Identification of Metal/Acid Matching Balance over Bifunctional Pd/Hβ toward Benzene Hydroalkylation

Abstract

Bifunctional Pd/Hβ catalysts with uniformly distributed palladium nanoparticles (Pd NPs) were successfully synthesized by a facile methanol-mediated weakly capping growth approach (WCGA). A series of Pd/Hβ catalysts with different metal loadings and Si/Al ratios were used for benzene hydroalkylation, and the identification of metal/acid matching balance over bifunctional Pd/Hβ toward benzene hydroalkylation performance was investigated. The obtained characterization and catalytic activity test results demonstrated that the weak acid site and Lewis acid site have greatly affected the benzene conversion, and the strong acid site as well as Brønsted acid site had more of an effect on the alkylation process. The best hydroalkylation performance was achieved by tuning the acid/metal molar ratio at 22.4 μmol of H + /μmol of exposed Pd with a high cyclohexylbenzene (CHB) selectivity of 51.7% at a benzene conversion of 63.4%, which is the best CHB yield currently obtained for all we know. In addition, the stability of Pd/Hβ catalysts was tested and compared with that prepared by the incipient wetness impregnation (IWI) method, which showed good stability, and no obvious particle aggregation was found. This work provides guidance for exploring the construction of bifunctional catalysts and the balance of metal/acid sites.

Tuning the selectivity of benzene hydroalkylation over PdZn/HBeta catalysts: identification of lattice contraction and electronic properties

“…According to the previous work, 8 beta-supported Pd with Si/Al ratio of 30 has excellent benzene HDA performance. The protonic form of the HBeta were prepared by the ion exchange method.…”

“…Hence, the high conversion and high selectivity could not be achieved simutaneously. 5,[7][8][9][10] In addition, the active metal surfaces with the face-centered cubic and hexagonal symmetry structure binds benzene too strongly to the desorption of CHE, resulting in deep hydrogenation to cyclohexane (CHA). 11 Therefore, precisely controlling the selective production of CHE by modifying the electronic and structural properties of the metallic sites and promoting its subsequent alkylation with benzene instead of further hydrogenation, is of great significance for the whole HDA process reaction.…”

Metal–Acid Bifunctional Catalysts toward Tandem Reaction: One-Step Hydroalkylation of Benzene to Cyclohexylbenzene

“…The benzene hydroalkylation reaction involves the hydrogenation of benzene at metal centers to generate CHE, which subsequently undergoes alkylation with benzene at acid centers for the production of CHB. , Noteworthily, when CHE is formed at the metal site, the competing reactions of deep hydrogenation and alkylation will lead to a low selectivity to a specific product; hence, the high selectivity of CHB requires proper dual-active-site synergy. Recent studies mainly focused on the construction of metal/acid center equilibrium in bifunctional catalysts. − For example, it has been reported that a metal/acid equilibrium range can be achieved by adjusting the Si/Al ratios as well as metal loadings of Pd/Hβ so as to obtain the optimal acid/metal molar ratio .…”

Fabrication of β-Zeolite Nanocrystal Aggregates for the Alkylation of Benzene and Cyclohexene

“…10−16 Liu et al reported that Pd/Hβ exhibited excellent catalytic performance in the hydroalkylation of benzene, with 63.4% conversion of benzene and 51.7% selectivity of CHB obtained by adjusting the metal/ acid matching equilibrium. 8 They also found that using 25% Ni/SiO 2 as the catalyst afforded >99.8% conversion of biphenyl and >96.4% selectivity of CHB after eight cycles of selective hydrogenation of biphenyl to CHB. 6 The hydroalkylation of benzene is not suitable for large-scale industrial production due to the use of expensive noble metal catalysts and high production costs.…”

“…At present, there are three main routes available for the synthesis of cyclohexylbenzene: (i) partial hydrogenation of biphenyl, , (ii) hydroalkylation of benzene, , and (iii) Friedel–Crafts alkylation of benzene with cyclohexene (or cyclohexanol, or halogen cyclohexane). − Liu et al reported that Pd/Hβ exhibited excellent catalytic performance in the hydroalkylation of benzene, with 63.4% conversion of benzene and 51.7% selectivity of CHB obtained by adjusting the metal/acid matching equilibrium . They also found that using 25% Ni/SiO 2 as the catalyst afforded >99.8% conversion of biphenyl and >96.4% selectivity of CHB after eight cycles of selective hydrogenation of biphenyl to CHB .…”