(584eq) Rapid Synthesis and Control of AFI-Type Zeolite Crystallization

Synthesizing phase-pure zeolite materials with controlled morphology, porosity, and framework composition is critical for advancing applications in adsorption, separations, and catalysis. Zeolite SSZ-24 (AFI-type) is particularly attractive due to its large, one-dimensional 10-membered ring channels that offer high diffusivity and shape selectivity. However, its synthesis remains challenging due to slow crystallization kinetics, narrow synthesis windows, and a tendency to form siliceous frameworks that resist heteroatom incorporation. In this presentation, we discuss a comprehensive investigation of AFI crystallization using both seeded and non-seeded hydrothermal synthesis routes. Systematic studies revealed the importance of silica source selection, organic structure-directing agent (OSDA) concentration, and NaOH content in achieving phase-pure AFI within 48 hours in the absence of seeds—significantly faster than multi-week syntheses typically reported. This rapid, seedless route was enabled by the use of colloidal silica which offered optimal particle size and composition when paired with tuned ratios of OSDA/Si and NaOH/Si. Time-resolved analyses using XRD, SEM, TEM and AFM revealed a two-stage growth mechanism: initial nonclassical transformation of an amorphous precursor, followed by a classical layer-by-layer process of crystal surface growth. Seed-assisted syntheses using different zeolite crystal structures as seeds (e.g., CHA, FAU, and AFI) demonstrated distinct nucleation kinetics and selective templating behaviors, which were further supported by computational studies probing interfacial compatibility and energy landscapes. In parallel, the incorporation of heteroatoms (e.g., Al, B, and Ga) into the AFI framework was evaluated. Our findings revealed that Al and Ga promoted the crystallization of competitive phases (e.g., CHA), whereas boron was introduced into the AFI lattice without compromising crystallinity or porosity. Furthermore, textural analysis confirmed that B-AFI retained high micropore volume and BET surface. Overall, this study advances our mechanistic and synthetic insights into AFI crystallization and provides a rational design approach for tailoring its properties for diverse applications.