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

Abstract

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 Mn4CeOx and MnCe4Ox catalysts for investigating their SCR catalytic performance. The results indicated that Mn4CeOx catalyst had a higher catalytic activity at 75–250 °C than that of MnCe4Ox catalyst, and the NOx conversion rate of Mn4CeOx catalyst reached the highest point at 150 °C, which was nearly 100%. Besides, N2 selectivity of Mn4CeOx catalyst was always slightly higher than that of MnCe4Ox catalyst in the testing temperature range. H2-TPR results showed that the redox ability of Mn4CeOx catalyst was higher than MnCe4Ox, which favored the SCR reaction. Meanwhile, NH3-TPD analysis revealed that Mn4CeOx catalyst had higher adsorption peak temperature and stronger surface acidity than that of MnCe4Ox catalyst, which effectively promoted the NH3 adsorption and activation. From XPS results, the relative content of Ce4+ in Mn4CeOx catalyst was 83.2%, which was higher than that of MnCe4Ox catalyst, indicating that Mn4CeOx 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 MnCe4Ox and Mn4CeOx catalysts was proposed.