The solid-state interaction between V2O5 and TiO2 at 400-500° gives rise to the formation of V(IV) sites, even in the absence of reducing agents. A V(IV) interacting layer on the whole surface of TiO2 anatase may be created. In TiO2 rutile-based samples, due to the competition of the migration of V ions toward the bulk of rutile, V2O4-like islands coherently intergrow in the main rutile TiO2 matrix. The in situ evolution of crystallites of V2O5 on the TiO2 surface during interaction with the o-xylene/air reagent mixt. involves, together with their spreading on the TiO2 surface, partial redn. and the formation of an amorphous phase characterized by a V(V):V(IV) ratio of 2:1 and an IR band centered at 995 cm-1. The phase does not form directly by redn., but involves a preliminary redn. to a phase with a lower mean oxidn. state. This reduced V oxide phase is then partially reoxidized to the active phase with a decrease in the formation of the intermediate phthalide and an increase in the selectivity to phthalic anhydride. [on SciFinder(R)]
In-situ evolution of vanadium pentoxide crystallites on titania during calcination and o-xylene oxidation
CENTI, Gabriele;
1990-01-01
Abstract
The solid-state interaction between V2O5 and TiO2 at 400-500° gives rise to the formation of V(IV) sites, even in the absence of reducing agents. A V(IV) interacting layer on the whole surface of TiO2 anatase may be created. In TiO2 rutile-based samples, due to the competition of the migration of V ions toward the bulk of rutile, V2O4-like islands coherently intergrow in the main rutile TiO2 matrix. The in situ evolution of crystallites of V2O5 on the TiO2 surface during interaction with the o-xylene/air reagent mixt. involves, together with their spreading on the TiO2 surface, partial redn. and the formation of an amorphous phase characterized by a V(V):V(IV) ratio of 2:1 and an IR band centered at 995 cm-1. The phase does not form directly by redn., but involves a preliminary redn. to a phase with a lower mean oxidn. state. This reduced V oxide phase is then partially reoxidized to the active phase with a decrease in the formation of the intermediate phthalide and an increase in the selectivity to phthalic anhydride. [on SciFinder(R)]Pubblicazioni consigliate
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