Investigations of surface VOx species and their contributions to activities of VOx/Ti0.5Sn0.5O2 catalysts toward selective catalytic reduction of NO by NH3 Original Research Article

High surface area Ti0.5Sn0.5O2 mixed oxide with rutile phase was prepared by a coprecipitation method. The surface area of Ti0.5Sn0.5O2 sample is 76.7 m2 g−1, and VOx/Ti0.5Sn0.5O2 catalysts were prepared using the mixed oxide as support. Characterizations using XRD, FT-IR, LRS, EPR, UV–vis, and TEM demonstrated that vanadium oxide species are highly dispersed on the surface of Ti0.5Sn0.5O2 support when the loading amount of vanadium oxide is ≤1.5 mmol V/100 m2 Ti0.5Sn0.5O2. The dispersed vanadium oxide species form epitaxial-growth layer on the support. In situ FT-IR (NH3 adsorption), combined with NH3-TPD, indicate that the catalyst with vanadium loading amount of 1.5 mmol V/100 m2 Ti0.5Sn0.5O2, which equals to the dispersion capability, possesses a maximum amount of Brønsted acid sites. The 1.5V/Ti0.5Sn0.5O2 catalyst exhibits the best catalytic performance and good resistance to water vapor poison for the “NO + NH3 + O2” reaction, indicating that surface dispersed polymeric vanadium oxide species are the primary active species. A possible reaction mechanism is proposed on the basis of in situ FT-IR results.