N2 Selectivity of NO Reduction by NH3 over MnOx-CeO2: Mechanism and Key Factors

In this work, the novel relationships of N-2 selectivity of NO reduction over MnOx-CeO2 with the gas hourly space velocity (i.e., GHSV) and the reactants' concentrations were discovered. Meanwhile, the mechanism of N2O formation during the low temperature selective catalytic reduction reaction (SCR) over MnOx-CeO2 was studied using in situ DRIFTS study and the transient reaction study. N2O formation over MnOx CeO2 mainly resulted from the Eley-Rideal mechanism (i.e., the reaction between overactivated NH3 and gaseous NO), and the Langmuir Hinshelwood mechanism (i.e., the reaction between adsorbed NH3 species and adsorbed NOR) did not contribute to N2O formation. There was an excellent linear relationship of NO reduction and N-2 formation with gaseous NO concentration. Meanwhile, the reaction order of N2O formation with respect to gaseous NO concentration was nearly 1. However, the reaction orders of NO reduction, N20 formation, and N2 formation over MnOx CeO2 with respect to gaseous NH3 concentration were all higher than 0 due to the adsorption competition between NH3 and NO+O-2. Therefore, N-2 selectivity of NO reduction over MnOx CeO2 remarkably increased with the increase of gaseous NO concentration, and it slightly decreased with the increase of gaseous NH3 concentration.