Interaction of NO with RuO2(110) Surface: A First Principles Study

We report results of density functional theory calculations of the interaction of NO with the stoichiometric RuO 2 (110) surface that provide insights into the experimentally observed lack of reactivity for the system. We find that NO adsorbs on top of the undercoordinated Ru (Ru-cus) with an upright axis, and the adsorption energy (with zero-point contribution) changes from 1.61 eV for 0.5 ML to 1.49 eV for 1 ML coverage. Once all Ru-cus sites are occupied, NO adsorbs on O-bridge sites with adsorption energy of 0.66 eV, forming an asymmetric O···N−O surface complex. We also find a high dissociation barrier of 3.22 eV for NO on Ru-cus. Although the activation energy for oxidation of NO is calculated to be about 1.2 eV, the location of the final state makes the formation of NO 2 only transient with a large probability of reverting back to NO. Additionally, the total energy difference for the reaction NO + NO → N 2 O + O on RuO 2 (110) is found to be about 1.35 eV. Comparison of results with those for a similar overlayer of CO on the surface show the NO−Ru-cus bond to be stronger than CO−Ru-cus, the difference arising from the contribution of the unpaired 2π* electrons for the former.