Fischer-Tropsch Catalysts: Preparation, Thermal Pretreatment and Behavior During Catalytic Reaction

Fischer-TropschFischer-Tropsch
CatalystsCatalysts
Preparation, Thermal PretreatmentPreparation, Thermal Pretreatment
and Behavior during Catalytic Reactionand Behavior during Catalytic Reaction
Gerard B. HawkinsGerard B. Hawkins
Managing DirectorManaging Director
GBH Enterprises Ltd.

Fischer-Tropsch ProcessFischer-Tropsch Process
 Reaction of carbon monoxide and hydrogen toReaction of carbon monoxide and hydrogen to
mainly liquid hydrocarbonsmainly liquid hydrocarbons
 Invented in Germany during the twenties of theInvented 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

ThemesThemes
 Dissociative adsorption of methane and carbon monoxideDissociative adsorption of methane and carbon monoxide
in competition with surface oxidation (catalytic partialin 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 lowerReducibility of metal oxides to metal oxides of lower
valencyvalency
 Different special procedures for producing supportedDifferent special procedures for producing supported
catalystscatalysts

Competitive DissociativeCompetitive Dissociative
AdsorptionAdsorption
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 700o
C

Competitive DissociativeCompetitive Dissociative
AdsorptionAdsorption
CO
C O H H
H2O
O
C
O C C C
CO2
C H C C H C H C H C
CnH2n(+2)
Relatively low
hydrogen coverage
Fischer-Tropsch
Relatively high
hydrogen coverage
methanation
C H H H C H H H H C H H
CH4

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 reduced
oxide phase
Formation of isolated
oxygen vacancies
CO C(ads) + O(ads)→←
CH4 → CO + 2H2

Feed Stock ofFeed Stock of
the Fischer-Tropsch Processthe Fischer-Tropsch Process
 Feed stock : Initially coalFeed stock : Initially coal
C + 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 involves
CHCH44 + 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

(Catalytic) Partial Oxidation(Catalytic) Partial Oxidation
 Pure oxygen required to performPure oxygen required to perform
2CH2CH44 + O+ O22 = 2CO + 4H= 2CO + 4H22
Desired HDesired H22/CO ratio/CO ratio
 Extremely good mixing of natural gas and oxygenExtremely 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 dioxideInitial highly exothermic reaction to carbon dioxide
and water; subsequent reaction of carbon dioxide andand water; subsequent reaction of carbon dioxide and
water with methane to carbon monoxide and hydrogenwater with methane to carbon monoxide and hydrogen

Heats of ReactionHeats of Reaction
 Reaction of methane to COReaction of methane to CO22 and Hand H22O very exothermicO very exothermic
 Reaction of methane to CO and HReaction of methane to CO and H22 strongly endothermicstrongly endothermic
 Proceeding of homogeneous reaction of methane withProceeding of homogeneous reaction of methane with
carbon dioxide and water limits temperature increasecarbon 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
HeatofReaction(kcal)
2CH4 + O2 = 2CO + 4H2
-20
-15
-10
-5
0
0 200 400 600 800 1000 1200 1400 1600
Temperature °C
Heatofreaction(kcal)

Heats of ReactionHeats of Reaction
 Reaction of methane with carbon dioxide and ofReaction of methane with carbon dioxide and of
methane with steam highly endothermicmethane with steam highly endothermic
CH4 + H2O = CO + 3H2
48
49
50
51
52
53
54
55
0 200 400 600 800 1000 1200 1400
Temperature °C
HeatofReaction
(kcal)
CH4 + CO2 = 2CO + 2H2
58
59
60
61
62
63
0 200 400 600 800 1000 1200 1400
Temperature °C
Heatofreaction
(kcal)

(Catalytic) Partial Oxidation(Catalytic) Partial Oxidation
 Initial highly exothermic reactionInitial highly exothermic reaction
2CH2CH44 + 4O+ 4O22 = 2CO= 2CO22 + 4H+ 4H22OO
 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 toAutothermal reforming : Adding steam and oxygen to
methanemethane
 Catalytic partial oxidation aims at achieving reaction ofCatalytic partial oxidation aims at achieving reaction of
CHCH44 to CO and Hto CO and H22 at lower temperature levels byat lower temperature levels by
promoting the reactionpromoting the reaction
2CH2CH44 + O+ O22 = 2CO + 4H= 2CO + 4H22

