Ce1-xGdxO2-δ固溶体中缺陷物种的拉曼光谱研究

采用溶胶-凝胶法制备一系列Ce1-xGdxO2-δ固溶体。利用紫外(325 nm)和可见(514 nm)Raman光谱,X射线粉末衍射(XRD),透射电子显微镜(TEM)和紫外可见漫反射光谱(UV-Vis DRS),考察了Ce1-xGdxO2-δ固溶体的缺陷物种的分布以及Gd含量对缺陷浓度的影响。结果表明:Ce1-xGdxO2-δ固溶体中存在氧缺位(～560 cm-1)和GdO8型缺陷结构(～600 cm-1)。根据样品对Raman激发光的吸收,紫外Raman光谱反映样品的表层信息,可见Raman光谱反映样品的整体信息。Ce1-xGdxO2-δ固溶体表层氧缺位(να)和GdO8型缺陷物种的浓度(νβ)均高于固溶体体相,这归因于缺陷物种的表面富集。然而,相比于GdO8型缺陷物种,体相中氧缺位浓度增加较表层中的更显著。     

载体对负载型金催化剂上甲醛催化氧化的影响

采用沉积.沉淀法和氨水络合法制备了Al2O3,TiO2,CeO2和SiO2负载的纳米金催化剂,利用元素分析、x射线衍射、氮气物理吸附、程序升温还原、透射电镜和拉曼光谱等技术对催化剂进行了表征,并考察了其低温催化甲醛氧化活性.结果表明,Au/CeO2的催化性能最佳,在40℃时甲醛转化率仍能保持在80%以上.催化剂的活性同时受Au的化学状态和载体性质的影响.Au/CeO2催化剂较高的低温活性可能与离子态的Au物种有关,同时AuxCe1-xO2-δ固溶体的形成产生了大量的氧缺位,提高了氧的活化能力,也有助于提高催化剂的低温活性.     

镍促进CuO-CeO2催化剂的结构表征及低温CO氧化活性（英文）

制备了一系列CO低温氧化的Ce20Cu5NiyOx催化剂,并采用氮气低温物理吸附、X射线衍射、程序升温还原、X射线光电子能谱以及拉曼光谱等手段对催化剂进行表征.结果表明,Ce20Cu5Ni0.4Ox催化剂活性最高.NiO的添加可以使得较多的Cu物种掺杂到CeO2晶格中,通过形成铈镍固溶体产生更多的氧空位.表征结果显示,Ce20Cu5Ni0.4Ox催化剂中存在大量的Cu+,Ce3+及晶格氧,催化剂中的Cu+很容易进入到氧化铈晶格,形成Cu-O-Ce固溶体,从而增强了在还原气氛下晶格氧的释放能力.Ce20Cu5Ni0.4Ox催化剂高的催化活性主要归因于大量Cu+以及形成的Cu-O-Ce和Ni-O-Ce固溶体.     

锰掺杂对铈锆复合氧化物储氧性能的影响

利用溶胶凝胶法制备了CeO2-ZrO2-MnOx复合氧化物，通过CO脉冲和CO-O2循环脉冲测试分别考察样品的完全储氧能力和动态储氧能力。掺杂方法使氧化锰和氧化铈在体相和表面均产生强相互作用。只有少部分Mn离子进入了CeO2晶体形成固溶体，其余以Mn3O4的形式弥散分布在表面。材料的储氧能力受到Mn掺杂量和Mn在CeO2晶格中的固溶度两个因素影响。当测试脉冲频率较低时，储氧能力主要取决于材料中可以储放氧成分的相对含量；而当脉冲频率较高时，材料中影响晶格氧迁移速度的缺陷浓度则成为影响OSC性能的主要因素。     

Ce1－xPrxO2－δ (x＝0.05～0.30)固溶体的合成及其性质研究

利用溶胶-凝胶法合成了固溶体Ce1－xPrxO2－δ (x＝0.05～0.30). X射线衍射(XRD)分析表明, 在x≤0.30的范围内形成了单相萤石结构固溶体Ce1－xPrxO2－δ; X射线光电子能谱(XPS)结果表明, 样品中氧缺位浓度随掺杂量增大而增大, 铈离子主要为Ce4＋离子, 镨离子以混合价态Pr3＋和Pr4＋存在; 拉曼光谱(Raman)观察到两个峰, 458 cm－1峰为特征F2g振动谱带, 较宽的570 cm－1峰与样品中氧离子缺位有关; 交流阻抗谱测试表明, 固溶体Ce1－xPrxO2－δ的电导率随掺杂量增加而增大, x＝0.2时, 电导率达到最大, 活化能较低, σ600 ℃＝3.28×10－2 S/cm, σ700 ℃＝6.06×10－2 S/cm, Ea＝0.54 eV (250～650 ℃), Ea＝0.49 eV (650～800 ℃).     

