DIFFUSION IN ZEOLITES MEASURED BY NEUTRON SCATTERING TECHNIQUES

Abstract

Neutron scattering techniques are being used to study the structure and dynamics of molecules adsorbed in zeolites. A very wide range of time scales can now be covered, from femtoseconds to microseconds. One can thus probe from fast vibrational modes down to slow diffusive motions. The technique was first used to obtain self-diffusivities of hydrocarbons, but transport diffusivities can also be derived for a variety of molecules, including N₂, O₂, CO₂, etc. The neutron results indicate that the corrected diffusivity is rarely constant. Recent experiments have shown that the neutron spin-echo technique pushes down the lower limit of diffusion coefficients accessible by neutron methods by two orders of magnitude.