1. CO Activation and Carbon-Carbon Bond Formation in Synthesis Gas Conversion
Brett Loveless and Enrique Iglesia
June 30, 2009
oxygenates
hydrocarbons
CO + H2
Why?
Oxygenates and hydrocarbons as fuels and chemicals.
Conversion of synthesis gas from diverse carbon sources (biomass, coal, natural gas, tar sands, …)
Known chemistries, yet unanswered mechanistic questions in CO hydrogenation.

2. CO Can Form Surface Monomers Via Two Routes – Unassisted and H
CO Can Form Surface Monomers Via Two Routes – Unassisted and H*-Assisted Activation
1. CO + * CO*
2. H2 + 2* H*

3. Unassisted CO activation
CO Can Form Surface Monomers Via Two Routes – Unassisted and H*-Assisted Activation
1. CO + * CO*
Unassisted CO activation
2. H2 + 2* H*
3. CO* + * C* + O*
4. C* + H* CH* + *
5. CO* + O* CO2 + 2*
10. CH* + H* CH2* + *

4. H*-assisted CO activation(2) Unassisted CO activation
CO Can Form Surface Monomers Via Two Routes – Unassisted and H*-Assisted Activation
1. CO + * CO*
H*-assisted CO activation(2)
Unassisted CO activation
2. H2 + 2* H*
6. CO* + H* HCO* + *
3. CO* + * C* + O*
7. HCO* + H* HCOH* + *
4. C* + H* CH* + *
8. HCOH* + * CH* + OH*
5. CO* + O* CO2 + 2*
9. OH* + H* H2O + 2*
10. CH* + H* CH2* + *
(2) - Ojeda, M., Nabar, R., Nilekar, A. U., Ishikawa, A., Mavrikakis, M., Iglesia, E., Unpublished Results.

5. H*-assisted CO activation(2) Unassisted CO activation
CO Can Form Surface Monomers Via Two Routes – Unassisted and H*-Assisted Activation
1. CO + * CO*
H*-assisted CO activation(2)
Unassisted CO activation
2. H2 + 2* H*
6. CO* + H* HCO* + *
3. CO* + * C* + O*
7. HCO* + H* HCOH* + *
4. C* + H* CH* + *
8. HCOH* + * CH* + OH*
5. CO* + O* CO2 + 2*
9. OH* + H* H2O + 2*
10. CH* + H* CH2* + *
Theory can help identify relevant surface species and reaction pathways…
(2) - Ojeda, M., Nabar, R., Nilekar, A. U., Ishikawa, A., Mavrikakis, M., Iglesia, E., Unpublished Results.

6. Pathways towards Monomer Formation
Theory Suggests H*-Assisted CO Activation on Co(0001) CO H2
Co (0001)

7. Pathways towards Monomer Formation
Theory Suggests H*-Assisted CO Activation on Co(0001)
Unassisted activation
CO*  C* + O* O H C H C O CO H2
H-assisted activation
CO* + H*  COH*
Co (0001) O O H H C C
H-assisted activation
CO* + H*  HCO* O O H H C C

8. Pathways towards Monomer Formation
Theory Suggests H*-Assisted CO Activation on Co(0001)
Unassisted activation
CO*  C* + O* O
Un-favored H C H C O CO H2
H-assisted activation
CO* + H*  COH* Ea = 1.3 eV
Co (0001) O O H H C C
H-assisted activation
CO* + H*  HCO* O O H H C C
Favored energetically

9. Pathways towards Monomer Formation
Theory Suggests H*-Assisted CO Activation on Co(0001)
Unassisted activation
HCO* Dissociation
CO*  C* + O*
HCO* + *  CH* + O* O
Un-favored O H H H C H C O C C O CO H2
H-assisted activation
Second H* Addition
CO* + H*  COH* Ea = 1.3 eV
Co (0001)
HCO* + H*  H2CO* + * O O H O H O H H H C C C C H
H-assisted activation
Second H* Addition
HCO* + H*  HCOH*
CO* + H*  HCO* O O O H H H O H H C C H C C
Favored energetically

