Deactivation of the USHY zeolite (Si/Al = 6.5) during m-xylene transformation under N 2 flow at 350 °C, is due to the rapid formation and retention of coke. In situ mx-transformation over regenerated coked zeolite samples after stripping at 500 °C under air, hydrogen, or nitrogen shows that the effectiveness of the stripping gas in coke removal follows the order air ⋙ H 2 ≫ N 2 . Coke is also characterized by temperature programmed oxidation (TPO) experiments. For the regenerated zeolite by TPO under O 2 , the micropore volume is completely restored while a small loss of total volume is noticeable. This is shown by the N 2 adsorption isotherms of the three fresh, coked and regenerated zeolites.
