Molecular dynamics of benzene in zeolite NaY studied by 2D deuteron NMR

2H NMR exchange experiments were performed to study the reorientational dynamics of benzene molecules at full occupancy of the large voids (supercages) of the synthetic faujasite-type zeolite NaY. The 2D spectra obtained, as well as the results of the 2D echo time-domain measurements, are compared with model calculations utilizing an appropriate parametrization of the data. Evidence is obtained for tetrahedral-like jumps of the benzene molecules between adjacent adsorption sites and concomitant small-angle reorientations. These small-angle reorientations of amplitude 5–7° are interpreted to be due to instantaneous relaxations after the hopping of neighbouring molecules in the supercages. Over the temperature range investigated, the small-angle jumps are about two times faster than the inter-site jumps which exhibit an activation energy of 40±2 kJ/mol.