Mechanisms of CO Activation, Surface Oxygen Removal, Surface Carbon Hydrogenation, and C–C Coupling on the Stepped Fe(710) Surface from Computation

Abstract

To understand the initial steps of Fe-based Fischer–Tropsch synthesis, systematic periodic density functional theory computations have been performed on the single-atom stepped Fe(710) surface, composed by p(3 × 3) Fe(100)-like terrace and p(3 × 1) Fe(110)-like step. It is found that CO direct dissociation into surface C and O is more favored kinetically and thermodynamically than the H-assisted activation via HCO and COH formation. Accordingly, surface O removal by hydrogen via H2O formation is the only way. On the basis of surface CHx hydrogenation (x = 0, 1, 2, 3), surface CHx + CHx coupling and CO + CHx insertion resulting in CHxCO formation followed by C–O dissociation, surface C hydrogenation toward CH3 formation is more favored kinetically than the formation of CHx-CHx and CHxCO, as well as thermodynamically. Starting from CH3, the formation of CH4 and CH3CO has similar barriers and endothermic reaction energies, while CH3CO dissociation into CH3C + O has low barrier and is highly exothermic. There...