Abatement of nitrogen oxides in a catalytic reactor enhanced by nonthermal plasma discharge

Removal of nitrogen oxides using a nonthermal plasma process (dielectric barrier discharge) combined with catalyst was investigated. In this system, selective catalytic reduction of nitrogen oxides is affected by the operating condition of the plasma process and, thus, the characteristics of the plasma process were separately examined before combining the two processes. The oxidation of NO to NO₂ in the plasma reactor easily took place at room temperature. As the temperature increased, however, the rate of the oxidation greatly decreased, which implies that an additive to increase the reaction rate is necessary. In the presence of ethylene as an additive, the oxidation of NO to NO₂ largely enhanced at a temperature range of 100°C-200°C. Comparison of AC with pulse voltage in terms of the energy efficiency for NO oxidation was made, and almost no difference between the two voltage types was observed. The removal of NO_x on the catalyst (V₂O₅/TiO₂) was found to largely increase by the plasma discharge. The byproduct formaldehyde formed from ethylene in the plasma reactor could be completely removed in the catalytic reactor while significant amount of carbon monoxide and ammonia slip were observed. The plasma-catalyst system used in this study was able to remove more than 80% of NO_x (energy yield: 42 eV/NO_x-molecule) at a temperature range of 100°C-200°C that is much lower than typical temperature window of selective catalytic reduction (250°C-450°C).