Preparation Of Montmorillonite-based Bifunctional Catalyst And Its Catalytic Performance For Hydroalkylation Of Benzene

Cyclohexylbenzene(CHB)is an important chemical intermediate,which is served as electrolyte additive for Li-ion batteries,a small amount of addition can improve the anti-overcharge performance of the battery without affecting the battery performance,and greatly improve the safety of batteries.The oxidative decomposition reaction of CHB can also produce phenol,which solves the problem of acetone overcapacity in the traditional process of producing phenol by isopropylbenzene,and co-produce another high value-added chemical cyclohexanone.With the development of the production line of oxidative decomposition of CHB to prepare phenol and cyclohexanone and the strong support for the development of energy storage industry,the demand for CHB will be enlarge a lot.At present,there are three main methods to synthesis CHB,including benzene alkylation with cyclohexene,biphenyl hydrogenation and benzene hydroalkylation.The former two methods are limited by high-cost raw material,environmental pollution and unsatisfactory catalytic efficiency.As benzene is a basic petrochemical product,its cheap and readily available property makes the large-scale production of CHB through benzene have great economic value.Hydroalkylation of benzene is a tandem reaction,which requires the synergistic metal-acid bifunction catalyst:partial hydrogenation of benzene at the metal site to cyclohexene,and then alkylation of cyclohexene with benzene at the acid site to CHB.However,at present,there is a problem of the imbalance between metal and acid sites in hydroalkylation bifunction catalysts,leading to relatively low CHB production.Therefore,it is still a challenge to develop hydroalkylation bifunction catalysts with high activity.In order to solve the above problems,based on the montmorillonite(MMT)was rich in surface area and have various modification methods,we prepare two MMT-based bifunctional catalyst in this paper.By adjusting the composition and modification of catalyst to control the surface acitve sites of bifunctional catalyst,the high activity and selectivity of benzene hydroalkylation to CHB can be achieved.Then we research the relationship between acitve sites and performance of catalyst and explain the reaction mechanism,which provide a theoretical for the design and preparation of high active catalyst to synthesis CHB by the hydroalkylation of benzene.The research content and results of this paper are as follows:1.Preparation of MMT-based bifunctional catalyst and its reaction performance for hydroalkylation of benzeneUsing MMT as precursor,hydrogenated metal was anchored on MMT by impregnation-reduction process,and the catalyst was modified by different methods,a series of Pd/MMT-X(X=Al,H,Ti)catalysts were prepared,the Pd/MMT-Al catalysts showed the best catalytic performance of hydroalkylation of benzene.After the optimization of reaction conditions,the yield of CHB can reach to 38.4%,which is the high level in the reported literature.XRD,SEM,BET and other characterization methods confirm that different modification methods have different impacts on the structure of the catalyst,and Py-IR characterization confirm that the catalyst modified by different methods had different strength of acid sites.The correlation between the relative amount of the B acid site and the alkylation performance is found to have a good linear relationship,confirming that the strength of the B acid site greatly affects the alkylation performance of the catalyst.2.Studies on the performance and mechanism of Pd-WO_xcatalyst on yhe benzene hydroalkylationUsing MMT as support,a series of hydroalkylation bifunctional catalyst with different WO_xloadings were obtained by two-step impregnation method.After the process-reinforced,the yield of CHB can reach to 45.1%,which is the highest level in the reported literature.XRD,TEM,Raman and UV-vis spectra show that the polymerization degree of WO_xon the catalyst gradually increased with the increase of WO_xloading.CO-DRIFT and XPS verify electron transfer between Pd and WO_x.A combination investigation based on controlled experiments,in-situ FT-IR,and DFT calculations reveals that the Pd-(WO_x)-H structure serves as bi-active-site for this reaction,which has adjacent Pd sites and B acid sites:benzene is partially hydrogenated at the interface Pd site to form cyclohexene,while the interface B acid active center in Pd-(WO_x)-H promotes the alkylation of cyclohexene with benzene to form CHB.