Oxygen-Coverage Effects on Molecular Dissociations at a Pt Metal Surface

The effects of adsorbate coverage on catalytic surface reactions are not well understood. Here, we contrast the rates of O-2 and NO2 dissociations, two competing reactions in NO oxidation catalysis, versus oxygen coverage at a Pt(111) surface. In situ x-ray photoelectron spectroscopy experiments show that the NO2 dissociation rate is less sensitive to O coverage than is O-2. Density-functional theory simulations reveal an NO2 reaction pathway that is more adaptable to an increasingly crowded surface than is O-2 dissociation. While the rates are comparable at low coverage, NO2 dissociation is many orders of magnitude faster at O coverages typical of NO oxidation catalysis.