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Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY

Chitac, Ruxandra G.; Zholobenko, Vladimir L.; Fletcher, Robin S.; Softley, Emma; Bradley, Jonathan; Mayoral, Alvaro; Turrina, Alessandro; Wright, Paul A.

Authors

Ruxandra G. Chitac

Vladimir L. Zholobenko

Robin S. Fletcher

Emma Softley

Jonathan Bradley

Alvaro Mayoral

Alessandro Turrina

Paul A. Wright



Abstract

The SWY-type aluminosilicate zeolite, STA-30, has been synthesized via different routes to understand its defect chemistry and solid acidity. The synthetic parameters varied were the gel aging, the Al source, and the organic structure directing agent. All syntheses give crystalline materials with similar Si/Al ratios (6-7) that are stable in the activated K,H-form and closely similar by powder X-ray diffraction. However, they exhibit major differences in the crystal morphology and in their intracrystalline porosity and silanol concentrations. The diDABCO-C8(2+) (1,1 '-(octane-1,8-diyl)bis(1,4-diazabicyclo[2.2.2]octan)-1-ium)-templated STA-30 samples (but not those templated by bisquinuclidinium octane, diQuin-C8(2+)) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 angstrom) that connect with the characteristic swy and gme cages of the SWY structure. This results in pore volumes up to 30% greater than those measured in activated diQuin-C8_STA-30 as well as higher concentrations of silanols and fewer Bronsted acid sites (BASs). The hierarchical porosity is demonstrated by isopentane adsorption and the FTIR of adsorbed pyridine, which shows that up to 77% of the BASs are accessible (remarkable for a zeolite that has a small-pore crystal structure). A structural model of single can/d6r column vacancies is proposed for the extra-large micropores, which is revealed unambiguously by high-resolution scanning transmission electron microscopy. STA-30 can therefore be prepared as a hierarchically porous zeolite via direct synthesis. The additional noncrystallographic porosity and, subsequently, the amount of SiOHs in the zeolites can be enhanced or strongly reduced by the choice of crystallization conditions.

Citation

Chitac, R. G., Zholobenko, V. L., Fletcher, R. S., Softley, E., Bradley, J., Mayoral, A., …Wright, P. A. (in press). Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY. Journal of the American Chemical Society, 145(40), 22097-22114. https://doi.org/10.1021/jacs.3c07873

Journal Article Type Article
Acceptance Date Sep 27, 2023
Online Publication Date Sep 27, 2023
Deposit Date Oct 9, 2023
Journal Journal of the American Chemical Society
Print ISSN 0002-7863
Electronic ISSN 1520-5126
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 145
Issue 40
Pages 22097-22114
DOI https://doi.org/10.1021/jacs.3c07873
Keywords Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis