An alumina-supported nickel oxide system with overstoichiometric oxygen (NiOx/Al2O3) was investigated with respect to heterogeneous catalytic decomposition of ozone, complete oxidation of volatile organic compounds (VOCs) and oxidation of CO. The catalyst was prepared by a deposition oxidation-precipitation method and was characterized by chemical analysis, XPS, XRD, IR techniques, magnetic and adsorption measurements. The experiments were performed in the temperature range of -50 to 250 degrees C in an isothermal plug-flow reactor. A very high activity of the catalyst towards ozone decomposition was observed even at temperatures below -45 degrees C and at the same time the catalyst remained active for a long time. The activity of the catalyst with respect to complete oxidation of VOCs and oxidation of carbon monoxide was studied in presence of different oxidizing agents (ozone or oxygen). A significant increase in catalytic activity and decrease in reaction temperature were observed using ozone as an oxidant. Two main reasons for this behaviour were found: (i) the high content of active and mobile oxygen obtained during the synthesis on the catalyst surface, and (ii) the catalytically active complex of Ni4+O(OH)(2), formed during the reaction of ozone decomposition and able to oxidize VOCs at room temperature. (c) 2006 Elsevier B.V. All rights reserved.