THE ROLE OF VANADIUM-OXIDE ON THE TITANIA TRANSFORMATION UNDER THERMAL TREATMENTS AND SURFACE VANADIUM STATES

High surface area titania-supported materials prepared from V(IV) prec ursors and calcined at high temperatures have been characterized by Vi s-UV diffuse reflectance, FT Raman, electron spin resonance, and X-ray photoelectron spectroscopies and tested in the partial oxidation of m ethane. Vanadium oxide loading and calcination temperature determine t he structure of V2O5/TiO2 materials. Below theoretical surface monolay er coverage, V(IV) species closely interacting with the support are ob served, Vanadiam oxide species anchor by reaction with titanium oxide surface hydroxyl groups. The V(IV) species are stabilized by interacti on with titania support and further stabilization occurs at high calci nation temperatures by their location in titania (rutile) lattice. Lar ger loadings of vanadium decrease the temperatures required for conver sion of titania (anatase) to titania (rutile), At higher vanadium load ing segregation into bulk V2O5 oxide takes place, thus decreasing inte raction with titania support. This enables a larger population of V(V) species than samples with surface dispersed vanadium oxide species. A lthough partial oxidation of methane is nonselective on titania (anata se), partial oxidation products are observed on titania (rutile)-suppo rted vanadium oxide catalysts, The higher selectivity to partial oxida tion product formaldehyde appears to be related to the high stability of V(IV) cations located on rutile lattice and the absence of V(V) sit es. (C) 1996 Academic Press, Inc.