Mechanisms and reaction pathways for simultaneous oxidation of NOx and SO2 by ozone determined by in situ IR measurements

Ozone (O-3) oxidation combined with wet scrubbing is a promising method for the simultaneous removal of SO2 and NOx in flue gas. In this study, the O-3 oxidation processes of NO and SO2, as well as their coexistence, were investigated using an in situ IR spectrometer. Experimental results showed that the O-3 concentration and the reaction temperature played critical roles in the O-3 oxidation process of NO. Around 80 degrees C, when inlet molar ratio of O-3/NO was less than 1, NO was mainly oxidized to NO2, while when the ratio was greater than 1, NO would be further oxidized to NO3, N2O5, and HNO3. NO3 was the key intermediate product for the formation of N2O5 and HNO3. However, the subsequent reactions of NO3 were temperature dependence. With the increase of reaction temperature above 100 degrees C, the concentration of NO2 increased whereas the concentrations of N2O5 and HNO3 decreased. The oxidation of SO2 by O-3 was negligible and SO2 had little influence on the oxidation of NO in the simultaneous oxidation of NO and SO2. Finally, based on the in situ IR results, the oxidation mechanism is discussed and the reaction pathways are proposed. (C) 2014 Elsevier B.V. All rights reserved.