Microdynamics of Guest Molecules in Zeolites Studied by Quasielastic Neutron Scattering and Nmr Pulsed Field Gradient Technique

Abstract

Summary Application of the quasi-elastic neutron scattering and NMR pulsed field gradient technique to molecular self diffusion studies of hydrocarbons in zeolites ZSM-5 and NaX leads to coinciding results in both the absolute values, the concentration dependence and activation energy of the intracrystalline self-diffusion coefficients. Further agreement between the neutron and NMR diffusion data is obtained by comparing the mean molecular jump lengths which by both techniques are found to be of the order of 1.2…0.25 nm, slightly decreasing with increasing loading. Due to the different time scales of the two experimental methods applied, the mean diffusion paths followed are of different magnitude: in neutron scattering experiments molecular translation is measured up to 6 nm; in the NMR pulsed field gradient technique the mean molecular displacements amount to some nm. However, in both methods, longrange self-diffusion is detected.