CO + H2O CO2 + H2
Reaction PathsReaction Paths
Catalytic Partial OxidationCatalytic Partial Oxidation
CH4 + O2 CO2 + H2O
CO + H2
CH4
CO + H2
Direct
Indirect
CO shift
Reforming

Direct vs Indirect Catalytic PartialDirect vs Indirect Catalytic Partial
OxidationOxidation
CH4
CO+ H2CO2 + H2O
Direct
Indirect
T cat
Axial position
2a
2b
1
1
2b
2a
kJ/mol
1 - 40
2a - 800
2b + 200
CH4
CO+ H2

Methane activationMethane activation
Problem : CH4 activation calls for high
temperature at which the reactivity of CO and H2
is relatively high
RT 100 350
roxidation
H2
CO CH4
T
(°C)

Methane ActivationMethane Activation
METALS (precious)
Low oxygen coverage
Pd,Pt,Ru,(Ni)
OXIDES
Strongly bound oxygen
Small amount of adsorbed oxygen
Small number of (isolated) sites
Y2O3, La2O3, ZrO2, TiO2
CH4
O
CO H2
CHx H
CH4
CO H2
O
H

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

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

Influence of Oxidizing /Influence of Oxidizing /
Reducing ConditionsReducing Conditions
Highly active but unstable reduced system
0
0.4
0.8
1.2
1.6
2
Time
pX(%)
CH4
O2
CO
CO2
O2 H2 pulse
0.5% Ru/TiO2 diluted with quartz
2% CH4 1% O2 in Ar

Catalytic Partial Oxidation ofCatalytic Partial Oxidation of
MethaneMethane
1 vol% CH4 0.5 vol% O2 in argon 100 ml(stp)/min
Mn oxide
on alumina
850 K

Catalytic Partial Oxidation onCatalytic Partial Oxidation on
Precious Metals (Nickel)Precious Metals (Nickel)
 Oxidation to carbon dioxide and waterOxidation to carbon dioxide and water
 Subsequent reaction of remaining methaneSubsequent reaction of remaining methane
with carbon dioxide and water to carbonwith carbon dioxide and water to carbon
monoxide and hydrogenmonoxide and hydrogen
 Catalyst bed not uniform being oxidized atCatalyst bed not uniform being oxidized at
entrance and reduced at exitentrance and reduced at exit
 Catalyst system not stable against deactivationCatalyst system not stable against deactivation
by oxidationby oxidation

Trade Time for TemperatureTrade Time for Temperature
 Catalytic partial oxidation at temperaturesCatalytic partial oxidation at temperatures
above 1100above 1100oo
CC
 High rate of reaction; no problem in keepingHigh rate of reaction; no problem in keeping
the surface of the precious metal reducedthe surface of the precious metal reduced
 Also reaction of methane with carbon dioxideAlso reaction of methane with carbon dioxide
and water proceeding rapidlyand water proceeding rapidly
 Problem to prevent deposition of carbon onProblem to prevent deposition of carbon on
precious metal particlesprecious metal particles
 Demands on materials at such elevatedDemands on materials at such elevated
temperaturestemperatures

OxidesOxides
OXIDES
Strongly bound oxygen
Small amount of adsorbed oxygen
Small number of (isolated) sites
TiO2, ZrOZrO22, Y2O3, La2O3

ZrOZrO22
0
20
40
60
80
100
450 550 650 750 850
T (°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

Effect of Residence TimeEffect of Residence Time
0
20
40
60
80
100
0 2 4 6 8 10
Methane conversion (%)
selectivity(%)
2% CH4, 1 % O2 in Ar T=550°C
30000 < GHSV < 150000 (Nl/l)hr-1
ZrO2 Gimex
ZrO2 Daiichi
CO
H2

Oxidation of HOxidation of H22 and CO on ZrOand CO on ZrO22
0
20
40
60
80
100
300 400 500 600 700
T (°C)
Conversion(%)
500 mg catalyst 1% CO / H2 , 1% O2 in He
CO oxidation
CH4 oxidation
H2 oxidation

Experimental Results on ZrOExperimental Results on ZrO22
ZrO2
Inactive reforming catalyst
Low activity CO-shift
Low activity H2 and CO oxidation
Primary reaction:
CH4 CO + H2 + H2O

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
2
2

Orders of the Reaction withOrders of the Reaction with
respect to Oxygen and Methanerespect to 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 withOxides : High orders of reaction with
respect to oxygenrespect to oxygen
• Re-oxidation of surface rate-determiningRe-oxidation of surface rate-determining

