N₂ Selectivity of NO Reduction by NH₃ over MnO_x–CeO₂: Mechanism and Key Factors

Abstract

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.

MnO supported on Fe–Ti spinel: A novel Mn based low temperature SCR catalyst with a high N2 selectivity

“…As shown in Fig. 11, there was an excellent linear relationship between the rate of NO reduction and gaseous NO concentration, which was consistent with the hint of Equation 26. Meanwhile, the rate of N 2 O formation hardly varied after the increase of gaseous NO concentration (shown in Fig.…”

“…Reactions 10 and 11) can be described as: (25) Our previous study demonstrated that NH 2 on the surface was independent of the concentrations of gaseous NO and NH 3 at the steady state [15,26], which was mainly related to k 9 , the concentrations of NH 3 adsorbed and M n+ on the surface (hinted by Equation 20).…”

“…The kinetic equations of N 2 and N 2 O formation through the Langmuir-Hinshelwood mechanism can be approximately described as: [15,19,26,31].…”

Efficient NH3-SCR removal of NOx with highly ordered mesoporous WO3(χ)-CeO2 at low temperatures

“…On the other hand, optimal combinations of different metal oxides can usually exhibit better SCR efficiency and thermal stability than single oxides. Li et al reported that MnO x -CeO x can improve the SCR activity, H 2 O-resistance and stability by mixing MnO x with CeO 2 [14–16]. Besides, they usually exhibit many interesting properties in energy conversion and storage, catalysis and adsorption [17,18].…”

A novel dual layer SCR catalyst with a broad temperature window for the control of NO emission from diesel bus

“…Although some SCR catalysts for example Mn based catalysts can operate at low temperatures [7], they are extremely restricted in the application due to the higher N 2 O selectivity and the lower NO x conversion at high temperatures [8]. Therefore, there is a strong demand for the SCR catalysts with a broad temperature window [9].…”