Transient kinetic studies of the catalytic reduction of NO by CO on platinum

Transient kinetic experiments were performed in order to study the catalytic reduction of NO by CO over a polycrystalline platinum surface. The experiments were performed by preadsorbing one reactant on the Pt surface at the reaction temperature and then rapidly introducing the second reactant in a pressure jump while monitoring the transient production of CO₂. The CO₂ production rate, R_CO2, was modeled as a function of NO and CO coverages (θ_NOand θ_CO). When NO was preadsorbed, the reaction rate can be described by R_CO2 = kθ_NOθ_CO (for the onset of the reaction) and R_CO2 = k′θ_NOθ_{free sites} (for the final portion). The onset of CO₂ production showed no detectable induction period in these experiments. When CO was preadsorbed, the reaction rate is described by R_CO2 = k″θ_NOθ_{free sites} (for the onset of the reaction) and R_CO2 = k″′(gq_CO)² (for the final portion). For CO preadsorption, a time delay in the onset of CO₂ production which varied with temperature and the initial amount of preadsorbed CO was observed. Our transient kinetic results indicate that the reaction proceeds over a wide range of reaction conditions via a dissociative mechanism in which NO_(a) first dissociates into N_(a) and O_(a), and then O_(a) reacts with CO_(a) to form CO₂.