1. CO Activation and C-C Bond Formation in Synthesis Gas Conversion
Brett Loveless, Matthew Neurock, and Enrique Iglesia
BP MC2 Teleconference, Syngas Conversion Group
April 6, 2010
biomass
hydrocarbons +
oxygenates rr
CO + H2
coal
natural gas
Co, 473 K, 2.0 MPa
The resurgence of interest in synthesis gas (H2 + CO) generated from non-petroleum-based sources provides an opportunity to study unresolved mechanistic details in the Fischer-Tropsch Synthesis (FTS). This work uses isotopic probe molecules as well as kinetic and theoretical analyses to interrogate CO* activation (before or after H-addition) paths, C-C coupling reactions, and the effects of water on monomer formation in FTS.

2. Fundamental Issues in Catalytic CO Hydrogenation Remain Controversial
How is CO* activated?
H-assisted
Unassisted
Huo, et al., (2008)
Fischer, F., Tropsch, H. (1926)
Ojeda, Iglesia, et al., (2010) O
Brady R. C., Pettit, R. (1981) O H C C C O

3. Fundamental Issues in Catalytic CO Hydrogenation Remain Controversial
How is CO* activated?
How does H2O affect rates and selectivities?
H-assisted
Unassisted
H2O-assisted O C H
Huo, et al., (2008)
Fischer, F., Tropsch, H. (1926)
Ojeda, Iglesia, et al., (2010) O
Brady R. C., Pettit, R. (1981) H O H H C C C O

4. Fundamental Issues in Catalytic CO Hydrogenation Remain Controversial
How is CO* activated?
How do surface alkyl chains grow?
How does H2O affect rates and selectivities?
H-assisted
Unassisted
H2O-assisted O C H
Huo, et al., (2008)
Fischer, F., Tropsch, H. (1926)
Ojeda, Iglesia, et al., (2010) O
Brady R. C., Pettit, R. (1981) H O H H C C C O
CHx Coupling
Alkyl Migration
CHx
CH3
CHx
CHx
CHx
CH3
HxCO
HxCO

5. This Work Features both Experimental and Theoretical Analyses
High pressure, gradientless re-circulating reaction unit (RRU)
Rapid data collection (GC, GC/MS)
Online analysis of species up to C12
Practical use of isotopically-labeled compounds
H2 12CO 13CH3OH
C2H4
CnH2n
CH4
C2H6
CnH2n+2
CHx
O13CHx
C1*
C2* …
Cn*

6. This Work Features both Experimental and Theoretical Analyses
Theory (Prof. Matt Neurock)
High pressure, gradientless re-circulating reaction unit (RRU)
Rapid data collection (GC, GC/MS)
Online analysis of species up to C12
Practical use of isotopically-labeled compounds
Density Functional Theory (DFT)
Calculations on CO-covered surfaces
Adsorption energetics and intrinsic activation barriers for surface reactions
H2 12CO 13CH3OH
C2H4
CnH2n
CH4
C2H6
CnH2n+2
CHx
O13CHx
C1*
C2* …
Cn*

7. Hydrocarbon Synthesis – CO Adsorption Behavior

8. Coverage Effects on CO Adsorption on Metal Particles and Periodic Metal Surfaces
Pt201-1ML CO C O
Pt201 -1CO
Ru201-1CO

9. Coverage Effects on CO Adsorption on Metal Particles and Periodic Metal Surfaces
Pt201-1ML CO C O
Pt201 -1CO
Ru201-1CO
Pt(111)
(Atop)
Ru(0001)
(3fold)

10. Coverage Effects on CO Adsorption on Metal Particles and Periodic Metal Surfaces
Pt201-1ML CO C O
Pt201 -1CO
Ru201-1CO
Pt(111)
(Atop)
d-band occupation (Pt > Ru) of metal determines structure sensitivity…
Ru(0001)
(3fold)

11. Extending FT Chemistry to Alcohol Synthesis
Hydrocarbon Synthesis – Monomer Identification
12CO, H2, 13CH3OH ? O H C + H

12. Extending FT Chemistry to Alcohol Synthesis
Methanol does not Incorporate into Larger Hydrocarbon Chains
12CO, H2, 13CH3OH ? O H C + H

13. X Methanol does not Incorporate into Larger Hydrocarbon Chains
Extending FT Chemistry to Alcohol Synthesis
Methanol does not Incorporate into Larger Hydrocarbon Chains
12CO, H2, 13CH3OH ? O H C + H
13C incorporation in all products < 2% at XCO = 0.5 CO
CH3OH H2
OCHx … X
H2/CO = 2, 20 bar, 473 K, 12CO/13MeOH = 11

14. Ongoing Work – CO Activation Paths Alternate CO Activation Paths
H-(H2O-)assisted
A mechanism for CO activation involving H-assisted paths generates a rate expression that agrees with experimental data.
Hypothesis – H-assisted CO activation path involving oxygenated intermediates
CH3OH does not incorporate into larger hydrocarbon chains at relevant FT conditions.

