particlesSmall oxide particlesreact to CoAl2O4,which only reducesat very elevatedtemperatures
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Estimation of Reducibility by Estimation of Reducibility by Measurement of the MagnetizationMeasurement of the Magnetization
Reducibilitydepends on size ofcobalt oxide particlesSmall oxide particlesreact to CoAl2O4,which only reducesat very elevatedtemperatures
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Fischer-Tropsch Synthesis on Fischer-Tropsch Synthesis on Supported Co catalysts at 525 KSupported Co catalysts at 525 K
Conversion of carbonmonoxide roughlyparallel with amountof metallic cobaltCatalysts reduced at 673 K
Measurements atatmospheric pressure; athigher pressures betterselectivities and conversionsMeasurement of 10Co1Ce/TiO2at 26 bar and 493 K for 135 hat H2/CO = 2 led to C5
+ 87%and CH4 = 7%
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Selectivities of Alumina-Supported Selectivities of Alumina-Supported Cobalt Catalysts at 525 KCobalt Catalysts at 525 K
Catalyst Reduction CO2(%) CH4(%) C2(%) C3+(%)
Temperature°C
20Ni/TiO2 573 21 78 1 0
20Ni/TiO2 673 20 80 0 0
20Ni/TiO2 773 3 54 13 30
Catalyst Reduction CO2(%) CH4(%) C2(%) C3+(%)
Temperature
Measurements at atmospheric pressure; at higher pressures better selectivities andconversions. Measurement of 10Co1Ce/TiO2 at 26 bar and 493 K for 135 h atH2/CO = 2 led to C5
+ 87% and CH4 = 7%
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Conclusions about Supported Cobalt Conclusions about Supported Cobalt CatalystsCatalysts
Reduction of alumina-supported cobalt catalysts difficultReduction of alumina-supported cobalt catalysts difficult Reaction to cobalt aluminate difficult to preventReaction to cobalt aluminate difficult to prevent Sasol is therefore coating alumina with silicium compoundSasol is therefore coating alumina with silicium compound Performance of cobalt catalysts in Fischer-Tropsch Performance of cobalt catalysts in Fischer-Tropsch
synthesis difficult to evaluate from measurement at synthesis difficult to evaluate from measurement at atmospheric pressureatmospheric pressure
With reduction of nickel and cobalt catalysts in technical With reduction of nickel and cobalt catalysts in technical reactors dew point of recirculating hydrogen highly reactors dew point of recirculating hydrogen highly importantimportant
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Supported Iron CatalystsSupported Iron Catalysts
Supported iron catalysts very difficult to reduceSupported iron catalysts very difficult to reduce Low water vapor pressure within pores of hydrophilic supports Low water vapor pressure within pores of hydrophilic supports
very difficult to achievevery difficult to achieve New procedure to produce supported metallic iron and iron alloy New procedure to produce supported metallic iron and iron alloy
particlesparticles• Application of complex insoluble cyanides on supportApplication of complex insoluble cyanides on support• Very rapid reduction to metals and alloys in hydrogen flowVery rapid reduction to metals and alloys in hydrogen flow• German patent describing catalyst preparation from complex German patent describing catalyst preparation from complex
cyanidescyanides• Very large metal or alloy particles resulting due to low Very large metal or alloy particles resulting due to low
interaction of metal or alloy with surface of supportinteraction of metal or alloy with surface of support
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Supported Iron CatalystsSupported Iron Catalysts
Our invention : Initial calcination of supported complex Our invention : Initial calcination of supported complex cyanide precursor to oxidecyanide precursor to oxide
Subsequent reduction leads to oxidic layer at interface Subsequent reduction leads to oxidic layer at interface between metal or alloy particles and support between metal or alloy particles and support
Oxidic layer anchors metal or alloy particles to surface Oxidic layer anchors metal or alloy particles to surface of support and provides stable catalystsof support and provides stable catalysts
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Supported Iron Alloy CatalystsSupported Iron Alloy Catalysts
Precipitation of complex cyanides with metal ions to be Precipitation of complex cyanides with metal ions to be present in alloypresent in alloy
