The adsorption and dissociation of methane on the IrO 2 (110) surface were investigated by density functional theory calculations. The adsorption energy of methane obtained in this study is −0.41 eV on the stoichiometric surface and −0.63 eV on the oxygen-rich surface, which are significantly higher than those calculated recently on other different catalytic systems. Analyses from density of states and electron density difference show a special interaction between the C−H bonding orbital and the d z 2 orbital of surface iridium atom. In addition, the first hydrogen atom abstraction of methane by the IrO 2 (110) surface is a reaction with low barrier and high exothermic energy. The lower reaction barrier than the desorption energy indicates that the IrO 2 (110) surface could provide not only high sticking coefficient but also high turnover frequency in methane dissociation reaction.

The oxidation of ammonia (NH 3 ) and the reduction of nitrogen (N 2 ) are two important processes in chemistry. In this study, we used density functional theory calculations to investigate the adsorptions of NH x (x ) 0-3) and N 2 on IrO 2 (110) surfaces, with density of states (DOS) analysis providing information relating to bond character and state interactions. These adsorbates have higher binding energies on the IrO 2 (110) surface than on the RuO 2 (110) surface because the former forms stronger σ bonds with the adsorbed molecules. The surface adsorptions of NH 2 and NH on the IrO 2 (110) surface proceed with similar binding energies and similar hybridizations of the nitrogen atoms. In addition, the orientations of NH 2 and NH adsorbed on the IrO 2 (110) surface are governed by lateral interactions with surface oxygen atoms (O cus or O br ), rather than by hydrogen bonding. We calculated the binding energy for the adsorption of N 2 on the IrO 2 (110) surface to be 1.10 eV. The weakening of the NtN triple bond was evident from our DOS results; strong bonding forces, including σ-and π-type interactions, exist between the N 2 molecule and the surface, suggesting that N 2 molecules are moderately activated by IrO 2 (110) surfaces.

In this study, we employed density functional theory (DFT) to investigate the oxidation of ammonia (NH(3)) on the IrO(2)(110) surface. We characterized the possible reaction pathways for the dehydrogenation of NH(x) species (x = 1-3) and for the formation of the oxidation products N(2), N(2)O, NO, NO(2), and H(2)O. The presence of oxygen atoms on coordinatively unsaturated sites (O(cus)) of the oxygen-rich IrO(2)(110) surface promotes the oxidation of NH(3) on the surface. In contrast, NH(3) molecules prefer undergoing desorption over oxidation on the stoichiometric IrO(2)(110) surface. Moreover, the O(cus) atoms are also the major oxidants leading to the formation of oxidation products; none of the oxidations mediated by the bridge oxygen atoms were favorable reactions. The energy barrier for formation of H(2)O as a gaseous oxidation product on the IrO(2)(110) surface is high (from 1.83 to 2.29 eV), potentially leading to the formation of nitrogen-atom-containing products at high temperature. In addition, the selectivity toward the nitrogen-atom-containing products is dominated by the coverage of O(cus) atoms on the surface; for example, a higher coverage of O(cus) atoms results in greater production of nitrogen oxides (NO, NO(2)).