β@MFI Nanozeolite with Complete Shell for Improving\nCatalytic Cracking of Ethylcyclohexane

Zeolites\nwith a core–shell structure can achieve a synergistic\neffect between core and shell zeolites to enhance the overall functionality\nof the zeolite. However, it is rather challenging to control the growth\narrangement of shell zeolites due to lattice mismatch. In this study,\na synthesis method was proposed for β@MFI nanozeolites via an\nin situ solid-phase synthesis. This strategy relies on the in situ\ncrystallization of MFI zeolite on a silica shell, which is prepared\nusing a surfactant-guided sol–gel approach to trap β\nnanozeolites. The silica shell alleviates the stress caused by the\ndirect lattice mismatch between the two zeolites, while steam-assisted\ncrystallization prevents nucleation in the liquid phase to preserve\nthe shell. The ratio of particle sizes of the shell nanozeolite to\nthe thickness of the shell was used to define core–shell nanozeolites\nwith a complete shell with values >1. By studying the synthetic\nintermediates,\nthe controlled in situ nucleation, growth, and fusion processes of\nshell zeolites on silica shells were demonstrated. Zeolites with a\ncore–shell structure exhibit enhanced hydrothermal stability\nof the core zeolite and improved selectivity toward light olefins\nin catalytic cracking, indicating that the synthesized β@MFI\nnanozeolites can enhance the catalytic cracking reaction performance.