Evidence for Subdomains in Large Crystals of NaX Zeolite

1. Introduction Pulsed Field Gradient (PFG) NMR has proved to be a valuable tool to probe the intracrystalline diffusion of molecules adsorbed in microporous materials [1]. It is well-known that the purely intracrystalline diffusivity D intra can only be attained, if the root mean square (rms) displacement of the molecules during the observation time is much smaller than the diameter of the crystallites. If it is not the case, a fraction of the diffusing molecules will feel the influence of the interface between the intra-and the inter-particle space. For PFG NMR measurements this condition requires the use of large-size crystals (typically more than 20 µm) which are rarely available commercially. The aim of this work was to exploit such a PFG-friendly sample of NaX zeolite and to follow the influence on D intra of a wide variety of parameters such as the temperature, the nature of the adsorbate and its concentration.