分子筛ZSM-5负载过渡金属催化氧化NO的量子化学研究

发布时间：2018-05-03 05:15

本文选题：NO + 催化氧化　；参考：《杭州电子科技大学》2016年硕士论文

【摘要】：当今中国环境污染日益严重,其中的NO_x是引起雾霾的一种很重要的污染物。工业上NO_x脱除的技术主要是SCR(Selective Catalytic Reduction,选择性催化还原法)和SCO(Selective Catalytic Oxidation,选择性催化氧化法)。由于单独的NO在参加SCR反应的时候效率不如NO和NO_2按一定比例参加反应时的高,所以发展出了快速SCR技术。不论快速SCR还是SCO,将NO催化氧化为NO_2的技术均占有重要的地位。而目前,对NO催化氧化的研究以实验为主,机理还不是很清楚。所以,基于NO的催化氧化在脱硝领域的重要作用,本文对其催化机理进行了详细地研究。首先,本文采用量子化学密度泛函理论对NO的直接氧化反应进行了计算研究,分析了优化方法与基组对计算所带来的影响,并以此作为与催化氧化反应对比的参照。之后,采用UB3LYP//SDD方法优化得到负载在分子筛ZSM-5不同原子附着位点(Si、Al、Ce)上的以Mn、Co为代表的过渡金属催化氧化NO相关反应的反应物、过渡态、中间体及产物,分析得到反应进程,并计算获得了反应的活化能。最后,通过分析总结,对反应机理进行了探究。计算表明:使用UB3LYP//SDD方法计算优化的情况下,Mn-ZSM5或Co-ZSM5催化剂的存在下NO氧化的活化能在40-80kJ/mol左右,而NO直接氧化的活化能在130kJ/mol以上,所以,Mn-ZSM5和Co-ZSM5具有明显的催化效果;催化剂的附着中心原子不同,活化能也有差异,其中以Ce和Al为附着位点的ZSM-5催化反应时的活化能在40kJ/mol左右,而以Si为附着位点的ZSM-5催化反应的活化能要高于70kJ/mol,可知,掺杂了Ce、Al氧化物的催化剂的催化活性更好;通过计算得出Mn-ZSM5与Co-ZSM5的催化活性相差不大,总体上比Mn-ZSM5稍好一些。与前人研究的实验结果比较后推断,温度、气体空速和载体等一系列因素都会对催化效果产生影响,所以,进行比较还需考虑更多因素。本文的量子化学计算揭示了Mn-ZSM5及Co-ZSM5对NO氧化的催化反应机理,为过渡态金属催化氧化NO的进一步研究提供了理论参考。同时,指出Ce、Al氧化物的掺杂对催化反应具有促进的效果,验证了实验研究的结论。最后,Mn-ZSM5与Co-ZSM5催化活性的比较可以为以后对反应引入更多因素的研究提供了参考。
[Abstract]:Nowadays, environmental pollution in China is becoming more and more serious, among which NO_x is a very important pollutant causing haze. Industrial NO_x removal techniques are mainly SCR(Selective Catalytic reduction, selective catalytic reduction, and SCO(Selective Catalytic oxidation, selective catalytic oxidation. Because the efficiency of single no in SCR reaction is not as high as that of no and NO_2 in a certain proportion, rapid SCR technology has been developed. The catalytic oxidation of no to NO_2 plays an important role in both rapid SCR and NO_2. At present, the catalytic oxidation of no is mainly experimental, and the mechanism is not clear. Therefore, based on the important role of no catalytic oxidation in denitrification, the catalytic mechanism of no is studied in detail. Firstly, the direct oxidation reaction of no is studied by using the density functional theory of quantum chemistry, and the influence of the optimization method and the base set on the calculation is analyzed, which is used as a reference to the catalytic oxidation reaction. After that, UB3LYP//SDD method was used to optimize the reactants, transition states, intermediates and products of the transition metal catalyzed oxidation of no on the different atom attachment sites of molecular sieve ZSM-5. The reaction process was analyzed. The activation energy of the reaction was calculated. Finally, through the analysis and summary, the reaction mechanism is explored. The results show that the activation energy of no oxidation is about 40-80kJ/mol in the presence of Mn-ZSM5 or Co-ZSM5 catalyst, but the activation energy of direct no oxidation is above 130kJ/mol, so Mn-ZSM5 and Co-ZSM5 have obvious catalytic effect. The activation energy of the ZSM-5 reaction with ce and Al as the attachment site is about 40kJ/mol, and the activation energy of the ZSM-5 reaction with Si as the attachment site is higher than 70 kJ / mol. The results show that the catalytic activity of Mn-ZSM5 and Co-ZSM5 is not different from that of Mn-ZSM5, and that the catalytic activity of the catalyst doped with Ce-Al oxide is better than that of Mn-ZSM5. Compared with the experimental results of previous studies, it is inferred that a series of factors, such as temperature, gas space velocity and carrier, will affect the catalytic effect, so more factors should be considered for comparison. The quantum chemical calculations in this paper reveal the catalytic mechanism of no oxidation by Mn-ZSM5 and Co-ZSM5, and provide a theoretical reference for the further study of the catalytic oxidation of no by transition metal. At the same time, it is pointed out that the doping of CEO Al oxides can promote the catalytic reaction, and the conclusion of the experimental study is verified. Finally, the comparison of the catalytic activity of Mn-ZSM5 with that of Co-ZSM5 can provide a reference for the further study of introducing more factors into the reaction.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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