IN-SITU C-13 FOURIER-TRANSFORM PULSED-FIELD GRADIENT NMR-STUDY OF INTRACRYSTALLINE DIFFUSION DURING ISOPROPANOL CONVERSION IN X-TYPE ZEOLITES

C-13 Fourier transform pulsed field gradient NMR was applied for the f irst time for the in situ observation of the self-diffusion of reactan t and product molecules during a zeolite-catalyzed reaction. The conve rsion of isopropanol in LiNaX-51, NaX, CsNaX-60, and CsNaX-60.8CsOH ei ther to acetone, as the product of base catalysis, or to propene, as t he product of acid catalysis, was chosen as a model reaction. In NaX a nd CsNaX-60, the self-diffusivities of isopropanol and propene were sh own to depend explicitly on the reaction time. In the considered cases any limitation of the overall reaction by intracrystalline diffusion could be excluded. It was found that, in CsNaX-60.8CsOH, the isopropan ol conversion probably follows the base-catalyzed reaction pathway, wh ile in the other cases formation of propene is indicative of a substan tial contribution of acid catalysis. (C) 1997 Academic Press.