In order to understand the effects of acidity and acid strength distribution on the nature of coke formed over ZSM-5 zeolite in n-heptane aromatization reaction, a series of ZSM-5 samples dealuminated to different degrees are prepared. Microcalorimetric ammonia adsorption studies indicated the presence 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 used to estimate the fraction of aromatic carbon and variation in aliphatic components with change in acidity of the ZSM-5 zeolites. Maximum selectivity to aromatics in n-heptane conversion is observed in the case of partly dealuminated ZSM-5 catalyst, whereas the aromatic nature of the coke is continuously decreased with steaming temperature, i.e. dealumination.