(169b) Elucidating the Mechanism of Faujasite Crystallization By in Situ Scanning Probe Microscopy

Zeolites are crystalline aluminosilicates with a wide range of industrial applications. The changing landscapes of the chemical economy coupled with the need for new catalyst materials to process different feedstocks create new opportunities for engineering zeolitic materials. To this end, it is essential to understand their crystallization mechanism(s) as a foundation for designing new synthesis methods to tailor their physicochemical properties. Faujasite (FAU) is one of the most widely used zeolites in industry with applications spanning from ion exchange in detergents to catalysis in the (petro)chemical industry. Despite the tremendous effort to elucidate the mechanisms of FAU nucleation and crystal growth, these pathways are generally not well understood, due in in large part to the inherent complexity of zeolite crystallization and synthesis conditions (i.e., high pH, high temperature, etc.) that render in situ characterization challenging.

In this presentation, we will present in situ atomic force microscopy (AFM) measurements of FAU surface growth under a range of synthesis conditions; and will also compare these results to more recent findings from our group with other zeolites (e.g. zeolite A). Using growth solutions prepared with a range of compositions, we directly visualize the dynamics of FAU surface growth in real time. Our findings reveal an unexpected outcome: growth by solution is limited to a narrow range of compositions wherein the mechanism involves 3-dimensional growth of features instead of the anticipated classical layer-by-layer mechanism. These observations constitute a unique mode of growth among reported cases of nonclassical crystallization, and emphasize the important role of the solid phase (as opposed to the liquid supernatant) in FAU syntheses. These findings have implications for the design of FAU growth media, including secondary growth procedures to prepare layered FAU materials.