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 MnO x –CeO 2 with the gas hourly space velocity (i.e., GHSV) and the reactants’ concentrations were discovered. Meanwhile, the mechanism of N 2 O formation during the low temperature selective catalytic reduction reaction (SCR) over MnO x –CeO 2 was studied using in situ DRIFTS study and the transient reaction study. N 2 O formation over MnO x –CeO 2 mainly resulted from the Eley–Rideal mechanism (i.e., the reaction between overactivated NH 3 and gaseous NO), and the Langmuir–Hinshelwood mechanism (i.e., the reaction between adsorbed NH 3 species and adsorbed NO x ) did not contribute to N 2 O formation. There was an excellent linear relationship of NO reduction and N 2 formation with gaseous NO concentration. Meanwhile, the reaction order of N 2 O formation with respect to gaseous NO concentration was nearly 1. However, the reaction orders of NO reduction, N 2 O formation, and N 2 formation over MnO x –CeO 2 with respect to gaseous NH 3 concentration were all higher than 0 due to the adsorption competition between NH 3 and NO+O 2 . Therefore, N 2 selectivity of NO reduction over MnO x –CeO 2 remarkably increased with the increase of gaseous NO concentration, and it slightly decreased with the increase of gaseous NH 3 concentration.