CeO2、CaO助剂对甲烷部分氧化制合成气Ni/MgOAl2O3催化剂结构和性能的影响

采用BET、H2 TPR、XRD、TEM和活性评价等表征手段，考察了CeO2、CaO助剂对Ni/MgOAl2O3催化剂物化性质和甲烷部分氧化制合成气反应性能的影响。实验结果表明，单独加入CeO2或CaO助剂可以改善Ni/ MgOAl2O3催化剂中镍物种的还原性能，以CaO尤为明显；CaO作为结构助剂可以降低还原态催化剂中的镍晶粒尺寸，使改性的催化剂具有较好的活性，而CeO2对催化剂的活性未产生显著影响。当CeO2与CaO两种助剂同时对Ni/MgOAl2O3进行改性时，虽然催化剂中镍物种的还原性能没有发生明显变化，但仍具有很好的反应性能，这与CeO2与CaO能够形成CaO-CeO2固溶体有关。CaO-CeO2固溶体不仅与镍物种间存在相互作用，提高了镍物种的分散度、减小了镍晶粒尺寸，还可以提高催化剂的储氧能力和晶格氧的流动性，从而有利于改善其甲烷部分氧化反应性能。     

CeO2分散度对Au/CeO2-SiO2催化剂上甲醛的催化氧化影响

采用浸渍法在高比表面积的SiO2上负载不同量的CeO2,得到了CeO2不同颗粒尺寸的CeO2-SiO2载体,并用沉积沉淀法制备了CeO2-SiO2负载的纳米金催化剂.通过元素分析、X射线衍射、程序升温还原、N2物理吸附、拉曼光谱和透射电镜等技术对催化剂进行了表征,并考察了催化甲醛氧化活性.结果表明,高分散度、小尺寸的CeO2有利于得到较小尺寸的Au颗粒,并增强了催化剂的还原能力和氧缺位浓度,从而有利于提高催化剂低温甲醛催化氧化活性.     

低温燃烧法制备纳米Ce1-xNdxO2-x/2(0≤x≤0.6) 粉体的研究

采用低温燃烧合成工艺，在甘氨酸-硝酸盐体系下制备出纳米Ce1-xNdxO2-x/2(0≤x≤0．6)系列粉体(NDC)。X射线衍射(XRD)结果表明。Nd^3 取代Ce^4 进入晶格内部，形成具有单相立方萤石型结构的固溶体，其晶格常数随Nd^3 掺杂浓度的增大而线性增加，晶粒尺寸在17～28nm之间。透射电镜(TEM)结果表明，粉体尺寸在30-40nm之间，具有较高的烧结活性。拉曼光谱(Rman spectrum)表明％宽化峰与掺杂后固溶体中产生的氧空位有关。     

拉曼光谱表征石墨烯材料的研究进展

石墨烯独特的二元化电子价键结构使其在纳米电子器件中具有良好的应用发展前景。拉曼光谱作为一种灵敏、便捷的技术,已被成功地用作表征石墨烯的结构和特性。本综述着重对沉积在不同基底以及掺杂的石墨烯拉曼光谱研究做了一个简单的总结。通过对铟锡氧化物、蓝宝石和玻璃基底上的石墨烯拉曼光谱进行观察,发现在不同基底上的石墨烯拉曼G峰与2D峰峰值会有不同程度的偏移,但2D峰峰值可判断石墨烯层数这一结论仍适用。掺杂可改变石墨烯的荷电状态,使石墨烯表现出空穴（p）型或电子（n）型掺杂特性,通过石墨烯拉曼光谱的变化可以定性石墨烯的掺杂类别并定量表征石墨烯的载流子浓度。     

