The selective catalytic reduction of N2O with CH4 on Na-MOR and Na-MFI exchanged with copper, cobalt or manganese

Abstract Cu-MOR, Cu-MFI, Co-MOR, Co-MFI and Mn-MFI were prepared by ion-exchange of Na-MOR or Na-MFI. On all samples, the catalytic activity for N2O decomposition, CH4 + N2O, CH4 + O2, and for the selective catalytic reduction (SCR) of N2O in the presence of O2 was studied in a flow apparatus with GC analysis of reactants and products. Extensively exchanged Cu-MOR and Cu-MFI were active for N2O decomposition. Cu-MOR and Cu-MFI exchanged at about 20% were much less active. All Co-MOR and Co-MFI catalysts, irrespective of the exchange-extent, were active for the same reaction. Mn-MFI was nearly inactive up to 773 K. All catalysts were active for CH4 + N2O. Cu-MOR and Cu-MFI were active for CH4 + O2, whereas Co-MOR, Co-MFI and Mn-MFI were much less active for this reaction. Irrespective of the exchange extent, Cu-MOR, Cu-MFI, Co-MOR, and Co-MFI were active for the SCR of N2O with CH4. Conversely, Mn-MFI was not active for this reaction. Turnover frequency was slightly higher for the various reactions on Me-MFI (Me = Cu or Co) than for the corresponding reactions on Me-MOR. We conclude that on Cu- and Co-zeolites, the SCR of N2O with CH4 consists of two nearly independent reactions: CH4 + N2O prevails at high temperature (673-773 K), and CH4 + O2 at lower temperature. The two reactions involve different catalytically active oxygen species: CH4 + O2 involves a molecular form, and CH4 + N2O a monoatomic form, arising from N2O. Because Co-MOR and Co-MFI are also active for the SCR of NOx, we suggest that these materials are promising catalysts for the simultaneous SCR of N2O and NOx with CH4.