Preparation And Investigation Of Pd/KL Catalyst For Selective Phenol Hydrogenation To Cyclohexanone

It is still a challenge to achieve high activity and high selectivity of cyclohexanone with a single catalyst under mild reaction conditions for selective phenol hydrogenation to cyclohexanone.Nowadays,many researchers are devoted to the development of highly efficient catalysts for this reaction.Due to zeolite L has special channel structure and alkaline site?in the channel must contain K⁺?,we study on synthesis of highly performance KL zeolite and supported Pd catalyst?Pd/KL?,and application in liquid phase selective hydrogenation of phenol to cyclohexanone.The first part of this paper is preparation and optimization of KL zeolite with different properties under different synthesis conditions.In the second part,Pd/KL catalysts were prepared by using KL as support and palladium as active component.The catalytic performance of different catalyst supports and reaction conditions was investigated by selective phenol hydrogenation to cyclohexanone.The main details are as follows:?1?KL zeolites were prepared by hydrothermal crystallization method using LUDOX,aluminum hydroxide and potassium hydroxide as silica source,aluminum source and potassium source,respectively.The obtained zeolites were characterizaed by XRD,SEM,the results showed that the synthesis temperature from 120?to 170?can prepare KL zeolite with good morphology,crystallinity,and its formed by nanoparticles.The particle size decreased with the reduction of the temperature,and pure phase KL zeolite can be formed in a short period of time at 170?.Furthermore,the particle size?length/width?increased with increasing the H₂O content,but with decreasing the SiO₂/Al₂O₃ or the K₂O content.In addition,by adding K₂CO₃into the synthetic solution,it was found that the particle size increased or decreased with changing the K⁺concentration or alkalinity of the solution.?2?Pd/KL catalysts were prepared by using KL with optimal catalytic performance as support,and application in liquid phase selective hydrogenation of phenol to cyclohexanone.The catalytic performance of different supported Pd catalysts was investigated by selective phenol hydrogenation to cyclohexanone.The results showed that compared with other catalysts,such as Pd/NaY,Pd/C,Pd/KL catalyst exhibited excellent catalytic performance under the mild reaction conditions?60?,1 MPa?and suitable catalyst calcination temperature?350??.The conversion of phenol and the selectivity of cyclohexanone could reach about 96.1%and 94.4%.Moreover,further study showed the properties of catalyst support have a great influence on the catalytic performance,stronger alkalinity of catalysts,higher catalytic performance was observed.After the introduction of Cs⁺by using ion exchange method?twice exchange?,the yield of cyclohexanone was still above 95%after 12 h of reaction.The activity of the catalyst metal active center was also different,the catalysts with better dispersibility of Pd nanoparticles could accelerate reaction rate.In addition,comparing the cycle performance of different catalysts,the results showed that supported Pd catalysts prepared by using 3-aminopropyltriethoxysilane?APTES?modified KL as support,have better cycle performance and stronger anti-deactivation ability.