The effect of oxygen vacancies and fluorine dopant over adsorption behaviours of V2O5/TiO2 for NO removal

Abstract

Oxygen vacancies are omnipresent on an oxide surface under ambient conditions. The addition of fluorine to V₂O₅/TiO₂ increases the number of oxygen vacancies which can react with O₂ to form a superoxide species. The adsorption of NO and NH₃ on the surface of the F-doped V₂O₅/TiO₂ catalyst is investigated by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Active oxygen species formed on the surface of the catalyst are detected by EPR. At 513 K, the adsorption of NO and NH₃ possibly lies in the vicinity of the surface superoxide radicals, and leads to a change in the nearby electronic structure of these sites. The present results show that F-doping can form more oxygen vacancies on the surface of the catalyst. The oxygen vacancies play an important role in the catalytic conversion of the nitrogen oxides, because they can improve the adsorption and activation of NO, NH₃ and O₂. Additionally, the results of NO-TPD and NH₃-TPD demonstrate that there is a close correlation between the adsorption amounts of NO or NH₃ and the oxygen vacancy concentrations of the catalysts. The stability and lifetime of the surface O₂⁻ anions are directly correlated to the structure of the adsorption site on the catalyst surface and influence the catalytic ability of the catalyst to adsorb reaction gases under the NH₃-SCR operating conditions.