(169a) Engineering Seed-Assisted Syntheses of Pentasil Zeolite Nanosheets

Zeolites are microporous aluminosilicates that are employed as commercial catalysts in numerous processes. The small pores of zeolites exhibit intrinsic diffusion limitations that pose problems for long-term catalyst activity. Two general approaches have been used to improve mass transport in zeolites: reduction of crystal size (i.e., nanosized zeolites) and introduction of mesopores and/or macropores (i.e., hierarchical zeolites). Seed-assisted synthesis has emerged as an interesting technique not only to accelerate synthesis time and eliminate impurities, but also to produce unique zeolite architectures such as hierarchical self-pillared pentasil (SPP). The latter has been demonstrated by Jain et al. [1], where zeolite seeds are used to generate intergrown pentasil (five-membered rings zeolite; MFI and MEL type) nanosheets without the use of costly organic structure-directing agents.

In this presentation, we will discuss diverse ways to tailor synthesis parameters to concomitantly optimize the physicochemical properties of SPP zeolites. We have elucidated how crystal growth mechanisms and properties are influenced by parameters such as growth solution composition, reagent selection, and the choice of seed crystal. Our findings reveal that pillared nanosheets form within a limited compositional space near the intersection of MFI, MEL, and MOR regions in kinetic phase diagrams. The concentration of the growth medium, adjusted by altering water content, tunes the degree of pillaring and branching. We also show how the judicious selection of the silica source can lead to different morphological features. Collectively, these modifications to synthesis conditions can have significant impact on the kinetics of zeolite crystallization. To this end, we have investigated the efficacy of seed selection and utilizing synergistic combinations of inorganic and organic structure-directing agents to achieve distinct SPP morphologies. Collectively, these studies create a foundation for understanding the effects of different parameters on the synthesis of hierarchical zeolites, which is a rapidly growing area of research with potential to create new paradigms for the use of pentasil zeolite catalysts in various industrial applications.

References:

[1] Jain, R., Chawla, A., Linares, N., Garcia Martinez, J., Rimer, J.D.: “Spontaneous Pillaring of Pentasil Zeolites” Adv. Mater.33 (2021) 2100897