Daniel E. Favre, Dieter J. Schaefer, Scott M. Auerbach
and Bradley F. Chmelka,
``Direct Measurement of Intercage Hopping in Strongly Adsorbing
Guest-Zeolite Systems,'' Phys. Rev. Lett. 81, 5852-5855 (1998).
Abstract
Solid-state exchange 13C 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 m2/s,
values which are well below the range of diffusivities accessible
from other equilibrium techniques.
Prof SM Auerbach
29 August 2000