Anaerobic oxidation of isobutane: I. Catalysis by Cu–V complex oxides

The anaerobic oxidation of isobutane over complex oxide catalysts of the type CunV2Ox (n = 0, 1, 2, 3, and 5) was studied. V2O5, CuV2O6, and Cu2V2O7 showed high oxidizing activity, and Cu3V2O8 and Cu5V2O10 were less active. Over the active catalysts, CO2 was selectively formed only at the beginning of the reaction, and the rate of CO2 formation decreased with reaction time. Isobutene formation became dominant 15–30 min after the start of the reaction. The rates of CO2 and isobutene formation were lower over the less active catalysts, Cu3V2O8 and Cu5V2O10. The catalytic activity at 623 K decreased in the order V2O5 > CuV2O6, Cu2V2O7 ≫ Cu3V2O8, Cu5V2O10. Because CO2 formed at the beginning of the reaction, this system should be applicable for the selective formation of isobutene at appropriate reduction degrees. We concluded that CuV2O6 and Cu2V2O7 should be applicable in a thin-layer reactor, in which isobutane and oxygen are separately supplied to opposite sides of the layer; in such a reactor, the catalyst surface on the isobutane side could be kept at a certain degree of reduction. Using the rate constants for isobutane consumption over Cu2V2O7, we calculated the apparent activation energy for anaerobic oxidation of isobutane to be 87.6 kJ/mol, which agrees well with the reported value for a metal oxide catalyst. XPS analysis indicated that not V5+ but Cu2+ was reduced during the reduction of Cu2V2O7 by H2 at 473 K. Our results indicate that selective oxidation should be achievable over complex oxides that contain highly redox-active metal ions such as Cu2+ if the reaction is carried out in a thin-layer reactor.

Anaerobic oxidation of isobutane was studied using CunV2Ox (n = 0, 1, 2, 3, and 5). V2O5, CuV2O6, and Cu2V2O7 showed high oxidizing activity, but Cu3V2O8 and Cu5V2O10 were less active. CO2 was selectively formed at beginning the reaction but isobutene was formed selectively over deeply reduced Cu2V2O7 after 120 min. These catalysts may be utilized a selective oxidation system using a thin layer.Figure optionsDownload as PowerPoint slide