Heterogeneous catalysis in the liquid-phase oxidation of olefin: V. Oxidation of cyclohexene with supported molybdenum-chromium binary oxide catalyst

Abstract

The oxidation of cyclohexene has been studied in the liquid phase, using as catalysts molybdenum-chromium binary oxides supported on γ-Al 2O 3. The activities were compared by measuring maximum rates of oxygen absorption. The binary system catalysts, in which the formations of chemical compounds were suggested, showed higher activities than the one component systems. The maximum rate was 0.4 order with respect to the catalyst in the region of low catalyst concentration; a much lower order was found for high concentration. There was a critical concentration of catalyst observed, above which the rate of oxidation dropped suddenly. For low catalyst concentration, the maximum rate proved to be first order with respect to the concentration of cyclohexene; a much higher order was observed for high concentrations. The apparent activation energies for oxidation ranged between 12.2 and 14.0 kcal/mol. Product distribution studies suggested that the epoxidation of cyclohexene with cyclohexenyl hydroperoxide proceeded on the molybdenum-rich catalysts and also that cyclohexenone was partly produced by the reaction between cyclohexenyl peroxy radicals and the catalyst. A degenerate chain branching mechanism is proposed in which the catalyst plays an important role in the initiation and termination steps.