ON THE REGENERATION OF COKED H-ZSM-5 CATALYSTS

Regeneration of H-ZSM-5 zeolite coked during ethylbenzene conversion i s studied. Selective removal and transformation of the carbonaceous co mpounds during reactivation in the presence of air, 0.5% O-2 in N-2 an d H-2 at 500 degrees C were examined using the combination of GC, TGA, xenon adsorption, IR, Xe-129, and C-13 CP-MAS NMR spectroscopy and et hylbenzene transformation as a test reaction, A rapid initial rate of regeneration is found while tile fouled catalysts were subjected to re generation in air. The intracrystalline cokes present near the Bronste d acid sites are preferentially removed to those present on the extern al surface of thee zeolite crystallites. The phenomenon is more obviou s when using H-2 as the regenerating gas. During the oxidative removal of the coke with air or 0.5% O-2 in N-2, a portion of the carbonaceou s compounds was transformed to more condensed structures before gettin g completely oxidized. In the presence of H-2, while the internal coke s were selectively removed by hydrocracking, the external cokes were p artially cracked from bulky alkyl polyaromatic compounds to less bulky polyaromatic compounds. Moreover, an increase in paradiethylbenzene s electivity was observed. (C) 1998 Academic Press.