Reduction of nitric oxide on the carbon pretreated Rh{331} single crystal surface; evidence for molecular CN? formation

The chemisorption of NO on the carbon pretreated Rh{331} single crystal surface has been investigated by XPS, LEED and SIMS. The carbon overlayer was prepared by dehydrogenation of chemisorbed C₂H₄. Results of NO adsorption at room temperature show that surface carbon blocks adsorption sites that normally coordinate molecular NO_ADS and its dissociated products, N_Ads and O_Ads, as determined by comparing to experiments performed on clean Rh{331}. Heating the surface which contains NO_Ads, n_Ads, O_Ads and C_Ads, induces a series of chemical reactions starting with the dissociation of molecular NO_Ads. Above 400 K, the C_Ads and N_Ads atoms combine to form CN^?. The formation of the latter species is confirmed by the temperature evolution of the Rh₂CN⁺ and CN^? SIMS ion yields. The C_Ads species also reacts with O_Ads to produce CO and/or CO₂. These processes occur preferentially over the desorption of N₂ and O₂. In general, it is demonstrated that by using the XPS and SIMS methods, it is possible to identify the reaction species present on the surface at any given temperature and to unravel rather complex reaction pathways.