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

WO 3 /TiO 2 , V 2 O 5 /TiO 2 and V 2 O 5 -WO 3 /TiO 2 catalysts (1 wt% V, 6 wt% W) were tested in NH 3 -SCR of NO x 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 VO 3+ /VO 2+ 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 W 6+ -O(H)-V 5+ bridges, accelerating surface acidity and V reduction rate. HCHO lowers NO x conversion and N 2 selectivity by reacting with NH 3 to formamide that decomposes to HCN. Formation of formamide is promoted by high surface acidity and redox activity. Water lowers NH 3 conversion by creating Brønsted sites that adsorb NH 3 and suppress oxidation to N 2 O, thereby improving N 2 selectivity.