Atomic mixing of components of alloyAtomic mixing of components of alloy Examples for iron-nickel alloy catalystsExamples for iron-nickel alloy catalysts
• FeFe2+2+ + K + K44Fe(CN)Fe(CN)66 ® Fe ® Fe22Fe(CN)Fe(CN)66 + K + K22FeFe(CN)FeFe(CN)6 6
• FeFe2+2+ + K + K33Fe(CN)Fe(CN)66 ® Fe ® Fe33Fe(CN)Fe(CN)66 + K + K22FeFe(CN)FeFe(CN)6 6
• FeFe2+2+ + Na + Na22Fe(CN)Fe(CN)55NO ® FeFe(CN)NO ® FeFe(CN)55 NO NO
• NiNi2+2+ + K + K44Fe(CN)Fe(CN)66 ® Ni ® Ni22Fe(CN)Fe(CN)66 + K + K22NiFe(CN)NiFe(CN)6 6
• NiNi2+2+ + K + K33Fe(CN)Fe(CN)66 ® Ni ® Ni22Fe(CN)Fe(CN)66 + K + K22NiFe(CN)NiFe(CN)6 6
• NiNi2+2+ + Na + Na22Fe(CN)Fe(CN)55NO® NiFe(CN)NO® NiFe(CN)55NONO
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Supported Iron Alloy CatalystsSupported Iron Alloy Catalysts
Reaction with potassium iron cyanide complexes leads Reaction with potassium iron cyanide complexes leads to catalysts containing potassiumto catalysts containing potassium
Since potassium is very well and homogeneously Since potassium is very well and homogeneously distributed within the iron containing moieties, distributed within the iron containing moieties, catalysts very well suited to investigate effect of catalysts very well suited to investigate effect of potassium on Fischer-Tropsch activitypotassium on Fischer-Tropsch activity
For preparation of potassium-free catalysts starting For preparation of potassium-free catalysts starting from Hfrom H44Fe(CN)Fe(CN)66 attractive attractive
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Supported Iron Alloy CatalystsSupported Iron Alloy Catalysts
Preparation of potassium-free iron and nickel-iron Preparation of potassium-free iron and nickel-iron catalystscatalysts
• NiNi2+2+ + H + H44Fe(CN)Fe(CN)66 ® Ni ® Ni22Fe(CN)Fe(CN)66
• 0.4Ni0.4Ni2+2+ + 0.6Fe + 0.6Fe2+2+ + NaFe(CN) + NaFe(CN)55NO ®NO ®
® (Ni ® (Ni0.40.4FeFe0.60.6)Fe(CN))Fe(CN)55NONO Comparison potassium-free and potassium Comparison potassium-free and potassium
containing catalystscontaining catalysts Titania as the support; Degussa P 25 50 mTitania as the support; Degussa P 25 50 m22/g/g
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Comparison of Potassium-Free and Comparison of Potassium-Free and Potassium Containing Iron CatalystsPotassium Containing Iron Catalysts
Important conclusion :Potassium containing iron catalysts no significant activity
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Comparison of Potassium-Free and Comparison of Potassium-Free and Potassium Containing NiFe CatalystsPotassium Containing NiFe Catalysts
Important conclusion :Potassium containing nickel-iron catalysts no significant activity
Ni2Fe/TiO2
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Comparison of Potassium-Free Fe and Comparison of Potassium-Free Fe and Ni-Fe CatalystsNi-Fe Catalysts
NiFe4/TiO2
NiFe/TiO2
Ni3Fe2/TiO2
Fe/TiO2
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Selectivities of Titania-Supported Fe Selectivities of Titania-Supported Fe and Fe-Ni Catalystsand Fe-Ni Catalysts
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Magnetization of K-Free andMagnetization of K-Free andK Containing Fe/TiOK Containing Fe/TiO22 Catalysts Catalysts
Both potassium containing and potassium-free catalysts react to iron carbides uponexposure to carbon monoxide-hydrogen at 525 K
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Magnetization of Spent Catalysts as a Magnetization of Spent Catalysts as a Function of Temperature in Flow of HFunction of Temperature in Flow of H22
Initial drop in magnetization at rising temperature due to Curie temperature ofiron carbide (523 or 530 K) Hydrogenation of carbon in iron carbide only above 700 K
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Magnetization of Iron-Nickel Catalysts during Magnetization of Iron-Nickel Catalysts during Fischer-Tropsch SynthesisFischer-Tropsch Synthesis
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Magnetization of Spent Catalysts as a Magnetization of Spent Catalysts as a Function of Temperature in Flow of HFunction of Temperature in Flow of H22
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Temperature-Programmed Reduction of Temperature-Programmed Reduction of Spent Fe and Fe-Ni CatalystsSpent Fe and Fe-Ni Catalysts
Potassium-containing catalyst no reaction to CH4; release of carbon monoxide likelyto be due to decomposition of potassium carbonate. The potassium-free catalystexhibits reaction to methane above about 750 K.
