PFG n.m.r. study of diffusion anisotropy in oriented ZSM-5 type zeolite crystallites

ZSM-5 zeolite crystallites are oriented by introducing them into a system of parallel capillaries. In this way, by applying pulsed-field gradient (PFG) n.m.r., a direct measurement of the orientation dependence of diffusion in ZSM-5 crystals has become possible. Using methane as a diffusant, the ratio D xy /D z between the diffusivities in the xy plane and in the z direction has been found to be of the order of 4.5. This value is in satisfactory agreement with the behavior expected from both MD calculations and a random walk model of molecular propagation in the two-channel network of ZSM-5-type zeolites.