Hierarchical core/shell structures with low Si/Al ratio core and continuous shell of high Si/Al ratio ZSM-5 were successfully fabricated by a novel two-step procedure. The final products were characterized by X-ray diffraction and scanning electron microscopy (SEM) methods to determine the morphologies and structural properties of the core/shell nanostructures. It was shown that MFI/MFI core-shell zeolite with high Si/Al shell could be synthesized by using ethylamine rather than TPAOH as organic template under mild hydrothermal conditions. It was achieved by in situ pre-seeding step on ZSM-5 cores and secondary growth of ZSM-5 shell on the modified ZSM-5 crystals, in which the pre-seeding step is a determining strategy during the synthesis. The MFI/MFI core-shell zeolite exhibited much lower deactivation rate than the core zeolite in the toluene methylation reaction.

Key words: zeolite, core-shell structure, synthesis, toluene methylation