The influence of the acid and basic properties of a catalyst on the selectivity of polystyrene transformation was studied. The properties of silicaalumina SiO2-Al2O3(45%) dotted with NaOH from 1 to 20 wt% and gamma-Al2O3 containing 1 to 8 wt% NaOH or H2SO4 were examined using the test reactions of cumene (acid) and diacetone alcohol (base) transformation. These catalysts were used in polystyrene transformations. It was found that polystyrene decomposition involves thermal and catalytic transformation. In the first case, two main reaction pathways are involved: gradual depolymerization to the monomer (styrene) and pyrolysis leading to the formation of different volatile oligomers (dimers, trimers, tetramers.). The latter species react solely over the catalyst active centers. Linear dimers of styrene activated by Bronsted acid sites undergo decomposition to styrene and ethylbenzene as well as to toluene and alpha-methylstyrene. Consecutive transformation of the products leads to a simultaneous hydrogen (H+ and H-) production and coke formation. The latter ions are active in hydrogen transfer reactions which causes hydrogenation of styrene to ethylbenzene. In the presence of base catalysts selective styrene formation takes place and transformation leading to coke are slower hence ethylbenzene formation is suppressed. In the presence of acid catalysts linear dimers can also isomerize to cyclic derivatives which after dealkylation give benzene and methylindane. The later product in isomerization and hydrogen transfer reactions forms methylindene and naphthalene. The higher styrene oligomers reactions are catalyzed by both acid and basic sites leading mainly the monomer, i.e. styrene formation. (C) 2012 Elsevier B.V. All rights reserved.