Three model reactions: decomposition of isopropanol, cyclisation of acetonylacetone and cumene decomposition have been used for characterisation of catalytically active centres in activated carbons modified in oxidising or reducing conditions. Oxidised activated carbon catalysts show high activity in isopropanol decomposition and the dominant product of this reaction is propene, which indicate that oxidation of activated carbons with liquid or gas agents stimulates formation of surface oxygen groups, mainly those of acidic character. Modification of activated carbon by reduction with hydrogen or by nitrogenation with ammonia causes partial removal of the oxygen functional groups leading to a decrease in the catalytic activity towards propene and a simultaneous increase in isopropanol conversion to acetone (basic centres formation). The influence of above modifications on the catalytic activity of activated carbons is confirmed by investigation of cyclisation of acetonylacetone. The dominant product of cumene decomposition performed over activated carbon samples studied is alpha-methylstyrene, which testifies to the presence of electron-transfer centres in these catalysts. (C) 2014 Elsevier B.V. All rights reserved.