(80d) Elucidating Complex Mechanisms Underlying Heteroatom-Incorporated Zeolite Crystallization

Zeolites are porous aluminosilicates widely used in commercial processes. Controlling the synthesis of zeolites to attain desired physicochemical properties is often challenging owing to their complex growth media and elusive crystallization mechanisms. A subject that has been gaining increased attention is the design of zeolites where aluminum is replaced by heteroatoms. Moreover, metals can be incorporated as inorganic structure-directing agents (ISDAs) or growth modifiers as alternative methods to alter the composition of zeolites. Determining the effects of metals on zeolite crystallization is nontrivial. Syntheses involve the formation of diverse precursors that evolve over the course of nucleation and growth. In this presentation, we will discuss the use of in situ high temperature atomic force microscopy (AFM) to examine zeolite surface growth at a near molecular level. This technique has been used to investigate the growth of several zeolite crystal structures wherein we have demonstrated that zeolite crystallization occurs by nonclassical pathways, such as crystallization by particle attachment, as well as classical layer-by-layer growth via monomer incorporation. AFM has proven to be a powerful tool for elucidating the complex mechanisms of zeolite crystallization.

The majority of in situ AFM investigations have focused on (alumino)silcates. Here we will highlight our recent studies of zeolites faujasite (FAU) and chabazite (CHA), which are commercialized zeolites heavily utilized in catalytic processes. We will present our recent findings on the effects of metals (e.g., zinc) on FAU surface growth [1]. Bulk crystallization experiments have revealed that zinc stabilizes FAU crystallization and prevents interzeolite transformations to more thermodynamically stable structures [2]. In this presentation, we will discuss our investigation of Zn-FAU growth using in situ AFM to explore the inhibitory effect of metal incorporation. These studies have been expanded to syntheses of CHA where we have observed organic-free methods of preparation using cooperative ISDAs accelerate crystallization beyond methods employed in conventional processes. These results highlight the important role of solvated ions in stabilizing particular zeolite structures and dramatically increasing rates of crystallization

References:

[1] Mallette et al., "Heteroatom manipulation of zeolite crystallization: stabilizing Zn-FAU against interzeolite transformation." JACS Au 2 (2022): 2295-2306

[2] Parmar et al., "Direct synthesis of highly siliceous ZnO-FAU zeolite with enhanced performance in hydrocarbon cracking reactions." ACS Materials Letters 5.1 (2022): 202-208

[3] Mallette et al., "Highly efficient synthesis of zeolite chabazite using cooperative hydration-mismatched inorganic structure-directing agents." Chemical Science 15.2 (2024): 573-583