COKING AND DEACTIVATION OF H-ZSM-5 ZEOLITES DURING ETHYLBENZENE DISPROPORTIONATION .1. FORMATION AND LOCATION OF COKE

The mode of deactivation and coke formation in a H-ZSM-5 zeolite durin g ethylbenzene disproportionation has been investigated by TGA, adsorp tion, IR, and Xe-129 NMR techniques. The initial rate of deactivation and the total coke content are found to increase with increasing conve rsion level. Within the range of conversion (54-63 %) covered in the p resent study, the location and extent of coke deposition can be divide d into three distinct regions. At low coke content, coke is found to d eposit on the Bronsted acid sites and resulted in a notable decrease i n catalytic activity. As the amount of coke increases (less than or eq ual to 7 wt%), while the catalytic activity decreases slightly, most o f coke still tends to deposit within the zeolite channels. The slight decrease in catalytic activity is ascribed to steric hindrance by coke residues. When the coke content exceeds 7 wt%, while the activity rem ains almost constant, the deposition of coke on the external surface o f the zeolite crystallites is evident. It is found that neither the po re opening nor the acid site were completely blocked off by coke resid ues even at the highest coke loading.