A b i n i t i o study of O, O2, and C2H4 interactions with Ag2 and Ag+2. A model for surface–adsorbate interactions

A b initio calculations of silver metal–adsorbate interactions were carried out by using a 36-electron relativistic effective core potential (RECP) for the core electrons of Ag and a 3s3p4d→2s2p2d basis for the valence electrons. Unpromoted surface interactions were modeled by a silver dimer while promoted interactions were modeled by a silver dimer cation. Molecular oxygen is predicted to bind as a π complex while the di-σ and π complexes are predicted to bind similarly for ethylene. The binding energy of O2 decreases on a promoted surface while the binding energy of C2H4 increases compared to an unpromoted surface. The dissociative adsorption of O2 on a promoted surface is found to be inhibited by the formation of a high energy intermediate. The binding energy of O on a silver surface is well reproduced when corrections are made for the electron affinity of the adsorbate and the ionization energy of the dimer.