The coke deposited in the HZSM-5 zeolite at higher coke levels causes a more important pore blockage than the coke deposited in the HZSM-5 zeolite at low coke content. On the other hand, it would appear that there is an important deactivation mode change in the USY coked zeolites during the cracking runs and when the coke level in the catalyst increases an important pore blockage is observed. In the HZSM-5 zeolite, it seems that the formation of insoluble coke during the several polymer cracking runs, as well as the possible location in the external surface could be responsible for the important pore blockage observed in this zeolite. In the USY coked zeolites, the study of the nature of the soluble coke suggests that the pyrene compounds and their evolution to insoluble coke could probably be responsible for the important pore blockage observed after the second cracking run. (C) 2008 Elsevier B.V. All rights reserved.