Qiaohong Zhang

Facile preparation of highly-dispersed cobalt- silicon mixed oxide nanosphere and its catalytic application in cyclohexane selective oxidation

Highly dispersed cobalt-silicon mixed oxide [Co-SiO2] nanosphere was successfully prepared with a modified reverse-phase microemulsion method. This material was characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible diffuse reflectance spectra, X-ray absorption spectroscopy near-edge structure, and N2 adsorption-desorption measurements. High valence state cobalt could be easily obtained without calcination, which is fascinating for the catalytic application for its strong oxidation ability. In the selective oxidation of cyclohexane, Co-SiO2 acted as an efficient catalyst, and good activity could be obtained under mild conditions.

Design of bifunctionalized hexagonal mesoporous silicas for selective oxidation of cyclohexane

Bifunctionalized hexagonal mesoporous silicas, CoPh-HMS, were designed and successfully synthesized by a one-step co-condensation route at ambient temperature. This new material possesses the typical wormhole structure of HMS material. Co2+ ions were incorporated into the frameworks in tetrahedral coordination along with phenyl groups immobilized on the surface, confirmed by a careful spectroscopic (Fourier transform infrared, ultraviolet–visible and 29Si magic-angle spinning nuclear magnetic resonance) study. It was used in the liquid-phase selective oxidation of cyclohexane with molecular oxygen under solvent-free conditions, and showed excellent performance. The results indicate the potential for intentional design of the catalytic environment at a nanometre level with the combination of transition metal incorporation and surface organofunctionalization for mesoporous siliceous materials.

Catalytic activity of Co-HMS modified by organic groups for cyclohexane oxidation

By a one-step co-condensation route using hexadecylamine as the template, various organic groups were successfully immobilized on the surface of hexagonal mesoporous silicas (HMS) along with Co2+ ions incorporated into the framework. The obtained bifunctionalized materials showed high activity in the selective oxidation of cyclohexane. The Co2+ cations were active for oxidation while the organic groups played the key roles in modifying the surface properties. During the oxidation reaction, a phenyl group was found to be better than methyl and propyl groups.