Effect of reaction temperature on NO_x removal and formation of ammonium nitrate in nonthermal plasma Process combined with selective catalytic reduction

This study investigated nonthermal plasma process combined with monolithic V₂O₅/TiO₂ catalyst for the removal of nitrogen oxides. The combination process was made in either one-stage (generation of plasma inside catalyst) or two-stage process (plasma reactor, followed by catalyst) in order to understand the role of nonthermal plasma. It was shown that nonthermal plasma does not activate catalyst, but merely changes the gas composition, especially NO and NO₂ concentrations. The effect of reaction temperature on the removal of NO_x and the formation of ammonium nitrate was examined to find out an appropriate operating condition. The formation of ammonium nitrate on catalyst surface that is the main cause of catalyst deactivation was identified by scanning electron microscope images. As a result of the change in the gas composition by the nonthermal plasma, the combination process allowed high NO_x removal efficiency at relatively low temperatures below 200°C. For the present process, the NO_x removal efficiency obtained in the range of 75°C-200°C was around 80%, which corresponds to an energy yield of 48 eV/NO_x-molecule removed. It was found that the combination process should be operated above 170°C to prevent ammonium nitrate from forming.