DRIFT Study of the SO2 Effect on Low-Temperature SCR Reaction over Fe−Mn/TiO2

SO2 would deactivate the low-temperature SCR (selective catalytic reduction) catalysts and reduce NO removal. In this study, Fe(0.1)−Mn(0.4)/TiO2 prepared by sol−gel method was selected to carry out the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) investigation for revealing the mechanism of the SO2 effect on the SCR reaction. The DRIFT spectroscopy showed that SO2 could be adsorbed on the surface of the catalyst as the bidentate mononuclear sulfate. This type of sulfate would retard the formation of NO complex on the surface of catalyst, resulting in the decrease of NO adsorption. For NH3 adsorption, the adsorption of SO2 had little effect on the coordinated NH3, but would increase the amount of NH4+ because of the formation of new Brønsted acid sites. Therefore, besides the deposition of ammonium sulfates, the competitive adsorption between SO2 and NO on the active sites of the catalysts also contributed to the poisoning effect of SO2 on the SCR reaction. When sulfate was formed on the catalyst, much less NO could be adsorbed and take part in the SCR reaction.