(532dg) Manipulation of Amorphous Precursors to Enhance Zeolite Nucleation

Crystallization in media comprised of amorphous precursors is now widely recognized as a common pathway for the preparation of numerous synthetic, biological, and natural materials that grow by a combination of classical and nonclassical pathways. Amorphous phases can exhibit a wide range of physicochemical properties that may evolve during nucleation and crystal growth. This creates challenges for establishing causal relationships between amorphous precursor properties and their effects on the selection of mechanistic pathways of crystallization and ultimately the composition and colloidal stability of amorphous (alumino)silicate precursors that are prevalent in nanoporous zeolite syntheses.

In this presentation, we evaluate how changes in amorphous precursors effect the rates of crystal formation. We examine differences in crystallization rates when silicate precursors are infused with alkali metals to facilitate the formation of porous crystal structures [1]. We also assess the impact of polymer additives with the potential to reduce precursor colloidal stability [2]. We posit that confined pockets of solution within the interstitial spaces of precursor aggregates play an important role in regulating the rate of zeolite crystallization. Here, we specifically selected three commercially relevant zeolites (mordenite, SSZ-13, ZSM-5) based on their diverse frameworks and methods of preparation. Our findings reveal that alkali infusion significantly reduces the crystallization times for mordenite and SSZ-13, but has little impact on ZSM-5 synthesis. Conversely, we find that polymer addition markedly enhanced rates of crystallization among all three zeolites, suggesting that this method may be a general approach to reduce zeolite synthesis times. Given the relatively high costs associated with commercial zeolite production, identifying new methods to improve the efficiency of hydrothermal synthesis can have significant practical implications beyond the fundamental benefits of developing new routes to tailor nonclassical crystallization.

References:

[1] Li et al., Anie. 57 (2018), 11283-11288

[2] Dai et al., Anie. 61 (2022) e202117742 (1-6)