Surface Acidity Modulation Of Metal Oxida Supports And The Performance In Catalytic Hydroalkylation Of Benzene By Loaded Pd-based Catalysts

Cyclohexylbenzene（CHB）is an important fine chemical intermediate that can be used as an anti-overcharge additive in lithium-ion battery electrolytes,a raw material for the synthesis of TFT liquid crystals,and a high boiling point solvent for the preparation of coatings.At the same time,the peroxidation-decomposition reaction of cyclohexylbenzene allows the co-production of phenol and cyclohexanone,avoiding the problems of the acetone surplus caused by the traditional isopropylbenzene oxidation Hock process.The benzene hydroalkylation option,with cheap and easily available substrates,high environmental friendliness and atomic economy,is considered more suitable for the large-scale production of cyclohexylbenzene.Previously,the source of acid sites in hydroalkylation catalysts was mainly based on zeolite catalysts,but they faced technical challenges such as high cost and complex pore structure.Therefore,low-cost,high-activity catalysts for the hydroalkylation of benzene urgently need to be prepared.In this paper,a series of Pd-loaded benzene hydroalkylation catalysts were constructed based on metal oxide support.The catalyst surface hydrogen spillover effect,the modulation of the support surface acidity and the synergistic effect between the components on the catalyst activity were investigated,and the possible reaction mechanism of benzene hydroalkylation was also explored.The main studies are as follows:（1）A series of WO_x-decorated nanostructured ZrO₂supported Pd metal-acid bifunctional catalysts were prepared by a multi-step impregnation method to achieve acidic modulation of the metal oxide support surface by changing the WO_xcontent in the support.Meanwhile,the atomically dispersed metal Pd can induce a hydrogen spillover effect on the catalyst surface.It not only enhances the oxygen vacancy content on the catalyst surface,which facilitates the adsorption of active hydrogen species,but also leads to the in situ transformation of surface Lewis acid to Br（?）nsted acid,which enhances the catalyst alkylation activity.At the same time,the modification effect of WO_xcan effectively regulate the activation behaviour of benzene and cyclohexene on the catalyst surface to achieve suitable adsorption intensity,which finally achieves efficient catalysis for the hydroalkylation of benzene to cyclohexylbenzene.（2）A series of Pd/Nb-W metal-acid bifunctional catalysts with enhanced surface acidity were prepared by a combination of hydrothermal and impregnation methods.A large number of W-O_v-Nb defect structures were constructed on the catalyst surface by Nb doping,which significantly enhanced the activity of the benzene hydrogenation process.At the same time,the doping of Nb significantly enhances the surface acidity of the metal oxide support,introduces more Br（?）nsted acid alkylation active centres,achieves an ideal metal-acid sites equilibrium relationship and effectively reduces the use of the noble metal Pd.In addition,the significant increase in surface acid sites facilitates the adsorption of cyclohexene intermediates and enhances the activity of the alkylation process.The present work provides a new feasible solution for the design of bifunctional catalysts for the hydroalkylation of benzene with enhanced surface acidity.