Initial Reduction of CO on Pd-, Ru-, and Cu-Doped CeO(111) Surfaces: Effects of Surface Modification on Catalytic Activity and Selectivity.

Surface modification by metal doping is an effective treatment technique for improving surface properties for CO reduction. Herein, the effects of doped Pd, Ru, and Cu on the adsorption, activation, and reduction selectivity of CO on CeO(111) were investigated by periodic density functional theory. The doped metals distorted the configuration of a perfect CeO(111) by weakening the adjacent Ce-O bond strength, and Pd doping was beneficial for generating a highly active O vacancy. The analyses of adsorption energy, charge density difference, and density of states confirmed that the doped metals were conducive for enhancing CO adsorption, especially for Cu/CeO(111). The initial reductive dissociation CO → CO* + O* on metal-doped CeO(111) followed the sequence of Cu- > perfect > Pd- > Ru-doped CeO(111); the reductive hydrogenation CO + H → COOH* followed the sequence of Cu- > perfect > Ru- > Pd-doped CeO(111), in which the most competitive route on Cu/CeO(111) was exothermic by 0.52 eV with an energy barrier of 0.16 eV; the reductive hydrogenation CO + H → HCOO* followed the sequence of Ru- > perfect > Pd-doped CeO(111). Energy barrier decomposition analyses were performed to identify the governing factors of bond activation and scission along the initial CO reduction routes. Results of this study provided deep insights into the effect of surface modification on the initial reduction mechanisms of CO on metal-doped CeO(111) surfaces.