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 N₂ 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 °C, corresponding to the reduction of V⁵⁺ species in distorted VO₄ units and to V⁵⁺ species belonging to bulk Mg orthovanadate, respectively.