Anaerobic oxidation of isobutane: II. Catalysis by Mg–V complex oxides

Abstract Anaerobic oxidation of isobutane was studied using MgV 2 O 6 , Mg 2 V 2 O 7 and Mg 3 V 2 O 8 . Isobutene, a small amount of CO x , and trace amount of oxygen containing compounds were formed. CO 2 was formed mainly at the beginning of the reaction and decreased with reaction time. Catalytic activity of Mg 2 V 2 O 7 was slightly higher than that of MgV 2 O 6 but the CO x formation over MgV 2 O 6 was more than over Mg 2 V 2 O 7 . Mg 3 V 2 O 8 was the least active. Therefore, Mg 2 V 2 O 7 is the most suitable for oxidative hydrogenation of isobutane under the anaerobic reaction conditions. The equilibration between 16 O 2 and 18 O 2 over MgV 2 O 6 was faster than over Mg 2 V 2 O 7 or Mg 3 V 2 O 8 at 673 K. The rate of equilibration between 18 O 2 and lattice oxygen over MgV 2 O 6 was similar to that over Mg 2 V 2 O 7 , which was faster than over Mg 3 V 2 O 8 . Highest yield of isobutene formation over Mg 2 V 2 O 7 would come from the character of Mg 2 V 2 O 7 , in which mobility of the lattice oxygen is great but surface reaction of isobutane was not so fast. Higher activity for isobutene formation may come from the nature of Mg 2 V 2 O 7 , of which mobility of the lattice oxygen is great but surface reaction of isobutane was not so much fast. Mn, Cr, Fe, Ni and Co can be introduced into Mg 2 V 2 O 7 to give a single phase. Substitution of Co, Cu and Cr for Mg increased the activity of Mg 2 V 2 O 7 for isobutane oxidation and substitution of Ni and Mn scarcely affected the activity but substitution of Fe and Zn decreased the activity. Substitution of all the metal ions slightly increased the isobutene selectivity. MgO, MgV 2 O 4 and Mg 3 V 2 O 8 were observed in the sample after the anaerobic oxidation of isobutane. Cu containing catalyst was reduced to give Cu metal.