Confined metal-acid units for boosting benzene hydroalkylation via efficient activation of key intermediate

Precisely tuning the micro-nanoscale characteristics and synergistic effect of metal-acid sites to regulate the distribution of hydroconversion products are significant but challenging. The protonated carbocation intermediates triggered by tandem reaction on metal-acid region hinder target product formation due to their high reactivity and instability. Supported M/Zeolite hydroconversion catalysts, which often excel in simple synthesis, ease of separation and recyclability. However, they usually consist of sterically unconstrained metal centers which are isolated from acid sites, only providing limited coupling-selectivity to target product. Herein, metal nanoparticles enveloped in acidic zeolite frameworks were developed and used for investigating the process of hydroalkylation of benzene to cyclohexylbenzene. We show that appropriate metal encapsulation comprising adequate efficient metal-acid units successfully avoids the more thermodynamically favorable hydrogenation of cyclohexene to cyclohexane, but steers to alkylation of cyclohexene with benzene to cyclohexylbenzene. This resulted in the highest cyclohexylbenzene yield of 47.7% among the reported work, and surpassed the performance of all supported M/Zeolite catalysts. Experimental and theoretical results supported that the abundant bifunctional metal-acid units enhance the activation frequency and probability of intermediate cyclohexene. This work might provide insights for the integration strategy of dual active site and guidance for the construction of efficient “metal-acid balance” in tandem reactions.