Density Functional Theory Study of the Oxidation of Ammonia on RuO2(110) Surface

We have used density functional theory (DFT) calculations to investigate the oxidation of ammonia (NH3) on a RuO2(110) Surface. We characterized the possible reaction pathways for the dehydrogenation of NHx species (x = 1-3) and the formation of the oxidation products N-2, NO, and H2O. The presence of oxygen atoms on coordinatively unsaturated sites (O-cus) promoted the oxidation of NH3 on the Surface. The oxidation of NH3 is possible on both stoichiometric and oxygen-rich RuO2(110) surfaces; in the absence of O-cus (stoichiometric surface), however, NH3 molecules prefer desorption over oxidation. Moreover, the O-cus atoms are the major oxidants in this process; the formations of H2O and NO from bridge oxygen atoms (O-br) are both unfavorable reactions. According to our energetic analysis, in the NHx dehydrogenation pathways, H atom migration from NH2-cus to O-br has the highest barrier by 0.86 eV it is much lower than the interaction energy of NH3 on the RuO2(110) Surface. In terms of nitrogen-atom-containing products, NO, N-2, and N2O are all possible products of the oxidation of NH3. The formation of the gaseous oxidation products H2O and NO is determined by their binding energies. whereas that of N-2 is controlled by the diffusion of N-cus atoms on the surface. In addition, the selectivity toward the nitrogen-atom-containing products N-2 and NO is dominated by the coverage of O-cus atoms on the surface; a higher coverage of O-cus atoms results in greater production of NO.