The working range of static field gradient NMR illustrated by measurements of the intracrystalline diffusion of water in NaA- zeolites

1. Introduction Measuring diffusion in zeolites is a long-lasting challenge. For more than 70 years many efforts have been made to determine the diffusion coefficient of host molecules in the porous framework of zeolites [1]. Actually the different techniques, which were applied, observed different processes and provided dissenting diffusion coefficients. Precisely, there are methods observing diffusion on a macroscopic or a microscopic scale, under equilibrium or non-equilibrium conditions. We are interested in the molecular dynamics of water inside a crystallite, i.e. the intracrystalline self-diffusion coefficient. Common zeolites, as used in our experiments, have crystallite radii of about 0.5 μm, therefore we need a high spatial resolution to determine the diffusion coefficient of the molecules inside the crystallites. Static field gradient NMR can provide such a high resolution under certain conditions. In our contribution we discuss the potential and limitations of this method.