Role of Steps in the NO-CO Reaction on the (111) Surface of Noble Metals

Artikel i vetenskaplig tidskrift, 2003

One of the most probable scenarios of the NO-CO reaction on the (111) surface of noble metals includes reversible NO and CO adsorption, NO dissociation, N-2 desorption, and CO2 formation due to reaction between adsorbed CO and 0 species. Adopting this scheme, we analyze the reaction kinetics in the situation when the surface contains steps. Employing the mean-field kinetic equations with the kinetic parameters corresponding to the case when the adsorbate coverage is high and the reaction rate is limited by NO dissociation, we show that the contribution of steps to the reaction rate may be appreciable. The adsorbate-diffusion-mediated communication between terraces and steps can play a constructive role in the reaction, i.e., the reaction rate may be higher with than without communication. In addition, we present Monte Carlo simulations demonstrating that, due to limitations in the rate of N diffusion, the adsorbate distribution along the surface may be non-uniform with the largest N coverage near steps. Such reaction regimes are found to be possible even for relatively high rates of N diffusion (e.g., in the case when the ratio of the rates of N jumps and CO or NO impingement is about 10(4)). The implications of these findings for the understanding of the specifics of the reaction under consideration are briefly discussed.