The diffusion of benzene in ZSM-5 was measured using neutron spin-echo methods. This technique permitted probing for much longer times (20ns here) than did conventional quasi-elastic spectrometers. In this zeolite, the diffusion coefficient of benzene extrapolated to 300K was 1.3 x 10-14m2/s at 300K; the activation energy being 30kJ/mol. This was one of the few systems in which agreement could be observed between a microscopic technique and macroscopic methods, that is, gravimetry, frequency-response, infra-red, and zero-length column techniques. Comparison with molecular simulation studies shows that inclusion of the lattice flexibility was crucial when the molecule was similar in size to the zeolite pore, as for benzene in MFI.

Diffusion of Benzene in ZSM-5 Measured by the Neutron Spin - Echo Technique. H.Jobic, M.Bée, S.Pouget: Journal of Physical Chemistry B, 2000, 104[30], 7130-3