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.

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

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

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

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*

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*

Hydrocarbon Synthesis – CO Adsorption Behavior

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

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)

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)

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

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

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

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 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

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

H2O Increases Average Product Molecular Weight and Olefin/Paraffin Ratios CO 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

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

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

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 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

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

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

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

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

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 ……

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