The modifications occurring to V2O5 crystallites supported on TiO2 (anatase or rutile) in contact with an o-xylene/air flow at ∼600 K are characterized by detg. the change in the valence state of V through chem. analyses, the variation in the V coordination environment through Fourier transform FT-IR and solid-state 51V NMR spectroscopies, and the modification in the nature and distribution of the V oxide phase by x-ray diffraction and XPS analyses. Results are analyzed with ref. to the time-onstream modifications in the catalytic behavior in o-xylene oxidn. to phthalic anhydride of these catalysts and to the catalytic behavior and physicochem. characteristics of V3O7 supported on TiO2 and of an unsupported partially reduced V oxide phase. On anatase samples, the TiO2 surface is covered homogeneously by a VIV-VV partially hydrated mono- or bilayer. Overlaying this phase a hydrated V3O-like phase (VV:VIV ratio of ∼2:1) is also present as amorphous multilayer patches. In rutile samples, the former phase is no longer present, but instead islands of partially oxidized V2O4 are found together with the same partially reduced V oxide phase as in the anatase samples. Both phases have roughly similar catalytic behaviors and that the role of the TiO2 support both in the anatase and rutile forms is to increase the no. of surface sites, but not to modify their nature which depends only on the modifications occurring during the catalytic tests. [on SciFinder(R)]

Surface structure and reactivity of vanadium-titanium oxide catalysts prepared by solid-state reaction. 2. Nature of the active phase formed during o-xylene oxidation

CENTI, Gabriele;
1991-01-01

Abstract

The modifications occurring to V2O5 crystallites supported on TiO2 (anatase or rutile) in contact with an o-xylene/air flow at ∼600 K are characterized by detg. the change in the valence state of V through chem. analyses, the variation in the V coordination environment through Fourier transform FT-IR and solid-state 51V NMR spectroscopies, and the modification in the nature and distribution of the V oxide phase by x-ray diffraction and XPS analyses. Results are analyzed with ref. to the time-onstream modifications in the catalytic behavior in o-xylene oxidn. to phthalic anhydride of these catalysts and to the catalytic behavior and physicochem. characteristics of V3O7 supported on TiO2 and of an unsupported partially reduced V oxide phase. On anatase samples, the TiO2 surface is covered homogeneously by a VIV-VV partially hydrated mono- or bilayer. Overlaying this phase a hydrated V3O-like phase (VV:VIV ratio of ∼2:1) is also present as amorphous multilayer patches. In rutile samples, the former phase is no longer present, but instead islands of partially oxidized V2O4 are found together with the same partially reduced V oxide phase as in the anatase samples. Both phases have roughly similar catalytic behaviors and that the role of the TiO2 support both in the anatase and rutile forms is to increase the no. of surface sites, but not to modify their nature which depends only on the modifications occurring during the catalytic tests. [on SciFinder(R)]
1991
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/1907315
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