Catalytic performance of CeO₂-NPs and α-MnO₂ mixed oxides catalysts for low-temperature NH₃-SCR of NO

CeO₂-NPs and α-MnO₂ were prepared separately by hydrothermal method. Then the CeO₂-NPs and α-MnO₂ were mixed by impregnation method to prepare Mn₄CeO_x and MnCe₄O_x catalysts for investigating their SCR catalytic performance. The results indicated that Mn₄CeO_x catalyst had a higher catalytic activity at 75–250 °C than that of MnCe₄O_x catalyst, and the NOx conversion rate of Mn₄CeO_x catalyst reached the highest point at 150 °C, which was nearly 100%. Besides, N₂ selectivity of Mn₄CeO_x catalyst was always slightly higher than that of MnCe₄O_x catalyst in the testing temperature range. H₂-TPR results showed that the redox ability of Mn₄CeO_x catalyst was higher than MnCe₄O_x, which favored the SCR reaction. Meanwhile, NH₃-TPD analysis revealed that Mn₄CeO_x catalyst had higher adsorption peak temperature and stronger surface acidity than that of MnCe₄O_x catalyst, which effectively promoted the NH₃ adsorption and activation. From XPS results, the relative content of Ce⁴⁺ in Mn₄CeO_x catalyst was 83.2%, which was higher than that of MnCe₄O_x catalyst, indicating that Mn₄CeO_x catalyst could generate more Mn⁴⁺, and thus produce more oxygen vacancies, which promoted the SCR reaction. Finally, a reaction mechanism model for low-temperature SCR over MnCe₄O_x and Mn₄CeO_x catalysts was proposed.