Er掺杂对CeO2(ZrO2)/TiO2催化剂脱硝性能的影响

氮氧化物(NOx)是大气污染的主要因素之一,对其排放的治理成为较为迫切的需求.氨气选择性催化还原法(NH3-SCR)是目前减少NOx排放中应用最为广泛的技术.目前,商业SCR催化剂主要是V2O5(WO3,MO3)/TiO2,但其具有活性温度窗口窄、N2选择性低和对环境影响大等缺点.因此,新型的催化活性高且活性温度窗口宽的环境友好催化剂成为脱硝催化剂的研究热点.CeO2因其独特的氧化还原性能和优异的储释氧能力在催化领域具有广泛应用,在NH3-SCR中也研发出较多类型的铈基催化剂.我们课题组前期研发了具有优异脱硝性能的CeO2(ZrO2)/TiO2催化剂,为拓展其应用范围,需要进行更深入的研究.理论上,Ti4+,Ce4+以及Zr4+离子的价态均高于Er3+,且离子半径相近.换言之,Er2O3能够与TiO2以及CeO2产生缺陷反应增大催化剂的缺陷浓度,进而提高催化剂的催化活性.本文以溶胶-凝胶法制备了一系列Er掺杂CeO2(ZrO2)/TiO2催化剂,测试了样品的NH3-SCR催化活性和N2选择性,并且在320℃下连续24 h测试了水蒸气、SO2以及两者混合作用对催化剂活性的影响.使用X射线衍射(XRD)、N2等温吸附-脱附(N2-BET)、NH3程序升温脱附(NH3-TPD)、H2程序升温还原(H2-TPR)、光致发光光谱(PL)、电子顺磁共振(EPR)以及X射线光电子能谱(XPS)对催化剂进行了表征.XRD结果显示,Er掺杂后催化剂的结晶程度降低,且图谱中没有出现明显的EF2O3衍射峰,即Er在催化剂上有较好的分散度且掺杂抑制了催化剂的晶化.NH3-TPD和H2-TPR结果表明,Er掺杂降低了酸强且提高了储释氧能力,催化剂的氧化还原能力则有所减弱.PL和EPR测试结果显示,掺杂后的催化剂氧空位浓度和Ti3+浓度有所增加,与前期理论设计一致.XPS测试结果表明,掺入Er后催化剂的化学吸附氧含量和Ti3+浓度增加,Ce3+浓度基本不变,推测是CeO2(ZrO2)/TiO2催化剂中掺入的Er主要与载体TiO2,而不是与活性组分CeO2或助剂ZrO2产生缺陷反应的结果.CeO2(ZrO2)/TiO2催化剂最高活性为94.28％,其活性温度窗口为230-390℃,掺入Er (Er∶Ce=0.10∶1)后,催化剂的整体活性尤其是350℃以下的催化活性具有明显提升,最高活性达到98.85％,活性温度窗口也拓展为220-395℃.单独的水蒸气对催化活性影响很小,SO2会部分降低催化剂活性,而当两者混合作用时,催化剂活性下降最为显著,且Er掺杂后CeO2(ZrO2)/TiO2催化剂的抗中毒能力有所增强.Er掺杂CeO2(ZrO2)/TiO2催化剂显示出较好的抗硫抗水中毒能力以及较高的NH3-SCR催化活性和N2选择性,应该是一种具有应用前景的SCR催化剂.Er掺杂降低了催化剂的酸强,抑制了TiO2和铈锆固溶体的晶化,提高了Ti3+和氧空位浓度并增强了储释氧能力,是CeO2(ZrO2)/TiO2催化剂活性提高的主要原因.     

Study of defect sites in Ce1-xMxO2-δ (x = 0.2) solid solutions using Raman spectroscopy

A series of Ce(1-x)M(x)O(2-δ) (M = Gd, Zr, La, Sm, Y, Lu, and Pr) samples were characterized by Raman spectroscopy to investigate the evolution of defect sites (oxygen vacancies and MO(8)-type complex) and their distributions in the samples. It was found that the evolution of oxygen vacancies was due to the different ionic valence state of dopant from that of Ce(4+), while the evolution of the MO(8)-type complex was due to the different ionic radius of dopant from that of Ce(4+). The distributions of defect sites were investigated using 325 and 514 nm excitation laser lines, indicating that the defect sites were surface enriched. Moreover, the increasing ordering level of the sample led to a decline in the concentration of the MO(8)-type complex in the sample but the constant concentration of oxygen vacancies, implying that the metastable MO(8)-type complex species were more disordered compared to the oxygen vacancies.     

