新疆稀土钙钛矿应用于机车尾气净化的密度泛函理论研究

发布时间：2018-01-18 16:07

本文关键词：新疆稀土钙钛矿应用于机车尾气净化的密度泛函理论研究　出处：《新疆大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文通过调研大量的文献资料,收集了新疆地区主要的稀土产地的地质资料及资源量数据,证实确如文献所载新疆拥有丰富的稀土资源。被誉为“工业维生素”的稀土因其特殊结构延伸出较多的特性,而被广泛应用各个行业,在环境治理方面它有着许多矿物材料无法媲美的优势。大气污染问题一直是人们热切关心地焦点,近年来我国多数城市出现了大范围的雾霾天气。引发雾霾的原因很大程度上来源于数量日益增长的机动车所排放的机车尾气构成的大气污染,治理机车尾气已然成为了迫在眉睫的任务。依靠新疆丰富的稀土矿产资源来研究治理大气污染的稀土钙钛矿催化剂不仅是地利,更是满足当前需求的天时。因此本文在考虑到上述亟待解决的问题以及拥有丰富物质基础的现实条件上,以新疆稀土为主要矿物原料制备成的稀土钙钛矿为研究对象,以密度泛函理论为核心理论而开发出来的计算模拟软件——Materials Studio,为研究工具。首先,在软件中建立了稀土钙钛矿LaCoO_3的晶体模型。随后,采用软件调查计算了它的晶体结构参数和微观电子性质。在搞清楚了其基本性质的基础上,紧接着设计了有着“大气污染中最大毒瘤”称号的NO吸附在LaCoO_3(0 0 1)面两种终端上的吸附构型并计算了其被吸附在界面上时,受到了LaCoO_3中O、La和Co元素的电子怎样的影响。最后确定了NO被稀土钙钛矿LaCoO_3氧化还原的反应路径,对计算出的结果进行分析以探究NO与界面的反应机理。以期计算的数据及分析成果能对制备出用于净化机车尾气的稀土钙钛矿催化剂提供一定的理论基础并预测一定的实验指导。主要结论由如下:(1)采用GGA-PBEsol-DN计算出的LaCoO_3的晶胞参数为a=5.453?,Co-O=1.933?,与实验值最为接近,偏差仅为0.2%。能带结构图、总态密度图和分波态密度图显示出,能量在-6 eV~0 eV上时,LaCoO_3中的Co原子与O原子存在着剧烈的相互作用,反映出Co的3d态和O的2p态的共价特性。分析发现是由于Co原子是位于钙钛矿结构中八面体中心上,这样的结构特点会使Co原子自己的3d电子轨道裂成t2g与eg轨道,其中的eg轨道与O的电子轨道相互作用改变了Co-O键的电子密度,致使LaCoO_3中Co-O的成键轨道和反键轨道受到影响从而引起了Co-O键的变化。最后,在能带图中最下端的两部分也发现了La-5p与O-2s有相互共价作用,但是相对较弱。本章主要计算出了LaCoO_3的晶体结构参数,以及结构中各原子的电子轨道的相互影响状况。(2)模拟了NO在LaCoO_3的CoO_2和LaO终端的(0 0 1)面的吸附构型并运用了GGA-PBE的方法计算了NO的吸附性质。从计算出的吸附能与Mulliken和Hirshfeid电荷构成的数据表及各原子的分波态密度图中,发现NO在CoO_2终端面上吸附的稳定性强于LaO终端面,并且NO的N原子吸附在LaCoO_3的CoO_2终端的(0 0 1)面的Co上是吸附最稳定的形式,并且分波态密度图展示出LaCoO_3中原子Co对吸附NO效果极佳,源于Co拥有的3d电子轨道与NO拥有的p电子轨道出现了杂化的现象。综合所有的结果来说,NO在LaCoO_3的CoO_2终端(0 0 1)面能被吸附形成多种较为稳定的形式,证明LaCoO_3有对NO吸附有较为活跃的贡献。(3)NO在稀土钙钛矿LaCoO_3的CoO_2终端(0 0 1)面上进行反应的分成两种形式:其一是氧化的形式,最佳反应路径为O_2→O~*+O~*→NO+O~*→NO_2~*→NO_2+O~*→NO_3~*,影响产物NO_3~*形成速率的关键步骤是O_2的分解,这个步骤的完成需突破的能垒为10.96 eV,较大的能垒直接制约着产物的生成速率和反应的进行。其二还原的形式,最佳反应路径为NO+NO→NOON~*→N_2O~*→N_2O→O_2+N_2,产物N_2+O_2形成的速率控制步骤是N_2O的形成,这个过程需要克服的能垒分别是0.13 eV、1.27 eV和0.79 e V,这些数值表示反应需要的最低能量相对较小。两个结果进行对比时发现,NO的氧化需要的最低能量略大于NO还原所需要的最低能量,这意味着NO在LaCoO_3催化剂上反应时还原较氧化易进行,选择性上还原强于氧化。
[Abstract]:In this paper, through a large number of research literature, geological data and data collection of the main resources of rare earth origin in Xinjiang, confirmed that the literature contained such as Xinjiang has rich rare earth resources. Known as the "industrial vitamin" rare earth because of its special structure extends more features, and is widely used in various industries, it there are many mineral materials can match the advantages in environmental governance. The air pollution problem has been the focus of concern, in recent years there has been a wide range of haze weather in China. Most of the city air pollution of locomotive vehicle exhaust caused by haze reason is largely due to the growing number of emissions constitute, management of locomotive exhaust has become an imminent task. Rare earth perovskite catalysts rely on Xinjiang's rich rare earth mineral resources on air pollution not only Place, it is meet the needs of the current day. Based on the consideration of the above problems to be solved and has rich material on the basis of the actual conditions, in Xinjiang rare earth rare earth perovskite prepared into main mineral raw materials as the research object, calculated by the density functional theory as the core theory and developed simulation software Materials Studio, as a research tool. First of all, in the software the crystal model of rare earth perovskite LaCoO_3 is established. Then, using the software to investigate its crystal structure parameters and micro electronic properties were calculated. The clear basis of its basic properties, followed by the design of a "cancer" in the title of the air pollution adsorption of NO on LaCoO_3 (001) surface