Hexavalent Metal Cations Doped into Ceria Inducing the Formation of Binuclear Sites Ce³⁺–O–Ce³⁺ to Boost the NH₃-SCR Reaction

The application of selective catalytic reduction with ammonia (NH3-SCR) technology urgently requires catalysts with good performance to control nitrogen oxide (NOx, x = 1, 2) emissions, and structural analysis of such catalysts is necessary and crucial to elucidate the performance of catalytically active sites. Thus, we prepared molybdenum (Mo)-doped CeO2 catalysts to achieve a substantial leap in catalytic performance. The results revealed that the emergence of Ce3+–O–Ce3+ structural units induced by Mo doping achieved the low-energy barrier activation of the NH3 molecule, which transformed the dominant reaction mechanism in the catalytic reaction and thus led to a much better SCR performance. Furthermore, we designed tungsten (W)-doped CeO2 catalysts with the same doping amount as Mo and found that the catalysts exhibited almost the same activity trend as the Mo-doped CeO2 catalysts, which further confirmed the pivotal role of the Ce3+–O–Ce3+ structural units. This study provides a basic theoretical foundation for the design of ceria-based SCR catalysts with efficient catalytic performance for NOx removal.