Hydroalkylation Of Benzene To Cyclohexylbenzene Catalyzed By Hβ Zeolite Supported Non-noble Metals

Cyclohexylbenzene（CHB）is an important chemical intermediate used in the production of phenol,cyclohexanone and other chemical products.Hydroalkylation of benzene to prepare cyclohexyl benzene has the advantages of abundant source of raw material benzene,simple process and low cost,which shows a good prospect for industrial application.In this paper,Hβacidic molecular sieve supported non-noble metals as bifunctional catalyst were used to explore the effect of equilibrium relationship between metal sites and acid sites on the selectivity of alkylation products,which aims at building an efficient and stable catalytic system for benzene hydroalkylation.Firstly,the non-noble metal components Ni,Co and Cu were loaded onto Hβmolecular sieve carrier by means of equal volume impregnation method.The suitable non-noble metal components were screened out and the effect of metal loading on catalytic performance was investigated.The results showed that Cu/Hβhad no catalytic activity in benzene hydroalkylation reaction under the same conditions,and Ni/Hβhad higher catalytic activity than Co/Hβwith the same loading amount.With the increase of amount of Ni loading,the hydrogenation active sites on the catalyst surface increased,the dispersion of Ni decreased,the amount of B acid decreased,the amount of L acid increased,and some new strong acid centers were generated.The dispersion of Ni affects the distance between the hydrogenation active site and alkylation active site,and the formation of strong acid center promotes the side reaction catalyzed by acid.The reaction evaluation results of catalysts with different loading amount showed that the catalytic performance of 2%Ni/Hβwas relatively good.2%Ni/Hβcatalyzed benzene hydroalkylation at 200℃for 3 h at hydrogen pressure of 2.5 MPa,the conversion rate of benzene was 36.7%,the selectivity of cyclohexylbenzene was 71.1%,cyclohexane was 3%,dicyclohexylbenzene was 8.9%.The others were mainly acid catalyzed side reaction products.Secondly,the effects of impregnation,calcination and reduction steps on the acidity of Ni/Hβcatalysts were investigated.The effects of metal dispersion and acid distribution on the catalytic performance of Ni/Hβfor hydroalkylation of benzene were investigated by changing the type of nickel salts,the ratio of silicon to aluminum,the impregnation method,the impregnation solvent and the introduction of metal additives.The results showed that a certain amount of strong acid centers were produced after Ni impregnation,and the amount of strong acid increased after reduction step.The best dispersion of Ni was obtained when nickel nitrate was used as nickel source.The catalyst prepared with Ni（Ac）₂had higher benzene conversion due to more weak acid centers.When the ratio of SiO₂/Al₂O₃of the Hβmolecular sieve was increased from 25 to 40,the specific surface area and pore volume of the catalyst were slightly decreased,and the pore size was increased.The acid strength and acid quantity of the carrier both decreased.The reaction evaluation results showed that the selectivity of cyclohexylbenzene decreased,the selectivity of dicyclohexylbenzene and cyclohexane increased,and the selectivity of acid by-products decreased.Different impregnation methods and solvents directly affect the performance of catalysts.The metal active centers of catalysts prepared by excessive impregnation method mainly distributed on the external surface of the support.The catalyst prepared by constant volume impregnation with H₂O as impregnating solvent had better performance.The introduction of metal additive La reduces the acidity of catalyst and made the dispersion of active component Ni decreased silightly.When La loading amount was 2%,benzene conversion was 37.7%,cyclohexylbenzene selectivity was 66.6%,cyclohexane selectivity was 9.6%,dicyclohexylbenzene selectivity was 15.5%,and other by-products selectivity decreased to 8.3%.Finally,2%Ni/Hβsamples were prepared by direct hydrogen reduction roasting at different reduction temperatures.Compared with the samples reduced by hydrogen after roasting,the active site Ni of catalysts prepared by this method was mainly dispersed on the surface of the carrier,and had little influence on the metal dispersion,while the particle size of Ni decreased.The samples with direct hydrogen reduction calcination at 400℃had more weak acid sites and Lewis acid sites,and the catalytic activity was relatively good.Under the optimized reaction conditions,the initial H₂pressure was 2.5 MPa,the amount of catalyst was4%of the total reaction liquid,and the reaction temperature was 190℃for 3h,the conversion rate of benzene was 38.4%,the selectivity of cyclohexylbenzene was 72.8%,cyclohexane was5.2%,dicyclohexylbenzene was 16.5%,and the selectivity of other by-products was reduced to 5.5%.After the catalyst was reused for five times,the benzene conversion rate decreased to30%and the selectivity of cyclohexylbenzene decreased to 67%.The specific surface area and pore volume of the recovered catalyst decreased significantly,which indicated the obvious problem of pore blocking.