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 first time for the in situ observation of the self-diffusion of reactant and product molecules during a zeolite-catalyzed reaction. The conversion of isopropanol in LiNaX-51, NaX, CsNaX-60, and CsNaX-60.8CsOH either to acetone, as the product of base catalysis, or to propene, as the product of acid catalysis, was chosen as a model reaction. In NaX and CsNaX-60, the self-diffusivities of isopropanol and propene were shown 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 isopropanol conversion probably follows the base-catalyzed reaction pathway, while in the other cases formation of propene is indicative of a substantial contribution of acid catalysis. (C) 1997 Academic Press.