Activities of V₂O₅/TiO₂ and V₂O₅/AI₂O₃ Catalysts for the Reaction of NO and NH³ in the Presence of O₂

The rate of NO-NH3 reaction on V₂O₅/TiO₂ or V₂O₅/AI₂O₃ catalyst under dilute gas condition was markedly increased by the addition of O₂ to 0.7%, and it was almost constant above this concentration. From the data of steady-state catalyst structures at various concentrations of 02 observed by using IR and ESR spectroscopy, the surface V⁵⁺=0 species was found to be the active oxygen species. The reaction rate under excess oxygen condition was measured for catalysts with various contents of V₂O₅ at 160-300°C. When the content of V₂O₅ was low (1, 2, or 5 mol %), V₂O₅/AI₂O₃ showed negligible activity for the reaction, while V₂O₅/TiO₂ exhibited high activity. On the other hand, when the content of V₂O₅ was high (25 or 50 mol %), V₂O₅/AI₂O₃ showed higher activity than V₂O₅/TiO₂. In spite of the significant difference in the rate of the reaction between V₂O₅/TiO₂ and V₂O₅/AI₂O₃, the rate was proportional to the number of surface V=0 bonds on the catalyst for all catalysts employed at any temperature between 160 and 300°C. This indicates a constant activity of the surface V=0 bond for the NO-NH3 reaction.