Study On Cu/ZnO/Al₂O₃ Catalyst For Hydrogenation Of Methyl Benzoate To Benzyl Alcohol

Benzyl alcohol is an important organic intermediate in industrial production,which is widely used in coatings,cosmetics,spices,food,medicine and other fields.The benzyl chloride hydrolysis method is a traditional method for preparing benzyl alcohol.However,the preparation process of the method is complicated,and the chlorinated product is inevitably contained in the benzyl alcohol produced.So this limits its wide application in pharmaceutical products,fragrances and food additives.Therefore,the development of green chemical processes for the synthesis of chlorinated benzyl alcohol is a key issue that needs to be solved urgently.In this paper,the research emphasis is to choose methyl benzoate as the raw material for hydrogenation to benzyl alcohol.A series of supported Cu/ZnO/Al₂O₃catalysts were designed and prepared according to the relevant characteristics of the reaction.The catalytic performance of the catalyst for hydrogenation of methyl benzoate to benzyl alcohol was evaluated in a batch high-pressure reactor.The effects of reaction conditions were investigated and optimized.In addition,the structure of the catalyst,active components and the surface acidity were studied by combining the related characterization methods,and the hydrogenation of methyl benzoate was further studied.The specific research work is as follows:?1?Cu/ZnO/Al₂O₃ catalysts were prepared by the coprecipitation method.The catalytic performance of Cu/ZnO/Al₂O₃ catalysts with different Cu/Zn/Al molar ratios?2:0:1²:3:1?was investigated.At the same time,the effects of temperature,H2 pressure and solvent on the catalytic performance were also investigated.The results show that the catalyst exhibits a relatively good catalytic performance when the molar ratio of Cu/Zn/Al is 2:2:1,the calcination temperature is 450°C,the reduction temperature is 250°C,the reaction temperature is 200°C,the H₂ pressure is3 MPa and the rotational speed is 500 r/min.?2?A series of characterization methods were used to study the effects of physical and chemical properties of catalysts on the hydrogenation of methyl benzoate to benzyl alcohol.The effects of the amount of ZnO added to the Cu/Al₂O₃catalyst on the structure,properties,surface acidity and reductivity of the catalyst were investigated.The effects of the amount of ZnO added on the Cu/Al2O3 catalyst on the structural properties,surface acidity and reducibility of the catalyst were investigated.In addition,combined with the relevant experimental results,the catalytic performance in the reaction system of hydrogenation of methyl benzoate to benzyl alcohol is not only related to the metal Cu,but also to the surface acidity of the catalyst.?3?T The effect of catalyst?T=350,450,550,650,750°C?on the hydrogenation of methyl benzoate to benzyl alcohol was studied when the molar ratio of Cu/Zn/Al was 2:2:1 and calcination temperature was T.The results showed that the catalyst exhibited better catalytic activity in a shorter catalytic time when the calcination temperature was 650°C.However,the toluene by-products are more in the reaction process,so in order to further improve the selectivity of benzyl alcohol,we re-optimized the reaction conditions.and the catalyst exhibits the best catalytic activity and selectivity in the reaction of methyl benzoate to hydrogenation of benzyl alcohol.The results show that CZA-2-650 catalyst has good catalytic performance when the reaction temperature is 160°C and the H₂ pressure is 7MPa.The conversion of methyl ester is as high as 93.9%,and the selectivity of corresponding benzyl alcohol is up to 88.0%.The results show that the high dispersion of Cu and the weak acidity of the catalyst surface are the key factors affecting the hydrogenation of methyl benzoate to benzyl alcohol.