Mechanistic insights into CO2 activation via reverse water - Gas shift on metal surfaces

By the means of density functional theory calculations, wefind that CO2activation 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 theinteractions between the adsorbed oxygen and the metals, which strongly affect the dissociation activation energy. In particular,CO2dissociation 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 scalesalmost linearly with the difference between the activation energy of the two competing paths, and therefore this quantity canbe used as a simple descriptor to discriminate which of the two mechanisms is dominant on different metals. Such findings allowrationalization of the different catalytic cycles reported in the literature for the r-WGS reaction on metal surfaces.