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Precise Structural and Dynamical Details in Zeolites Revealed by Coupling-Edited 1 H- 17 O Double Resonance NMR Spectroscopy.
- Source :
-
Journal of the American Chemical Society [J Am Chem Soc] 2024 Mar 25. Date of Electronic Publication: 2024 Mar 25. - Publication Year :
- 2024
- Publisher :
- Ahead of Print
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Abstract
- Despite the extensive industrial and research interests in zeolites, their intrinsic catalytic nature is not fully understood due to the complexity of the hydroxyl-aluminum moieties. <superscript>17</superscript> O NMR would provide irreplaceable opportunities for much-needed fine structural determination given the ubiquitous presence of oxygen atoms in nearly all species; however, the low sensitivity and quadrupolar nature of oxygen-17 make its NMR spectroscopic elucidation challenging. Here, we show that state-of-the-art double resonance solid-state NMR techniques have been combined with spectral editing methods based on scalar (through-bond) and dipolar (through-space) couplings, which allowed us to address the subtle protonic structures in zeolites. Notably, the often-neglected and undesired second-order quadrupolar-dipolar cross-term interaction ("2nd-QD interaction") can actually be exploited and can help gain invaluable information. Eventually, a comprehensive set of <superscript>1</superscript> H- <superscript>17</superscript> O/ <superscript>1</superscript> H- <superscript>27</superscript> Al double resonance NMR with J -/ D -coupling spectral editing techniques have been designed in this work and enabled us to reveal atomic-scale precise structural and dynamical details in zeolites including: 1) The jump rate of the bridging acid site (BAS) proton is relatively low, i.e., far less than 100 s <superscript>-1</superscript> at room temperature. 2) The Al-OH groups with <superscript>1</superscript> H chemical shift at 2.6-2.8 ppm, at least for nonseverely dealuminated H-ZSM-5 catalysts, exhibit a rigid bridging environment similar to that of BAS. 3) The Si-OH groups at 2.0 ppm are not hydrogen bonded and undergo fast cone-rotational motion. The results in this study predict the 2nd-QD interaction to be universal for any rigid - <superscript>17</superscript> O-H environment, such as those in metal oxide surfaces or biomaterials.
Details
- Language :
- English
- ISSN :
- 1520-5126
- Database :
- MEDLINE
- Journal :
- Journal of the American Chemical Society
- Publication Type :
- Academic Journal
- Accession number :
- 38528765
- Full Text :
- https://doi.org/10.1021/jacs.3c14787