Selective oxidation of cyclohexane over the bi-functional catalysts Co-MO-TUD-1 (MO = Al2O3, CeO2, NiO, or ZnO)

The selective oxidation of cyclohexane was catalyzed by applying a new series of catalytic materials. The new catalytic series consists of two different active sites incorporated into the three-dimensional siliceous mesoporous TUD-1 material. The first active site was isolated Co(II) ions, while the second active site was nanoparticles of Al2O3, CeO2, NiO, or ZnO. The two active sites were incorporated into TUD-1 by applying one-step synthesis procedure based on sol–gel technology. X-ray powder diffraction (XRD), inductive coupled plasma (ICP), N2 sorption measurements, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and ultraviolet–visible spectroscopy (UV–Vis) were applied to characterize the prepared catalysts. The produced catalytic materials were tested in the liquid phase selective oxidation of cyclohexane without the use of any solvent. The catalytic activity study was performed by using tert-butyl hydroperoxide (TBHP) as an oxidant at 70 °C. The catalytic performance of the prepared materials which containing two catalytic sites was better than the corresponding materials which containing one catalytic site. The best performed material was the material which containing Co and CeO2, in which 14.5% conversion was obtained and the selectivity towards KA oil was 78.8%. Moreover, the production of the intermediate; cyclohexyl hydroperoxide, was very small in the case of bi-functional catalysts compared to the solo-active site catalysts. Finally, the stability of the prepared catalysts was investigated, and it showed that Co and CeO2 active sites are stable and minor leaching from the silica framework was observed.