INVESTIGATION OF COKING PHENOMENA IN ZEOLITE HY USING DEUTERIUM NMR

In this paper we demonstrate the use of variable temperature deuterium line shape and relaxation time studies to characterise the modificati on to adsorption sites and thermally activated inter-site jump process es occurring within zeolite HY at various stages during coke depositio n. In the examples presented here the adsorption and transport propert ies of probe benzene molecules are studied. Coke was produced using tw o different feed molecules; ethanol and n-hexane. The data presented s how that the extent to which the sites for benzene adsorption are modi fied during coking depends both on the time-on-stream and the nature o f the feed molecule producing the coke. The results suggest that coke produced by ethanol deactivates the zeolite by selective coverage of o ne of the two types of site initially available for benzene adsorption . After 15 h on stream there is evidence that the effective co-ordinat ion of the pore network has been reduced from 4 to 3.4. In contrast, d eactivation by n-hexane cracking causes deposition of coke within the pore structure which blocks adsorption of probe molecules onto the nat ive adsorption sites of the zeolite.