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

Extensive density functional theory calculations of the O1s 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 O1s 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 O1s binding energy of 530 eV that is thought to be active in ethylene epoxidation. Instead, we show that the only species with O1s binding energies near 530 eV are covalently bound, which we find in our calculations, for example, when hydrogen or carbon are present.