15. Ongoing Work – CO Activation Paths Alternate CO Activation Paths
H-(H2O-)assisted
A mechanism for CO activation involving H-assisted paths generates a rate expression that agrees with experimental data.
Hypothesis – H-assisted CO activation path involving oxygenated intermediates
CH3OH does not incorporate into larger hydrocarbon chains at relevant FT conditions.
Ongoing Experimental Work
C1 oxygenate co-feed studies
Ongoing Theoretical Work
DFT treatment of CO activation processes on CO-covered metal surfaces H C O
Increasing “Monomer” Quality

16. H2O* May Activate CO* without an Increase in Chain Termination
CMRU, 458 K, 2.0 MPa, H2/CO=2.01, 12 wt% Co/SiO2

17. H2O Increases Average Product Molecular Weight and Olefin/Paraffin RatiosCO
C5+ C5 C8
CH4
CMRU, 458 K, 2.0 MPa, H2/CO=2.01, 12 wt% Co/SiO2
H2O-assisted O C H
CnH2n+2 H H x
COH OH
CnH2n+1

18. H2O Increases Average Product Molecular Weight and Olefin/Paraffin Ratios
Added H2O
0.06 MPa
0 MPa
Added H2O C3
0.06 MPa
0 MPa
CH4
0.06 MPa
0 MPa
0 MPa C5
0.06 MPa
RRU, 473 K, 1.6 MPa, H2/CO=2.02, 30 wt% Co/SiO2 C1 C2 Cn
CO* + H*
kt1[C1*]
ktn[C2*]
ktn[Cn*]
HCO*
C1*
C1*
C2* …
Cn*
CO* + HOH*
kg[C1*][C*]
kg[C2*][C*]
kg[Cn-1*][C*]
ki[HCO*]
Bertole, et al., J. Catal. 210 (2002) 84

19. H2O-assisted Activation Appears Competitive with H-assisted Paths
Loveless, Neurock, Iglesia (this work)
Ojeda, Iglesia, et al., (2010)
CO* + H2O* COH* + *OH
CO* + H* COH* + *
ΔEa = 100 kJ mol-1
ΔEa = 125 kJ mol-1
CO* + H2O* HCO* + *OH
CO* + H* HCO* + *
ΔEa = 147 kJ mol-1
ΔEa = 138 kJ mol-1 C1 C2 Cn
CO* + H*
kt1[C1*]
ktn[C2*]
ktn[Cn*]
HCO*
C1*
C1*
C2* …
Cn*
CO* + HOH*
kg[C1*][C*]
kg[C2*][C*]
kg[Cn-1*][C*]
ki[HCO*]
Bertole, et al., J. Catal. 210 (2002) 84

20. Ongoing Work – Effects of H2O H2O-assisted CO Activation Paths
Effects of H2O on FTS
H2O-assisted CO Activation Paths
H2O increases CO consumption rates, α-olefin to n-paraffin ratios, and C5+ selectivity on Co/SiO2 catalysts.
Hypothesis – H2O-assisted CO activation path

21. Ongoing Work – Effects of H2O H2O-assisted CO Activation Paths
Effects of H2O on FTS
H2O-assisted CO Activation Paths
H2O increases CO consumption rates, α-olefin to n-paraffin ratios, and C5+ selectivity on Co/SiO2 catalysts.
Hypothesis – H2O-assisted CO activation path
Ongoing Experimental Work
α-olefin+H2O co-feed studies
CO/H2/H2O infrared studies
Kinetic studies with H2O
Ongoing Theoretical Work
DFT treatment of CO activation processes on CO-covered metal surfaces
H2 13CO H2O
CHx
HxCO
12C2H4

22. Ongoing Work – C-C Bond Formation Paths C-C Bond Formation Paths
Adapted from Iglesia, et al., Adv. Catal. 39 (1993) 221
Data suggest difficulty in forming the initial C-C bond in CO hydrogenation
Ongoing Experimental Work
α-olefin co-feed studies
Relative rates of (de)propagation
βH,1 ≈ 1.1
βH,2-30 ≈ 0.06

23. Ongoing Work – C-C Bond Formation Paths C-C Bond Formation Paths
Adapted from Iglesia, et al., Adv. Catal. 39 (1993) 221
Data suggest difficulty in forming the initial C-C bond in CO hydrogenation
Ongoing Experimental Work
α-olefin co-feed studies
Relative rates of (de)propagation
βH,1 ≈ 1.1
βH,2-30 ≈ 0.06
Olefin re-insertion reactions in CO hydrogenation
RRU, 463 K, 1.8 MPa, H2/CO=2.2, 12 wt% Co/SiO2
13CO/12C3H6 = 20

24. Ongoing Work – C-C Bond Formation Paths
Adapted from Iglesia, et al., Adv. Catal. 39 (1993) 221
Alternate Paths?
βH,1 ≈ 1.1
βH,2-30 ≈ 0.06
Alkyl Migration
CH3
CH3
HxCO
HxCO
Ease of migration with increasing chain length…
Berke and Hoffman, JACS, (1978) 100

25. Other CO hydrogenation catalysts –
Mn-promoted Rh-based catalysis for C2+ oxygenate synthesis
Rh-Mn/SiO2
(5 MPa, H2/CO=1) O O O
C2H5
CH3 C H C C

26. Other CO hydrogenation catalysts –
Mn-promoted Rh-based catalysis for C2+ oxygenate synthesis
Rh-Mn/SiO2
(5 MPa, H2/CO=1)
esterification
condensation
carbonylation
alkyl migration ……

27. Acknowledgements
Prof. Matt Neurock
Prof. Enrique Iglesia
bp MC2
LSAC