Influence of reducibility of vanadium-magnesium mixed oxides on the oxidative dehydrogenation of propane

A series of vanadium-magnesium mixed oxides used for the propane oxidative dehydrogenation were synthesized by combining the impregnation and precipitation methods. Several techniques such as, FTIR, XRD and TPR-H-2 were applied to characterize physicochemical properties. XRD analysis confirms that the V-Mg-O oxides consist of Mg3V2O8 structure with VO4 tetrahedral units together with periclase phase. Magnesium incorporation with vanadium inhibits the formation of V2O5 containing exposed V=O bonds. TPR-H-2 results show two peaks located between 500 and 750 degrees C, which, respectively, correspond to reduction of V5+ species in distorted VO4 units and V5+ species belonging to bulk Mg orthovanadate. The highest activity and selectivity were obtained on catalysts in which isolated VO4 tetrahedral are present. A relationship between reducibility degree of V5+ distorted species (into unities VO4), and catalytic activity was observed. In order to get a higher activity a maximum content of 45% as vanadium oxide. (c) 2005 Elsevier B.V. All rights reserved.