Reactions of CO, H₂O, CO₂, and H₂ on the Clean and Precovered Fe(110) Surfaces – A DFT Investigation

Abstract

The reactions of CO and H₂O on the clean Fe(110) surface as well as surfaces with 0.25 monolayer O, OH, and H precoverage have been computed on the basis of density functional theory (GGA-PBE). Under the considerations of the reductive nature of CO as reactant and H₂ as product as well as the oxidative nature of CO₂ and H₂O, we have studied the potential activity of metallic iron in the water-gas shift reaction. On the clean surface, CO oxidation following the redox mechanism has a similar barrier as CO dissociation; however, CO dissociation is much more favorable thermodynamically. Furthermore, surfaces with 0.25 monolayer O, OH, and H precoverage promote CO hydrogenation, while they suppress CO oxidation and dissociation. On the surfaces with different CO and H₂O ratios, CO hydrogenation is promoted. On all of these surfaces, COOH formation is not favorable. Considering the reverse reaction, CO₂ dissociation is much favorable kinetically and thermodynamically on all of these surfaces, and CO₂ hydrogenation should be favorable. Finally, metallic iron is not an appropriate catalyst for the water-gas shift reaction