Orders of the Reaction withOrders of the Reaction with
Respect to Oxygen of Metal OxidesRespect to Oxygen of Metal Oxides
0
0.2
0.4
0.6
0.8
1
TiO2 ZrO2 Y2O3 La2O3
CH4
O2

DiscussionDiscussion
OxidesOxides
TiOTiO22 ,, ZrOZrO22 ,Y,Y22 OO33 ,La,La22 OO33
Low activity
High selectivity
High reaction order O2
Low number of (isolated) sites

on Metalson 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

on Oxideson 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

Fischer-Tropsch SynthesisFischer-Tropsch Synthesis
 Reaction : CO + 2HReaction : CO + 2H22 →→ ‘CH‘CH22’ + H’ + H22OO
 Undesired reactions CO + 3HUndesired reactions CO + 3H22 →→ CHCH44 + H+ H22O, carbonO, carbon
deposition on supported metal particles, and carbondeposition on supported metal particles, and carbon
monoxide shift conversionmonoxide shift conversion
• Higher hydrogen pressure promotes formation ofHigher hydrogen pressure promotes formation of
methanemethane
 Highly undesired : Growth of carbon nanofibersHighly undesired : Growth of carbon nanofibers
• Mechanically very strong carbon fibers plug reactorMechanically very strong carbon fibers plug reactor
and can even pierce reactor walland can even pierce reactor wall
• With bubble column reactor and suspended catalystWith bubble column reactor and suspended catalyst
bodies growth of carbon nanofibers less disastrousbodies growth of carbon nanofibers less disastrous

Carbon Fibers Grown in CatalystCarbon Fibers Grown in Catalyst
BedBed
Scanning
electron-
micrograph

Carbon FibersCarbon Fibers
Transmission electron
micrograph
Thick and thin carbon fibers
have grown from this catalyst

Nickel Particle at End ofNickel Particle at End of
Carbon FiberCarbon Fiber
Transmission
electron micrograph
Carbon fibers grown from silica-
supported nickel particles
Nickel particle present at end of
carbon fiber
90 nm

Catalysts forCatalysts for
 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 carbonRemoval 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 toConsiderable extent of reduction of supported precursor to
metal particlesmetal particles
 Oxidation by water resulting from the Fischer-Tropsch reactionOxidation by water resulting from the Fischer-Tropsch reaction
to be consideredto be considered

 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 notDissociation 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 lowerSelectivity 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

 Dissociation of carbon monoxide not on most stableDissociation of carbon monoxide not on most stable
Ni(111) surfaceNi(111) surface
• Hydrogen from Ni(111) surface migrates towardHydrogen from Ni(111) surface migrates toward
carbon atoms resulting from dissociation of carboncarbon atoms resulting from dissociation of carbon
monoxide on other crystallographic surfacesmonoxide on other crystallographic surfaces
• Abundance of hydrogen leads to undesiredAbundance 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
H
H
H
H
C
C C
C
C
C
C
C
C
C C
C

Promoted Nickel CatalystsPromoted Nickel Catalysts
 Assisted dissociation of carbon monoxide atAssisted dissociation of carbon monoxide at
edge of nickel particles by supportedge of nickel particles by support
 Comparison of silica-supported nickel andComparison of silica-supported nickel and
titania-supported nickeltitania-supported nickel
 Titania support reducible to lower valentTitania support reducible to lower valent
metal oxidemetal oxide
 Application of nickel on support byApplication of nickel on support by
deposition-precipitationdeposition-precipitation
Titania
COOC

Preparation of SupportedPreparation of Supported
Nickel CatalystsNickel Catalysts
 Injection of nickel nitrate into suspension ofInjection of nickel nitrate into suspension of
silica or titania supportsilica or titania support
 Maintaining pH at constant level of 9 byMaintaining pH at constant level of 9 by
simultaneous injection of ammoniasimultaneous injection of ammonia
 Suspension of finely divided supports inSuspension of finely divided supports in
waterwater
 After separation from the liquid, washed andAfter separation from the liquid, washed and
dried in vacuum at room temperaturedried in vacuum at room temperature
 Shaped and subsequently calcined at 573 KShaped and subsequently calcined at 573 K
for 3 hoursfor 3 hours

