Self-limiting oxidation of AgPdF nanoalloy models: A computational investigation

Determining the chemical state of the catalytically active surfaces of nanoalloys under reaction, the conditions have been a long-standing challenge for theoretical calculations due to nanoalloys, being prone to suffer oxidation. In this study, the oxidation process over the (1 1 1) facet of AgPd systems including AgPd, AgPdO, and AgPdF nanoalloys is investigated using the density functional theory (DFT) calculations. Firstly, surface oxygen atoms are adsorbed in the hollow site of three models, subsurface oxygen atoms are adsorbed in the octahedral site of AgPd, tetrahedral site of AgPdO, and octahedral site of AgPdF with adsorption energies of 0.40,-0.51 and 0.84 eV. Secondly, the diffusion energy barriers of surface oxygen atoms from the hollow site to subsurface octahedral sites are 1.44, 0.50, and 1.51 eV, the same barriers to subsurface tetrahedral sites are 1.42, 0.71, and 1.59 eV for AgPd, AgPdO, and AgPdF nanoalloys. It is revealed that, as compared with AgPd nanoalloys, the surface oxygen atoms on AgPdO nanoalloys are more readily embedded into the subsurface sites and induce the over-oxidation, however, the oxygen atoms are stable on the surface of AgPdF nanoalloys to inhibit the over -oxidation. This work is helpful to develop oxidation-resistant AgPd nanoalloy catalysts.