Abstract：After pre-treated with citric acid solution, the low-silica ZSM-5 crystals were used as core material to fabricate the MFI/MFI core/shell zeolite. The product was characterized by X-ray diffraction, N2 adsorption, scanning electron microscopy, transmission electron microscopy, X-photoelectron spectroscopy and infrared spectroscopy methods to determine the morphology and properties of the core/shell structures. The results showed that the pre-treatment process was crucial to form the shell. Without pre-treating the cores with acid, only twinned crystals were found in the product. While continuous high-silica MFI shell grew on the leached core, and the coverage was 99 %. Further investigation indicated that the silica-rich structure and surface defects which were formed during the dealumination process played an important role in the nucleation and growth of the high-silica shell zeolite. In toluene methylation, the high-silica MFI coating not only enhanced para-selectivity up to 61 %, but also prevented the deactivation of the catalyst.
