INFLUENCE OF THE NATURE AND CONTENT OF SEVERAL ELEMENTS OF MoVTe(Sb)NbO CATALYSTS ON THEIR CATALYTIC PROPERTIES.

摘要

Among the best catalysts proposed for light alkanes oxidation, the multi-component MoVTe(Sb)NbO catalysts are the most promising. The active phase of these catalysts, called Ml, is a solid solution containing the four metallic cations with V/Mo, No/Mo and Te(Sb)/Mo ratios that can vary, but are most frequently close to 0.3, 0.and 0. respectively (1-10). The influence of the Ml phase composition is difficult to study since pure Ml phase is difficult to obtain; elements such as Mo and V can distribute over several crystallographic sites depending upon the phase content whereas others, like Te or Sb, can be present in substoichiometry and can exhibit several oxidation states (10). While these variations do not alter the crystal structure, they may affect the activity and selectivity of the catalyst. Vanadium in one or several of these sites has been described as involved in the activation of the alkanes molecules. A better understanding of the impact of the composition of the phase and the corresponding elemental distribution is of interest as it will define the active sites or modify their environment and consequently their catalytic properties. The aim of this work was to contribute to this understanding; pure Ml phase with various compositions were studied as catalyst in the oxidative dehydrogenation (ODH) of ethane.