| The commercial processes of cyclohexane oxidation to cyclohexanone and cyclohexanol generally show many problems, such as low conversion, poor selectivity, complicated technology, high-energy consumption and environmental pollution. So it seems to be of great academic and practical interesting to study and develop highly efficient and environmentally friendly catalytic cyclohexane oxidation processes. The aim of this work is to develop a novel catalyst, which is applied to catalyze selective oxidation of cyclohexane using molecular oxygen (air) as oxidation in liquid-phase. It can not only catalyze the reaction under relatively mild conditions, but also has gotten better catalytic performance.Monodispersed gold nanoparticles with different diameters were successfully synthesized by one step process at room temperature, using HAuCl4 and NaBH4 as the reactants, Na3C6H5O7 as the protecting agent. Characterization results indicate that the as-prepared gold nanoparticles are spherical, and their structure is face center cubic (FCC). Using sodium citrate not only improves monodispersity and stability of Au nanoparticles, but also inhibits the crystal growth, making the particle size is controllable and has a narrow distribution. The peak positions of UV-Vis absorption spectra of colloidal gold shift to the long wavelength as the crystal size increases.Au/SiO2 catalysts were prepared by self-assembly technique. X-ray diffraction (XRD), transmission election microscopy (TEM), atom absorption spectrometry (AAS), ultraviolet-visible spectroscopy (UV-Vis) and nitrogen adsorption/desorption (specific surface area and pore structure analysis) were used to characterize the catalysts. The as-prepared Au/SiO2 catalysts exhibited excellent catalytic performance for selective oxidation of cyclohexane by air in the system without any promoter. The influences of gold content, reaction pressure, reaction temperature, reaction time and calcination temperature of catalyst on the catalytic performance were studied. The conversion of cyclohexane and total selectivity of cyclohexanone and cyclohexanol over the catalyst with 1% gold loading and calcination temperature 500℃, were up to ~10.0% and ~92.0% respectively, under the conditions of reaction temperature 150℃, 3.0 MPa air, reaction time 4 h.Four kinds of simple transition metal complexes were synthesized from tetraphenylporphyrin and transition metal acetate. Results reveal that using UV-Vis and FTIR techniques can determine the valence state and position in the periodic table of the central ions in transition metal porphyrin complexes. The catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol in air as probe reaction was performed without any organic solvent or cocatalyst, and the influences of the amount of metal porphyrin, reaction pressure, reaction temperature and reaction time on the catalytic activity were investigated. It was found that manganese porphyrin had the highest activity, and a maximum 15.4% of cyclohexane conversion and 93.9% selectivity of cyclohexanone and cyclohexanol could be obtained under the suitable conditions.A Mn(Ⅲ) TPP-Au/SiO2 composite catalyst was obtained by immobilizing Manganese(Ⅲ) porphyrin on Au/SiO2 (5% Au loading) using mercaptopyridine with sulfhydryl and pyridyl groups as bridging agent, and it was used for the aerobic oxidation of cyclohexane for the first time. Experimental results show that the activity of the catalyst was higher than that of the pure 5% Au/SiO2 catalyst. Under the suitable conditions of reaction temperature 170℃, 1.5 MPa air and reaction time 6 h, the conversion of cyclohexane and the total selectivity of cyclohexanone and cyclohexanol were 5.39% and 88.7% respectively. In addition, the catalyst can be used repeatedly.
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