Catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol by oxygen in a solvent-free system over metal-containing ZSM-5 catalysts

Heterogeneous oxidation of liquid cyclohexane by molecular oxygen was carried out over metal-containing ZSM-5 catalysts in a solvent-free system. Among those M-ZSM-5 and M/ZSM-5 catalysts tested, Co-containing ZSM-5 catalysts including Co/ZSM-5 (prepared by ion-exchange and calcination) and Co-ZSM-5 (prepared by ion-exchange and drying) showed the best activity for the oxidation of cyclohexane to cyclohexanone and cyclohexanol. Co/ZSM-5 had almost the same activity as Co-ZSM-5 for the cyclohexane oxidation; however, the leaching of cobalt from Co-ZSM-5 readily occurred. Co/ZSM-5 (calcined) catalyst could achieve about 10 mol% conversion of cyclohexane and 97% selectivity of KA-oil (the mixture of cyclohexanone and cyclohexanol) at 393 K under the pressure of 1.0 MPa O2. In addition, other factors like the temperature, the pressure, the time, various metals, the tert-butylhydroperoxide (TBHP) addition, and the catalyst reuse were investigated carefully. For the titled oxidation, Co/ZSM-5 was recyclable, and could behave as a truly heterogeneous catalyst.