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 Mg 3V 2O 8 structure with VO 4 tetrahedral units together with periclase phase. Magnesium incorporation with vanadium completely inhibits the formation of V 2O 5 containing exposed VO bonds. TPR results showed two peaks located between 500 and 750 °C, corresponding to the reduction of V 5+ species in distorted VO 4 units and to V 5+ species belonging to bulk Mg orthovanadate, respectively.