Mechanistic Study on Water Gas Shift Reaction on the Fe3O4 (111) Reconstructed Surface

We present a first-principles study using periodic density functional theory on a water gas shift reaction on a Feoct2-tetr terminated Fe3O4 (111) surface. We show that water can easily undergo dissociative adsorption to form OH and H adatom species on the surface. Three possible reaction mechanisms (i.e., redox mechanism, associative mechanism, and coupling mechanism) were systematically explored based on minimum energy path calculations. It was identified that the redox mechanism is the energetically most favorable pathway for the water gas shift reaction on the Feoct2-tet1- terminated Fe3O4 (111) surface. The COO* desorption was found to be the rate-limiting step with a barrier of 1.04 eV, and the OH dissociation has the second-highest activation barrier (0.81 eV). Our results are consistent with results of kinetic and isotope exchange experiments. Our studies suggest that it is necessary to develop a promoter to reduce the activation barriers of the COO*desorption and OH dissociation steps in order to improve the catalyst performance.