The diffusion of benzene in ZSM-5 has been measured by neutron spin-echo. T
his technique allows probing for much longer times (20 ns in this work) tha
n with conventional quasi-elastic spectrometers. In this zeolite, the diffu
sion coefficient of benzene extrapolated to 300 K is 1.3 x 10(-14) m(2) s(-
1) at 300 K, the activation energy being 30 kJ/mol. This is one of the few
systems in which agreement can be observed between a microscopic technique
and macroscopic methods, that is, gravimetry, frequency-response, infrared,
and zero-length column (ZLC) technique. Comparison with molecular simulati
on studies shows that inclusion of the lattice flexibility is crucial when
the molecule is similar in size to the zeolite pore, as for benzene in MFI.