Insights into the Electronic Structure of the Oxygen Species Active in Alkene Epoxidation on Silver

Extensive density functional theory calculations of the O-1s, binding energies, adsorption energies, and the experimentally measured in situ X-ray photoelectron spectra of oxygen on silver are reported in an effort to clarify which species are present during ethylene epoxidation. We find that the O-1s binding energy of an oxygen adatom increases near linearly with its adsorption energy due to the ionic nature of the Ag/O interaction. Thus, contrary to widespread assignments, a weakly bound oxygen adatom does not account for the electrophilic species with an O-1s binding energy of 530 eV that is thought to be active in ethylene epoxidation. Instead, we show that the only species with O-1s, binding energies near 530 eV are covalently bound, which we find in our calculations, for example, when hydrogen or carbon are present.