Influence of preparation methods on the physicochemical properties and catalytic performance of MnO -CeO2 catalysts for NH3-SCR at low temperature

This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx-CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3-SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation, hydrothermal treatment, co-precipitation, and a sol-gel technique, were used to synthesize MnOx-CeO2 catalysts. The catalysts were characterized in detail, and an NH3-SCR model reaction was chosen to evaluate the catalytic performance. The results showed that the preparation methods affected the catalytic performance in the order: hydrothermal treatment > sol-gel > co-precipitation > impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content, oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sites and acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalyst formed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalytic performance, and good H2O resistance in NH3-SCR reaction. This was attributed to incorporation of Mnn+ into the CeO2 lattice to form a uniform ceria-based solid solution (containing Mn-O-Ce structures). Strengthening of the electronic interactions between MnOx and CeO2, driven by the high-temperature and high-pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment-friendly route to synthesizing low-temperature denitrification (deNOx) catalysts.