Mean Size of Nickel OxideMean Size of Nickel Oxide
ParticlesParticles
 Assessment of mean size of nickel oxide particles inAssessment of mean size of nickel oxide particles in
calcined catalysts by evaluation of XPS resultscalcined catalysts by evaluation of XPS results
Catalyst Mean Particle Size
nm
2Ni/TiO2 1.2
5Ni/TiO2 1.8
10Ni/TiO2 1.9
20Ni/TiO2 4.9
2Ni/SiO2 2.5
10Ni/SiO2 5.7
20Ni/SiO2 10.6

Temperature-Programmed Reduction ofTemperature-Programmed Reduction of
Silica-Supported Nickel CatalystsSilica-Supported Nickel Catalysts
Initial peak due to
reduction of
non-stoichiometric
oxygen NiO1+x
20 wt.% Ni
10 wt.% Ni
2 wt.% Ni
Second peak :
Reduction of NiO
Third peak :
Reduction nickel
containing
clay mineral

Titania-Supported Nickel CatalystsTitania-Supported Nickel Catalysts
Initial peak due to
reduction of
non-stoichiometric
oxygen NiO1+x
Reduction of
NiO second peak
Reduction of
nickel titanate
final peak
Extent of reduction
of nickel
110 % indicating
reduction of titania
5 wt.%
20 wt.% Ni/TiO2
10 wt.% Ni/TiO2
2 wt.%
50 mg samples
5 K/min from
300 to 1123 K

Infra-Red Spectra of Carbon MonoxideInfra-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 edge
of nickel particles

CO Hydrogenation at 525 K onCO Hydrogenation at 525 K on
Silica-Supported Nickel CatalystsSilica-Supported Nickel Catalysts
20 wt.% Ni/SiO2
reduced at temperatures
indicated

Selectivities of Fischer-TropschSelectivities of Fischer-Tropsch
Synthesis on Ni/SiOSynthesis on Ni/SiO22 CatalystsCatalysts
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

H2/CO = 2
for reaction to
CH4 required
H2/CO = 3
+
(%)
Temperature
°C
20Ni/TiO2 573 21 78 1 0
20Ni/TiO2 673 20 80 0 0
20Ni/TiO2 773 3 54 13 30

Comparison T.P.R. and Activity at 525 KComparison T.P.R. and Activity at 525 K
of Ni/TiOof Ni/TiO22 CatalystsCatalysts
20 wt.% Ni/SiO2
indicated
Temperature-Programmed Reduction (T.P.R.) of
Ni/SiO2 catalysts. Ni content (wt.%) indicated at
T.P.R. curves
50 mg samples
5 K/min from
300 to 1123 K

Comparison T.P.R. and Activity atComparison T.P.R. and Activity at
525 K of Ni/TiO525 K of Ni/TiO22 CatalystsCatalysts
20 wt.% Ni/TiO2
indicated
Temperature-Programmed Reduction (T.P.R.) of
Ni/TiO2 catalysts. Ni content (wt.%) indicated at
T.P.R. curves
50 mg samples
5 K/min from
300 to 1123 K

CO conversion at 525 K
of Ni/TiO2 catalysts of
different nickel loadings
reduced at 673 K
Reaction to C3
+
at 525 K
of Ni/TiO2 catalysts of
different nickel loadings
reduced at 673 K
CO conversion at 525 K
of 2 wt.% Ni/TiO2 catalyst
reduced at the different
temperatures indicated
in the figure

+
(%)
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

Magnetization ofMagnetization of
Measured after reduction at 673 K
during exposure to H2/CO = 2
at 525 K
Drop in magnetization 31 % with
20Ni/TiO2 and no less than 70 %
with 2Ni/TiO2
Measured after reduction at 673 K
and Fischer-Tropsch synthesis
at 525 K during temperature-
programmed hydrogenation in
2 % hydrogen in helium
Heating rate 2 K/min

Temperature-ProgrammedTemperature-Programmed
Hydrogenation of Nickel CarbidesHydrogenation of Nickel Carbides
20 wt.% Ni/TiO2 catalyst reduced
at 673 and 773 K
Measured after Fischer-Tropsch synthesis at 525 K
Heating rate 5 K/min
Surface carbide is hydrogenated at
relatively low temperatures
Transport of carbon to the metal surface
calls for elevated temperatures

