(401e) Engineering Zeolite Syntheses with Inorganic Structure-Directing Agents

Zeolites are composed of negatively charged aluminosilicate frameworks balanced by extra-framework cations ranging from atomic species (e.g., H⁺, Na⁺) to complex organic molecules. During zeolite synthesis, the presence of positively charged ions impacts the organization and crystallization of ordered structures. Often, organic structure-directing agents (OSDAs) are used to tailor zeolite formation, where established heuristics elucidate how the organic structure will influence resultant zeolite properties; however, owing to the hazardous and/or costly nature of OSDAs, it is preferable to use inorganic structure-directing agents (ISDAs). One significant challenge is predicting how ISDA selection will affect synthesis progress. Recent studies^1,2 have demonstrated that tailoring the composition of one or more alkali cations in zeolite synthesis mixtures leads to substantial improvements in control over zeolite phase and/or properties.

In this presentation, we will discuss strategies for tuning the properties of industrially relevant zeolite crystals in the presence of alkali cations (e.g., Na, Li, and K). We systematically explore how altering the composition of zeolite synthesis mixtures can tune zeolite phase selection. These findings substantiate prior claims that decreasing hydrothermal treatment temperature can assist in the generation of smaller zeolite crystals. We also demonstrate how the judicious selection of silica sources can be used as a design parameter to tailor morphological features of zeolite products. Based on these findings, we propose a comprehensive explanation for the nature of interzeolite transformations. Lastly, we demonstrate several facile approaches to optimize the synthesis of zeolites, such as CHA, in organic-free media. Collectively, these results highlight the significant influence of alkali cations and the tremendous potential for using ISDAs to engineer the physicochemical properties of zeolitic materials.

References

[1] Ghojavand, Sajjad, et al. Journal of Colloid and Interface Science 604 (2021): 350-357.

[2] Maldonado, Miguel, et al. Journal of the American Chemical Society 135.7 (2013): 2641-2652.