Pr和Ce掺杂的氧化锆表面上一氧化碳和镍团簇的吸附

发布时间：2018-01-08 20:27

本文关键词：Pr和Ce掺杂的氧化锆表面上一氧化碳和镍团簇的吸附　出处：《昆明理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文研究了CO在Ce、Ca和Pr掺杂ZrO_2表面上的吸附,Pr、Ti等掺杂对ZrO_22构和氧空位形成能的影响,以及镍原子在Ce掺杂ZrO_2表面上的吸附。通过第一性原理研究我们得到了如下研究成果:首先通过研究Pr、Ti等掺杂后ZrO_2的结构和氧空位形成能发现氧空位最容易出现在ZrO_2(111)表面。氧空位形成能在未掺杂的ZrO_2晶胞中是-2.33 eV,在Ti和Pr掺杂后氧空位形成能分别是-2.54 eV和-2.91 eV。这表明Ti和Pr掺杂后更有利于氧化锆中氧空位的形成。Pr掺杂会有更小的带隙值1.41 eV,Ti掺杂时的带隙是1.82 eV,Pr掺杂时邻近掺杂位置的四个氧原子比在Ti掺杂时有更大的电荷,Pr掺杂对降低ZrO_2的还原性有更明显的作用。通过对氧空位在不同ZrO_2表面的表面能计算研究表明ZrO_2(111)面是最稳定的面。在ZrO_2(111),(110),(100)三个表面中氧空位更容易在ZrO_2(111)表面的最外表面形成。研究表明掺杂对Zr02的晶格结构,电荷分布,以及氧化还原性都有很大的影响。掺杂会使邻近掺杂位置的氧原子的布里居电荷在掺杂后比掺杂前明显偏大。掺杂还会改变Zr02的带隙,掺杂后的ZrO_2带隙都会变小,这是因为掺杂后有电子填充了空带从而使得带隙变得狭窄。其次对CO在Ce、Ca和Pr掺杂ZrO_2表面上的吸附研究发现CO在清洁ZrO_2(111)表面最稳定的吸附位置是锆桥位。CO在纯ZrO_2(111)表面的吸附能是-0.35eV,在Ca掺杂ZrO_2(111)表面的吸附能是-0.41 eV,在Ce掺杂的ZrO_2(111)表面的吸附能是-0.67 eV,在Pr掺杂的ZrO_2(111)表面吸附能是-0.73eV。这表明CO在Pr掺杂的ZrO_2(111)表面的吸附是最稳定的。同时我们发现吸附最稳定的表面态密度左移越明显,这表明吸附后系统的能量降低。最后对孤立Ni原子和Ni7团簇分别在ZrO_2(111)和Zr1-xCexO_2(111)表面的吸附研究发现对于单个镍原子的吸附最稳定的吸附位置是Zr1-Zr2桥位。吸附后Ni原子失去电子,Ni0被氧化成Ni+2,两个Zr原子得到电子,Zr+4被还原成Zr+3。Ni7团簇在化学计量的Zr02(111)表面的吸附能是-5.87eV,电荷是-0.18e。这说明吸附后Ni7得到电子,一些在Ni7中的Ni原子将从Ni0还原成Ni+1,这和单个镍原子的吸附是完全相反的,这是一个很有趣的结果。Ce原子的引入会引起Ni7吸附能的增加,这表明Ce掺杂对Zr02的催化性能有很大的影响。Ce掺杂可能是增加ZrO_2催化性能的有效办法,Ni7/Zr0.667Ce0.333O_2催化剂有很好的催化性能。研究发现吸附能和电荷的绝对值是同增同减的,表面电荷转移是催化剂催化性能改变的重要因素。
[Abstract]:In this paper, the influence of CO doping on ZrO_22 structure and oxygen vacancy formation energy on CeCa-Ca and Pr-doped ZrO_2 surfaces has been investigated. And the adsorption of nickel atoms on ce doped ZrO_2 surface. We obtained the following results through the first principle study: first, through the study of pr. The structure and oxygen vacancy formation of Ti doped ZrO_2 can be found to be the most likely to occur in ZrOW _ 2111). Surface. The oxygen vacancy formation energy is -2.33eV in the undoped ZrO_2 cell. The oxygen vacancy formation energies after Ti and pr doping are -2.54 EV and -2.91 respectively. This indicates that Ti and pr doping are more favorable to the formation of oxygen vacancies in zirconia. Pr doping will have a smaller band gap value of 1.41 EV. The band gap of Ti doping is 1.82 EV / pr doping. The four oxygen atoms adjacent to doping position have higher charge than that of Ti doping. Pr doping has a more obvious effect on the reduction of ZrO_2. The surface energy of oxygen vacancies on different ZrO_2 surfaces is calculated. The plane is the most stable surface. Oxygen vacancies in the three surfaces are easier to form on the outermost surface of ZrO2C111). The results show that the lattice structure and charge distribution of doped Zr02 are observed. Doping can make the BGP of oxygen atoms near the doping position obviously larger than that before doping. Doping will also change the band gap of Zr02. After doping, the band gap of ZrO_2 becomes smaller, which is due to the doping of electrons filled with empty band, which makes the band gap narrow. Secondly, the CO in ce. The adsorption of CO on the surface of Ca and pr doped ZrO_2 shows that the most stable adsorption site of CO on the surface of clean ZrOs 2111 is zirconium bridge. Co in pure ZrO2111). The adsorption energy of the surface is -0.35 EV. The adsorption energy on Ca doped Zro _ 2J _ (111) surface is -0.41 EV, and on ce doped ZrO _ (2) S _ (111) surface is -0.67 EV. The adsorption energy on pr doped ZrO2111) surface is -0.73 EV, which indicates that CO is present in pr doped ZrO2111). The adsorption on the surface is the most stable, and we find that the density of states on the surface of the adsorbed is the most stable. The results show that the energy of the system decreases after adsorption. Finally, the isolated Ni atoms and Ni7 clusters are found in ZrOW _ 2J _ (111) and Zr _ 1-xC _ x O _ 2111s, respectively. It is found that the most stable adsorption site for a single nickel atom is the Zr1-Zr2 bridge, and the Ni atom loses electrons after adsorption. Ni0 was oxidized to Ni _ 2 and two Zr atoms produced electrons. The adsorption energy of Zr _ 4 was -5.87 EV on the stoichiometric Zr _ 02N _ (111) surface. The charge is -0.18e. this indicates that after adsorption, Ni7 gets electrons, and some Ni atoms in Ni7 will be reduced from Ni0 to Ni _ 1, which is completely opposite to the adsorption of a single nickel atom. This is an interesting result. The introduction of ce atoms leads to an increase in the adsorption energy of Ni7. This indicates that ce doping has a great influence on the catalytic performance of Zr02. Ce doping may be an effective way to increase the catalytic performance of ZrO_2. Ni7/Zr0.667Ce0.333O_2 catalyst has good catalytic performance. It is found that the absolute value of adsorption energy and charge is the same as increasing and decreasing. Surface charge transfer is an important factor to change the catalytic performance of catalysts.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O469

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