Reactivity of Oxygen Adatoms on the Au(111) Surface

Abstract

The adsorption and reaction of CO, CO2, NO2, H2O, CH3OH, and C2H4 were studied on clean and oxygen-precovered Au(111) surfaces. High coverages of oxygen adatoms, ΘO, up to one monolayer were formed under clean, UHV conditions by exposure of Au(111) to ozone. Neither CO nor CO2 adsorbed on clean or oxygen-precovered Au(111) surfaces, but the CO oxidation reaction occurs readily at low temperatures. The Langmuir-Hinshelwood (LH) mechanism was found to be in operation over the entire range of oxygen coverage; we observed negative apparent activation energies (Eapp = -2.5 kcal/mol) with no strong dependence on oxygen coverage. The activation of NO2, H2O, CH3OH, and C2H4 by oxygen adatoms on Au(111) is also discussed and compared to Au(110). We find that H2O and C2H4 are unreactive at low temperatures, and CH3OH has an intermediate reactivity, being less reactive than CO.