Improvement in selective catalytic reduction of nitrogen oxides by using dielectric barrier discharge

The behavior of the selective catalytic reduction of nitrogen oxides (NO_x) 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 NO_x) 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.