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キーワード:
silver, oxygen, ethylene, epoxidation, X-ray photoelectron spectroscopy,
density functional theory
要旨:
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.
