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