Why is a noble metal catalytically active? The role of the O-Ag interaction in the function of silver as an oxidation catalyst.

Extensive density-functional theory calculations, and taking into account temperature and pressure, afford a comprehensive picture of the behavior and interaction of oxygen and Ag(111), and provides valuable insight into the function of silver as an oxidation catalyst. The obtained phase diagram reveals the most stable species present in a given environment and thus identifies (and excludes) possibly active oxygen species. In particular, for the conditions of ethylene epoxidation, a thin oxidelike structure is most stable, suggesting that such atomic O species are actuating the catalysis, in contrast to hitherto proposed molecularlike species.