# Chlorobenzene Removal Using DBD Coupled with CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) Catalyst
## 3 Results and Discussion
### Byproducts Analysis and Reaction Mechanism
observed a high proportion of oxalic acid (C\({}_{2}\)) and maleic acid (C\({}_{4}\)) when analyzing the degradation products of chlorobenzene in the DBD reactor and attributed the production of oxalic acid (C\({}_{2}\)) and maleic acid (C\({}_{4}\)) to the cracking of chlorobenzene under high-energy electron collision. The degradation process of chlorobenzene is divided into three steps: firstly, chlorobenzene breaks down into H atom and chlorophenyl under the attack of high-energy electrons, then chlorophenyl is decomposed into oxalic acid (C\({}_{2}\)), chloromaleic acid (C\({}_{4}\)), and other short-chain aliphatic acids under the attack of OH, O, and H. Finally, these short-chain aliphatic acids are further oxidized to CO\({}_{2}\) and H\({}_{2}\)O [62]. However, the cracking of the benzene ring requires relatively high electron energy. As a result, during the degradation process, a high proportion of the aromatic compounds will keep the benzene ring unopened. Thus, some free radicals in the reaction region will combine with the benzene ring to form various kinds of substitution products. These reactions not only occur in the weak discharge region but also on the surface of the catalyst. Moreover, the probability for the formation of polysubstituted aromatic compounds in the discharge region is relatively low due to the short lifetime of active substances such as OH radicals and Cl atoms. On the surface of the catalyst, the survival time of these active particles is longer than that in the discharge space. Therefore, it is easier to produce aromatic compounds with multiple substituents on the catalyst surface. However, since the toxicity of the aromatic compounds with multiple substituents may be higher than that of the original pollutants, it is vital to avoid the production of such substances and the effect of plasma catalysis on the formation of those harmful byproducts is not negligible. In this study, 4-chloro-2-nitrophenol, 2,4-dichloro-5-nitrophenol, 2,4-dichlorophenol, biphenyl, and other substances were detected in the byproducts. It was worth noting that the above multiple substituted aromatic compounds could be formed by the same disubstituted aromatic compound 4-chlorophenol with different active substances (OH, Cl and NO\({}_{2}\)). However, 4-chlorophenol was not detected in the byproducts, while dichlorobenzene and chlorointobenzene, the reaction product of chlorobenzene with Cl or NO\({}_{2}\) were detected. Considering the oxidation potential (2.8 eV) of hydroxyl radical is higher than that of chlorine atom (1.36 eV) and nitro radical (0.96 eV), the possibility of forming the two latter substances alone without forming 4-chlorophenol in the discharge region is relatively low. In addition, the existence of 2-chlorophenylphenyl ether also supports the production of 4-chlorophenol during the reaction process since 2-chlorophenyl ether is most likely to be produced by the dehydration of two 4-chlorophenols. Furthermore, it is easier for chlorobenzene to produce paradisubstituted compounds during the reaction. On the other hand, the detected polysubstituted aromatic compounds all have two or more inert groups (-Cl, -NO\({}_{2}\)), which indicates that most of the easily oxidized organic compounds produced in the degradation process are rapidly converted into higher oxidized organic compounds (finally CO\({}_{2}\) and H\({}_{2}\)O). Moreover, these reactions can be considered as the non-rate-determining step for the degradation of chlorobenzene. In this process, the aromatic compounds with multiple substituents formed by the combination of a chlorine atom and nitro radical are not easy to participate in the reaction due to their strong inertia. In this study, it is speculated that chlorobenzene is firstly attacked by high-energy electrons to form chlorophenyl in the reaction region. Then the chlorophenyl will react with nitro radicals, Cl atoms, and OH radicals to form 4-chlorophenol, dichlorobenzene, and chlorointobenzene.