Nickel (Surface) CarbideNickel (Surface) Carbide
C
C
C C C
C
CC
CC C
C
CC C
C C
C C C
C
Surface carbide leading to methane
Magnetization only slightly decreased
Hydrogenation of surface carbon at
relatively low temperatures
Bulk carbide leading to higher
hydrocarbons. Magnetization strongly
decreased. Hydrogenation of carbon at
more elevated temperatures due to
transport of carbon through metal

Schematic Description of Silica-Schematic Description of Silica-
Supported Nickel CatalystsSupported Nickel Catalysts

Schematic Description of Titania-Schematic Description of Titania-
Supported Nickel CatalystsSupported Nickel Catalysts

Conclusions about Fischer-Conclusions about Fischer-
Tropsch on NickelTropsch on Nickel
 Promotion of dissociative adsorption ofPromotion of dissociative adsorption of
carbon monoxide required for synthesis ofcarbon monoxide required for synthesis of
higher hydrocarbonshigher hydrocarbons
 Promotion by reducible support, which is notPromotion 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 withReaction to bulk carbide goes together with
Fischer-Tropsch synthesis to higherFischer-Tropsch synthesis to higher
hydrocarbonshydrocarbons

Preparation of Supported CobaltPreparation of Supported Cobalt
Catalysts by Impregnation and DryingCatalysts by Impregnation and Drying
 AluminaAlumina AA22
STST g-aluminag-alumina
pore 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 referenceCatalyst according to Exxon patent as reference
catalyst 10Co1Ce/TiOcatalyst 10Co1Ce/TiO22

Shape of Drop dried onShape of Drop dried on
GlassGlass
Drop of solution of copper(II) nitrate dried on microscope glass slide
Note preferential build up of crystallites at the rim of the drop

Shape of Drop dried onShape of Drop dried on
GlassGlass
Drop of solution of copper(II) citrate dried on microscope glass slide
Note absence of large crystallites

Mean Particle Size of SupportedMean Particle Size of Supported
Cobalt Oxide by XPSCobalt Oxide by XPS
 CatalystCatalyst Mean particle size (nm)Mean particle size (nm)
2.5Co/Al2.5Co/Al22OO33 nitratenitrate 7.37.3
2.5Co/Al2.5Co/Al22OO33 citratecitrate 1.71.7
2.5 Co/Al2.5 Co/Al22OO33 EDTAEDTA 0.70.7
5 Co/Al5 Co/Al22OO33 nitratenitrate 15.515.5
5 Co/Al5 Co/Al22OO33 citratecitrate 3.93.9

Estimation of Reducibility byEstimation of Reducibility by
Measurement of the MagnetizationMeasurement of the Magnetization
Reducibility
depends on size of
cobalt oxide particles
Small oxide particles
react to CoAl2O4,
which only reduces
at very elevated
temperatures

Fischer-Tropsch Synthesis onFischer-Tropsch Synthesis on
Supported Co catalysts at 525 KSupported Co catalysts at 525 K
Conversion of carbon
monoxide roughly
parallel with amount
of metallic cobalt
Measurements at
atmospheric pressure; at
higher pressures better
selectivities and conversions
Measurement of 10Co1Ce/TiO2
at 26 bar and 493 K for 135 h
at H2/CO = 2 led to C5
+
87%
and CH4 = 7%

Selectivities of Alumina-SupportedSelectivities of Alumina-Supported
Cobalt Catalysts at 525 KCobalt Catalysts at 525 K
+
(%)
Temperature
°C
20Ni/TiO2 573 21 78 1 0
20Ni/TiO2 673 20 80 0 0
20Ni/TiO2 773 3 54 13 30
+
(%)
Temperature
Measurements at atmospheric pressure; at higher pressures better selectivities and
conversions. Measurement of 10Co1Ce/TiO2 at 26 bar and 493 K for 135 h at
H2/CO = 2 led to C5
+
87% and CH4 = 7%

Conclusions about SupportedConclusions about Supported
Cobalt CatalystsCobalt Catalysts
 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 siliciumSasol is therefore coating alumina with silicium
compoundcompound
 Performance of cobalt catalysts in Fischer-TropschPerformance of cobalt catalysts in Fischer-Tropsch
synthesis difficult to evaluate from measurement atsynthesis difficult to evaluate from measurement at
atmospheric pressureatmospheric pressure
 With reduction of nickel and cobalt catalysts in technicalWith reduction of nickel and cobalt catalysts in technical
reactors dew point of recirculating hydrogen highlyreactors dew point of recirculating hydrogen highly
importantimportant

