The circulation and regeneration experiments were employed to evaluate the lifetime of the two different catalysts (HZSM-5 and 0.3 mol·L-1 NaOH modified HZSM-5). The spent and regenerated catalysts were characterized by N2 adsorption-desorption and NH3-TPD techniques to analyse the reason of deactivation

and the spent catalysts were characterized by SEM

TGA

FTIR and UV-Vis techniques to analyse the coke deposited on the catalyst. The deactivation of the two different zeolites was become more and more serious along with the increase of the number of cycles. The difference was that the performance of 0.3 mol·L-1 NaOH modified HZSM-5 was better than the one of unmodified HZSM-5 after four cycles. The coke of the spent catalysts was removed through calcination in air at high temperature and the catalytic activity was recovered to a large extent. The performance of 0.3 mol·L-1 NaOH modified HZSM-5 was still better than the one of unmodified HZSM-5 after regeneration. The amount of coke deposited on the modified HZSM-5 was less than the one of unmodified HZSM-5. The coke of the modified HZSM-5 contains more condensed aromatics relatively.