Depth investigation of the regulation mechanism of SiO2 on the denitrification performance and sulfur resistance of MnCe/Ti SCR catalyst

The “deep peaking” of coal-fired units presents great challenges for SCR catalysts’ de-NOx activity at wide temperatures. Mn-based catalysts have good de-NOx activity at low temperatures, but their poor sulfur resistance is one of the key issues affecting industrial applications. In this study, the effects of SiO2 doping on the denitrification, sulfur resistance, and physicochemical performance of the MnCe/Ti catalyst were investigated. The results showed that SiO2 improved the de-NOx activity of catalysts at high temperatures and enhanced SO2/H2O resistance at wide temperatures. Under short reaction time conditions, the MnCe/Ti0.9Si0.1 catalyst exhibited the highest NO conversion rate at 400 °C, which was 33% higher than that of the MnCe/Ti catalyst. The NO conversion rates of Si-doped MnCe/Ti catalysts increased rapidly to over 85% (65% of the MnCe/Ti catalyst) as the reaction temperature increased from 200 °C to 250 °C under SO2-containing atmosphere due to the promoting effects of SiO2 on the decomposition of ammonium bisulfate. MnCe/Ti0.7Si0.3 catalyst exhibited the optimal sulfur and H2O resistance, with NO conversion rate higher than 85% with 600 min under SO2/H2O-containing atmospheres. SiO2 inhibited the crystallization of anatase TiO2, and increased the specific surface area to 306.60 m2/g. Additionally, the ratios of Mn4+/Mnn+ and Ce3+/Cem+, and the surface adsorbed oxygen and weak-medium acid amount also increased due to the multiple interactions between the TiO2-SiO2 and Mn/Ce, resulting in the higher de-NOx activity. Compared with the MnCe/Ti catalyst, Si-doped MnCe/Ti catalysts have lower SO2(g) adsorption amount and the sulfation of Mn, and higher SO3(a) desorption performance, resulting in better sulfur resistance at wide temperatures.