When seeing is not believing: Oxygen on Ag(111), a simple adsorption system?

A number of recent studies indicate that, under the oxygen rich conditions of oxidation catalysis, some transition metal catalysts may be covered by thin oxide overlayers. Moreover, it has been suggested that such “surface-oxide” layers are catalytically active, possibly more active than the pure metal surfaces as was traditionally assumed. This contemporary picture can be traced back to Ag catalysis, where over 30years ago it was suggested that the top layer of Ag(111) reconstructed to an epitaxial Ag2O like overlayer upon exposure to oxygen Rovida et al., Surf. Sci. 43, 230 (1974). Extensive experimental work, including scanning tunneling microscopy studies in which the oxide was apparently imaged with atomic resolution, as well as density-functional theory calculations, largely confirmed this interpretation. However, a review of published experimental data and new density-functional theory results presented here indicate that previous conclusions are significantly incomplete and that the structure of this original surface oxide must be reconsidered.