10. Pathways towards Monomer Formation
Theory Suggests H*-Assisted CO Activation on Co(0001)
Unassisted activation
HCO* Dissociation
CO*  C* + O*
HCO* + *  CH* + O* O
Un-favored O H H H C H C O C C O CO H2
H-assisted activation
Second H* Addition
CO* + H*  COH* Ea = 1.3 eV
Co (0001)
HCO* + H*  H2CO* + * O O H O H O H H H C C C C H
H-assisted activation
Second H* Addition
HCO* + H*  HCOH*
Ea = 0.46 eV
CO* + H*  HCO* O O O H H H O H H C C H C C
Favored energetically

11. Fundamental Chemical Questions Remain in CO Hydrogenation
H2 / CO
CHx
OCHx
CH3OH
C2H5OH
CnH2n+1OH
(Alcohol Synthesis)
Co, Co-M
Rh, Rh-M
C1*
C2* …
Cn*
MoSx-K
(Fischer-Tropsch)
CH4
C2H6
CnH2n+2
C2H4
CnH2n

12. Fundamental Chemical Questions Remain in CO Hydrogenation
H2 / CO
CHx
OCHx
CH3OH
C2H5OH
CnH2n+1OH
(Alcohol Synthesis)
Co, Co-M
Rh, Rh-M
C1*
C2* …
Cn*
MoSx-K
(Fischer-Tropsch)
CH4
C2H6
CnH2n+2
C2H4
CnH2n
One of the challenges is the first C-C bond formation…
How can we interrogate C-C bond formation pathways?

13. Fundamental Chemical Questions Remain in CO Hydrogenation
H2 / CO
CHx
OCHx
CH3OH
C2H5OH
CnH2n+1OH
(Alcohol Synthesis)
Co, Co-M
Rh, Rh-M
C1*
C2* …
Cn*
MoSx-K
(Fischer-Tropsch)
CH4
C2H6
CnH2n+2
C2H4
CnH2n
One of the challenges is the first C-C bond formation…
How can we interrogate C-C bond formation pathways?
Isotopically labeled compounds (13CO, 13CH3OH) to track the carbon.
Other questions…
Can we explain the effects of H2O on FTS?
What is the monomer for product formation?
How is CO* activated?

14. Isotopic and Kinetic Assessment of Chain Growth Processes
Gradient-less RRU
H2/CO
micropump
XCO t °C
Catalyst
GC/MS
≤ 20 bar GC
Sampling port
Cold Trap
Heated Enclosure (130 °C)
Continuous on-line analysis of C15- products
Plug-flow reactor analog with gradient-less conditions

15. Water Increases Chain Growth Rates, O/P Ratios
Dry
Wet
CO conversion (%)
10.4
9.7
Site-time yield (h-1)
260
270
C1 Selectivity
(CO2-free, %) 24 18
C5+ Selectivity 60 69
C3 O/P Ratio 1 2
Crossed symbols – w/ 0.6 bar H2O
Filled symbols - dry
C5+
CH4
473 K, 1.6 MPa, H2/CO=2, 15 mg 30 wt% Co/SiO mg SiO2 ( MPa H2O)

16. Water Increases Chain Growth Rates, O/P Ratios
Dry
Wet
CO conversion (%)
10.4
9.7
Site-time yield (h-1)
260
270
C1 Selectivity
(CO2-free, %) 24 18
C5+ Selectivity 60 69
C3 O/P Ratio 1 2
Crossed symbols – w/ 0.6 bar H2O
Filled symbols - dry
C5+
CH4
(H2O* + CO* HCO* + OH*)
Bertole, et. al., J. Cat. 210, 84 (2002)
473 K, 1.6 MPa, H2/CO=2, 15 mg 30 wt% Co/SiO mg SiO2 ( MPa H2O)

17. Can CH3OH Act as a Chain Initiator in CO Hydrogenation?
495K, 0.1 MPa, H2/CO = 1
510K, 0.8 MPa, H2/CO = 1
0.1 MPa data from Kummer and Emmett, JACS, 75, 5177 (1953).
0.8 MPa data from Hall, et. al, JACS, 79, 2983 (1957).

