M. Satozawa, K. Kunimori, and S. Hayashi
[Bull. Chem. Soc. Jpn., Vol.70, pp.97-105, 1997]

¹³C and ¹H MAS NMR spectra have been measured at room temperature for benzene and p-xylene adsorbed in H-ZSM-5, Na- and H-type mordenites with different Si/Al₂ ratios, H-Y, Na-Y, Na-X, and FSM-16 to study the dynamics of the guest species in the host materials, as shown in Fig. 1. The second moments M₂ evaluated from the SSB intensity in ¹³C CP/MAS NMR spectra were used to predict the motion of the guest species. Benzene molecules rotate about the C₆ axis freely, and reorientation of the C₆ axis takes place in H-ZSM-5. The para axis of p-xylene molecule is fixed in H-ZSM-5. The reorientations of the guest species become isotropic in the faujasite-type zeolites, Na-Y, H-Y, and Na-X. In FSM-16, translation diffusion takes place in addition to the isotropic rotation like in the liquid state. The mobilities of benzene molecules are in the following order, mordenite < H-ZSM-5 < Na-Y < Na-X < H-Y < FSM-16, while those of p-xylene molecules are in the following order. H-ZSM-5 < mordenite < Na-Y < Na-X approx H-Y < FSM-16. There is a good correlation between the pore size and the mobility of the guest species, with the exception of the mordenite/benzene systems.