IN-SITU PFG NMR-STUDY OF INTRACRYSTALLINE DIFFUSION DURING ETHENE CONVERSION IN ZSM-5

Pulsed field gradient (PFG) NMR spectroscopy has been applied to measu re the self-diffusivity of an inert probe species in situ during a zeo lite-catalyzed reaction, Specifically, F-19 PFG NMR was used to measur e 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 sensitiv e to changes in the composition of the reacting system with time for t he conversion of ethene in H-ZSM-5. Also, the self-diffusivity of CF4 in well-defined nonreacting mixtures could be correlated with the mobi lity and changing composition of the reacting system, Studies of the r eaction kinetics were performed by C-13 MAS NMR and with a recirculati on reactor, At low temperatures (approx. 373 K) ethene is converted ma inly to paraffins. The gasphase products observed in the recirculation system ranged from C-2 to C-7 alkanes. (C) 1996 Academic Press, Inc.