The microscopic oxidation mechanism of NH3 on CuO(111): A first-principles study

Abstract

Understanding the oxidation of ammonia (NH3) over CuO surface and then the formation routes of N2 and NOx is rather crucial to provide a favorable direction for the rational design of high-performance Cu-based oxygen carriers in chemical looping combustion (CLC) and CuO-containing catalysts in selective catalytic reduction (SCR). This study aims to investigate the reaction mechanisms of nitrogen-containing species using density functional theory (DFT) calculations. The potential dehydrogenation pathway is identified as NH3* → NH2* + H* → NH(1)* + 2H* → N(2)* + 3H*, and the rate-determined step is the NH2* dehydrogenation. Additionally, we consider 10 dominating elementary reactions for the formation of N2, NO, NO2 and N2O; two skeletal schemes of the NH3 oxidation under low or high temperature conditions are then proposed. Under the low temperature condition of SCR, the majority of gaseous N2 comes from the Eley–Rideal reaction between NH2* fragment and gaseous NO, while the lateral recombination of N* to form N2 might play a more crucial role under the high temperature condition of CLC. The high temperature and surface adsorbed oxygen provide positive impacts on the yield of gaseous NO and NO2, respectively. Finally, the effects of O2 and H2O on the fate of nitrogen during heterogeneous reactions have also been determined.