Pulsed field gradient (PFG) NMR spectroscopy has been applied to measure the self-diffusivity of an inert probe species in situ during a zeolite-catalyzed reaction. Specifically, 19F PFG NMR was used to measure CF4 intracrystalline mobility during ethene conversion in H-ZSM-5 as a function of reaction time in sealed glass samples. CF4 was shown to be a suitable probe species, and its mobility was seen to be sensitive to changes in the composition of the reacting system with time for the conversion of ethene in H-ZSM-5. Also, the self-diffusivity of CF4 in well-defined nonreacting mixtures could be correlated with the mobility and changing composition of the reacting system. Studies of the reaction kinetics were performed by 13C MAS NMR and with a recirculation reactor. At low temperatures (approx. 373 K) ethene is converted mainly to paraffins. The gas-phase products observed in the recirculation system ranged from C2 to C7 alkanes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry