(78a) Mechanistic Aspects of CO Hydrogenation On Iron and Other Group VIII Metal Surfaces: DFT Studies

Aiming at the remediation of the current world fuel shortage and spearheaded by heterogeneous catalysis, hydrocarbon production from natural gas, coal or biomass via synthesis gas (CO + H₂) and the Fischer-Tropsch synthesis is at the heart of some of the main efforts currently taking place within the chemical energy industry. Understanding the fundamental surface chemistry of CO, CxHy species, and eventually of the paraffinic and olefinic hydrocarbon products on the metals involved is an essential requirement for obtaining molecular level insight in (details of) the FTS mechanism. 

Ab-initio total-energy calculations of the elementary reaction steps starting from CO and H₂ leading to water, methane, ethylene and ethane formation and their decomposition are described. The scope for H-assisted CO dissociation as well as trends in the formation of olefins and paraffins on the group VIII metals will be discussed. Alongside the endothermicity of all the hydrocarbon formation reactions, the crucial role played by adsorbed ethyl as main precursor towards both ethylene and ethane formation, characterises the surface reactivity towards C₂H_x hydrocarbon formation in the low coverage limit. Finally, the monotonous endothermicity of the hydrocarbon formation reaction sequence leads to a significant difference between the total-apparent activation energy scales for the forward and for the reverse elementary steps, and in turn, it is responsible for the coexistence of many intermediates on the catalyst surface at common Fischer-Tropsch reaction temperatures.

• Direct versus Hydrogen-Assisted CO Dissociation on the Fe(100) Surface: a DFT Study, M. Elahifard, M. Perez-Jigato, J.W. Niemantsverdriet, ChemPhysChem 13 (2012) 89 
• Ab-initio calculations of the direct and hydrogen-assisted dissociation of CO on Fe(3 1 0), M. Elahifard, M. Perez-Jigato, J.W. Niemantsverdriet, Chem. Phys. Lett. 534 (2012) 54
• The Surface Chemistry of Water on Fe(100): A Density Functional Theory Study, A. Govender, D. Curulla-Ferre, J.W. Niemantsverdriet, ChemPhysChem 13 (2012) 1583
• A Density Functional Theory Study on the Effect of Zero-Point Energy Corrections on the Methanation Profile on Fe(100), A. Govender, D. Curulla-Ferre, J.W. Niemantsverdriet, ChemPhysChem 13 (2012) 1591