Effect of manganese oxide catalyst on the toluene removal efficiency, byproducts inhibition and hydroxyl radical (HO*) formation were studied in dielectric barrier discharge (DBD) system. It was found that with MnO(x) catalyst, the toluene removal efficiency was nearly two times than that of without catalyst, but the HO* yield in gas streams was only one eighth of that without catalyst at a specific energy density (SED) of 50 Wh/m(3) Meanwhile, byproducts of O(3) and NO(x) were in much lower concentrations with the catalyst. The experiment about quantities of HO* radicals in the gas phase and on the surface of catalyst proves that HO* would be attached on the surface of catalyst In order to investigate the performance of MnO(x) catalyst, a characterization of the catalyst was performed by BET surface area detector, X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The results of XPS suggested that various oxygen species and some compounds containing N element deposited on the catalyst after plasma reaction. As a result, catalytic control in situ could be one of the most effective approaches to increase toluene removal efficiency and achieve a higher selectivity of CO(2) (C) 2010 Elsevier B V All rights reserved