Preparation Of Nickel-based Nanocatalysts And Their Application In Synthesis Of 4-methoxycyclohexanone

Catalytic hydrogenation,which has the characteristic of atomic economy and accords with the development requirements of green chemistry,is one of the most hotspots of research.Catalytic hydrogenation of phenolic compounds can produce alcohols or ketones,which are widely used in the synthesis of medicines,pesticides,dyes and so on.Presently,the hydrogenation of phenolic compounds mainly use palladium or other precious metal based catalysts,which are expensive,and sometimes with low conversion or selectivity.In order to solve these problems,catalytic hydrogenation of 4-methoxyphenol was first carried out over supported nickel-based nanocatalysts.The relationship between the structure and activity or stability of the catalysts was investigated.The oxidation conditions in the synthesis of 4-methoxycyclohexanone were also optimized.Firstly,catalytic hydrogenation of 4-methoxyphenol was carried out over two supported nickel-based catalysts,which were prepared by a deposition-precipitation method and an impregnation method,respectively.The influence of preparation methods and reaction conditions on the activity and stability of the catalysts for hydrogenation was investigated.As demonstrated by X-ray diffraction?XRD?,H2-temperature programmed reduction?H2-TPR?and Transmission electron microscopy?TEM?characterizations,the Ni/Al₂O₃-DP catalyst,prepared by a deposition-precipitation method,exhibited higher dispersion,smaller particle,and stronger interaction between the active particles and the support,compared with the Ni/Al₂O₃-IMP catalyst that prepared by an impregnation method.Then,a series of Ni-X/Al₂O₃ catalysts was prepared and applied in the hydrogenation of 4-methoxyphenol to further improve the activity and stability of Ni/Al₂O₃-DP catalyst.The influence of modified metals and reaction solvents on the activity and stability was mainly investigated.The relationship between the structure and the stability of the catalyst was also discussed.The results showed that the Ni-Mg/Al₂O₃ catalyst have better stability in n-hexane,which can be recycled 27 times without significant loss of its initial activity.Finally,the hydrogenation solutions were further oxidized by hydrogen peroxide catalyzed by the complex of oxalic acid and sodium tungstate to improve the total selectivity for 4-methoxycyclohexanone,the target product.The effect of the oxidation conditions was particularly investigated to achieve better results.It was found that the total selectivity for 4-methoxycyclohexanone can reach 95.3% under the optimum oxidation conditions.The results of this study have a good reference for the green synthesis of ketones.