Unveiling the Mechanistic Origin of High Efficiency in Selective Reduction of NO by NH3 over Mn–W/CeO2 Catalysts: Sufficient Acidity and Appropriate Reducibility
Achieving remarkable activity in selective catalytic reduction of NO by NH3 (NH3-SCR) over CeO2-based catalysts was crucial for their industrial application but still faces a tough challenge, mainly owing to the insufficient acidity and overoxidation ability. Herein, the surface acidity and reducibility of CeO2 catalysts were finely tuned over Mn–W/CeO2 to efficiently eliminate NO and reveal the mechanistic origin of superior catalytic properties. Systematic surface and structure analyses revealed that Mn3O4 interacted with WO3 species in the possible form of Mn–O–W, which could enhance the dispersion of WO3 over the CeO2 surface. The resulting well-dispersed WO3 increased the concentration of both Brønsted acid sites and strong acid sites, effectively suppressing the generation of inactive nitrates and thus providing abundant catalytically active sites for the adsorption and activation of NH3. Importantly, the electron withdrawal from Mn by W atoms associated with the shortened Mn–O bond distance resulted in the appropriate reducibility over Mn–W/CeO2. Accordingly, the undesirable overoxidation of NH3 was weakened, thereby greatly increasing the high-temperature (250–400 °C) NH3-SCR activity. DFT calculations and detailed in situ DRIFTS analysis demonstrated that both “E–R” and “L–H” mechanisms contributed mainly to this superior performance.
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