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

Heterogenization of homogeneous catalysts is a long-term pursuit in the field of catalysis application. Traditional alkylation of arenes with olefins is usually achieved using acid catalysts in a homogeneous system, with high catalytic activity and selectivity but difficulty in catalyst separation and reusability. Herein, H3PW12O40 (HPW), an excellent homogeneous Brønsted acid catalyst, was anchored to the faujasite (FAU) cage of ultrastable Y (USY) zeolite with high dispersion (HPW@USY). 100% conversion of cyclohexene (CHE) with 99.9% yield of cyclohexylbenzene was obtained by the alkylation of benzene (C6H6) and CHE (VC6H6/VCHE= 7:1). No obvious deactivation was observed over HPW@USY after eight cycles. Our experimental and 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 the encapsulated HPW. Benefiting from the formation and stabilization of a reaction intermediate (C6H11•) 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 aromatic hydrocarbons with high yields of alkylated products. This work provides a promising heterogeneous catalyst strategy, making the alkylation efficiency of aromatics and olefins as high as that of homogeneous catalysts.