Analytical Sciences

Analysis of NMR Adsorption Isotherms of Zeolite ZSM-5: Adsorption Profiles Derived from the Pressure and Temperature Dependences of ¹²⁹Xe NMR Chemical Shift and Signal Intensity

Hideaki FUJIWARA,*,** Hirohiko IMAI,*** Yuko ADACHI,* and Atsuomi KIMURA*

*Department of Medical Physics and Engineering, Area of Medical Imaging Technology and Science, Division of Health Sciences, Graduate School of Medicine, Osaka University, 1-7 Yamadaoka, Suita, Osaka 565-0871, Japan
**MR MedChem Research, LLC, 2-11-28 Aoshinke, Minoo, Osaka 562-0024, Japan
***Division of Systems Informatics, Department of Systems Science, Graduate School of Informatics, Kyoto University, Yoshida-Honmachi, Sakyo, Kyoto 606-8501, Japan

¹²⁹Xe NMR spectroscopy of nanomaterials, such as zeolites, can provide valuable information on the nanostructure and physicochemical properties of adsorption. In the present study the pressure and temperature dependences of the ¹²⁹Xe NMR chemical shift and the signal intensity were investigated in detail with a zeolite ZSM-5. The pressure dependence of the signal intensity at constant temperature was analyzed based on the Langmuir and Dubinin–Radushkevich (D-R) models, from which the thermodynamic parameters and energetic profiles of adsorption were obtained together with information concerning the nanospace size. From this isotherm analysis the coverage, θ, was calculated and used for isotherm analysis of the chemical shift. The θ dependence of the chemical shift was successfully fitted by an exponential function, and the results were discussed in relation to the chemical shift at zero coverage, that at full coverage and the curvature of the exponential function. The chemical shift data reported with the zeolites NaA and KA, where separated signals were observed for the different number of encapsulated Xe atoms in the α cage, were analyzed and discussed collectively.

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