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Temperature-Programmed Reduction of Temperature-Programmed Reduction of Spent Fe and Fe-Ni CatalystsSpent Fe and Fe-Ni Catalysts
NiFe50_C Catalyst NiFe33_A(K) CatalystMeasured after 6 hours Fischer-Tropsch synthesis at 525 K
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Infra-Red Spectra of Adsorbed Carbon Infra-Red Spectra of Adsorbed Carbon MonoxideMonoxide
Infra-red spectra of carbon monoxide adsorbed on reduced catalystNiFe33_A(K) spectrum (a) and NiFe40_B spectrum (b)
No molecular adsorption of carbon monoxide on potassium-containingcatalyst NiFe33_A(K)
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Conclusions about Effect of Conclusions about Effect of PotassiumPotassium
Potassium does not prevent reaction of iron or nickel-Potassium does not prevent reaction of iron or nickel-iron alloy to carbideiron alloy to carbide
Potassium completely suppresses adsorption of Potassium completely suppresses adsorption of molecular carbon monoxidemolecular carbon monoxide
Potassium suppresses hydrogenation of carbidic Potassium suppresses hydrogenation of carbidic carbon to hydrocarbonscarbon to hydrocarbons
Potassium segregated on the surface of iron or nickel-Potassium segregated on the surface of iron or nickel-iron particles and suppresses adsorption of carbon iron particles and suppresses adsorption of carbon monoxide and hydrogenmonoxide and hydrogen
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Zirconia-Supported Iron CatalystsZirconia-Supported Iron Catalysts
Zirconia as a support to limit reaction of iron(II) with Zirconia as a support to limit reaction of iron(II) with the support, which impedes reduction to metallic ironthe support, which impedes reduction to metallic iron
Zirconia of AZirconia of A22ST, surface area 49 mST, surface area 49 m22/g; pore volume /g; pore volume 0.28 ml/g0.28 ml/g
Impregnation with ammonium iron citrateImpregnation with ammonium iron citrate Loading only 2.5 wt.% iron; small iron particles to Loading only 2.5 wt.% iron; small iron particles to
suppress encapsulation by graphite layers and suppress encapsulation by graphite layers and growth of nanofibersgrowth of nanofibers
Activity measurements at elevated pressuresActivity measurements at elevated pressures
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Fischer-Tropsch Synthesis on Zirconia-Fischer-Tropsch Synthesis on Zirconia-Supported Iron CatalystSupported Iron Catalyst
Space velocity does not affect level of conversion !Oxidation by water formed in the reaction
Synthesis at 24 bar,623 K, H2/CO = 1.0Note much moreelevated conversionat higher pressure
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Selectivity of Zirconia-Supported Selectivity of Zirconia-Supported Iron CatalystIron Catalyst
Synthesis at 24 bar,623 K, H2/CO = 1.0Note much moreelevated conversionat higher pressure
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Fischer-Tropsch Synthesis on Zirconia-Fischer-Tropsch Synthesis on Zirconia-Supported Iron CatalystSupported Iron Catalyst
Synthesis at 24 bar,623 K, H2/CO = 1.71880 h-1
Note much moreelevated conversionat higher pressure
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Selectivity of Zirconia-Supported Iron Selectivity of Zirconia-Supported Iron CatalystCatalyst
Synthesis at 24 bar,623 K, H2/CO = 1.71880 h-1
Note much moreelevated conversionat higher pressure
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Production of OlefinsProduction of Olefins
Measurements in nanoflow apparatusMeasurements in nanoflow apparatus Relatively large production of olefinsRelatively large production of olefins
• C1 C2 C3C1 C2 C3 C2=/C2+C2= C3=/C3+C3= C2=/C2+C2= C3=/C3+C3= C C
• 573 K 4.1 7.3 12.6 76.6 91.3 3.4573 K 4.1 7.3 12.6 76.6 91.3 3.4• 623 K 9.9 13.9 19.7 59.7 88.8 623 K 9.9 13.9 19.7 59.7 88.8
10.910.9 Production of olefins promising as well as stability of Production of olefins promising as well as stability of
catalyst catalyst
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Conclusions (1)Conclusions (1)
Preparation of supported iron, cobalt, nickel, and iron-Preparation of supported iron, cobalt, nickel, and iron-nickel catalysts well developednickel catalysts well developed
Complementing range of analytical techniques for Complementing range of analytical techniques for characterizing catalysts before, during and after Fischer-characterizing catalysts before, during and after Fischer-Tropsch synthesisTropsch synthesis• Mossbauer experiments and results not dealt withMossbauer experiments and results not dealt with
Earlier mentioned items, competitive dissociative Earlier mentioned items, competitive dissociative adsorption and effect not completely reducible metal adsorption and effect not completely reducible metal oxides well identified oxides well identified
Reduction of cobalt catalysts prepared by impregnation Reduction of cobalt catalysts prepared by impregnation extensively investigatedextensively investigated
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Conclusions (2)Conclusions (2)
Deposition-precipitation, impregnation with Deposition-precipitation, impregnation with badly crystallizing compounds (citrates, EDTA badly crystallizing compounds (citrates, EDTA complexes) successfully appliedcomplexes) successfully applied
Complex cyanides very interesting precursors Complex cyanides very interesting precursors for metals and alloys difficult to reduce or to for metals and alloys difficult to reduce or to prepare with uniform chemical compositionprepare with uniform chemical composition
Reliable and significant investigation of activity Reliable and significant investigation of activity and selectivity of Fischer-Tropsch catalysts can and selectivity of Fischer-Tropsch catalysts can only be performed at elevated pressuresonly be performed at elevated pressures
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