Oxidation of Isobutane over Complex Oxides Containing V and Mg_2V_2O_7 Catalysts Partially Substituted by Transition Metal Ions

摘要

The oxidation of isobutane was investigated over various complex vanadium oxide catalysts.Mg_2V_2O_7,MgV_2O_6,and Mg_3V_2O_8 are effective catalysis for isobutene formation at >300 deg C,Cu_2V_2O_7 and CaV_2O_6 showed intermediate activity and BiVO_4 and Ca_7V_4O_(17) were slightly active.The active catalysts had relatively strong acidic sites,and H abstraction from the t-carbon of isobutane 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 Mg_2V_2O_7 crystal lattice formed Mg_(1.8)V_2M_(0.2)O_7 (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_(1.8)V_2M_(0.2)O_7 catalysts.Decreased W/F,increased the selectivity for isobutene to approaching 100%,suggesting that the initial reaction is the oxidative dehydrogenation of isobutane without parallel CO_x formation.