Manufacture of b-Oriented ZSM-5/Silicalite-1 Core/Shell Structured Zeolite Catalyst

A b-oriented MFI shell was formed on the ZSM-5 crystal by pretreating the core using ammonia prior to the hydrothermal synthesis in tetrapropyl ammonium hydroxide medium. The effect of surface structure of the core material on synthesis of MFI/MFI zeolite was investigated. The surface Si-OH groups and amorphous aluminate may play an important role in forming the b-oriented coating. The shell composition changed from high-silica ZSM-5 to silicalite-1 after twice coating synthesis, while the shell coverage increased from 85% to 99%. In toluene methylation, the silicalite-1 shell not only prevented the deactivation of the catalyst, but also enhanced para-selectivity up to 61%.