日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

In-situ high-pressure ¹²⁹Xe NMR spectroscopy revealed new aspects of the local structure and the intermolecular interactions for xenon confined in the typical zeolite compounds with alumino-silicate frameworks. Assuming the local structure of xenon confined in the nanospace as Xe_n-clusters, the dependence of the ¹²⁹Xe chemical shift value on the filling of pore volume with xenon led to the population of Xe_n-clusters on the xenon adsorption process. Furthermore, the ¹²⁹Xe chemical shift showed the linear relation with the effective xenon density in the nanospace in the low density region. Applying the virial expansion of the chemical shift with xenon density to the density dependence of the chemical shift, the slope gives the second virial coefficient, δ₁, which is affected by xenon-xenon interactions. We found that δ₁ depends on the reciprocal pore size as well as pore types. In the plot of δ₁ against the reciprocal pore size, micropore and mesopore gave the separate curves with the different slopes. These aspects suggest that the xenon-xenon interaction given by the ¹²⁹Xe chemical shift is a useful probe to investigate the local structure of the confined xenon as well as the pore structure. In this article, we review our recent studies on molecular sieves 5A, 13X and ZSM-5 zeolites and propose the new possibility of characterization on the porous materials with in-situ high-pressure NMR spectroscopy.