The role of Oad in the decomposition of NH3 adsorbed on Ir(110): a combined TPD and high-energy resolution fast XPS study

Abstract

High energy resolution fast XPS combined with TPD experiments were used to study the effect of chemisorbed oxygen on the adsorption and dissociation of NH₃ on Ir(110). Below 250 K the presence of O_ad does not influence NH₃ decomposition. Above 250 K O_ad enhances NH₃ dissociation, which results in three times as much N₂ formation and less molecular NH₃ desorption compared to the experiments without O_ad. The effect of O_ad can be attributed to destabilization of NH_ad on the surface, resulting in a further dehydrogenation towards N_ad. The presence of O_ad on the surface lowers the temperature at which the N_ad combination reaction takes place by as much as 200 K, due to repulsive interaction between N_ad and O_ad. NO is formed above 450 K if both N_ad and O_ad are present on the surface.