Investigation of the common intermediates over Fe-ZSM-5 in NH-SCR reaction at low temperature by in situ DRIFTS.

The surface species formed in the reaction of NO and NO with pre-adsorbed NH over a Fe-ZSM-5 catalyst (1.27 wt.% Fe, SiO/AlO = 25) at low temperature (140°C) were studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Through using a background spectrum of NH-saturated Fe-ZSM-5, we clearly observed the formation of common intermediates resulting from the reaction of NO or NO + O with pre-adsorbed NH. This presents strong evidence that the oxidation of NO to form surface nitrates and nitrites is the key step for standard SCR at low temperature. In addition, the results suggest that in the SCR reaction at low temperature, the NH ions absorbed on Brønsted acid sites are less active than NH adsorbed on Lewis acid sites related to Fe species.