氮氧化物在三氧化钨表面吸附反应的第一性原理研究
本文选题:密度泛函理论 切入点:WO_3 出处:《天津理工大学》2017年硕士论文
【摘要】:随着工业自动化的迅速发展,我们对传统燃料的需求日益提高。燃烧废气中的氮氧化物一直以来对自然环境和动植物都有着很大的危害。为了能科学治理废气排放和有效检测废气浓度,气体检测器应运而生,它们的基本原理是:通过把气体分子在检测器表面吸附时所引发的一系列物理化学变化转变为电信号,从而直观的表示出气体浓度的变化。但是由于吸附反应十分迅速,实验结果常常无法从微观角度揭示吸附反应历程。本课题以密度泛函理论为基础,运用计算软件模拟研究NO和NO_2分子在WO_3表面的吸附反应机理。通过完整地研究气体分子在不同吸附位点上的吸附平衡结构和电子转移情况,来揭示NO和NO_2分子在WO_3表面上的吸附反应机理。通过搜索过渡态和描绘反应路径能量变化,我们深入研究NO分子在WO_3表面的催化氧化过程,以期用理论结果指明实验研究方向,理论研究成果如下:1.模拟研究NO分子在WO_3(001)方向的两种不同切面上的吸附情况,在不同切面上同时考虑了氧缺陷对于吸附的影响。吸附能的结果表示出NO在以钨氧原子为切面的WO_3表面吸附效果最好;氧缺陷的存在增加了WO_3对于NO气体的敏感性。在以钨氧原子为切面的WO_3表面上,有氧缺陷的表面比完美表面多转移0.24e。2.模拟研究NO_2分子在WO_3(001)方向的两种不同切面上的吸附情况。在以氧原子为切面的WO_3表面,桥位氧原子会与NO_2分子发生反应,生成类硝酸盐。在以钨氧原子为切面的WO_3表面,NO_2分子的一个氧原子会填补到氧缺陷位上,剩余的NO分子则吸附在五配位的钨原子上。NO_2在不同切面的吸附反应中会引起WO_3表面的电阻升高。3.模拟研究NO分子在以钨氧原子为切面的WO_3(001)表面上的催化氧化反应。计算结果表明,在NO分子高覆盖度的情况下,NO分子倾向于和WO_3表面的晶格氧原子发生反应并产生吸附态的NO_2,这会导致WO_3出现氧缺陷;而在低覆盖度的情况下,氧分子吸附在WO_3表面上解离为氧原子,NO分子会与吸附态的氧原子发生反应。所以NO分子的覆盖度高低会影响反应历程。
[Abstract]:With the rapid development of industrial automation, Our demand for traditional fuels is increasing. Nitrogen oxides in burning exhaust gas have always been a great hazard to the natural environment, animals and plants. Gas detectors emerge as the times require. Their basic principle is to convert a series of physical and chemical changes caused by the adsorption of gas molecules on the surface of the detector into electrical signals. But because the adsorption reaction is very rapid, the experimental results often can not reveal the adsorption reaction process from the microscopic point of view. This topic is based on density functional theory. The adsorption mechanism of no and NO_2 molecules on the surface of WO_3 was studied by computer simulation. The adsorption equilibrium structure and electron transfer of gas molecules at different adsorption sites were studied. By searching the transition state and describing the energy change of the reaction path, we studied the catalytic oxidation process of no molecule on the surface of WO_3, with a view to pointing out the experimental research direction with the theoretical results. The theoretical research results are as follows: 1. Simulating the adsorption of no molecules on two different tangent planes in the WO _ 3C _ (001) direction, At the same time, the effect of oxygen defect on adsorption was considered on different surface. The adsorption energy showed that no adsorbed best on the surface of WO_3 with tungsten oxygen atom as the tangent plane. The presence of oxygen defects increases the sensitivity of WO_3 to no gas. On the surface of WO_3 with tungsten oxygen atoms as the tangent plane, The surface of oxygen defect transfers 0.24e.2. the adsorption of NO_2 molecules on two different sections in the direction of WO _ 3 / 001) is simulated. On the surface of WO_3 with oxygen atom as the plane, the oxygen atom at the bridge will react with the NO_2 molecule. The formation of nitrate-like nitrates. An oxygen atom of the NOS2 molecule on the surface of WO_3 with tungsten oxygen atoms as the cut will fill in the oxygen defect site. The remaining no molecules were adsorbed on five-coordinated tungsten atoms. NOS2 could cause the resistance of WO_3 surface to increase in different surface adsorption. 3. The catalytic oxidation reaction of no molecules on the WO _ 3T _ (001) surface with tungsten oxygen atom as the tangent plane was studied by simulation. The results of the calculation show that. No molecules tend to react with lattice oxygen atoms on the surface of WO_3 and produce adsorbed no _ 2 under the condition of high coverage of no molecules, which will lead to oxygen defects in WO_3, while in the case of low coverage, The oxygen molecule adsorbed on the surface of WO_3 is dissociated that the no molecule will react with the oxygen atom in the adsorbed state, so the coverage of no molecule will affect the reaction process.
【学位授予单位】:天津理工大学
【学位级别】:硕士
【学位授予年份】:2017
【分类号】:O647.31
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