In-Situ Reduction Of Phenol To Cyclohexanone With Hydrogen From Aqueous-Phase Reforming

Cyclohexanone is an important petrochemical material which is widely used in medicine,paint,dyes and other fine chemicals,and it is an important intermediate in the production of nylon.Both the endothermic aqueous-phase reforming of methanol for hydrogen generation and the exothermic hydrogenation of phenol to cyclohexanone are performed over the same type of catalyst under the close conditions of temperature and pressure.In the present work,a novel method of liquid-phase in-situ hydrogenation of phenol to cyclohexanone was proposed,in which the active hydrogen came directly from the aqueous-phase reforming of methanol.A series of Pd/Al₂O₃ catalysts modified with different metals were prepared by incipient wetness impregnation method.Liquid phase in-situ hydrogenation of phenol to cyclohexanone as a model reaction was employed to characterize the catalytic performance of the prepared catalysts,and the physical and chemical properties of the catalyst modified with different metals were explored.The performance of the Ba-Pd/Al₂O₃ catalysts in the "phenol+methanol+water" system was explored.The effects of reaction conditions,such as the additive amount of barium,reaction temperature,phenol concentration and the ratio of raw materials on the reaction of liquid-phase in-situ hydrogenation of phenol to cyclohexanone have been explored.The results indicated that the presence of barium increased the activity of the Pd/Al₂O₃ highly for the liquid phase in-situ hydrogenation of phenol.The conversion of phenol on the Ba-Pd/Al₂O₃ reached 100%and the yield of cyclohexanone was up to 80%,under optimal hydrogenation conditions:T=493 K;P(Ar)=3.5 MPa;LHSV= 1.33 h^-1;phenol concentration=0.2 mol/L;and the Ba loading is 3wt.%.Additionally,BET,CO chemisorption,XRD,CO₂-TPD,and TEM were employed to investigate the effect of barium on the Pd/Al₂O₃.The results suggested that the presence of barium increased the Pd dispersion and enhanced the basicity of the catalyst highly.Therefore,the barium modified Pd/Al₂O₃ catalysts is effective for the in-situ hydrogenation of phenol for cyclohexanone.