Effect of CeO₂ on Low-temperature Denitrification Performance of MnO<italic> _x </italic> Catalysts and Its Mechanism

Nitrogen oxides (NO x ), as main atmospheric pollutants in China, are usually removed through ammonia selective catalytic reduction (NH 3-SCR) technology to achieve ultra-low emissions. Low-temperature NH3-SCR has gained much attention due to its low energy consumption and cost. However, MnO x -based catalysts generally suffer from insufficient stability and are susceptible to SO2 and H2O poisoning at 120 ℃. To improve the denitrification performance of MnO x -based catalysts under low temperature and lean flue gas conditions, CeO2/MnO x catalysts were prepared by precipitation-calcination decomposition method in this study. Influence of CeO 2 modification on structure, surface properties and low-temperature NH 3-SCR performance of catalyst was systematically studied. Combining first principles calculations, influence of CeO2 modification on catalytic mechanism for reducing activation energy of the reaction was revealed at microscopic level. The results showed that addition of CeO2 refined micro particle size of catalyst, reduced proportion of main crystalline phase MnO2, significantly increased concentration of weak acid sites in the catalyst, augmented proportion of Mn3+/Mn and O α /O, and improved surface acidity and redox performance of the catalyst. The prepared Mn10Ce3 and Mn10Ce5 catalysts achieved a NO conversion rate of over 98%, maintaining stability even at 120 ℃. Addition of CeO2 dispersed the aggregated MnO x and reduced concentration of Mn 4+ distribution, which to some extent hindered excessive oxidation of NH 3 and NO by high valence Mn4+, thereby suppressing N2O formation and improving N2 selectivity of the catalyst. First principles calculations further confirmed that CeO2 modification reduced the activation energy of various intermediate states in reaction pathway, lowering the reaction temperature and improving the low-temperature NH 3-SCR efficiency.