The importance of Fe loading on the N2O reduction with NH3 over Fe-MFI: Effect of acid site formation on Fe species

Effect of the loading amount of Fe over ion-exchanged Fe-MFI catalysts on the catalytic performance of N2O reduction with NH3 was investigated, and the results indicated that the turnover frequency (TOF) was almost constant in the Fe/Al range between 0.05 and 0.40. The activity of N2O + NH3 reaction was much lower than that of N2O + CH4 reaction over Fe-MFI (Fe/Al = 0.40), and the preadsorption of NH3 decreased drastically the activity of N2O + CH4 reaction. The temperature-programmed desorption (TPD) of NH3 showed the formation of stronger acid sites on Fe-MFI (Fe/Al = 0.24 and 0.40), and the amount of the acid sites agrees well with the desorption amount O2 in O2-TPD in the low temperature range. The acid sites gave a 3610 cm−1 peak (Brønsted acid) in FTIR observation. These results suggest that the acid sites were formed on the bridge oxide ions in binuclear Fe species. Adsorbed NH3 on the strong acid sites inhibited N2O dissociation, which can be related to the low activity of N2O + NH3 reaction over Fe-MFI with high Fe loading.