ZSM-5@β Nanozeolite with Complete Shell for Improving Catalytic Cracking of n‑Tetradecane

Through the thoughtful design of core–shell zeolite structures, the performance of zeolites in targeted applications can be optimized. However, the formation of complete zeolite shells, such as complete β zeolite shells, is extremely challenging due to stringent synthesis conditions. In this study, an in situ solid-phase synthesis strategy was developed to prepare ZSM-5@β nanozeolite with a complete shell. Initially, β zeolite seeds were grown on the surface of the core ZSM-5 nanozeolite using a hydrothermal method. Subsequently, a surfactant-directed sol–gel method was employed to form a silica shell that traps the ZSM-5/β nanocomposite. The incorporation of β zeolite seeds addresses the difficulty of β zeolite nucleation within the synthesis system, while the silica shell mitigates the stress caused by the lattice mismatch between the two zeolite phases. Steam-assisted crystallization restricts the long-range diffusion of materials, ensuring that the nucleation, growth, and recrystallization of the shell β zeolite occur in situ on the silica shell. The synthesized ZSM-5@β exhibits a complete zeolite shell, with a ratio of shell nanozeolite particle size to shell thickness of >1, and is rich in intragranular mesopores. During the catalytic cracking of n-tetradecane by ZSM-5@β, the shell and core zeolites work synergistically, significantly enhancing the yield and selectivity of C_2–4 olefins compared to β and physically mixed zeolites. This suggests that the synthesized ZSM-5@β nanozeolite holds promising application potential in the catalytic cracking of macromolecules to produce light olefins.