Role of V and W Sites in V2O5−WO3/TiO2 Catalysts and Effect of Formaldehyde during NH3−SCR of NOx

Abstract

AbstractWO3/TiO2, V2O5/TiO2 and V2O5−WO3/TiO2 catalysts (1 wt % V, 6 wt % W) were tested in NH3‐SCR of NOx with/without formaldehyde and water and analyzed by in situ FTIR and operando EPR spectroscopy. Activity decreased in the order V−W−Ti>V−Ti≫W−Ti. Two VO3+/VO2+ sites with different redox behavior exist in V‐containing catalysts. Sites I were less active with restricted accessibility by reactants while activity is mainly driven by undercoordinated sites II exposed on the surface. In V−W−Ti, sites II can form W6+−O(H)−V5+ bridges, accelerating surface acidity and V reduction rate. HCHO lowers NOx conversion and N2 selectivity by reacting with NH3 to formamide that decomposes to HCN. Formation of formamide is promoted by high surface acidity and redox activity. Water lowers NH3 conversion by creating Brønsted sites that adsorb NH3 and suppress oxidation to N2O, thereby improving N2 selectivity.