Influence of the Content and Distribution of Vanadium in the M1 Phase of the MoVTe(Sb)NbO Catalysts on their Catalytic Properties in Light Alkanes Oxidation
Résumé
Phase-pure MoVTe(Sb)NbO mixed oxides, with an M1 structure, and various compositions were prepared, characterized and tested as catalysts for the oxidative dehydrogenation of ethane, in order to study the influence of vanadium content and its distribution over the crystallographic sites on the catalytic properties of these oxides. A linear variation in catalytic activity was observed, as a function of the total vanadium content. This property, which has already been demonstrated for propane oxidation, is shown to remain unaffected by the alkane reaction, the nature of the propene alpha-dehydrogenation elements (Te or Sb), the presence or absence of niobium. The use of XPS to study the surface composition of the catalysts allowed a direct proportionality to be established between the rate of ethane conversion and the V5+ surface content, thus explaining the first correlation observed with bulk V content. This result also emphasizes the fact that a maximum level of intrinsic catalytic activity can be found, and that high vanadium content might be detrimental to this activity, or to the stability of the catalysts. Finally, crystallographic data found in the literature are used to further interpret and discuss these results.