Studies on acidity, activity and coke deactivation of ZSM-5 during n-heptane aromatization

In order to understand the effects of acidity and acid strength distributio n on the nature of coke formed over ZSM-5 zeolite in n-heptane aromatizatio n reaction, a series of ZSM-5 samples dealuminated to different degrees are prepared. Microcalorimetric ammonia adsorption studies indicated the prese nce of very strong acid sites (DeltaH>140 kJ/mol) in the catalysts steamed at 400 and 500 degreesC. C-13 CP/MAS NMR along with dipolar dephasing is us ed to estimate the fraction of aromatic carbon and variation in aliphatic c omponents with change in acidity of the ZSM-5 zeolites. Maximum selectivity to aromatics in n-heptane conversion is observed in the case of partly dea luminated ZSM-5 catalyst, whereas the aromatic nature of the coke is contin uously decreased with steaming temperature, i.e. dealumination. (C) 2001 El sevier Science B.V. All rights reserved.