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Abstract:
We report on theoretical and experimental studies of the reactivity of ethylene with oxygen in two well-known oxygen induced surface reconstructions on silver, the p(2 × 1) reconstruction on the Ag(110) surface and the p(4 × 4) reconstruction on the Ag(111) surface. Density functional theory calculations demonstrate that ethylene can react with oxygen on both surfaces to form an oxametallacycle that can decompose into either ethylene oxide or a CO2 precursor, acetaldehyde. The activation energy associated with acetaldehyde formation is predicted to be 0.4 eV lower than that associated with epoxide formation on both surfaces, though we find lower barriers for all elementary steps on the p(4 × 4) reconstruction due to its unique structural dynamics. Our calculations predict these dynamics make the p(4 × 4) reconstruction active in acetaldehyde formation at room temperature. Experiments performed by exposing the p(4 × 4) reconstruction to ethylene at room temperature support this finding with CO2, the only carbonaceous product formed during temperature-programmed desorption. Our results unambiguously demonstrate that, alone, these oxygen reconstructions are not selective in ethylene epoxidation on silver.
