Effect of SO2 on the Low-Temperature Denitrification Performance of Ho-Modified Mn/Ti Catalyst

Abstract The Ho was employed to modify the Mn/Ti catalyst to enhance its SO2 resistance. The deactivation mechanism of SO2 on the Ho Modified Mn/Ti catalyst were investigated through activity tests and various characterization methods. The results showed that Ho-modified catalyst exhibited superior SO2 resistance compared to Mn/Ti catalyst. The presence of 100 ppm SO2 and 10% H2O would cause a drop of NOx conversion of 0.2HoMn/Ti, while the NOx conversion totally recovered when stopping SO2 and H2O. The characterization results showed that the specific surface area of the catalyst significantly decreased due to the deposited ammonium sulfate salt. Sulfating of Mn atoms led to a decrease of the concentration of Mn4+ and surface adsorbed oxygen, affecting the oxidation of NO to NO2 and the adsorption and activation ability of NH3. In situ DRIFTS results confirmed the strong competitive adsorption between SO2 and NH3, SO2 and NO on the surface of Mn/Ti catalyst, which led to the low catalytic activity. However, for the Ho modified catalyst, SO2 had a weak influence on the adsorption and activation of NO on the catalyst surface, and the adsorption and activation of NH3 was not affected. Therefore, the Ho modified catalyst exhibited a better sulfur resistance.