Competitive Formation of NO, NO2, and O3 in an Air-Flowing Plasma Reactor: A Central Role of the Flow Rate

Beyond ozone (O3) generation, diverse applications of dielectric barrier discharge (DBD) have been developed. When using ambient air, one of the longstanding challenges of DBD reactors has been the selective production of nitric oxide (NO), nitrogen dioxide (NO2), and O3. In this work, we report the competitive formation of NO, NO2, and O3 in an air-flowing surface DBD reactor. The temporal evolution of each chemical species was obtained by using in situ optical absorption spectroscopy. The possibility to select the plasma-chemistry mode (i.e., NO–, NO2–, or O3-dominant conditions) by adjusting the gas flow rate of the reactor was demonstrated with constant temperature and input power. As the flow rate increased from 260 to 1380 standard cubic centimeters per minute, the dominant chemical species changed from NO to NO2 [the achieved purity of NO2/(NO + NO2 + O3) was 99%]. With even higher flow rates, O3 appeared and dominated in the reactor [O3/(NO + NO2 + O3) was nearly 100%]. The experimental results were compared with zero-dimensional modeling, and the reactions involving NO, NO2, and O3 were analyzed in depth. Our findings will provide great guidance for future studies and for plasma applications of DBD reactors.