Advanced nuclear magnetic resonance technique reveals precise structural, dynamical details in zeolites

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Advanced nuclear magnetic resonance technique reveals precise structural, dynamical details in zeolites

Credit: Journal of the ********* Chemical Society (2024). DOI: 10.1021/jacs.3c14787

Zeolites are widely used in many industries, yet their intrinsic catalytic nature is not completely understood, due to the complexity of the hydroxyl-aluminum moieties.

Atomic-scale analysis of local environments for the hydroxyl species is essential for revealing the intrinsic catalytic activity of zeolites and guiding the design of high-performance catalysts. However, many unfavorable factors prohibit the elucidation of their fine structures such as low quantity, meta-stable property, structural similarity, hydrogen-bonding environment, and long-range disordered nature.

Recently, a research team led by Prof. Hou Guangjin and Prof. Chen Kuizhi from the Dalian Institute of Chemical Physics (DICP) of the ******** Academy of Sciences (CAS) unraveled the precise structure of complex hydroxyl groups in zeolites with a comprehensive set of self-developed coupling-edited ¹H-¹⁷O solid-state nuclear magnetic resonance (NMR) methods.

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was published in the Journal of the ********* Chemical Society.

The ¹⁷O solid-state NMR would be a candidate to improve the analytical precision of zeolites if it could overcome the technical difficulties related to the extremely low natural abundance, low gyromagnetic ratio, and quadrupolar nature of the ¹⁷O isotope. Therefore, researchers employed a novel ¹⁷O-enrichment method and developed a series of ¹⁷O-NMR-based spectral editing pulse sequences, allowing them to improve the spectral resolution and address the subtle protonic structures within zeolites.

The precise and high-resolution species identification was attributed to comprehensively addressing an often-neglected and undesired NMR interaction, namely, the 2nd-order quadrupolar-dipolar cross-term interaction (2nd-QD interaction), which was indeed helpful in gaining invaluable information on zeolite structures.

In addition, researchers quantitatively probed Al···H, O···H proximities within both one-bond and multi-bond ranges, and semi-quantitatively realized the dissociation rates of hydroxyl protons such as BrØnsted acid site. They revealed the atomic-scale local environment of the catalytically important Al-OH and Si-OH moieties.

The NMR techniques developed in this study might be further applied in providing high-resolution analysis of subtle protonic structures in other circumstances such as metal-oxide surfaces, metal-organic frameworks, and biomaterials. “Our study may provide a generic strategy for high-resolution analysis of the subtle protonic structures in zeolites with ¹⁷O solid-state NMR,” said Prof. Hou.

More information:
Yi Ji et al, Precise Structural and Dynamical Details in Zeolites Revealed by Coupling-Edited ¹H–¹⁷O Double Resonance NMR Spectroscopy, Journal of the ********* Chemical Society (2024).

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Advanced nuclear magnetic resonance technique reveals precise structural, dynamical details in zeolites (2024, April 17)
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