INFLUENCE OF INTRACRYSTALLINE CONFINEMENT ON PULSED-FIELD GRADIENT NMR DIFFUSION STUDIES WITH ZEOLITE CRYSTALLITES OF FINITE-SIZE

The measurement of zeolitic diffusion by pulsed held gradient (PFG) NM R may be drastically limited by the finite size of the zeolite crystal lites. It is shown that this limitation may be partially circumvented by quantitatively taking into account the confinement exerted by the e xternal crystallite surface on intracrystalline diffusion. The validit y of the procedure is demonstrated by comparing the diffusivity data f or acetone in zeolite NaX obtained in the proposed way for commercial (i.e., small) crystallites with those obtained with laboratory-synthes ized large crystallites. Using isopropanol and propene as adsorbates, the method is applied for the first measurements of intracrystalline d iffusion in commercial zeolites of type Y.