Abstract: Nitrogen oxides (NO_x), as the main atmospheric pollutants in China, are usually removed through ammonia selective catalytic reduction ((NH₃-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. The influence of CeO₂ modification on structure, surface properties, and low-temperature NH₃-SCR performance of catalyst was systematically studied. Combining first principles calculations, the influence of CeO₂ modification on catalytic mechanism and underlying reasons for reducing activation energy of the reaction was revealed at microscopic level. The results showed that the addition of CeO₂ refined the micro particle size of catalyst, reduced the proportion of main crystalline phase MnO₂, significantly increased the concentration of weak acid sites in the catalyst, increased the proportion of Mn³⁺/Mn and O_α/O, and improved the surface acidity and redox performance of catalyst. The prepared Mn10Ce3 and Mn10Ce5 catalysts with Mn∶Ce molar ratios of 10∶3 and 10∶5 achieved a NO conversion rate of over 98% and good stability at 120 ℃. The addition of CeO₂ dispersed the aggregated MnO_x and reduced the concentration of Mn⁴⁺ distribution, which to some extent hindered the excessive oxidation of NH₃ 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 the reaction pathway, thereby lowering the reaction temperature and improving the low-temperature NH₃-SCR efficiency.

Key words: low-temperature ammonia selective catalytic reduction, CeO₂/MnO_x catalyst, reaction mechanism