Unveiling the Origin of Selectivity in the Selective Catalytic Reduction of NO with NH3 over Oxide Catalysts

This study reveals the origin of thedistinct differencein selectivity of oxide catalysts in the NH3-SCR reaction. The trade-off between activity and selectivity is a century-oldpuzzle in catalysis. In the selective catalytic reduction of NO withNH(3) (NH3-SCR), various typical oxide catalystsexhibit distinct characteristics of activity and selectivity: Mn-basedcatalysts show outstanding low-temperature activity and poor N-2 selectivity, mainly caused by N2O formation, whileFe- and V-based catalysts possess inverse characteristics. The underlyingmechanism, however, has remained elusive. In this study, by combiningexperimental measurements and density functional theory calculations,we demonstrate that the distinct difference in the selectivity ofoxide catalysts is determined by the gap in the energy barriers betweenN(2) formation and N2O formation from the consumptionof the key intermediate NH2NO. The gaps in the energy barriersfollow the order of alpha-MnO2 < alpha-Fe2O3 < V2O5/TiO2, incorrespondence with the order of N-2 selectivity of thecatalysts. This work discloses the intrinsic link between the targetreaction and side reactions in the selective catalytic reduction ofNO, providing fundamental insights into the origin of selectivity.