Physicochemical and textural characterization of vanadium-magnesium mixed oxides

A series of vanadium-magnesium mixed oxides (V-Mg-O) with a mesoporous structure used for the propane oxidative dehydrogenation was synthesized by combining the impregnation and precipitation methods. Several techniques such as N-2 physisorption, X-ray diffraction (XRD), FTIR and temperature-programmed reduction (TPR) were applied to characterize the textural properties, phase composition and surface oxygen reduction features of the oxides. Textural properties of the calcined V-Mg-O oxides were found very sensitive to chemical composition: bimodal or multimodal pore size distributions was developed, which progressively varied with vanadium content. XRD analysis and infrared (IR) characterization confirm that the V-Mg-O oxides consist of a Mg3V2O8 Structure with VO4 tetrahedral units together with periclase phase. Magnesium incorporation with vanadium completely inhibits the formation Of V2O5 containing exposed V=O bonds. TPR results showed two peaks located between 500 and 750 degreesC, corresponding to the reduction of V5+ species in distorted VO4 units and to V5+ species belonging to bulk Mg orthovanadate, respectively. (C) 2004 Elsevier B.V. All rights reserved.