The mechanism of the effect of H2O on the low temperature selective catalytic reduction of NO with NH3 over Mn–Fe spinel

Abstract

H₂O showed a notable inhibition on the low temperature selective catalytic reduction (SCR) reaction over Mn based catalysts. However, the mechanism of H₂O effect was not clear. In this work, the mechanism of H₂O effect on the low temperature SCR reaction over Mn–Fe spinel was studied using the transient reaction study and the steady-state kinetic analysis. According to the steady-state kinetic analysis, the reaction kinetic rate constants of NO reduction over Mn–Fe spinel (including the rate constants of N₂ formation through the Eley–Rideal mechanism and the Langmuir–Hinshelwood mechanism, and the rate constants of N₂O formation) in the presence of H₂O and in the absence of H₂O were compared. According to the transient reaction study, the effect of H₂O on the elementary reactions of NO reduction over Mn–Fe spinel through both the Eley–Rideal mechanism and the Langmuir–Hinshelwood mechanism was investigated. The results indicated that the effect of H₂O on the low temperature SCR reaction over Mn–Fe spinel was not only attributed to the competition adsorption of H₂O with NH₃ and NO_x, but also related to the decrease in the oxidation ability and the inhibition of the interface reaction.