Oxidation of isobutane over complex oxides containing V and Mg₂V₂O₇ catalysts partially substituted by transition metal ions

The oxidation of isobutene was studied over various complex vanadium oxide catalysts. Mg₂V₂O₇,Mg₃V ₂0₈, and Mg₃V₂0₈ are effective catalysts for isobutene formation at > 300°C. Cu₂V₂O₆ and CaV₂O₆ catalysts showed intermediate activity, and BiVO₄ and Ca₇V₄0₁₇ were slightly active. The active catalysts had relatively strong acidic sites, and H abstraction from the t-carbon of isobutene by acidic site was considered to be the initial and rate-determining step because a linear relationship was observed between the amount of acidic sites and the catalytic activity of the catalysts. The introduction of transition metals into the Mg sites of the Mg₂V₂0₇ crystal lattice formed Mg_1.8V₂M_0.20₇ (M = Mn, Cr, Fe, Co, Ni) catalysts. This substitution significantly promoted the catalytic activity without changing the selectivity for isobutene. Introduction of these transition metals increased the reactivity of lattice oxygen in Mg_1.8V₂catalysts. Decreased W/F increased the selectivity for isobutene approaching it to 100%, which suggests that the initial reaction is the oxidative dehydrogenation of isobutene without parallel COx formation.