Controllable synthesis of core-shell structured ZSM-22 via one-pot approach

ZSM-22 zeolite with core-shell structure was synthesized via a facile one-pot/three-step synthesis route. The crystallinity , morphology, chemical composition , textural and acidic properties of core-shell ZSM-22 were characterized to reveal the formation mechanism in the crystallization process by various techniques, such as XRD , SEM, ICP , FTIR, Py-IR, N 2 -physisorption, and XPS analysis . The as-fabricated core-shell zeolites possess increased specific surface area (>150 ​m 2  ​g −1 ) and decreased Brønsted acid sites (81 ​μmol ​g −1 ). The acid sites located on the external surface of Al-rich zeolite nanocrystals were passivated by the epitaxy growth of high silica ZSM-22 shell. The size (radial dimension tune in the 30–65 ​nm range, axial dimension tune in 100–350 ​nm), structural properties, and acidity property of core-shell ZSM-22 can be adjusted freely by only modulating the alkalinity of the synthetic system in separate steps without adding silicon source and OSDAs. Moreover, it provides excellent tunability and controllability to both the size of products and the thickness of the Si-rich shell. The synthesis method herein may provide a generic platform for the design of other core–shell zeolites with potentially broader applicability.