关键词: ZSM-5, SAPO-5, 核壳结构分子筛, 气相转移法

Abstract: The main drawback of the synthesized ZSM-5(core)/AlPO₄-5(shell) binary structure zeolites is large numbers of self-existent AlPO₄-5 zeolites and low acidity of the aluminophosphate molecular sieve. In order to overcome these problems, a series of ZSM-5(core)/SAPO-5(shell) binary structure zeolites were synthesized by vapor-phase transport technique(VPT). Phosphoric acid, pseudoboehmite, and silica sol were used as phosphorus, aluminum and silicon sources, respectively. Triethylamine(TEA) was used as the template. These synthesized samples were characterized by means of X-ray diffraction, scanning electron microscope, X-ray energy dispersive spectroscopy, Fourier transformed infrared spectroscopy and N₂-adsorption, respectively. The results indicate that the synthesized samples belong to binary structure zeolies with a ZSM-5 core and a SAPO-5 shell. The condition for preparing dry-gel and composition of liquid phase affect the crystallization of zeolites. Crystallinity of the synthesized samples increases as the crystallization temperature increased and the crystallization time is protracted. Using VPT technique for the synthesis of binary structure zeolites could reduce the SAPO-5 and composite molecular sieves size, and improve the distribution of SAPO-5 on the ZSM-5 surface. The experiments of heavy oil cracking show that the core/shell binary structure zeolite samples were more favourable for formation of light olefins than the mechanical mixture.

Key words: ZSM-5, SAPO-5, Core-shell binary structure zeolite, Vapor-phase transport technique