Using 1D- and 2D-exchange 13C NMR techniques it was shown that n-pentane translation in zeolite ZK-5 occurs by hopping between neighboring α and γ cages. Owing to the structure of the ZK-5 pore network, these techniques give direct information about the translational part of molecular intercage motion, which represents the elementary step of sorbate self-diffusion. Between 247 and 317K the hopping rates obtained for n-pentane in H- and K-ZK-5 at respective loadings of 8.1 and 9.9 molecules per unit cell were of the order of 1-103/s. This corresponded to intra-zeolite self-diffusion constants of 10-18-10-15m2/s. Non-exponential time-correlation functions indicate heterogeneity, possibly reflecting the different loading states of the individual cages at the microscopic level. The temperature dependence of hopping shows that it was an activated process with a barrier of 28kJ/mol for both H-ZK-5 and K-ZK-5. The apparent activation entropy determined from a two-site exchange analysis was 130J/Kmol for both H- and K-ZK-5.

n-Pentane Hopping in Zeolite ZK-5 Studied with 13C NMR. P.C.M.M.Magusin, D.Schuring, E.M.Van Oers, J.W.De Haan, R.A.Van Santen: Magnetic Resonance in Chemistry, 1999, 37, S108-17