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 hydrophilicLow water vapor pressure within pores of hydrophilic
supports very difficult to achievesupports very difficult to achieve
 New procedure to produce supported metallic iron and ironNew procedure to produce supported metallic iron and iron
alloy particlesalloy particles
• Application of complex insoluble cyanides on supportApplication of complex insoluble cyanides on support
• Very rapid reduction to metals and alloys in hydrogenVery rapid reduction to metals and alloys in hydrogen
flowflow
• German patent describing catalyst preparation fromGerman patent describing catalyst preparation from
complex cyanidescomplex cyanides
• Very large metal or alloy particles resulting due to lowVery 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

Supported Iron CatalystsSupported Iron Catalysts
 Our invention : Initial calcination of supported complexOur invention : Initial calcination of supported complex
cyanide precursor to oxidecyanide precursor to oxide
 Subsequent reduction leads to oxidic layer at interfaceSubsequent reduction leads to oxidic layer at interface
between metal or alloy particles and supportbetween metal or alloy particles and support
 Oxidic layer anchors metal or alloy particles to surfaceOxidic layer anchors metal or alloy particles to surface
of support and provides stable catalystsof support and provides stable catalysts

Supported Iron Alloy CatalystsSupported Iron Alloy Catalysts
 Precipitation of complex cyanides with metal ions toPrecipitation of complex cyanides with metal ions to
be present in alloybe present 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)66
• FeFe2+2+
+ K+ K33Fe(CN)Fe(CN)66 ® Fe® Fe33Fe(CN)Fe(CN)66 + K+ K22FeFe(CN)FeFe(CN)66
• FeFe2+2+
+ Na+ Na22Fe(CN)Fe(CN)55NO ® FeFe(CN)NO ® FeFe(CN)55 NONO
• NiNi2+2+
+ K+ K44Fe(CN)Fe(CN)66 ® Ni® Ni22Fe(CN)Fe(CN)66 + K+ K22NiFe(CN)NiFe(CN)66
• NiNi2+2+
+ K+ K33Fe(CN)Fe(CN)66 ® Ni® Ni22Fe(CN)Fe(CN)66 + K+ K22NiFe(CN)NiFe(CN)66
• NiNi2+2+
+ Na+ Na22Fe(CN)Fe(CN)55NO® NiFe(CN)NO® NiFe(CN)55NONO

 Reaction with potassium iron cyanide complexes leadsReaction with potassium iron cyanide complexes leads
to catalysts containing potassiumto catalysts containing potassium
 Since potassium is very well and homogeneouslySince 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 ofcatalysts very well suited to investigate effect of
potassium on Fischer-Tropsch activitypotassium on Fischer-Tropsch activity
 For preparation of potassium-free catalysts startingFor preparation of potassium-free catalysts starting
from Hfrom H44Fe(CN)Fe(CN)66 attractiveattractive

 Preparation of potassium-free iron and nickel-ironPreparation 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 potassiumComparison 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

Comparison of Potassium-Free andComparison of Potassium-Free and
Potassium Containing IronPotassium Containing Iron
CatalystsCatalysts
Important conclusion :
Potassium containing iron catalysts no significant activity

Comparison of Potassium-Free andComparison of Potassium-Free and
Potassium Containing NiFe CatalystsPotassium Containing NiFe Catalysts
Important conclusion :
Potassium containing nickel-iron catalysts no significant activity
Ni2Fe/TiO2

Comparison of Potassium-Free FeComparison of Potassium-Free Fe
and Ni-Fe Catalystsand Ni-Fe Catalysts
NiFe4/TiO2
NiFe/TiO2
Ni3Fe2/TiO2
Fe/TiO2

Selectivities of Titania-SupportedSelectivities of Titania-Supported
Fe and Fe-Ni CatalystsFe and Fe-Ni Catalysts

Magnetization of K-Free andMagnetization of K-Free and
K Containing Fe/TiOK Containing Fe/TiO22 CatalystsCatalysts
Both potassium containing and potassium-free catalysts react to iron carbides upon
exposure to carbon monoxide-hydrogen at 525 K

Magnetization of Spent Catalysts as aMagnetization 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 of
iron carbide (523 or 530 K) Hydrogenation of carbon in iron carbide only above 700 K

Magnetization of Iron-Nickel CatalystsMagnetization of Iron-Nickel Catalysts
during Fischer-Tropsch Synthesisduring Fischer-Tropsch Synthesis

Magnetization of Spent CatalystsMagnetization of Spent Catalysts
as a Function of Temperature inas a Function of Temperature in
Flow of HFlow of H22

Spent Fe and Fe-Ni CatalystsSpent Fe and Fe-Ni Catalysts
Potassium-containing catalyst no reaction to CH4; release of carbon monoxide likely
to be due to decomposition of potassium carbonate. The potassium-free catalyst
exhibits reaction to methane above about 750 K.

