Molecular diffusion in zeolites with a 1-dimensional channel structure was studied by means of pulsed field gradient nuclear magnetic resonance techniques. It was found that, contrary to the case of normal diffusion, the mean square displacement increased in proportion to the square root of time. This was explained by assuming that the molecules were unable to pass each other, and exhibited so-called single-file diffusion. The diffusivity of an isolated molecule, as estimated from the mobility in the single-file system, was 2 orders of magnitude higher than the highest intra-crystal diffusivities which had been reported for zeolites.

K.Hahn, J.Kärger, V.Kukla: Physical Review Letters, 1996, 76[15], 2762-5