Fabrication of core/shell structure via overgrowth of ZSM-5 layers on mordenite crystals

Hierarchical core/shell structures with mordenite (MOR) core and continuous ZSM-5 (MFI) shell were successfully fabricated by a novel two-step procedure. The mordenite core crystals were ca. 90% enwrapped by polycrystalline ZSM-5 shells. It was achieved by pre-treatment of mordenite cores in organic amine solution and secondary growth of ZSM-5 shell on the modified mordenite crystals. The final products were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), N2 adsorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods to determine the morphologies and structural properties of the core/shell nanostructures. Pre-treatment step was a determining strategy during the synthesis. The growth kinetics of the polycrystalline ZSM-5 shell was further investigated by analysis of the products obtained with different secondary crystallization time. Tiny particles appeared on the mordenite surfaces in the early stage and developed into continuous polycrystalline ZSM-5 films finally, which underwent the so-called “from point to surface” growth process. On the basis of systematic investigation into the formed structures and growth process, a plausible formation mechanism for these particular core/shell composites was proposed. The flexible nature of current approach would allow the synthesis of other couples of core/shell zeolite overgrowth despite the structural or chemical incompatibilities.