## 3 Results and Discussion  
### Performances of the DBD-NH\({}_{3}\)-Ch\({}_{4}\)-SCR and DBD-NH\({}_{3}\)-SCR Hybrid System  
The effect of SIE (specific input energy) on the NO removal efficiency for the DBD-NH\({}_{3}\)-CH\({}_{4}\)-SCR and DBD-NH\({}_{3}\)-SCR hybrid system is shown in Figure 1. A maximum NO conversion of approximately 70.5% was achieved at 512 J/L for the DBD-NH\({}_{3}\)-SCR hybrid system, with 0% O\({}_{2}\) in the feed. The NO conversions ranged from 0% to 38.1% for the DBD-NH\({}_{3}\)-CH\({}_{4}\)-SCR hybrid systems. In the process of DBD-SCR, the temperature of the plasma reaction zone was determined by the SIE. In two cases, with the rise of SIE, the reaction temperature increased from 293 to 348 K. At 348 K, the experiment results indicated that no obvious NO conversion was found over the V\({}_{2}\)O\({}_{5}\)-WO\({}_{3}\) catalyst, only by thermal activation without DBD. Therefore, the heat effect of DBD on NO conversion can be neglected in this work. The enhancement in SCR activation by plasma processes is generally attributed to the direct interaction of the radicals, electrons, and UV photons created by the plasma, with the catalyst and  
Figure 1: Schematic diagram of the experimental setup of the DBD–NH\({}_{3}\)–CH\({}_{4}\)–SCR system. molecules adsorbed on its surface. With the condition of O\({}_{2}\) absence, the reactions of NO + NO \(\AA\)\(\rightarrow\) N\({}_{2}\) + O\({}_{2}\) and NO + NH\({}_{2}\)\(\rightarrow\) N\({}_{2}\) + H\({}_{2}\)O cannot be ignored. Because NH\({}_{3}\) is more likely to be converted to NH\({}_{2}\) by DBD, as shown in Figure 2, the increasing SIE promoted NO conversion, and the performance of the DBD-NH\({}_{3}\)-SCR hybrid system was better with O\({}_{2}\) free in the feed. The overall conversion of NO in the presence of O\({}_{2}\) was presented in Figure 3. For the DBD-NH\({}_{3}\)-SCR process, the NO conversion was reduced from 70.5% to 43.3%, with an increase in O\({}_{2}\) concentrations from 0% to 12%. Following the presence of methane in the reaction system, the results became different. For DBD-NH\({}_{3}\)-CH\({}_{4}\)-SCR, the NO conversion increased rapidly from 38.1% to 77% as the O\({}_{2}\) concentration reached 2%, and the NO conversion reached 85.2% when the O\({}_{2}\) concentration was 6%. In conclusion, the NO removal in the DBD-NH\({}_{3}\)-SCR reactor was better than that in the DBD-NH\({}_{3}\)-CH\({}_{4}\)-SCR system with O\({}_{2}\) free; however, the opposite result was observed when the O\({}_{2}\) concentration was higher than 2%. This result indicates that O\({}_{2}\) has a negative effect on NO abatement in DBD-NH\({}_{3}\)-SCR. N\({}_{2}\)O and NO\({}_{2}\) are known to be critical in the formation of N\({}_{2}\) in SCR reactions, and thus, the production of N\({}_{2}\)O and NO\({}_{2}\) in the DBD-NH\({}_{3}\)-SCR and DBD-NH\({}_{3}\)-CH\({}_{4}\)-SCR processes is also examined. The effect of SIE on N\({}_{2}\)O and NO\({}_{2}\) concentration in the reaction system is shown in Figure 4a,b. For the DBD-NH\({}_{3}\)-SCR process, the N\({}_{2}\)O and NO\({}_{2}\) concentration is obviously higher than that in the DBD-NH\({}_{3}\)-CH\({}_{4}\)-SCR processes under the condition of 12% O\({}_{2}\). Therefore, these results  
Figure 3: Effect of O\({}_{2}\) concentration on the NO conversion of the DBD-NH\({}_{3}\)–SCR and DBD–NH\({}_{3}\)–CH\({}_{4}\)–SCR process. The SIE of DBD was kept at 512 /L, O\({}_{2}\) concentration ranged from 0% to 12% and other reaction conditions were the same as those in Figure 2.  
Figure 2: Effect of specific input energy (SIE) on the NO conversion of the DBD–NH\({}_{3}\)–SCR and DBD–NH\({}_{3}\)–CH\({}_{4}\)–SCR processes. Reaction conditions: 400 ppm NO, O\({}_{2}\) free, balance N\({}_{2}\). (1) DBD–NH\({}_{3}\)–SCR: 90 ppm NH\({}_{3}\). (2) DBD–NH\({}_{3}\)–CH\({}_{4}\)–SCR: 45 ppm CH\({}_{4}\) and 45 ppm NH\({}_{3}\).