Diffusion behavior of the benzene molecule in faujasite-type zeolite studied by double quantum filtered NMR

Deuteron NMR relaxation methods including double quantum filtered (DQF) spectral analyses were examined to study the dynamics of benzene molecules adsorbed in faujasite-type zeolite. To describe the dynamics of benzene molecules, a modified cone model involving in-plane rotation, wobbling motion and the characteristic order parameter was applied. The characteristic order parameter describes the intracage restricted reorientation for a single-site adsorption. For multiple-site adsorption such as in NaY, the site-to-site hopping processes result in cage disorder and yield a small characteristic order parameter. The wobbling motion is induced by the diffusive motion and therefore the correlation time of wobbling motion may be invoked to estimate the self-diffusion coefficient of benzene adsorbed in NaY, DAY, USY and NaX. Comparisons with kinetic Monte Carlo calculation, pulsed field gradient measurement, and other NMR relaxation studies are discussed.