Oxidative Dehydrogenation of Propane on γ-Al 2O 3 Supported Vanadium Oxides

γ-Al 2O 3 supported vanadium oxides have been prepared following the continuous adsorption method. The superficial loading and the nature of the precursor species were monitored by varying the pH of the impregnation ammonium vanadate solution. The vanadium coordination was investigated by UV-visible, near infrared, Raman, 51V NMR, and ESR spectroscopies, respectively after drying, calcination and catalytic oxidative dehydrogenation of propane in the 300-450°C temperature range. It is shown that mainly tetrahedral V 5+ cover the alumina surface. Bridging VOV groups from the two-dimensional VO 4 array, occurring at high coverage, are suggested to be the active sites for catalytic oxidation. These species are converted to vanadyl ions (V==O 2+) in a C4 v environment during propane oxidation. A mechanism for the structural transformation is proposed.