As a well-known oxidation catalyst, platinum is currently being used to convert NO to $\mathrm{N}{\mathrm{O}}_2$ for absorption in so-called $\mathrm{N}{\mathrm{O}}_x$ traps under excess oxygen conditions, where direct conversion of NO to nitrogen gas is prohibitive. By performing kinetic Monte Carlo simulations with parameters derived from density-functional theory, we show that this oxidation process is not an inherent property of the platinum catalyst itself. In fact, the intrinsic $\mathrm{N}\mathrm{O}+\mathrm{O}\to \mathrm{N}{\mathrm{O}}_2$ reaction is found to be inhibited (endothermic) rather than promoted on Pt(111), due to strong oxygen–platinum bonds. Only at sufficient oxygen chemical potential does platinum become an efficient oxidation catalyst, as its oxygen bonds are weakened with increasing coverage, and the $\mathrm{N}{\mathrm{O}}_2$ formation reaction becomes exothermic. At that point, Pt catalyzes the reaction by lowering the activation barrier for the kinetic reaction. Congruent with flow-reactor experiments, we note a strong temperature dependence for the turnover frequency, which should encourage further ultra-high vacuum studies.

• Received 9 August 2004

DOI:https://doi.org/10.1103/PhysRevB.71.115406