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

We systematically investigated the reaction mechanism and effect of O-2 on N2O reduction by NH3 over an Fe Mordenite (MOR) catalyst. O-2 has no inhibitory effect on N2O reduction, and NH3 selective catalytic reduction (SCR) of N2O is superior to NH3 oxidation by O-2. 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 N-2/O, receddizing 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 N-2 and water. In addition, some NO may join with O to form NC2, which reacts with NH4+ to produce NH4NO2 and further decomposes to N-2 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)center dot center dot center dot Fe(III) pairs, as the active sites for this N-NO breaking, resulting in the high activity of Fe-MOR.