Synthesis of MFI zeolites with hierarchical porosity by dry-gel conversion

Abstract

Dry-gel conversion (DGC), which directly converts zeolite gel into crystals by vapor, is considered a promising method for reducing amounts of zeolite precursors and easily controlling crystallization. Synthesis of MFI zeolites employing the DGC method with different amounts of tetrapropylammonium bromide (TPABr) and sodium hydroxide (NaOH) was studied to investigate the effect of TPABr and NaOH on the crystallization of MFI zeolite, with the optimal condition for synthesis found to be 0.05625 for both NaOH/SiO₂ and TPABr/SiO₂. Additionally, carbon black (CB) was added onto the MFI zeolite precursor gel as a hard template to generate mesopores into zeolite frameworks. The resultant MFI zeolite with CB synthesized by the DGC method showed mesoporosity, with pore size distribution similar to the particle size of CB. However, the conventional hydrothermal method could not generate mesopores in MFI zeolite due to the separation of zeolite crystals from CB templates during crystallization.