## 3 Results and Discussion
### Model Results
#### 3.2.4 Co\({}_{2}\) Splitting
Oxygen molecules, O\({}_{2}\), are formed mainly by the reaction of oxygen atoms with the CO\({}_{2}\) gas through neutral dissociation and 3-body recombination, reactions 17 and 20, respectively. Figure 16 shows the model results of the spatial distribution of the O\({}_{2}\) density at times 2, 6, 10, 14, and 18 ms. The maximum values of this density correspond to positions where O and CO\({}_{2}\) densities are higher. Figure 13: Spatial distribution of the CO\({}_{2}\)+ density for times (**a**) 2 ms, (**b**) 6 ms, (**c**) 10 ms, (**d**) 14 ms, and (**e**) 18 ms for the reactor at 22 kV AC voltage and 1 cm distance between electrodes. Density of O\({}^{-}\) Ion  
The electrons traveling to the electrodes can produce negative ions by attachment with the species present in the plasma. This was the case for the negative ion O\({}^{-}\) (reaction 15). Figure 14: Spatial distribution of the CO density for times (**a**) 2 ms, (**b**) 6 ms, (**c**) 10 ms, (**d**) 14 ms, and (**e**) 18 ms for the reactor at 22 kV AC voltage and 1 cm distance between electrodes. Figure 15: Spatial distribution of the O density for times (**a**) 2 ms, (**b**) 6 ms, (**c**) 10 ms, (**d**) 14 ms, and (**e**) 18 ms for the reactor at AC 22 kV voltage and 1 cm distance between electrodes. The spatial distribution of the density of O\({}^{-}\) ions produced by this process for times 2, 6, 10, 14, and 18 ms are shown in Figure 17.  
Figure 16: Spatial distribution of the O\({}_{2}\) density for times (**a**) 2 ms, (**b**) 6 ms, (**c**) 10 ms, (**d**) 14 ms, and (**e**) 18 ms for the reactor at AC 22 kV voltage and 1 cm distance between electrodes. Figure 17: Spatial distribution of the O- ion density for times (**a**) 2 ms, (**b**) 6 ms, (**c**) 10 ms, (**d**) 14 ms, and (**e**) 18 ms for the reactor at 22 kV AC voltage and 1 cm distance between electrodes. The negative O\({}^{-}\) ions moved toward the electrodes and were aggregated there according to electron density. This negative oxygen ion density increased quickly and became constant after the first millisecond. The electron dissociative attachment that produced the O\({}^{-}\) ions was higher in the inlet/outlet pipes. The high densities and low temperatures in these positions favored the electron attachment in these zones. Density of CO\({}_{2}\) Molecules  
Reactions 7, 9, and 15 mainly describe the CO\({}_{2}\) conversion and the density distribution of this molecule in the reactor. The spatial distribution of CO\({}_{2}\) density between the two electrodes inside the AC-PPP reactor is presented in Figure 17. The CO\({}_{2}\) density decreased near the electrodes due to the high values of electron density and temperature in this position. A zoom of the zone near the electrodes was plotted in Figure 18. Due to the plasma is still active inside the conductor inlet/outlet pipes, the CO\({}_{2}\) was also discomposed inside these pipes. As is shown, during the positive voltage (2, 6, and 10 ms), the maximum CO\({}_{2}\) decomposition was near the powered electrode, where the electron density was highest. Conversely, the maximum value was near the ground electrode during the negative voltage (14 and 18 ms). A theoretical estimation of the CO\({}_{2}\) conversion factor was made with the time averages of the CO\({}_{2}\) density over a period, T = 20 ms, in the outlet tube position, which could be compared with the experimental results of gas chromatography. A good agreement between experimental and theoretical results was found (see Figure 4a).