CO oxidation mechanism on CeO(2)-supported Au nanoparticles

Density functional theory was used to study the CO oxidation catalytic activity of CeO(2)-supported Au nanoparticles (NPs). Experimental observations on CeO(2) show that the surface of CeO(2) is enriched with oxygen vacancies. We compare CO oxidation by a Au(13) NP supported on stoichiometric CeO(2) (Au(13)@CeO(2)-STO) and partially reduced CeO(2) with three vacancies (Au(13)@CeO(2)-3VAC). The structure of the Au(13) NP was chosen to minimize structural rearrangement during CO oxidation. We suggest three CO oxidation mechanisms by Au(13)@CeO(2): CO oxidation by coadsorbed O(2), CO oxidation by a lattice oxygen in CeO(2), and CO oxidation by O(2) bound to a Au-Ce(3+) anchoring site. Oxygen vacancies are shown to open a new CO oxidation pathway by O(2) bound to a Au-Ce(3+) anchoring site. Our results provide a design strategy for CO oxidation on supported Au catalysts. We suggest lowering the vacancy formation energy of the supporting oxide, and using an easily reducible oxide to increase the concentration of reduced metal ions, which act as anchoring sites for O(2) molecules.     

MnO_x-CeO_2上表面氧性质及其催化碳烟燃烧性能

运用TPO,XRD,BET,O2-TPD,H2-TPR,XPS等技术,研究了在CeO2中引入不同Mn含量对催化剂表面氧性质的影响,并重点探讨了吸附于氧空位上的原子吸附氧O-与催化碳烟燃烧活性的关联。结果表明:将Mn中引入CeO2后,MnOx-CeO2晶格中可形成较CeO2更多的氧空位,并有利于氧的活化和迁移,生成了较多原子吸附氧O-;MnOx(0.4)-CeO2在碳烟起燃温度区间有最多的原子吸附氧O-,其碳烟起燃活性最高,对应的起燃温度是346℃,比无催化剂时降低了111℃,比CeO2降低了35℃。     

CO在CeO2(111)表面的吸附与氧化

采用密度泛函理论计算了CO在CeO2(111)表面的吸附与氧化反应行为. 结果表明, O2在洁净的CeO2(111)表面为弱物理吸附, 而在氧空位表面是强化学吸附, 且O2分子活化程度较大, O—O键长为0.143 nm. CO在CeO2(111)表面吸附行为的研究表明, CO在洁净表面及氧空位表面上为物理吸附, 吸附能均小于0.42 eV; 当表面氧空位吸附O2后, CO可吸附生成二齿碳酸盐中间体或直接生成CO2, 与原位红外光谱结果相一致. 表面碳酸盐物种脱附生成CO2的能垒仅为0.28 eV. 计算结果表明, 当CeO2表面存在氧空位时, Hubbard参数U对CO吸附能有一定的影响. CeO2载体在氧化反应中可能的催化作用为, 在氧气氛下, CeO2表面氧空位吸附O2分子, 形成活性氧物种, 参与CO催化氧化反应.     

氮气气氛下焙烧的CeO_2载体负载Ni基催化剂的顺酐加氢性能研究

在氮气气氛中合成了具有较高氧缺陷浓度的CeO_2载体,采用浸渍法制备了Ni含量为10%的Ni/CeO_2-N催化剂,考察了其顺酐液相加氢性能,并与氧气气氛中制得的CeO_2载体负载Ni催化剂作了对比.N_2低温物理吸脱附,X-射线衍射,拉曼光谱,H_2程序升温还原等表征手段表明,在氮气气氛中合成的CeO_2具有较高浓度的氧缺陷位,在催化剂还原过程中可促进NiO物种的还原,同时在催化剂表面生成更多的氧缺陷位.该氧缺陷位可与活性金属Ni物种协同作用,显著提高催化剂的C=C及C=O加氢活性.     

