Researchers at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, led by Dr. Guangjin Hou and Dr. Kuizhi Chen, have made significant progress in the study of hydroxyl group structure analysis in molecular sieves. They have developed a series of coupled-edited 1H-17O solid-state nuclear magnetic resonance (NMR) double resonance spectroscopy methods, enabling high-resolution and precise analysis of hydrogen species and their local environments within the molecular sieve channels. The findings have been published in the Journal of the American Chemical Society.
The schematic diagram of the method. Provided by Dalian Institute of Chemical Physics.
Zeolite molecular sieves find wide applications in the industrial sector. They harbor a diverse array of hydroxyl and aluminum species within their structure, serving as catalytic active sites and adsorption sites, directly influencing the performance of zeolite catalyzed reactions. Atomic-scale resolution of the structure of hydroxyl species and their local environments within zeolites is crucial for understanding their intrinsic catalytic activity and guiding the controlled preparation of high-performance zeolite catalysts.
Due to the lack of long-range order, metastable states, and sensitivity to the environment, elucidating the structure of hydroxyl species within zeolites poses significant challenges. Therefore, the development of spectroscopic characterization methods that are high-resolution, sensitive, and non-destructive is paramount. Solid-state 17O NMR spectroscopy is a powerful tool for non-destructively resolving hydroxyl species within zeolites. However, its limited natural abundance, low gyromagnetic ratio, and quadrupolar nature hinder its widespread application in the structural analysis of zeolites.
In this work, researchers have developed a series of spectral editing 1H-17O solid-state NMR double resonance methods and employed novel 17O enrichment techniques to enhance the resolution of 17O solid-state NMR through multidimensional multinuclear correlation experiments. The team has also discovered and elucidated the spectral effects of second-order quadrupole-dipole interactions in 1H-17O spectra, extracting crucial structural and kinetic information of hydroxyl species within zeolites. Particularly noteworthy is the semi-quantitative revelation of the proton dissociation rates of hydroxyl species such as BAS in zeolites, and the quantitative determination of spatial distances between Al···H and O···H, thereby accurately resolving the atomic-scale local environments of Si-OH and Al-OH species within zeolite channels that play crucial catalytic roles.
The solid-state NMR spectroscopic methods developed in this work hold promise for high-resolution analysis of hydroxyl environments in metal oxides surfaces, metal-organic frameworks, and biological materials.
Related paper information: https://doi.org/10.1021/jacs.3c14787
