Deep oxidation of NO via catalytic ozonation

In addition to selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) which are available to remove NO_x from flue gas, oxidation method is receiving more and more attention because this method makes it possible to remove NO_x and SO₂ from flue gas simultaneously by wet scrubbing. O₃ as a strong oxidant has a high oxidation capacity and it can oxide NO to N₂O₅ which has a higher water solubility compared with NO₂. However, it needs a long reaction time and the escape of unreacted ozone may cause secondary pollution. In this study, FeMnCo/Al₂O₃ catalyst and FeMnCe/Al₂O₃ catalyst were prepared and applied to enhance the deep oxidation of NO_x with ozone and reduce O₃ slip. Effects of various operating parameters such as O₃/NO ratio, gas residence time, and operating temperature were evaluated, and the results demonstrate that N₂O₅ began to generate when O₃/NO ratio was higher than 1.0 and increased with increasing O₃/NO ratio. Little residual O₃ was formed in the presence of catalyst, while 350 ppm O₃ was measured at the outlet gas when O₃/NO ratio was controlled at 2.0. The N₂O₅ conversion efficiency increased with increasing gas residence time and operating temperature, and the highest N₂O₅ conversion efficiency was achieved at 100°C. Furthermore, the conversion efficiency remained around 90% during 20 h operation over FeMnCe/Al₂O₃ catalyst with an O₃/NO ratio of 1.73, a gas residence time of 1.2 s, and a temperature of 100°C. On the other hand, the N₂O₅ conversion efficiency remained around 80% during 3 h operation over FeMnCo/Al₂O₃ catalyst. Overall, FeMnCe/Al₂O₃ catalyst reveals good potential for deep oxidation of NO by O₃ and can be further developed as a viable catalyst for reducing NO emission from industries.<i>Implications</i>: In this study, FeMnCo/Al₂O₃ catalyst and FeMnCe/Al₂O₃ catalyst were applied to enhance the deep oxidation of NO into N₂O₅ with O₃. The catalysts can improve the conversion of NO into N₂O₅, shorten the reaction time and reduce the unreacted O₃ slip, which are beneficial to reduce the size of the reactor required and cost of APCDs (air pollution control devices) in practical application. This method can make it possible to simultaneously remove NO_x and SO₂ from flue gas by wet scrubbing for reducing NO emissions from industries, especially small and medium scaled industries, to meet increasingly stringent emission standards.