Mechanistic Insights into CO2 Activation via Reverse Water−Gas Shift on Metal Surfaces

By the means of density functional theory calculations, we find that CO2 activation via reverse water−gas shift (r-WGS) follows different elementary steps on different metals (Pt, Rh, Ni, Cu, Ag, and Pd). We relate these differences to the interactions between the adsorbed oxygen and the metals, which strongly affect the dissociation activation energy. In particular, CO2 dissociation is favored on metals that present high affinity toward oxygen. As the O interaction with the metals weakens, CO2 hydrogenation becomes more favored at the expenses of the dissociation. We found that the binding energy of oxygen scales almost linearly with the difference between the activation energy of the two competing paths, and therefore this quantity can be used as a simple descriptor to discriminate which of the two mechanisms is dominant on different metals. Such findings allow rationalization of the different catalytic cycles reported in the literature for the r-WGS reaction on metal surfaces.