Effect of reaction temperature on NOx 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 NOx 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 NOx removal efficiency at relatively low temperatures below 200 degreesC. For the present process, the NOx removal efficiency obtained in the range of 75 degreesC-200 degreesC was around 80%, which corresponds to an energy yield of 48 eV/NOx-molecule removed. It was found that the combination process should be operated above 170 degreesC to prevent ammonium nitrate from forming.