(179g) Insights into the Incorporation and Removal of Heteroatoms in Zeolite Catalysts

Metal-incorporated zeolites are promising materials for a broad range of applications owing to their versatility of composition. Optimization of zeolite properties is facilitated by knowledge of their multifaceted crystallization mechanisms, which are more elusive for zeolites prepared by heteroatom incorporation in comparison to their aluminosilicate analogues. The majority of studies examining zeolite crystallization rely on ex situ techniques due to the complex growth media and conditions employed in zeolite syntheses. In this presentation, we will discuss pioneering methods developed in our group to probe zeolite growth in situ using high temperature atomic force microscopy (AFM) to visualize zeolite surface growth at a near molecular level. We have shown that zeolite crystallization is predominantly a result of nonclassical pathways (e.g., crystallization by particle attachment) with contributions from classical layer-by-layer growth via monomer incorporation depending on the growth conditions and the stage of zeolite crystallization (e.g., early vs. late synthesis times).

Here we report our recent observations of modified faujasite (FAU) growth. We have demonstrated that FAU (hydro)thermal stability and corresponding catalytic performance is enhanced by the incorporation of zinc [1]; however, the mechanism of FAU formation in the presence of Zn remains unclear. In this presentation, we will highlight new insight of Zn-FAU crystallization using in situ AFM to probe the inhibitory effect of metal incorporation. We will also discuss demetallation approaches for various heteroatoms in commercially relevant zeolites of different pore topologies, including *BEA, MFI, and CHA frameworks. The removal of framework metals has the potential to introduce defects in the zeolite structures that can stabilize extra-framework species, thereby tuning their physicochemical properties beyond those of their pristine crystalline counterparts [2].

References:

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

[2] Medeiros-Costa et al., "Silanol defect engineering and healing in zeolites: opportunities to fine-tune their properties and performances." Chemical Society Reviews 50 (2021): 11156-11179