adsorption configuration two terminal and the calculation of the adsorbed on the interface by LaCoO_3, O, La and Co of electronic elements. The how After determining the reaction path of the oxidation of NO rare earth perovskite LaCoO_3 reduction, the reaction mechanism of the calculated results were analyzed to explore the NO and interface. The data and analysis results in order to calculate the prepared for rare earth perovskite catalysts for purification of vehicle tail gas to provide a theoretical basis and experimental guidance. The main prediction the conclusion is as follows: (1) the cell parameters calculated by using GGA-PBEsol-DN LaCoO_3 a=5.453?, Co-O=1.933?, and most close to the experimental value, deviation is only 0.2%. band structure, total density of state and partial density map shows that the energy in the -6 eV~0 eV, LaCoO_3 Co with the O atoms and the interaction exists severe, reflecting the characteristics of the 2p covalent 3D state and O Co. The analysis found that due to the Co atom is located in the center of the perovskite structure with eight sides, so the structure characteristics of the Co atom 3D electronic track their split into t2g and eg orbitals, electron orbit eg orbital and O where the interaction changes the electron density of Co-O bond, resulting in LaCoO_3 Co-O bonding and antibonding orbitals affected to cause changes in the Co-O bond. Finally, in the two part to the bottom in the band diagram the La-5p and O-2s have also found each other but relatively weak covalent interaction. This chapter mainly calculated the crystal structure parameters of LaCoO_3, the mutual influence of electronic and atomic structure in orbit. (2) simulated NO in CoO_2 and LaO terminal of the LaCoO_3 (001) surface configuration and use the method of GGA-PBE adsorption properties of the NO were calculated. The calculated adsorption energy of Mulliken and Hirshfeid and charge the data table and each atom of the PDOS map, found that the stability of NO adsorption on CoO_2 end face is stronger than the LaO and NO terminal. The adsorption of N atoms in the CoO_2 terminal of the LaCoO_3 (001) Co surface is the most stable adsorption form, and partial density of states shows atom Co LaCoO_3 on adsorption of NO effect is excellent, P orbits of 3D orbits and NO derived from Co have appeared with hybrid phenomenon. All the results for NO in the CoO_2 terminal LaCoO_3 (001) surface can be absorbed to form a variety of relatively stable form, have proved that LaCoO_3 adsorption of NO have more active contributions. (3) the CoO_2 terminal NO in rare earth perovskite LaCoO_3 (001) surface reactions were divided into two forms: one is the oxidized forms, the optimum path for the O_2 - O~*+O~* - NO+O~* - NO_2~* - NO_2+O~* - NO_3~*, product NO_3~* is the key step in the formation rate of O_2 decomposition, this step need to break the barrier of 10.96 eV, high energy barrier directly restricts the product Generation rate and reaction. The reduction of the form, the best reaction path for the NO+NO - NOON~* - N_2O~* - N_2O - O_2+N_2, the rate controlling step is the formation of the N_2O product of N_2+O_2 formation, this process needs to overcome the energy barrier are 0.13 eV, 1.27 eV and 0.79 e V, the value that the minimum energy reaction the relatively small. Compared two results, the lowest energy minimum energy of NO oxidation than NO reduction required, which means that the NO reaction on LaCoO_3 catalyst. The oxidation reduction is easy, is stronger than the original selective oxidation.

【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X734.2

【参考文献】