COMPARING CO DISSOCIATION PATHWAYS ON THE VARIOUS IRON SURFACES AS FE(100) AND FE(110)

CO dissociation is generally seen as the first step in the mechanism of the Fischer-Tropsch process, which converts synthesis gas (CO and hydrogen) into hydrocarbons. Dissociation of an adsorbed CO may be direct, i.e. CO→C+O or assisted by adsorbed H-atoms, schematically indicated as H+CO↔ HCO→CH + O or CO+H↔COH→C+OH. In this paper we compare the energetics of these steps on the Fe(100) and Fe(110) surfaces on the basis of density functional theory (DFT) calculations and demonstrate that formation of HCO and subsequent dissociation to CH and O may at best compete with direct dissociation on open-packed Fe (100) surface. Howevere, H-assisted dissociation is the preferred mechanism for the close-packed Fe (110) surface