SCR催化剂脱硝及中毒机理的量子化学研究

发布时间：2018-06-04 19:00

本文选题：量子化学 + SCR催化剂　；参考：《华北电力大学》2017年硕士论文

【摘要】：氮氧化物(NO_X)是环境污染的重要组成物质之一,其排放量表现逐年增加的趋向,火电厂已成为我国NO_X排放最主要的来源。目前以NH_3为还原剂的选择性催化还原(SCR)烟气脱硝技术应用最为广泛且最高效。催化剂作为SCR脱硝系统中重要的组成部分,其性能对系统的脱硝效率和脱硝成本会造成很大影响。在实际应用中毒失活是催化剂不可避免的问题。本文运用密度泛函理论(DFT)结合V_6O_(15)和V_6O_(15)~+两种团簇模拟钒基催化剂的分子结构,分析研究了SCR催化剂的脱硝机理和金属中毒原理,为提高脱硝效率及催化剂抗中毒能力提供一定的理论指导。介绍了量子化学的一些基本原理即基本方程、基本计算方法以及Gaussian软件。利用DFT计算方法,构造V6O15和V6O15+簇模型模拟SCR催化剂的分子结构,并进行几何构型优化、单点能和电荷分析。以优化后的模型为基础,依次探讨了钒基催化剂具备的化学特性-良好的酸性、较好的氧化性以及被还原后的分子被重氧化的难易程度。在优化后的V_6O_(15)和V_6O_(15)~+簇模型上模拟Lewis位吸附水分子形成吸附位V-OH的微观机理,得到了反应过程中形成的中间体和过渡态的结构,并进行了IRC路径分析。模拟NO、NH_3在催化剂上的吸附情况,结合吸附能、静电势及电荷转移情况,分析了SCR脱硝反应机理。讨论了碱金属及碱土金属对V_6O_(15)和V_6O_(15)~+分子团簇的影响,并对中毒前后催化剂的分子结构参数、吸附能、LUMO轨道能量和加氢反应放热量进行计算。得出结论,催化剂在掺入K、Na、Ca金属原子后催化活性下降。对于V_6O_(15)团簇,中毒影响顺序为:K掺杂Na掺杂Ca掺杂未掺杂;对于V_6O_(15)~+团簇,中毒影响顺序为:Ca掺杂K掺杂Na掺杂未掺杂。
[Abstract]:Nox (Nox) is one of the most important components of environmental pollution, and its emission is increasing year by year. Thermal power plants have become the main source of NO_X emissions in China. At present, selective catalytic reduction (NH_3) flue gas denitrification technology with NH_3 as reducing agent is the most widely used and most efficient. As an important part of SCR denitrification system, the performance of catalyst has great influence on the denitrification efficiency and denitrification cost. It is inevitable for the catalyst to be deactivated by poisoning in practice. In this paper, the molecular structure of vanadium-based catalysts simulated by two kinds of clusters, V _ 6O _ O _ T _ (15) and V _ S _ 6O _ T _ (15), were studied by using density functional Theory (DFT), and the mechanism of denitrification and the principle of metal poisoning of SCR catalyst were studied. It provides some theoretical guidance for improving the denitrification efficiency and the ability of the catalyst to resist poisoning. Some basic principles of quantum chemistry, such as basic equation, basic calculation method and Gaussian software, are introduced. V6O15 and V6O15 cluster models were constructed to simulate the molecular structure of SCR catalysts by using DFT calculation method, and the geometric configuration optimization, single point energy and charge analysis were carried out. Based on the optimized model, the chemical properties of vanadium-based catalysts were discussed in turn, such as good acidity, good oxidation and the degree of reoxidation of reduced molecules. The microscopic mechanism of Lewis adsorbed water molecules forming adsorption site V-OH was simulated on the optimized V _ 6O _ S _ (15) and V _ 6O _ S _ T models. The structure of intermediate and transition state in the reaction process was obtained, and the IRC path analysis was carried out. The mechanism of denitrification of SCR was analyzed by simulating the adsorption of NO-NH3 on the catalyst, combining the adsorption energy, electrostatic potential and charge transfer. The effects of alkali metal and alkali earth metal on the molecular clusters of V _ (6) O _ (15) and V _ (6) O _ (1) were discussed. The molecular structure parameters, adsorption energy, energy of LUMO orbital and heat release of hydrogenation reaction before and after poisoning were calculated. It is concluded that the catalytic activity of the catalyst decreases after the addition of K ~ (2 +) Na ~ (2 +) Ca. For the V _ 6O _ _ (15) cluster, the order of poisoning effect is: (1) K doped, Na doped, Ca doped, and, for V _ (6) O _ (+) _ (15) C _ (+) cluster, the poisoning order is: (1) Ca ~ (2 +) doped K ~ (2 +) doped Na ~ (2 +),
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ426;X773

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