Preparation Of Efficient Magnesium-based Catalysts And Their Catalytic Performance In Cyclohexanone Oxidation

ε-caprolactone is widely used in the chemical industry.It can be used not only as a solvent,but also as a drug carrier.The biggest application ofε-caprolactone is the preparation of Poly-caprolactone to produce degradable plastics,which is an effective way to solve the increasingly serious"white pollution".At present,the traditional peroxy acid oxidation method is used in the industrial production ofε-caprolactone,which has the problem of high production cost and low output,and does not meet the requirements of green chemistry.Therefore,there is an urgent need to develop new production methods to replace peroxy acid oxidation.In this paper,the H₂O₂ oxidation method is selected as the research object.The oxidant H₂O₂ used is a green oxidant,but it cannot directly oxidize cyclohexanone.It needs a high-efficiency catalyst to catalyze the reaction.Therefore,research and development of efficient catalysts is the key to the industrial production of H₂O₂ oxidation.In this paper,four preparation methods:one-pot method,co-impregnation method,continuous impregnation method,and Mg-MCM-41 impregnation method were adopted to prepare Mg-Zn-MCM-41 catalyst.A series of Mg-Zn-MCM-41 catalysts with different Mg/Zn molar ratios were prepared by one-pot method.The experimental results show that the catalysts prepared by the co-impregnation method and the one-pot method present better catalytic effects.In addition,the experimental results show that Mg₇-Zn₃-MCM-41 under the optimal reaction conditions,the conversion of cyclohexanone reaches 51.5%,and the selectivity toε-caprolactone can reach 86.8%,and the yield ofε-caprolactone can reach 44.7%.Under the same catalytic effect,the amount of used H₂O₂ is reduced.The research show that the introduction of Zn improves the acidity,basicity and hydrophilicity of the catalyst,which is more favorable for the activation of cyclohexanone and H₂O₂.A suitable Mg/Zn ratio（0.7:0.3）formed Mg-Zn-O bonds,leading to suitable interactions,resulting in a higher relative content of Mg on the catalyst surface and a more uniform dispersion.Replacing Mg with an appropriate amount of Zn with a smaller atomic radius makes the catalyst have a better mesoporous structure and a larger specific surface area,which is beneficial to the catalytic reaction.The Mg-Zn-MCM-41 catalyst prepared by the one-pot method present good stability due to the tighter bonding of the metal components and the carrier,and the activity remains good after four cycles.Secondly,in this paper,a more active Mg-Zn-Al-HT catalyst was prepared by introducing Zn on the basis of Mg-Al-HT by co-precipitation method.The experimental results show that under the optimal reaction conditions of Mg₇-Zn₃-Al-HT,the conversion of cyclohexanone can reach 68.2%,the selectivity toε-caprolactone can reach 78.4%,and the yield ofε-caprolactone can reach 53.64%.Compared with the reported literature,the conversion of cyclohexanone is improved,the amount of H₂O₂is reduced,and the cost is reduced.The research show that due to the larger ionic radius of Zn²⁺,the introduction of Zn increases the interlayer spacing of the Mg-Zn-Al-HT catalyst,exposing the active sites and facilitating the entry of the substrate,further improving the catalytic activity.In addition,the content of Zn has a great influence on the hydrophilic properties of the catalyst,and the introduction of Zn will increase the content of Al³⁺on its surface,making the catalyst hydrophobic.The Mg-Al-Zn-HT catalyst can only be recycled twice due to the easy loss of active components in an acidic environment,but the catalytic activity can be recovered after the deactivated catalyst is treated with saturated Mg（OH）₂solution.