(521cf) Controlling the Crystallite Shape, Size, and Polydispersity of SSZ-13 Using Stabilizing Agent

Tailoring the physical properties of advanced functional materials is crucial to ensure their superior performance for relevant applications. Developing suitable interventions in synthesis requires a detailed understanding of their mechanistic growth pathways. Here, we are investigating the industrially relevant zeolite, SSZ-13, used in the selective catalytic reduction and Methanol to Olefin reaction, among others. Tuning the zeolite crystals' polydispersity, size, and morphology has been a significant challenge for efficient catalyst design. We explored a novel synthetic protocol to develop SSZ-13 crystals with desired attributes. The SSZ-13 crystals were synthesized under dynamic conditions by modulating the growth conditions of the mother liquor to produce crystals with varying size ranges and improved dispersity. To establish better control over the dispersity of particles, we investigated the effect of various salts acting as counter ions or stabilizing agents on the growth dynamics of the mother liquor. The zeolite formed without any modifier showed bimodal distribution where the smaller crystals are ~400 nm in dimension and larger crystals are of the order of 6 µm.

The new synthesis protocol achieved the monodisperse population resulting in bulk crystals of ~500 nm by adding counter ions. Similarly, increased valency helped us obtain a bigger (~2 µm) and yet monodisperse population. With a suitable selection of these stabilizing agents, we modulated particle morphology from cubic shape to polyhedron, which is unique to SSZ-13 synthesis. The use of the synergistic effect of additives further enhanced the potency of the design protocol to achieve a smaller monodisperse particle (~260 nm). Detailed tracking of particle distribution by volume and numbers during crystallization helped us to understand the growth phenomena. To this end, we will showcase the complete library of particles generated using this novel method and mechanistic insights relevant to controlling the polydispersity of crystallites.