Direct measurement of intercage hopping in strongly adsorbing guest-zeolite systems

Solid-state exchange C-13 NMR has been used to measure directly discrete intercage hopping of strongly adsorbed molecules on a nanoporous zeolite. Such intercage motions represent the molecular transport events that are central to macroscopic diffusion of guest molecules through zeolite pore spaces. Apparent activation energies of 73 and 76 kJ/mol have been measured for intra- and intercage hopping, respectively, of benzene molecules on Ca-Y zeolite. Exchange NMR measurements at 338 to 368 K yield benzene self-diffusion coefficients from 10(-19)-10(-18) m(2)/s, values which are well below the range of diffusivities accessible from other equilibrium techniques.