Theoretical insight into H2O impact on V2O5/TiO2 catalysts for selective catalytic reduction of NOx

Abstract

H₂O in flue gas causes the deactivation of V₂O₅/TiO₂ catalysts for selective catalytic reduction (SCR) of NO_x with NH₃ at low temperatures. Developing water resistance requires understanding the theoretical mechanism of H₂O impact on the catalysts. The aim of this work was to clarify the adsorption process of H₂O and the deactivation mechanism induced by H₂O through density functional theory (DFT). The process of H₂O adsorption was studied based on a modeled V₂O₅/TiO₂ catalyst surface. It was found that H₂O had a strong interaction with exposed titanium atoms. Water adsorption on the catalyst surface significantly alters the electronic structure of VO_x sites, transforming Lewis acid sites into Brønsted acid sites. Exposed titanium sites contribute to the decrease of Lewis acidity via adsorbed water. Ab initio thermodynamic calculations show that H₂O adsorption on V₂O₅/TiO₂ is stable at low coverage but less favorable at high coverage. Adsorption of NH₃ is the most critical step for the SCR of NO_x, and the adsorption of H₂O can hinder this process. The H₂O coverage below 15% of adsorption sites could enhance the NH₃ adsorption rate and have a limited effect on the acidity, while higher coverage impeded the adsorption ability of VO_x sites. This work provided electron-scale insight into the adsorption impact of H₂O on the surface of V₂O₅/TiO₂ catalysts, presented thermodynamic analysis of the adsorption of H₂O and NH₃, paving the way for the exploration of V₂O₅/TiO₂ catalysts with improved water resistance.