N2 selectivity of Fe–Mn nano-sized catalysts in selective catalytic reduction of ammonia

Fe–Mn nano-sized catalysts show remarkable deNOx activities at low temperatures. However, there is a noticeable disparity in N2 selectivity before and after the addition of Fe element, and the cause of this difference remains unknown. In this study, Fe–Mn nano-sized catalysts were prepared by using the hydrothermal method and their deNOx performance and physicochemical properties were examined. Based on the results of experimental research, the simplified computational models for Fe–Mn nano-sized catalysts before and after introducing Fe element were constructed, namely α-MnO2 (200) surface and Fe–Mn cluster model. The mechanism of N2 generation during the NH3-SCR process of Fe–Mn nano-sized catalysts was thoroughly investigated by using the density functional theory. The Mn sites of Fe–Mn clusters are more favorable for NH3 dehydrogenation reaction compared to the Mn sites on the α-MnO2 (200) surface. Furthermore, compared to the α-MnO2 (200) surface, the NH2NO intermediate tends to undergo dehydrogenation on the Fe–Mn clusters to generate N2. These results will help to gain insight into the microscopic mechanism of Fe–Mn nano-sized catalysts in N2 generation during NH3-SCR and lay the foundation for enhancing the N2 selectivity of Fe–Mn catalysts.