Suppression of water formation over stepped Pt(335) by Au

A partial monolayer of Au strongly modifies the kinetics of water adsorptio n and formation on the stepped Pt(335) surface. The effects are more than p assivation. With a Au coverage of 0.7 ML as measured by Auger spectroscopy, saturation H and O adsorption are only 15% and 8.5%. respectively, of thei r values on bare Pt, Adsorption at step sites is nearly eliminated. Water f ormation is reduced to 5% of its bare: Pt value: one-sixth of what would be expected if each Au atom blocked one site. Water formation on Pt has multi ple reaction pathways. The partial Au layer eliminates only the low-tempera ture pathway. The PI recombination temperature is reduced relative to bare Pt, so H recombination competes with water formation and reduces its effici ency. The partial Au layer also changes the desorption spectrum of water. A t low water coverage, there is a single desorption peak, intermediate in te mperature between those seen on Pt and Au.