18. Can CH3OH Act as a Chain Initiator in CO Hydrogenation?
MeOH “Incorporation”
Run
0.1 MPa (see ref)
1 in 10-15
0.8 MPa (see ref)
1 in 35
2.0 MPa -
495K, 0.1 MPa, H2/CO = 1
463K, 2.0 MPa, H2/CO = 2, 30 wt% Co/SiO2, ηMeOH = 0.11
510K, 0.8 MPa, H2/CO = 1
0.1 MPa data from Kummer and Emmett, JACS, 75, 5177 (1953).
0.8 MPa data from Hall, et. al, JACS, 79, 2983 (1957).

19. Can CH3OH Act as a Chain Initiator in CO Hydrogenation?
MeOH “Incorporation”
Run
0.1 MPa (see ref)
1 in 10-15
0.8 MPa (see ref)
1 in 35
2.0 MPa -
495K, 0.1 MPa, H2/CO = 1
463K, 2.0 MPa, H2/CO = 2, 30 wt% Co/SiO2, ηMeOH = 0.11
CnH2n+1OH
CnH2n+2
510K, 0.8 MPa, H2/CO = 1
CnH2nO
CnH2n
H2 / CO
CHx
OCHx
0.1 MPa data from Kummer and Emmett, JACS, 75, 5177 (1953).
0.8 MPa data from Hall, et. al, JACS, 79, 2983 (1957).

20. Fundamental Chemical Questions Remain in CO Hydrogenation
H2 / CO
CHx
OCHx
CH3OH
C2H5OH
CnH2n+1OH
(Alcohol Synthesis)
Co, Co-M
Rh, Rh-M
C1*
C2* …
Cn*
MoSx-K
(Fischer-Tropsch)
CH4
C2H6
CnH2n+2
C2H4
CnH2n
One of the challenges is the first C-C bond formation…
How can we interrogate C-C bond formation pathways?
Isotopically labeled compounds (13CO, 13CH3OH) to track the carbon.
Other questions…
Can we explain the effects of H2O on FTS?
What is the monomer for product formation?
How is CO* activated?

21. Fundamental Chemical Questions Remain in CO Hydrogenation
H2 / CO
CHx
OCHx
CH3OH
C2H5OH
CnH2n+1OH
(Alcohol Synthesis)
Co, Co-M
Rh, Rh-M
C1*
C2* …
Cn*
MoSx-K
(Fischer-Tropsch)
CH4
C2H6
CnH2n+2
C2H4
CnH2n
One of the challenges is the first C-C bond formation…
How can we interrogate C-C bond formation pathways?
Density functional theory (DFT) calculations
Other questions…
Can we explain the effects of H2O on FTS?
What is the monomer for product formation?
How is CO* activated?

22. Theory Can Give Insight to Surface Coverage & Catalysis
Ge, Q., and Neurock, M., J. Phys. Chem B, 110 (2006) 15368

23. Theory Can Give Insight to Surface Coverage & Catalysis
Ge, Q., and Neurock, M., J. Phys. Chem B, 110 (2006) 15368
M. Neurock, Personal Communication (2009)
DErxn = 55 kJ mol-1
DErxn = 67 kJ mol-1
CO* + H2O* COH* + OH*
CO* + H2O* HCO* + OH*

24. CO* Activation Paths at High Coverages Remain Unstudied in DFT…
HCOH CO

25. CO* Activation Paths at High Coverages Remain Unstudied in DFT…
- H2O
H2COH
+ H* CH CO
HCOH CO
+ H*
+ H*
CH4
CH3OH
A unified theory in CO hydrogenation…

26. CO* Activation Paths at High Coverages Remain Unstudied in DFT…
- H2O
H2COH
+ H* CH CO
HCOH CO
+ H*
+ H*
CH4
CH3OH
Interrogating FTS Chemistry on Surface Defects CO CO CO C O H CO CO
CO* activation on steps?
H2O* (H*) “cleaning” the steps?
Geerlings, J. J. C., et. al., App. Cat. A 186 (1999) 27