The performance of acid-treated halloysite catalysts in the degradation of polystyrene (PS) was investigated in this study. The degradation was carried out in a semi-batch reactor with a mixture of PS and catalyst at 400-450degreesC. The acid-treated halloysites showed good catalytic activity for the degradation of PS with very high selectivity to aromatic liquids. The effects of catalyst acidity, reaction temperature and contact time on the distribution of aromatics are discussed. The increase of contact time and surface acidity enhanced the production of ethylbenzene. High degradation temperature favored the selectivity to styrene monomer. (C) 2004 Elsevier B.V. All rights reserved.