| Nitrogen oxides remain a major source for air pollution, which contributed to photochemical smog, acid rain, ozone depletion, and greenhouse effects. NOx is harmful to human health and ecosystem. Now, how to control and treat these pollutions has become one of the most important issues on environment protection. A superior effective method for NOx removal was presented in this work, which combined the non-thermal plasma technology and catalytic technology. Firstly, catalytic oxidation of NOx over unsupported and supported catalysts was carried out without the assistant of plasma. Secondly, catalysts with the assistant of plasma were investigated. The research works in this paper were summarized as follow,1. Manganese oxide catalysts and manganese-rare earth oxide catalysts were prepared by Low temperature solid phase reaction method, Citric acid method, Co-precipitation method and Excessive dipping method respectively. The crystal structure of prepared oxides was examined by XRD to validate the formation of the desired crystalline structure. Catalysts were also analyzed by SEM and BET. The results showed the crystal structure of MnOx catalyst prepared by Citric acid method was better than other catalysts. And the MnOx catalysts which calcined at 400℃had higher NO conversion than at 150℃and had a more broaden activity window. The XRD results showed the MnOx-CA-400℃contained by Mn2O3,Mn3O4 and Mn8O5. The effect of the doping different rare earth oxides was also investigated and the results showed that doping cerium would be better on NO oxidation. The most active catalyst was obtained with a molar Ce/(Mn+Ce) ratio of 0.3 prepared by co-precipitation method. Compared with all the catalysts, the catalysts which have larger average pore radius and Mn3O4 crystal have higher NO conversion at low temperature and had a more broaden activity window.2. The generator of Dielectric Barrier Discharge (DBD) was set up. In order to explore the properties of gas phase chemistry in the plasma, the plasma gas phase chemistry was investigated. The experiment results show that the plasma promotes part of NOx decomposed into N2 and O2. Moreover, with the promotion of discharge voltage, the decomposition efficiency of NOx was improved. In addition, N2 reacted with O2 and product NO2 by plasma. As the apply voltage increased (18v-50v), the more NO2 was generated. NO2 began to decompose when the apply voltage was beyond 50v.3. The plasma assisted catalytic oxidation system was set up. The mixture gas contained NO in rich condition was activated by plasma reactor (Dielectric Barrier Discharge, DBD). Catalytic reactor (Fixed bed tube reactor) with MnOx catalyst was placed downstream. The results showed a remarkable synergetic effect. The plasma not only promoted the catalytic oxidation of NO but also decreased the catalysis temperature. And the activity window of the catalysts was broadened. The increasing activities at low temperature (50～100℃) were more apparently higher than high temperature by plasma. Compared with other catalysts (CP-Mn:Ce=7:3 catalysts) still obtained 58% NO covertion at 50℃, and had a high activity at 200℃.4. The reaction mechanism and kinetics of plasma assisted catalytic oxidation over MnOx-CA-400℃catalyst were studied at the condition of the concentration of NO was under 500ppm the concentration of O2 was between 3% and 11%. The results showed that the reaction order of NO was 0.9984 and the reaction order of O2 was 0.947. O2 was partly adsorbed in the catalyst and partly was gas-phase molecular forms participation in the reaction and NO was gas-phase molecular forms participation in the reaction. |
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