(754d) Time-Resolved Dynamics of Intracrystalline Mesoporosity Generation in USY Zeolite
More specifically, in this presentation we will show the dynamics of surface reconstruction that occurs during the surfactant-templating of USY zeolite captured using in situ atomic force microscopy (AFM).5 The development of surfactant-templated mesoporosity and the concurrent healing of defects that are characteristic of steamed zeolites occur in less than one hour at room temperature, which emphasizes the low energy barriers needed to reorganize the crystalline structure of this zeolite. We also monitored this transformation by X-ray diffraction, N2 adsorption, and TEM analysis of ultramicrotomed samples to confirm that the rapid formation of surfactant-templated mesoporosity and the reconstruction of the zeolite crystals occur not only on the surface of the zeolite, but homogeneously throughout the whole zeolite. This process involves a significant and rapid breaking and re-formation of bonds; however, the zeolite does not dissolve during this process as solids recovery at any given time of the treatment is approximately 100% and the concentration of soluble Si or Al species in the liquid is negligible. Parametric analysis revealed that excessive NaOH leads to the partial transformation of zeolite into an amorphous mesoporous solid, while insufficient quantity of base and/or treatment time can lead to an incomplete mesostructuring of the zeolite, which highlights the importance of judiciously selecting the treatment conditions for every given zeolite. Collectively, these findings provide new and unequivocal insights that confirm surfactant templating is a facile and efficient method to induce reconstruction of the crystal and the healing of defects towards the generation of optimal zeolites for catalytic applications.
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(4) Chawla, A et al. Mol. Syst. Des. Eng. 3 (2018) 159-170
(5) Chawla, A et al. Chem. Mater. (2019) In Press DOI: 10.1021/acs.chemmater.9b00435