(670c) Controlling Defects and Si/Al of High-Silica LTA Zeolites Using Charge Balancing Approach | AIChE

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(670c) Controlling Defects and Si/Al of High-Silica LTA Zeolites Using Charge Balancing Approach

Authors 

Fan, W. - Presenter, University of Massachusetts - Amherst
Wang, T., University of Massachusetts-Amherst
Luo, S., Umass Amherst, Department of Chemical Engineering
Shah, M., University of Massachusetts Amherst
Balogun, M. L., University of Massachusetts Amherst
Auerbach, S. M., University of Massachusetts
Controlling structures, compositions, and defects in zeolite catalysts is crucial for tuning their adsorption and catalytic properties. A conventional wisdom in zeolite synthesis is that F- ions act as structure-directing agents, especially for dense building units such as the double-4-membered ring (D4R), but until now, little direct evidence (i.e., during crystallization) exists to support this notion. A second assumption in zeolite synthesis is that F- ions balance positive charges from organic structure-directing agents (OSDAs), thereby producing low-defect or defect-free zeolites. But it remains unclear whether there is a limit to fluoride’s capacity for balancing positive charge, and what defects may arise when this limit is surpassed. We have performed an integrated zeolite synthesis, spectroscopy, and density functional theory study of LTA zeolite formation as a case study to investigate the roles of OSDAs and F- ions in structure-direction and charge-balancing during crystallization. High-silica LTA zeolite was synthesized with a primary OSDA and various concentrations of tetramethyl ammonium (TMA+) as a secondary OSDA. We demonstrated that the number of defects in LTA can be controlled by using TMA as a secondary OSDA [1-3]. We also discovered that the defects can be maintained by calcining using ozone [4]. The charge balancing approach also provides an opportunity to control the composition of the LTA zeolites, leading to Si/Al ratios in LTA heretofore unobtainable [5]. Their catalytic activity will also be discussed in the talk.

References:

  1. Tongkun Wang and Song Luo et al. Am. Chem. Soc. 2019, 141, 51, 20318-20324.
  2. Song Luo and Tongkun Wang et al. Mater. 2021, 33, 17, 6794-6803.
  3. Song Luo and Tongkun Wang et al. Mater. 2022, 34, 1789−1799
  4. Tongkun Wang and Song Luo et al. Chem. Mater. 2024, 36, 2, 870-880.
  5. Song Luo and Tongkun Wang et al. Synthesis of High-silica LTA with Controllable Si/Al ratios. in preparation.

Topics 

Catalysis
Catalysts
Nanomaterials

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