CeO2(111)表面上CO的吸附行为和催化过程的第一性原理研究

First-Principles study on the adsorption behavior and catalytic process of CO on CeO2(111) surface

缪鹏程

11749031

硕士

物理学

徐虎

2019-05-14

2019-07-10

哈尔滨工业大学

深圳

现代人类社会的科技取得了持续不断的进步和发展，环境污染问题已经日趋严重，并影响到了人类正常的生活。一方面，汽车逐渐成为人类出行必不可少的工具，数量急剧增加的汽车排放出大量的尾气中存在着CO等有害气体，另一方面工厂和电力公司燃烧煤炭也产生了大量的CO。因此关于一氧化碳的吸附和催化氧化问题逐渐成为人们研究的热点。长期以来，贵金属一直是CO的理想氧化催化剂，但是由于贵金属成本高昂，人们逐渐研究出了非贵金属的催化剂,其中二氧化铈CeO2催化剂凭借具有氧化CO的优异催化活性而受到广泛关注和应用，并成为目前CO催化氧化最好的载体。因此本文研究了CO吸附在CeO2表面的各种物理特性以及吸附行为，并模拟了CO在CeO2（111）表面的催化氧化过程。首先，本文通过第一性原理计算，确定了CeO2（111）原胞的K点取值、晶格常数、最大截断能等基础性质，为CO在CeO2（111）表面上的吸附提供精确的参数依据。然后，通过比较CO在3个O-Ce-O层2×2超胞的CeO2表面上的不同吸附位置的吸附能了解到CO在CeO2表面上的各种吸附行为，并初步确定了CO的最优吸附位置。本文再通过比较不同层数和不同的超胞结构的CeO2表面上CO的吸附行为来研究CeO2的层数和超胞结构对CO的吸附产生的影响，并为接下来的研究CO的吸附选择合适的CeO2层数和超胞结构。其次，在CO在CeO2表面吸附形成CO2并形成氧空位的情况下，本文通过移动CeO2的表面氧原子向氧空位靠拢来实现电荷的转移并改变Ce3+的位置，来研究Ce3+的不同位置与CO吸附能的关系。结论显示Ce3+在氧空位次近邻位置时，CO的吸附能最低。紧接着，本文通过研究存在氧空位的CeO2表面上Ce3+的位置与氧空位形成能的关系来进一步验证Ce3+与氧空位的相对位置对体系能量的影响。接着，本文研究发现CO在吸附形成CO2后可以继续吸附形成碳酸盐CO32-形式，CO的吸附能进一步降低。随后本文研究了CO2与CeO2表面氧和次表面氧成键的吸附过程和吸附能差异，并最终确认了CO与两个表面氧形成碳酸盐形式为CO的最低吸附能状态，并通过neb方法将CO到CO2到CO32-的形成过程演示出来。最后，本文通过将未掺杂和掺杂贵金属Pd、Cu的CeO2表面上CO的吸附行为进行对比，更直观的理解了贵金属提高反应活性和催化反应的机理。接着，本文通过CO在CeO2表面吸附形成CO2，O2在存在氧空位的CeO2表面吸附以及CO在O2吸附后继续吸附形成CO2的研究，呈现出了CO在CeO2表面上的催化氧化的循环过程。

With the continuous development of human science and technology and the continuous advancement of society, the problem of environmental pollution has become increasingly serious and has affected the normal life of mankind. On the one hand, cars have become an indispensable tool for human travel, and a large number of cars emit a large amount of exhaust gas, which contains harmful gases such as CO. On the other hand, factories and power companies burn coal and produce a large amount of CO. Therefore, the adsorption and catalytic oxidation of carbon monoxide has become a hot topic. Precious metals have long been the ideal oxidation catalyst for CO, but due to the high cost of precious metals, non-precious metal catalysts have been developed. Among them, cerium oxide CeO2 catalyst has been widely concerned and applied by virtue of its excellent catalytic activity for oxidizing CO, and has become the best carrier for catalytic oxidation of CO. Therefore, the physical properties and adsorption behavior of CO adsorption on CeO2 surface were studied, and the catalytic oxidation process of CO on CeO2 surface was simulated. Firstly, based on the first-principles calculation, the basic properties of the K-point value, lattice constant, maximum cut-off energy and surface energy of CeO2(111) cells are determined, which provides the accurate parameters of the adsorption of CO on the surface of CeO2(111). Then, the adsorption behavior of CO on the surface of CeO2 was observed by comparing the adsorption of CO on different adsorption sites on the surface of CeO2 of 3 O-Ce-O layer 2×2 supercells, and the optimal adsorption position of CO was preliminarily determined. In this paper, we compare the adsorption behavior of CO on the surface of CeO2 with different layers and different supercellular structures to study the influence of the number of layers of CeO2 and the structure of supercellular structure on CO adsorption, and select the appropriate number of CeO2 layers and the supercellular structure CO adsorption for in the next study. Secondly, in the case where CO adsorbs on the surface of CeO2 to form CO2 and form oxygen vacancies, this paper studies the different positions of Ce3+ by moving the surface oxygen atoms of CeO2 toward oxygen vacancies to transfer charge and change the position of Ce3+ to study the relationship between the different position of Ce3+ and the adsorption energy of CO. The results show that the adsorption energy of CO is the lowest when Ce3+ is in the next position of oxygen vacancies. Then, by studying the relationship between the position of Ce3+ on the surface of CeO2 with oxygen vacancies and the formation energy of oxygen vacancies, the influence of the relative position of Ce3+ and oxygen vacancies on the energy of the system is further verified. Thirdly, the study found that CO can adsorb to form CO32-carbonate on the basis of adsorption of CO2, and the adsorption energy of CO is further reduced. Subsequently, the adsorption process and adsorption energy difference between CO forms a bond with CeO2 surface oxygen atoms and subsurface O atoms were studied. Finally, we can see that the lowest adsorption energy state of CO is CO forms a bond with two surface O atoms in the form of carbonate. The formation process of CO to CO2 to CO32- was demonstrated by the neb method. Finally, by comparing the adsorption behavior of CO on the surface of CeO2 undoped and doped with precious metals Pd and Cu, the mechanism of the reaction activity and catalytic reaction of noble metals is verified more intuitively and effectively. Then, this paper studies about CO is adsorbed on the surface of CeO2 by CO, O2 adsorbs on the surface of CeO2 with oxygen vacancies and CO adsorbs to form CO2 after O2 adsorption. The cyclic oxidation process of CO on the surface of CeO2 is presented.

第一性原理计算 CO吸附 CO2与CO32- neb方法 催化氧化

First principles calculation CO adsorption CO2 and CO32- neb method catalytic oxidation

中文

联合培养

南方科技大学

缪鹏程. CeO2(111)表面上CO的吸附行为和催化过程的第一性原理研究[D]. 深圳. 哈尔滨工业大学,2019.