Insight into the alkali metal poisoning sensitivity of V₂O₅-WO₃/TiO₂ catalysts for NO_x abatement via machine learning and in situ Raman spectroscopy

V₂O₅–WO₃/TiO₂ (VWTi) catalysts for NH₃–SCR suffer severe poisoning by alkali metals, especially K, yet the site-specific poisoning mechanism remains unclear. Herein, we elucidate the poison mechanism based on a comprehensive investigation consisting of experimental work, theory calculation, and machine learning, conducted by controlling the VO_x density and K/V ratio. Using a variety of characterization techniques, we found that the SCR activity of a VWTi catalyst was governed by its redox ability and the Lewis acidity dominated by V⁴⁺. The terminal V=O group is a Lewis acid and can adsorb NH₃, while the bridging V–O–V group serves as a redox center, capable of activating NO/O₂. K poisons a VWTi catalyst by attacking the strong Brønsted acids first and then the strong Lewis sites, resulting in a nonlinear progression of activity decline, which is slow initially but accelerates with increasing K accumulation. This phenomenon is especially evident for high–V loading catalysts dominated by the polymeric VO_x species. Density functional theory calculations reveal that K poisons VWTi catalysts by binds K to the terminal V=O sites, forming the chemically inactive KVO₃ compound and weakening the NH₃ adsorption on the neighboring VO_x. This work offers a comprehensive understanding of the site-specific sensitivity of VO_x species to alkali metal poisoning and provides important insights to the deactivation process, which could be used to design practical VWTi catalysts for commercial applications.