Effect of Additives on the Structure and Reactivity of the Surface Vanadium Oxide Phase in V2O5/TiO2 Catalysts

doi:10.1006/jcat.1994.1072

Journal of Catalysis

Volume 146, Issue 2, April 1994, Pages 335-345

https://doi.org/10.1006/jcat.1994.1072 Get rights and content

Abstract

Additives on a 1% V₂O₅/TiO₂ catalyst exhibit two types of interactions with the surface vanadium oxide phase which are observed by Raman spectroscopy under dehydrated conditions and methanol oxidation. Under dehydration conditions, noninteracting additives (WO₃, Nb₂O₅, and SiO₂) coordinate directly to the oxide support without significantly interacting with the surface vanadium oxide phase. Furthermore, the effect of the noninteracting additives on the surface vanadium oxide phase is independent of the order of preparation or precursor used. These noninteracting additives do not affect the methanol oxidation activity and selectivity. Interacting additives (K₂O and P₂O₅), however, directly coordinate with the surface vanadium oxide phase. Addition of K₂O progressively titrates the surface vanadium oxide sites, as observed from the changes in the structure and reactivity of the surface vanadium oxide phase. The effect of P₂O₅ on the surface vanadium oxide phase depends on the concentration and sequence of preparation. Addition of higher concentrations of P₂O₅ forms vanadium phosphate compounds, and results in a change in methanol oxidation activity and selectivity. The addition of 1% V₂O₅ to a 5% P₂O₅/TiO₂ sample, however, does not show any evidence of compound formation, but a part of the surface vanadium oxide phase appears to be titrated. Under ambient conditions, the additives change the pH at point of zero charge of the surface moisture layer which controls the structure of the surface vanadium oxide layer. Thus, depending on the nature of the additive, interacting or noninteracting, the dehydrated structure and reactivity toward methanol oxidation of the surface vanadium oxide phase are affected or remain essentially unchanged, respectively.

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Regular ArticleEffect of Additives on the Structure and Reactivity of the Surface Vanadium Oxide Phase in V2O5/TiO2 Catalysts

Abstract

Regular Article
Effect of Additives on the Structure and Reactivity of the Surface Vanadium Oxide Phase in V₂O₅/TiO₂ Catalysts