Physicochemical and textural characterization of vanadium–magnesium mixed oxides (original) (raw)

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 3 V 2 O 8 structure with VO 4 tetrahedral units together with periclase phase. Magnesium incorporation with vanadium completely inhibits the formation of V 2 O 5 containing exposed VMO bonds. TPR results showed two peaks located between 500 and 750 jC, corresponding to the reduction of V 5 + species in distorted VO 4 units and to V 5 + species belonging to bulk Mg orthovanadate, respectively. D 2004 Elsevier B.V. All rights reserved.