One of the most attractive processes is the catalytic degradation of polystyrene (PS). This process enables to get styrene monomer (SM) at relatively low temperature with a high selectivity. In this study, the modified Fe-based catalysts were employed for the catalytic degradation of EPSW (expandable PS waste), where carboanion may lead to high selectivity of SM in the catalytic degradation of PS. The yield of oil (Y-Oil) and SM (Y-SM) were increased in the presence of Fe-based catalysts and with increasing reaction temperature. Y-Oil and Y-SM were obtained over Fe-K/Al2O3 at the relative low reaction temperature (400 degreesC) 92.2 and 65.8 wt.%, respectively. The value of E-a (activation energy) is obtained as 194 kJ/mol for the thermal degradation of EPSW. However, the E-a was decreased considerably from 194 to 138 kJ/mol in the presence of the catalysts (Fe-K/Al2O3). (C) 2003 Elsevier B.V. All rights reserved.