The Oxygen Isotopic Exchange Reaction on Vanadium Oxide Catalysts

Author： Doornkamp C. Clement M. Gao X. deo G. Wachs I.E. Ponec V.

ISSN： 0021-9517

Source： Journal of Catalysis, Vol.185, Iss.2, 1999-07, pp. : 415-422

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Abstract

The reactivity of lattice oxygen of vanadium oxide catalysts was studied with the oxygen isotopic exchange reaction. The reactivity of pure V₂O₅is compared with the reactivity of Li_0.33V₂O₅, V₂O₅/TiO₂, V₂O₅/Al₂O₃, V₂O₅/SiO₂, δ-VOPO₄, and (VO)₂P₂O₇. According to their behaviour in the oxygen exchange reaction, two types of vanadium oxide catalysts could be distinguished. The first type of catalysts only showed exchange activity in theR²exchange mechanism and the second type showed activity in both theR¹andR²exchange mechanisms (mechanisms in which, respectively, one or two oxygen atoms of the gas phase molecule are exchanged with oxygen atoms of the metal oxide). The catalysts which belong to the first group are bulk V₂O₅and δ-VOPO₄and the catalysts which belong to the second group are Li_0.33V₂O₅, V₂O₅/TiO₂, V₂O₅/Al₂O₃, V₂O₅/SiO₂, and (VO)₂P₂O₇. If only theR²mechanism is observed then diffusion of lattice oxygen is probably faster than when both theR¹andR²mechanisms are observed. The activity of the supported vanadium oxide catalysts in the oxygen exchange reaction is dependent on the support. The reactivity order is V₂O₅/TiO₂>V₂O₅/Al₂O₃∼V₂O₅/SiO₂.