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) NMR may be drastically limited by the finite size of the zeolite crystallites. It is shown that this limitation may be partially circumvented by quantitatively taking into account the confinement exerted by the external crystallite surface on intracrystalline diffusion. The validity of the procedure is demonstrated by comparing the diffusivity data for acetone in zeolite NaX obtained in the proposed way for commercial (i.e., small) crystallites with those obtained with laboratory-synthesized large crystallites. Using isopropanol and propene as adsorbates, the method is applied for the first measurements of intracrystalline diffusion in commercial zeolites of type Y.