The behavior of the selective catalytic reduction of nitrogen oxides (NOx) assisted by a dielectric barrier discharge was investigated. The principal function of the dielectric barrier discharge in the present system is to generate ozone, which is continuously fed to a chamber where the ozone and NO-rich exhaust gas (NO forms the large majority of NOx) are mixed. In the ozonization chamber, a part of NO contained in the exhaust gas is oxidized to NO2, and then the mixture of NO and NO2 enters the catalytic reactor. The ozonization method proposed in this study was found to be more energy-efficient for the oxidation of NO to NO2 than the typical nonthermal plasma process. The degree of NO oxidation was approximately equal to the amount of ozone added to the exhaust gas, implying that the decomposition of ozone into molecular oxygen was relatively slow, compared to its reaction with NO. When the exhaust gas was first treated by ozone to produce a mixture of NO and NO2, a remarkable enhancement in the catalytic reduction of nitrogen oxides was observed. Neither NO3 nor N2O5 was formed in the present system, but small amounts of ozone and N2O (less than 5 ppm) were detected in the outlet gas. (c) 2005 Elsevier B.V. All rights reserved.