Identification of the Encapsulation Effect of Heteropolyacid in the Si-Al Framework toward Benzene Alkylation

Heterogenization of homogeneous catalysts is along-term pursuit in thefield of catalysis application. Traditionalalkylation of arenes with olefins is usually achieved using acidcatalysts in a homogeneous system, with high catalytic activity andselectivity but difficulty in catalyst separation and reusability.Herein, H3PW12O40(HPW), an excellent homogeneous Bronstedacid catalyst, was anchored to thefaujasite(FAU) cage ofultrastable Y (USY) zeolite with high dispersion (HPW@USY).100% conversion of cyclohexene (CHE) with 99.9% yield ofcyclohexylbenzene was obtained by the alkylation of benzene(C6H6) and CHE (VC6H6/VCHE= 7:1). No obvious deactivation wasobserved over HPW@USY after eight cycles. Our experimentaland theoretical results demonstrated that W-OH exposed in HPW, encapsulated in the FAU cage, is the active site for alkylation.The excellent performance of the HPW@USY catalyst was attributed to the homogeneous chemical environment and stability of theencapsulated HPW. Benefiting from the formation and stabilization of a reaction intermediate (C6H11 center dot) during the CHE activation,the encapsulation effect of HPW in the Si-Al framework played a significant role in the alkylation between CHE and other aromatichydrocarbons with high yields of alkylated products. This work provides a promising heterogeneous catalyst strategy, making thealkylation efficiency of aromatics and olefins as high as that of homogeneous catalysts.