Unraveling the Positive Role of WO₃ on Supported Vanadium Catalysts for NO<i>_x</i> Reduction by Operando Spectroscopy

Selective catalytic reduction of nitrogen oxides (NO <i>_x</i> ) by ammonia (NH₃-SCR) over supported vanadium catalysts is a commercial technology for NO <i>_x</i> abatement in combustion exhaust. The addition of tungsten oxide (WO₃) significantly enhances the performance of supported vanadium catalysts (V₂O₅/TiO₂), but the mechanism underlying this enhancement remains controversial. In this study, we employed combined operando spectroscopy (DRIFTS-UV-vis-MS) to investigate the dynamic state of active sites (acid sites and redox sites) on V₂O₅-WO₃/TiO₂ during the NH₃-SCR reaction. Our findings confirmed that WO₃ occupied the TiO₂ surface and reduced the available surface sites for V₂O₅ anchoring, thus promoting the agglomeration of vanadia species. This structural effect significantly improved the reducibility of VO <i>_x</i> on V₂O₅-WO₃/TiO₂ catalysts, consequently enhancing the efficiency for NO <i>_x</i> reduction. The heightened reducibility rendered the reoxidation of vanadia species a rate-limiting step, resulting in the presence of vanadia species in a lower oxidation state (V⁴⁺) during the NH₃-SCR reaction.