Facile synthesis of ZSM-5 composites with hierarchical porosity

Abstract

Hierarchically structured composites (TUD-M) with ZSM-5 nanocrystals embedded in a well-connected mesoporous matrix were synthesized by employing only one organic templating/scaffolding molecule (TPAOH). Micro- and mesopores form separately under different synthesis conditions. Both the size of the zeolite crystals and the mesopore size in the amorphous matrix can be tuned. A lower Si/Al ratio results in a slower growth of zeolite crystals and improves the hydrothermal stability of this new type of composite. Solid state NMR reveals that the aluminium species are all tetrahedrally coordinated, and that silicon species condense further during crystal growth. A carbon replica of TUD-M proves that the mesopores are interconnected, and also hints at the similarities between the meso-structures of TUD-M and TUD-1. The scaffolding mechanism at the basis of the mesostructure is not limited to TPAOH. Other zeolite/meso-structure composites could also be synthesized based on the same concept.