(196c) Fin-like Zeolite Crystals: A New Class of Hierarchical Catalysts

Zeolites are microporous crystals that have been widely used in catalysis, separation, and adsorption processes owing to their unique properties, such as high surface area, controllable acidity, ion exchange capacity, and shape selectivity. However, the small pore sizes (4 - 7 Å) of typical zeolites can impose severe mass-transfer limitations for internal diffusion. Our group and others have shown that reduced crystal size lessens the rate of catalyst deactivation and can alter product selectivity, e.g. promote the olefin cycle in methanol-to-hydrocarbon (MTH) reactions.¹ Reported methods to reduce diffusion limitations include the preparation of nano-sized zeolites² as well as 2-dimensional materials,³ which often involve expensive multi-step processes. Inspired by conventional fins which enhance interfacial heat transfer, we report the synthesis of fin-like zeolite crystals with improved catalyst performance in MTH reactions.

In this presentation, we will discuss the preparation of hierarchical ZSM-5 and ZSM-11 catalysts using both one-pot and seeded growth methods. Catalytic testing revealed a nearly three-fold decrease in the rate of catalyst deactivation during MTH reaction relative to conventional zeolite crystals. The fin-like zeolite catalysts also promoted the olefins cycle of the hydrocarbon pool (HCP) mechanism. HRTEM and tomography measurements confirmed the rough surface protrusions were well-aligned with the seed crystal, without potential pore blockage. Operando UV-vis spectroscopy of these fin-like crystals revealed the slower evolution of heavy coking species. Collectively, our findings indicate that this novel synthesis method enhanced the performance of ZSM-5 and ZSM-11 catalysts, thus offering an efficient and versatile platform to synthesize optimal zeolite catalysts with reduced diffusion limitations for diverse applications in the (petro) chemical industry.

1. Shen, Y., et al. ACS Catalysis.8 (2018) 11042-11053.
2. Tosheva, L. and V.P. Valtchev; Chem. Mater. 17 (2005) 2494-2513.
3. Jeon, M.Y., et al. 543 (2017) 690.