Dehydrocracking of n-Octane to Light Olefins Over Sn-Containing HZSM-5 Composite Zeolite

Achieving a high propylene-to-ethylene ratio alongside an increased yield of light olefins constitutes a primary challenge in the catalytic cracking process for light olefin production. Herein, a Sn-containing HZSM-5 composite zeolite catalyst was constructed via secondary hydrothermal treatment, and the structure-performance relationship in the catalytic cracking of n-octane was systematically investigated. Through atom-planting, Sn is introduced onto zeolite supports, where it interacts with silanol nests and is incorporated into the zeolite framework in a tetrahedrally coordinated manner (Sn(IV)), thereby generating strong Lewis acid sites (LAS). These strong LAS substantially promote the dehydrocracking of n-octane and increase the contribution of bimolecular cracking pathways, which consequently facilitates formation of propylene. Notably, the secondary hydrothermal treatment induces crystallization of new HZSM-5 zeolite onto the Sn-containing HZSM-5, thereby introducing additional Brønsted acid sites (BAS) into the catalyst. The resulting Sn-containing HZSM-5 composite zeolite enables synergistic BAS-LAS catalysis in the dehydrocracking of n-octane, substantially boosting the production of ethylene and propylene.