The solid-state interaction between V2O5 and TiO2 in the 700-800 K range gives rise to the formation of VIV sites even in the absence of reducing agents. A VIV interacting layer covering the entire surface of TiO2 anatase may be created in the absence of any indication of partial transformation to the rutile phase. The nature, amt., and distribution of these VIV sites are characterized by means of titrn. combined with selective extn., reactivity measurements in o-xylene oxidn., evaluation of redox properties, and by x-ray diffraction, XPS, and ESR analyses. The amt. of VIV depends on the crystallog. nature (anatase or rutile) and surface area of the TiO2 and on the conditions of the heat treatment. In the anatase sample the VIV sites can be reduced to VIII, but not oxidized to VV due to the strong interactin with the TiO.infin. surface. In rutile samples part of the VIV may be reduced to VIII, but also oxidized to VV. The remaining VIV sites are present in solid soln. in the rutile matrix and are not accessible to redox reagents. The model of a VIV-modified TiO2 (anatase) surface is discussed with ref. to the problem of surface diffusion of V species on the anatase surface. In TiO2 (rutile)-based samples, due to the competition of the migration of V ions toward the bulk of the rutile with respect to surface diffusion, V2O4-like islands form that are coherently intergrown into the main rutile TiO2 matrix. [on SciFinder(R)]

Surface structure and reactivity of vanadium-titanium oxide catalysts prepared by solid-state reaction. 1. Formation of a vanadium(IV) interacting layer

CENTI, Gabriele;
1991-01-01

Abstract

The solid-state interaction between V2O5 and TiO2 in the 700-800 K range gives rise to the formation of VIV sites even in the absence of reducing agents. A VIV interacting layer covering the entire surface of TiO2 anatase may be created in the absence of any indication of partial transformation to the rutile phase. The nature, amt., and distribution of these VIV sites are characterized by means of titrn. combined with selective extn., reactivity measurements in o-xylene oxidn., evaluation of redox properties, and by x-ray diffraction, XPS, and ESR analyses. The amt. of VIV depends on the crystallog. nature (anatase or rutile) and surface area of the TiO2 and on the conditions of the heat treatment. In the anatase sample the VIV sites can be reduced to VIII, but not oxidized to VV due to the strong interactin with the TiO.infin. surface. In rutile samples part of the VIV may be reduced to VIII, but also oxidized to VV. The remaining VIV sites are present in solid soln. in the rutile matrix and are not accessible to redox reagents. The model of a VIV-modified TiO2 (anatase) surface is discussed with ref. to the problem of surface diffusion of V species on the anatase surface. In TiO2 (rutile)-based samples, due to the competition of the migration of V ions toward the bulk of the rutile with respect to surface diffusion, V2O4-like islands form that are coherently intergrown into the main rutile TiO2 matrix. [on SciFinder(R)]
1991
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/1907321
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