Plasma-catalytic synergistic oxidation of NO in the non-thermal plasma system: Insight into the active sites effect

Superoxide radicals-dominated oxidation plays a crucial role in the removal of NOx in gas treatment schemes, especially in the catalytic oxidation of NO at room temperature. However, the specific mechanism underlying radical oxidation processes remains unclear. In this study, a series of transitional metal (Mn, Co, Cr) catalysts anchored on graphitic carbon nitride (g-C3N4) were prepared and then introduced into non-thermal plasma (NTP) system to produce highly reactive superoxide free radicals (center dot O2- ) for deep oxidation of NO. Experimental results revealed that the optimized CrCN catalyst, in combination with the NTP technique, exhibited an impressive oxidation efficiency of up to 100 %, which was 10 % and 30 % higher than that of MnCN and CoCN, respectively. Moreover, it was 1.56 times higher than that of NTP alone, indicating a synergistic effect of the NTP system and catalysis. The characterization results demonstrated that CrCN catalyst, with higher specific surface area and smaller grain sizes, was beneficial to increase the chemisorbed oxygen content and produce superoxide free radicals, which were proved by XPS, ESR technologies. Furthermore, the possible catalytic mechanism was proposed, which provided a basis for further understanding of the catalytic oxidation activity.