Oxidative dehydrogenation of isobutane over pyrophosphates catalytic systems

Abstract

The catalytic effect of metal pyrophosphates (i.e., Mn2P2O7, Ni2P2O7, CeP2O7, Mg2P2O7, ZrP2O7, Ba2P2O7, V4(P2O7)3 and Cr4(P2O7)3) on the oxidative dehydrogenation of isobutane to isobutene in the reaction temperature range of 400-600°C has been investigated. CeP2O7 gives the highest isobutene yield and selectivity (71%), however, V4(P2O7)3 is the most active catalyst with an isobutane conversion of 33.5% at 500°C. Increasing the reaction temperature results in higher isobutane conversions and lower isobutene selectivity. Reaction by-products are propylene, CO, CO2 and traces of methane and ethylene. No oxygenate products are formed under the used reaction conditions. The sum of selectivities of CO, CO2 and methane is approximately equal to that of propylene, indicating their formation from total oxidation of C1 species accompanying the isobutane crack reactions. Working at temperatures higher than 550°C, the homogeneous gas phase reactions become significant and the oxygen conversion reaches 100%.