# Nitrogen Oxide Removal by Coal-Based Activated Carbon for a Marine Diesel Engine
## 3 Results and Discussion
### Effect of AC on NO + O\({}_{2}\) and NO + O\({}_{2}\) + NH\({}_{3}\)  
The diesel engine exhaust gas contains a large amount of O\({}_{2}\). O\({}_{2}\) can not only oxidize NO to NO\({}_{2}\), but also is the reactant of standard SCR reaction Equation (3). Therefore, O\({}_{2}\) will have a great influence on the denitration ability of AC. When the inlet gas is 1000 uL/L NO + 5% O\({}_{2}\), the denitration ability of AC at different temperatures is shown in Figure 8, which shows that it takes 660 min for outlet NOx to reach 900 uL/L at 15 \({}^{\circ}\)C and 500 min at 50 \({}^{\circ}\)C. Compared with the experiment without O\({}_{2}\) at 15 \({}^{\circ}\)C (Figure 2), the adsorption saturation time of AC is greatly prolonged, indicating that O\({}_{2}\) can greatly promote the chemical adsorption of NO on the surface of AC. In addition, NO\({}_{2}\) starts to appear at the outlet after 300 min at 15 \({}^{\circ}\)C. Then NO\({}_{2}\) gradually increases and finally stabilizes, while NO basically maintains about 300 uL/L. When the temperature is 50 \({}^{\circ}\)C, NO\({}_{2}\) starts to appear at the outlet after 200 min and since then NO maintains about 480 uL/L. The trends of NO and NO\({}_{2}\) are similar to that at 15 \({}^{\circ}\)C. The above experimental phenomenon is mainly due to the different adsorption sites (C\({}_{\text{f}}\)-A and C\({}_{\text{f}}\)-B) on the surface of AC for NO and NO\({}_{2}\). C\({}_{\text{f}}\)-A can adsorb NO and NO\({}_{2}\), but it is easier to adsorb NO, while C\({}_{\text{f}}\)-B can adsorb NO\({}_{2}\) only [27]. At the beginning of the experiment, gaseous NO can be directly adsorbed on the oxygen-containing functional groups and then converted into C\({}_{\text{f}}\)-A-NO\({}_{2}\), or it can be adsorbed on the activated sites to form C\({}_{\text{f}}\)-A-NO, and then oxidized to C\({}_{\text{f}}\)-A-NO\({}_{2}\) by O\({}_{2}\). Due to the combination force of NO\({}_{2}\) on C\({}_{\text{f}}\)-A-NO\({}_{2}\) being relatively small, NO\({}_{2}\) is easy to desorb or directly transfer to the adjacent C\({}_{\text{f}}\)-B to form C\({}_{\text{f}}\)-B-NO\({}_{2}\). When C\({}_{\text{f}}\)-B is saturated, the desorbed NO\({}_{2}\) will be out of the reactor. Finally, the adsorption and oxidation of NO balance the adsorption and desorption of NO\({}_{2}\) dynamically. The outlet concentrations of NO and NO2 remain roughly stable. As can be seen from Figure 8, the conversion rates of AC to catalyze the oxidation of NO to NO\({}_{2}\) at 15 \({}^{\circ}\)C and 50 \({}^{\circ}\)C are 62.3% and 43.8%, respectively. When ships use low-sulfur fuel oil, the wet scrubber desulfurization will no longer be needed and the temperature of the exhaust gas entering the SCR reactor is higher than that coming out of the scrubber in a high-sulfur case. Therefore, it is necessary to study the denitration ability of AC at higher temperatures. As shown in Figure 9, the denitration ability of AC are simulated with or without NH\({}_{3}\) at 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, and 300 \({}^{\circ}\)C, respectively. Each experiment is divided into three stages: the first stage is the heating process (from room temperature to the set temperature), and the second and third stages are maintained at the set temperature. In the first stage and the third stage, the inlet gas is 1000 uL/L NO + 5% O\({}_{2}\), and in the second stage, 1000 uL/L NH\({}_{3}\) is added. It can be seen from Figure 9 that in the first 60 min, the NO concentration in the outlet rises rapidly during the heating process. The faster the heating rate, the higher the NO concentration in the outlet. When the temperature is stable, the outlet NO gradually decreases and eventually stabilizes.