【作者】 李华；

【导师】 唐晓龙；

【作者基本信息】 昆明理工大学 ， 环境工程， 2009， 硕士

【摘要】 NOx是大气污染的主要物质,不仅危害人体的健康,同时也是酸雨、光化学烟雾形成的主要物种和引发物,对整个生态环境会造成严重破坏。因而控制和治理NOx已成为当前环境保护中最活跃的课题之一。文中提出了用等离子体协同催化技术催化氧化去除NOx的技术路线,探讨了等离子体协同催化过程催化氧化去除NOx的可行性,首先以过渡金属锰氧化物为活性组分制备了负载型和非负载型催化剂,并考察了其催化氧化活性；然后将这些催化剂,进行了等离子体协同催化氧化NOx的研究,通过等离子体协同催化作用,在模拟的富氧环境中,达到了低温催化氧化去除NOx的目的。本文的一些研究结果如下：1.以过渡金属锰和稀土金属为催化剂主要活性组分,用浸渍法、柠檬酸法、液相共沉淀法、低温固相法等制备了负载型和非负载型催化剂,并利用XRD、SEM、BET比表面积分析等手段,探讨了催化剂的结构和形貌等特性,以及催化剂制备方法对其结构和性能的影响；分析结果表明,利用柠檬酸法制备的MnOx催化剂结晶度较好,在400℃焙烧的催化剂在150℃NO转化率最高,且活性窗口较宽,XRD表征结果显示MnOx-CA-400℃含有Mn203、Mn304和Mn805；在非负载型催化剂中以液相共沉淀法掺入稀土元素铈时对催化剂改性效果最好,最佳掺入比为Mn：Ce=7：3,掺入稀土铈后催化剂活性窗口变宽,掺入稀土镧的效果不如铈。从上述催化剂的研究结果可知,催化剂的比表面积对催化剂的低温催化氧化活性影响较小,催化剂的平均孔径以及结晶形态影响较大,其中,较大平均孔径和结晶态的Mn304等锰氧化物的混合物有利于催化氧化NO。2.在模拟气体中,研究不同输入电压,不同气氛条件下的具体等离子体气相化学过程和特性。通过分析认为,等离子体的作用会促进NO的分解,并且随着电压的增大,NO的分解率也增大；等离子体的作用会使N2和O2反应生成N02,且随着电压的增加N02的量逐渐增多(18-45v),大于50v后生成的N02逐渐分解。3.建立了等离子体-催化实验系统。将经过等离子体反应器活化后的气体通入装有催化剂的固定床反应器,结果显示等离子体协同催化剂催化氧化NO的活性均高于只有催化剂催化氧化NO的活性,且活性窗口均有所变宽。等离子体的加入在低温下(50-100℃)较大的促进了NO的催化氧化。高温时等离子体虽然也能促进NO的氧化,但程度明显不如低温状态。在50℃时对比其他催化剂(CP-Mn:Ce=7:3)显示出58%的最高活性。在高温200℃时CP-Mn:Ce=7:3催化剂仍然具有较好的活性,活性窗口最宽。4.初步分析了在等离子体反应器和固定床反应器中NO氧化的机理,并进一步研究了在MnOx-CA-400催化剂协同等离子体催化氧化NO的反应中,当NO浓度低于5×10-4,氧气浓度3%～11%时的动力学特性。研究表明NO的反应级数为0.9984,O2的反应级数为0.947；在固定床反应器中O2是以吸附在氧化物上的吸附态和气相分子参与反应的,而对于NO可以推断它是以气相分子形式参与反应。更多还原

【Abstract】 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.更多还原