(767f) Facile Synthesis of Mesoporous ZSM-5 Without Using Secondary Template

Due to the intrinsic ordered micropore structures and unique catalytic activity, zeolites are extensively used as heterogeneous acid catalysts in crude oil refineries and petrochemical processes. However, the micropore structures and high intrinsic activities frequently lead these materials to be subject to diffusion limitations that restrict reactant accessibility to the active sites on the interior surfaces of zeolites and inhibit the full utilization of zeolite catalysts. Synthesis of hierarchical zeolites with mesoporosity is a proven strategy for reducing the diffusion limitation in zeolite catalysts [1,2]. Current synthesis methods, however, request either utilization of hard templates (e.g. carbon and polymer) or synthesis of complicated surfactants. In this study, we report on one-step synthesis of mesoporous ZSM-5 by precisely controlling formation and self-assembly of the zeolite precursors formed in the initial stage of the crystallization. The synthesized ZSM-5 with a particle size of ~2 μm possesses a core-shell structure with a core comprising 30-50 nm nanocrystals and a continuous shell formed by stacking of coffin-shape crystals of ~100 nm. The properties and pore structures of the synthesized mesoporous ZSM-5 were characterized by secondary electron microscope, high-resolution transmission electron microscope and N₂ adsorption/desorption techniques. Disordered mesopores with a broad distribution were located within the core, and formed by random assembly of the aggregates. The formation of zeolite precursors, their assembly and the evolution of mesopores within the formed ZSM-5 samples can be precisely tailored by the Si/Al ratio and silicon source used in the synthesis. The synthesis approach provides a facile way to synthesize mesoporous zeolites with controllable catalytic properties.

[1] Fan, W.; Synder, M. A.; Sandeep, K.; Lee, S. P.; Yoo, C. W.; McCormick, A. V.; Penn, L. R.; Stein, A.; Tsapatsis, M. Hierarchical nanofabrication of microporous crystals with ordered mesoporosity. Nature Materials, 2008, 7, 984-991.

[2] Chen, H.; Wydra J.; Zhang, X.Y.; Lee, S. P.; Wang, Z, Fan, W.; Tsapatsis, M. Hydrothermal Synthesis of Zeolites with Three-Dimensionally Ordered Mesoporous-Imprinted Structure. Journal of the American Chemical Society, 2011, 133, 12390-12393.