本文關(guān)鍵詞：Pr和Ce摻雜的氧化鋯表面上一氧化碳和鎳團簇的吸附　出處：《昆明理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 摻雜 密度泛函理論 ZrO_2 CO 吸附

【摘要】：本文研究了CO在Ce、Ca和Pr摻雜ZrO_2表面上的吸附,Pr、Ti等摻雜對ZrO_22構(gòu)和氧空位形成能的影響,以及鎳原子在Ce摻雜ZrO_2表面上的吸附。通過第一性原理研究我們得到了如下研究成果:首先通過研究Pr、Ti等摻雜后ZrO_2的結(jié)構(gòu)和氧空位形成能發(fā)現(xiàn)氧空位最容易出現(xiàn)在ZrO_2(111)表面。氧空位形成能在未摻雜的ZrO_2晶胞中是-2.33 eV,在Ti和Pr摻雜后氧空位形成能分別是-2.54 eV和-2.91 eV。這表明Ti和Pr摻雜后更有利于氧化鋯中氧空位的形成。Pr摻雜會有更小的帶隙值1.41 eV,Ti摻雜時的帶隙是1.82 eV,Pr摻雜時鄰近摻雜位置的四個氧原子比在Ti摻雜時有更大的電荷,Pr摻雜對降低ZrO_2的還原性有更明顯的作用。通過對氧空位在不同ZrO_2表面的表面能計算研究表明ZrO_2(111)面是最穩(wěn)定的面。在ZrO_2(111),(110),(100)三個表面中氧空位更容易在ZrO_2(111)表面的最外表面形成。研究表明摻雜對Zr02的晶格結(jié)構(gòu),電荷分布,以及氧化還原性都有很大的影響。摻雜會使鄰近摻雜位置的氧原子的布里居電荷在摻雜后比摻雜前明顯偏大。摻雜還會改變Zr02的帶隙,摻雜后的ZrO_2帶隙都會變小,這是因為摻雜后有電子填充了空帶從而使得帶隙變得狹窄。其次對CO在Ce、Ca和Pr摻雜ZrO_2表面上的吸附研究發(fā)現(xiàn)CO在清潔ZrO_2(111)表面最穩(wěn)定的吸附位置是鋯橋位。CO在純ZrO_2(111)表面的吸附能是-0.35eV,在Ca摻雜ZrO_2(111)表面的吸附能是-0.41 eV,在Ce摻雜的ZrO_2(111)表面的吸附能是-0.67 eV,在Pr摻雜的ZrO_2(111)表面吸附能是-0.73eV。這表明CO在Pr摻雜的ZrO_2(111)表面的吸附是最穩(wěn)定的。同時我們發(fā)現(xiàn)吸附最穩(wěn)定的表面態(tài)密度左移越明顯,這表明吸附后系統(tǒng)的能量降低。最后對孤立Ni原子和Ni7團簇分別在ZrO_2(111)和Zr1-xCexO_2(111)表面的吸附研究發(fā)現(xiàn)對于單個鎳原子的吸附最穩(wěn)定的吸附位置是Zr1-Zr2橋位。吸附后Ni原子失去電子,Ni0被氧化成Ni+2,兩個Zr原子得到電子,Zr+4被還原成Zr+3。Ni7團簇在化學(xué)計量的Zr02(111)表面的吸附能是-5.87eV,電荷是-0.18e。這說明吸附后Ni7得到電子,一些在Ni7中的Ni原子將從Ni0還原成Ni+1,這和單個鎳原子的吸附是完全相反的,這是一個很有趣的結(jié)果。Ce原子的引入會引起Ni7吸附能的增加,這表明Ce摻雜對Zr02的催化性能有很大的影響。Ce摻雜可能是增加ZrO_2催化性能的有效辦法,Ni7/Zr0.667Ce0.333O_2催化劑有很好的催化性能。研究發(fā)現(xiàn)吸附能和電荷的絕對值是同增同減的,表面電荷轉(zhuǎn)移是催化劑催化性能改變的重要因素。
[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.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O469

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本文編號：1398571