Investigation of Selective Catalytic Reduction of N₂O by NH₃ over an Fe–Mordenite Catalyst: Reaction Mechanism and O₂ Effect

Abstract

We systematically investigated the reaction mechanism and effect of O2 on N2O reduction by NH3 over an Fe–Mordenite (MOR) catalyst. O2 has no inhibitory effect on N2O reduction, and NH3 selective catalytic reduction (SCR) of N2O is superior to NH3 oxidation by O2. We found that the mechanism of NH3 SCR of N2O involves the redox cycle of Fe(III)–OH sites, with Fe(III)–OH reduction by NH3 as the first and rate-determining step. Then N2O is activated at the reduced Fe(II)–OH sites into NO/N or N2/O, reoxidizing the Fe(II)–OH into Fe(III)–OH sites. Next, the NO formed in situ reacts with adsorbed NH2 to form NH2NO, which further decomposes to N2 and water. In addition, some NO may join with O to form NO2, which reacts with NH4+ to produce NH4NO2 and further decomposes to N2 and water. It is possible that under the steady state, N–NO breaking accounts for two-thirds of N2O splitting. The formation of NO intermediates plays a crucial role in this reaction. The structural arrangement of MOR zeolites and the high content of Fe ions provides two proximal Fe ions, that is, Fe(III)···Fe(III) pairs, as the active sites for this N–NO breaking, resulting in the high activity of Fe–MOR.