Solid-state exchange 13C NMR was used to measure directly discrete intercage hopping of strongly adsorbed molecules on a nanoporous zeolite. Such intercage motions represent the molecular transport events that were central to macroscopic diffusion of guest molecules through zeolite pore spaces. Apparent activation energies of 73 and 76kJ/mol were measured for intra- and intercage hopping, respectively, of benzene molecules on Ca-Y zeolite. Exchange NMR measurements at 338 to 368K yield benzene self-diffusion coefficients from 10-19 to 10-18m2/s; values which were well below the range of diffusivities accessible using other equilibrium techniques.

Direct Measurement of Intercage Hopping in Strongly Adsorbing Guest-Zeolite Systems. D.E.Favre, D.J.Schaefer, S.M.Auerbach, B.F.Chmelka: Physical Review Letters, 1998, 81[26], 5852-5