| Summary: | The SO2-poisoning on a Cu-supported Ti–Zr mixed oxide catalyst (Cu/Ti0.7Zr0.3O2−δ) in selective catalytic reduction (SCR) of NOx with C3H6 was investigated, and the different effects of SO2 at varying reaction temperatures were clarified by in situ Fourier transform infrared (FTIR) spectroscopy combined with density functional theory (DFT) calculations. In situ FTIR results of the catalyst at low temperatures (150–250 °C) implied that the formation of sulfates on the surface inhibited the activation of NO and C3H6 as well as the reactivity of nitrates and NO2. The weakened capacity of the catalyst toward acetate formation is an important reason for the decline of catalytic activity at low temperatures. At high temperatures (above 275 °C), the negative effect of SO2 on the C3H6 activation to acetate is quite weak. More importantly, the generation of −NCO species is enhanced significantly via the reaction −CN + SO2/SO42– → −NCO, which is confirmed by both in situ FTIR experimental observations and DFT calculations. The promotion in the generation of −NCO species is the primary reason for the elevation of SCR activity at high temperatures.
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