Novel Effect of H2O on the Low Temperature Selective Catalytic Reduction of NO with NH3 over MnOx-CeO2: Mechanism and Kinetic Study

H2O generally shows a strong inhibition on the low temperature selective catalytic reduction (SCR) reaction. However, a novel phenomenon was discovered that the low temperature SCR reaction over MnOx-CeO2 was promoted by H2O. The rate constants of N-2 and N2O formation over MnOx-CeO2 were calculated using the steady-state kinetic study. It showed that both the rate constants of N-2 and N2O formation decreased in the presence of H2O, and the promotion of the SCR reaction over MnOx-CeO2 by H2O was mainly attributed to the inhibition of N2O formation. Meanwhile, the influence of H2O on the elementary reaction of N2O formation over MnOx-CeO2 was studied using the transient reaction study. It indicated that the inhibition of N2O formation over MnOx-CeO2 by H2O was not only attributed to the competition adsorption of H2O with NH3 but also related to the decrease of the oxidation ability of MnOx-CeO2 in the presence of H2O.