ZSM-5@β Nanozeolite with Complete Shell for Improving Catalytic Cracking of <i>n</i>-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 C2–4 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.