Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

Abstract

Diffuse reflection electronic spectroscopy and ESR spectroscopy have been used in a study of the valence and coordination state of vanadium ions in vanadium-alumina and vanadium-magnesia catalytic systems that are effective in the oxidative dehydrogenation of hydrocarbons. On the surface ofγ-Al2O3, vanadium ions in octahedral coordination with the oxygen of the immediate surtoundings may be grouped primarily in clusters of 10–12 ions, providing stability of the V5+ ions against reduction to lower degrees of oxidation, and also providing easy reoxidizability of V4+ at ∼20°C. On the surface of MgO, the vanadium ion clusters that are formed are mostly small — two or three ions. Modification with KOH, K2SO4 and CdO tends to stabilize the V5+ under the reaction conditions in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of nitrobenzene.