Preparation of nano-crystalline MFI zeolite via hydrothermal synthesis in water/surfactant/organic solvent using fumed silica as the Si source

Abstract

The preparation of nano-crystalline MFI zeolites (Silicalite-1 and ZSM-5) was carried out by hydrothermal synthesis in a water/surfactant/organic solvent using fumed silica and aluminum sulfate as the Si and Al source, respectively. It was confirmed that the surfactant in the solution affected the nucleation rate of the MFI zeolite. Moreover, the crystal size of the MFI zeolite decreased with increasing surfactant concentration, and nanometer-sized MFI zeolites was obtained at a surfactant concentration of 0.25–0.5 mol/L. The successful preparation of MFI zeolite nanocrystals was ascribed to the stabilization of the MFI zeolite precursors and/or crystals by the adsorbed surfactant on their surface. This method was applied to the preparation of nano-crystalline ZSM-5 zeolite. ZSM-5 zeolite with a crystal size of approximately 50 nm was obtained. The nano-crystalline ZSM-5 zeolite was well-crystallized without octahedral Al atoms in the external framework, and exhibited almost the same acidity as a reference ZSM-5 zeolite.