The nature of mono- and polynuclear species of V on the TiO2 (anatase) surface formed by solid-state interaction of V2O5 with TiO2 during calcination and/or during catalytic tests in o-xylene oxidn. to phthalic anhydride are discussed with special ref. to the local structure of V sites and their role in the catalytic mechanism. VIV mononuclear sites form by solid-state interaction even in the absence of reducing agents and the amt. of VIV species present may reach a value nearly equiv. to that necessary for complete surface coverage. The VIV species can be reduced to VIII, but not oxidized to VV due to the strong interaction with the TiO2 surface. During catalytic reaction, a bidimensional polynuclear mixed valence species of V with a VIV to VV ratio of 1:2 forms, which is the active and selective phase in o-xylene oxidn. However, the part of the V2O5 crystallites which does not spread on the TiO2 surface also is modified in the reaction environment to form a massive polynuclear hydrated V3O7-like phase, whose physicochem. and reactivity characteristics are analogous to those of the bi-dimensional phase. This massive polynuclear V3O7-like phase also contributes to the catalytic activity in o-xylene oxidn. [on SciFinder(R)]
Mono- and poly-nuclear species of vanadium on the titania (anatase) surface
CENTI, Gabriele;
1991-01-01
Abstract
The nature of mono- and polynuclear species of V on the TiO2 (anatase) surface formed by solid-state interaction of V2O5 with TiO2 during calcination and/or during catalytic tests in o-xylene oxidn. to phthalic anhydride are discussed with special ref. to the local structure of V sites and their role in the catalytic mechanism. VIV mononuclear sites form by solid-state interaction even in the absence of reducing agents and the amt. of VIV species present may reach a value nearly equiv. to that necessary for complete surface coverage. The VIV species can be reduced to VIII, but not oxidized to VV due to the strong interaction with the TiO2 surface. During catalytic reaction, a bidimensional polynuclear mixed valence species of V with a VIV to VV ratio of 1:2 forms, which is the active and selective phase in o-xylene oxidn. However, the part of the V2O5 crystallites which does not spread on the TiO2 surface also is modified in the reaction environment to form a massive polynuclear hydrated V3O7-like phase, whose physicochem. and reactivity characteristics are analogous to those of the bi-dimensional phase. This massive polynuclear V3O7-like phase also contributes to the catalytic activity in o-xylene oxidn. [on SciFinder(R)]Pubblicazioni consigliate
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