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The nature of surface oxygen species on/in a silver powder catalyst and their reactivity with ethylene were systematically investigated with multiple spectroscopies and DFT calculations. Unique quasi in situ HS-LEIS, in situ NAP-XPS, and in situ Raman spectroscopy demonstrated that the silver surface is covered by a thin oxide layer (1–3 nm) after an oxidation treatment and during ethylene oxidation. Periodic DFT models allowed assignments of oxygen species detected by in situ Raman spectroscopy with detailed structures on p(4 × 4)–O–Ag(111) surfaces. In situ NAP-XPS and Raman spectroscopy suggest that Ag4–O2 on oxidized Ag is the active oxygen species for ethylene epoxidation. The experimental and theoretical methodologies developed in the present work serve as an efficient toolbox for the scientific investigation of the silver–oxygen system for selective oxidation reactions and rational guidance of computational calculations coupled with experimental findings.
Pu et al. (Tue,) studied this question.