Study On Process For Catalytic Hydrogenation Of ?-aryl Ethyl Ketone To ?-aryl Ethanol

Aromatic alcohols are common precursors for the preparation of flavors,fragrances and intermediates of medicine,which play a significant role in fine chemistry.The synthesis of 4-isobutyl phenylethanol?IBPE?from 4-isobutyl phenylethanone?IBAP?is an important step in the clean synthetic ibuprofen process by BHC method.The main sources of aromatic ketones are by-products of many chemical processes.So the catalytic hydrogenation of aromatic ketones to prepare aromatic alcohols are conducive to rational utilization of resources and conforms to the principle of atomic economy.In this work,taking acetophenone?AP?as an example,the catalytic activity of noble metal catalysts supported on activated carbon?Pd/C,Pt/C,Ru/C,Rh/C?,Ni/SiO₂ and Cu/SiO₂ catalysts were compared.It was found that Pd/C had a good catalytic activity in noble metal catalysts.The conversion of acetonphenone?AP??99.43%? and the selectivity of phenylethanol?PhE??97.18%? were high.The adding of NaOH could effectively inhibit the formation of by-products.Ni/SiO₂ catalyst could activate benzene ring and carbonyl group in AP at the same time.Compared with the first two kinds of catalysts,the AP conversation and PhE selectivity were high over Cu/SiO₂ catalyst,?99.2% and 98.5%,respectively?.Besides,simplification of preparation technology and low price were also valuable advantages about Cu/SiO₂ catalyst.Beyond that,Cu/SiO₂ catalysts were prepared by homogeneous precipitation and co-precipitation with different precipitants.These catalysts were characterized by ICP,XRD,H₂-TPR,FT-IR,TEM,NH₃-TPD and XPS.The results showed that the catalysts prepared by co-precipitation method had larger particles,smaller specific surface area,single pore structure and poor hydrogenation performance.The catalysts prepared by homogeneous precipitation method contained rich structure of copper silicate.The catalyst prepared by the steamed ammonia method had lower copper content than the theoretical value.However,the copper content of Cu/SiO₂ catalyst prepared by urea homogeneous co-precipitation method was close to the theoretical value.Besides,the above catalyst had high specific surface area(547.1 m² g^-1),abundant pore structure,good dispersion of the active component,and small particle size of CuO in the catalyst.The hydrogenation performance was good as well.The content of copper and the influence of reaction conditions on the catalytic performance of Cu/SiO₂ were also studied.The results showed that the conversion of AP and the selectivity of PhE were 99.2% and 98.5%,respectively,under the optimal conditions(copper content of 25wt%,reaction temperature of 80?C,reaction pressure of 2.0 MPa,liquid hourly space velocity of 1.0 h^-1and the ratio of hydrogen to hydrocarbon of 20).In addition,the catalyst maintained a high catalytic performance continuously running for 500 h,indicating that Cu/SiO₂ catalyst had high stability.The above catalyst was used for hydrogenation of other aromatic ketones such as 4-isobutyl acetophenone and 4-methoxy acetophenone.Hydrogenation of aromatic ketones with electron-donating group and carbonyl group in?site showed excellent hydrogenation performance.The results showed that the nano Cu/SiO₂ catalyst could be used for the hydrogenation of?-aryl ethyl ketone.Finally,the activity mechanism of Cu/SiO₂ catalyst was investigated.The result showed that the synergistic effect of Cu⁰ and Cu⁺ improved the catalytic performance of Cu/SiO₂ catalyst.Hydrogen was dissociated and adsorbed on the Cu⁰ surface.While Cu⁺ had the function of electrophilic reactivity and could provide lewis acid sites,which polarize and stabilize the carbonyl group in aromatic ketone.So AP had a strong adsorption on Cu/SiO₂ catalyst.The phenyl group in the aromatic alcohol had the effect of electrostatic repulsion with Cu,which caused the rapid desorption of the aromatic alcohol on catalyst surface.So the hydrogrnation products of aromatic ring and ethylbenzene were reduced.According to the above research results,nano Cu/SiO₂ catalyst prepared by urea homogeneous co-precipitation method had high catalytic performance for aromatic ketone hydrogenation,which had a good industrial application prospect.