Spent Fe and Fe-Ni CatalystsSpent Fe and Fe-Ni Catalysts
NiFe50_C Catalyst NiFe33_A(K) Catalyst
Measured after 6 hours Fischer-Tropsch synthesis at 525 K

Infra-Red Spectra of Adsorbed CarbonInfra-Red Spectra of Adsorbed Carbon
MonoxideMonoxide
Infra-red spectra of carbon monoxide adsorbed on reduced catalyst
NiFe33_A(K) spectrum (a) and NiFe40_B spectrum (b)
No molecular adsorption of carbon monoxide on potassium-containing
catalyst NiFe33_A(K)

Conclusions about Effect ofConclusions 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 ofPotassium completely suppresses adsorption of
molecular carbon monoxidemolecular carbon monoxide
 Potassium suppresses hydrogenation of carbidicPotassium 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 carboniron particles and suppresses adsorption of carbon
monoxide and hydrogenmonoxide and hydrogen

Zirconia-Supported Iron CatalystsZirconia-Supported Iron Catalysts
 Zirconia as a support to limit reaction of iron(II) withZirconia 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 A22
ST, 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 toLoading only 2.5 wt.% iron; small iron particles to
suppress encapsulation by graphite layers andsuppress encapsulation by graphite layers and
growth of nanofibersgrowth of nanofibers
 Activity measurements at elevated pressuresActivity measurements at elevated pressures

Fischer-Tropsch Synthesis onFischer-Tropsch Synthesis on
Zirconia-Supported Iron CatalystZirconia-Supported 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 = 1.0
Note much more
elevated conversion
at higher pressure

Selectivity of Zirconia-Selectivity of Zirconia-
Supported Iron CatalystSupported Iron Catalyst
623 K, H2/CO = 1.0
Note much more
elevated conversion
at higher pressure

Fischer-Tropsch Synthesis on Zirconia-Fischer-Tropsch Synthesis on Zirconia-
Supported Iron CatalystSupported Iron Catalyst
623 K, H2/CO = 1.7
1880 h-1
Note much more
elevated conversion
at higher pressure

Selectivity of Zirconia-SupportedSelectivity of Zirconia-Supported
Iron CatalystIron Catalyst
623 K, H2/CO = 1.7
1880 h-1
Note much more
elevated conversion
at higher pressure

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= CC2=/C2+C2= C3=/C3+C3= 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 88.8623 K 9.9 13.9 19.7 59.7 88.8
10.910.9
 Production of olefins promising as well as stability ofProduction of olefins promising as well as stability of
catalystcatalyst

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 forComplementing 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 dissociativeEarlier mentioned items, competitive dissociative
adsorption and effect not completely reducible metaladsorption and effect not completely reducible metal
oxides well identifiedoxides well identified
 Reduction of cobalt catalysts prepared by impregnationReduction of cobalt catalysts prepared by impregnation
extensively investigatedextensively investigated

Conclusions (2)Conclusions (2)
 Deposition-precipitation, impregnation withDeposition-precipitation, impregnation with
badly crystallizing compounds (citrates, EDTAbadly crystallizing compounds (citrates, EDTA
complexes) successfully appliedcomplexes) successfully applied
 Complex cyanides very interesting precursorsComplex cyanides very interesting precursors
for metals and alloys difficult to reduce or tofor metals and alloys difficult to reduce or to
prepare with uniform chemical compositionprepare with uniform chemical composition
 Reliable and significant investigation of activityReliable and significant investigation of activity
and selectivity of Fischer-Tropsch catalysts canand selectivity of Fischer-Tropsch catalysts can
only be performed at elevated pressuresonly be performed at elevated pressures

Fischer-Tropsch Catalysts: Preparation, Thermal Pretreatment and Behavior During Catalytic Reaction

Fischer-Tropsch Catalysts: Preparation, Thermal Pretreatment and Behavior During Catalytic Reaction

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