The Role of Vanadium Oxide on the Titania Transformation under Thermal Treatments and Surface Vanadium States

Vanadia-titania catalyst: II. Qualitative kinetic behavior

“…These finding are in agreement with previous investigations of titania-supported vanadia catalysts [13]. The assignment of the different reduction peaks to specific morphologies of the deposited vanadia cannot be based on TPR profiles alone and requires complementary characterization techniques [8][9][10]. We fbund for the 3. catalysts with a relatively low coverage a broad peak centered at 7 l 3 K with a hydrogen consumption of 0.13 mL, probably due to the presence of VxOy polymeric species.…”

“…We fbund for the 3. catalysts with a relatively low coverage a broad peak centered at 7 l 3 K with a hydrogen consumption of 0.13 mL, probably due to the presence of VxOy polymeric species. For the 7.5 VTi catalyst, with the same weight, the hydrogen consumption volume is 3.2 times higher, and one asymmetric peak was recorded at 853 K with two evident shoulders at 763 and 913 K. This is due to the presence of preferred growth of 2D patches on the titania support (bidimensional VxOy species) as well as crystalline VzO5 phase, according to ESR measurements reported previously [9]. Crystalline bulk vanadia shows a more complex reduction profile, consisting of at least three distinguishable peaks: No spectrum is recorded for the TiO2 in the temperature range up to 1000 K. Above this temperature, several hydrogen consumption features have been recorded, which are associated with substochiometric titania species formation.…”

“…Below theoretical surface monolayer coverage V(IV)species are interacting closely with the support. At higher vanadium loading segregation into bulk VzO5 takes place, thus decreasing interaction with titania support [9]. Coordinated polymeric surface species of vanadia appear to be more active than bulk VzO.~.…”

“…The interaction of oxygen with the catalyst activates oxygen making it more reactive, thus promoting cumene oxidation, apart from the decomposition of hydroperoxide enhanced by the catalyst surface. The presence of partially reduced vanadium oxide species on these catalytic systems [9] will provide sites for adsorption of oxygen thus increasing reactivity. Supported vanadium oxide is a reactive catalyst, perhaps, due to its higher reducibility, which rapidly convert sites for oxygen activation.…”

A Novel Method for Preparing V-doped Titanium Dioxide Thin Film Photocatalysts with High Photocatalytic Activity Under Visible Light Irradiation

“…A. Davidson et al demonstrated the substitution of V 4+ ions in TiO 2 rutile matrix by an ESR technique [26]. Furthermore, it has reported that the isolated mono-oxo vanadyl (not V 2 O 5 ) centers exist on the surface of TiO 2 at low coverage [27,28]. This indicates the strong dispersion ability of the surface of TiO 2 to V ions, which prevents to a certain extent the formation of pure vanadium oxides phases on the newly-grown interface of V-doped TiO 2 thin films in the LPD process.…”