First-principles investigation of transition metal atom M (M = Cu, Ag, Au) adsorption on CeO2(110)

Transition metal atom M (M = Cu, Ag, Au) adsorption on CeO(2)(110), a technologically important catalytic support surface, is investigated with density-functional theory within the DFT+U formalism. A set of model configurations was generated by placing M at three surface sites, viz., on top of an O, an O bridge site, and a Ce bridge site. Prior to DFT optimization, small distortions in selected Ce-O distances were imposed to explore the energetics associated with reduction of Ce(4+) to Ce(3+) due to charge transfer to Ce during M adsorption. Charge redistribution is confirmed with spin density isosurfaces and site projected density of states. We demonstrate that Cu and Au atoms can be oxidized to Cu(2+) and Au(2+), although the adsorption energy, E(ads), of Au(2+) is less favorable and, unlike Cu(2+), it has not been experimentally observed. Oxidation of Ag always results in Ag(+). For M adsorption at an O bridge site, E(ads)(2NN) > E(ads)(3NN) > E(ads)(1NN) where NN denotes the nearest neighbor Ce(3+) site relative to M. Alternatively, for M adsorption at a Ce bridge site, E(ads)(3NN) > E(ads)(2NN) > E(ads)(1NN). The adsorption behavior of M on CeO(2) (110) is compared with M adsorption on CeO(2)(111).