Effects of deposited Pt particles on the reducibility of CeO2(111)

The interaction of Pt particles with the regular CeO(2)(111) surface has been studied using Pt(8) clusters as representative examples. The atomic and electronic structure of the resulting model systems have been obtained through periodic spin-polarized density functional calculations using the PW91 exchange-correlation potential corrected with the inclusion of a Hubbard U parameter. The focus is on the effect of the metal-support interaction on the surface reducibility of ceria. Several initial geometries and orientations of Pt(8) with respect to the ceria substrate have been explored. It has been found that deposition of Pt(8) over the ceria surface results in spontaneous oxidation of the supported particle with a concomitant reduction of up to two Ce(4+) cations to Ce(3+). Oxygen vacancy formation on the CeO(2)(111) surface and oxygen spillover to the adsorbed particle have also been considered. The presence of the supported Pt(8) particles has a rather small effect (～0.2 eV) on the O vacancy formation energy. However, it is predicted that the spillover of atomic oxygen from the substrate to the metal particle greatly facilitates the formation of oxygen vacancies: the calculated energy required to transfer an oxygen atom from the CeO(2)(111) surface to the supported Pt(8) particle is only 1.00 eV, i.e. considerably smaller than 2.25 eV necessary to form an oxygen vacancy on the bare regular ceria surface. This strongly suggests that the propensity of ceria systems to store and release oxygen is directly affected by the presence of supported Pt particles.     

Atomic and electronic structure of unreduced and reduced CeO2 surfaces: a first-principles study

The atomic and electronic structure of (111), (110), and (100) surfaces of ceria (CeO2) were studied using density-functional theory within the generalized gradient approximation. Both stoichiometric surfaces and surfaces with oxygen vacancies (unreduced and reduced surfaces, respectively) have been examined. It is found that the (111) surface is the most stable among the considered surfaces, followed by (110) and (100) surfaces, in agreement with experimental observations and previous theoretical results. Different features of relaxation are found for the three surfaces. While the (111) surface undergoes very small relaxation, considerably larger relaxations are found for the (110) and (100) surfaces. The formation of an oxygen vacancy is closely related to the surface structure and occurs more easily for the (110) surface than for (111). The preferred vacancy location is in the surface layer for CeO2(110) and in the subsurface layer (the second O-atomic layer) for CeO2(111). For both surfaces, the O vacancy forms more readily than in the bulk. An interesting oscillatory behavior is found for the vacancy formation energy in the upper three layers of CeO2(111). Analysis of the reduced surfaces suggests that the additional charge resulting from the formation of the oxygen vacancies is localized in the first three layers of the surface. Furthermore, they are not only trapped in the 4f states of cerium.     

A concerted migration mechanism of mixed oxide ion and electron conduction in reduced ceria studied by first-principles density functional theory

Ceria based oxides are regarded as key oxide materials for energy and environmental applications, such as solid oxide fuel cells, oxygen permeation membranes, fuel cell electrodes, oxygen storage, or heterogeneous catalysis. This great versatility in applications is rendered possible by the fact that rare earth-doped ceria is a pure oxygen ion conductor while undoped ceria, CeO(2-δ), is a mixed oxygen ion-electron conductor. To get deeper insight into the mixed conduction mechanism of oxygen ions and electrons from atomistic and electronic level viewpoints we have applied first-principles density functional theory (DFT + U method). The calculation results show that oxygen vacancies strongly attract localized electrons, forming associates between them. The migration energy of an oxygen vacancy in such an associate is substantially lowered compared to the unassociated case due to the simultaneous positional rearrangement of localized electrons during the ionic jump process. Accordingly, we propose a concerted migration mechanism of oxygen vacancies and localized electrons in reduced ceria; this mechanism results in an increased diffusivity of oxygen vacancies supported by localized electrons compared with that in pure oxide ion conductors.     

Comparative study of CeO2 and doped CeO2 with tailored oxygen vacancies for CO oxidation

We report on the preparation and characterization of CeO(2) nanofibers (CeO(2)-NFs) and nanocubes (CeO(2)-NCs), as well as Sm- and Gd-doped CeO(2) nanocubes (Sm-CeO(2)-NCs and Gd-CeO(2)-NCs), synthesized by a simple hydrothermal process for CO catalytic oxidation. The samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence spectroscopy. Their oxygen-storing capacity (OSC) was examined by means of hydrogen temperature-programmed reduction (H(2)-TPR) and oxygen pulse techniques. Their catalytic properties for CO catalytic oxidation were comparatively investigated. The results showed that the CeO(2)-NFs possessed a higher catalytic activity compared to the CeO(2)-NCs because of their smaller size and the greater number of oxygen vacancies. The activity of the Sm-CeO(2)-NCs was higher than that of the CeO(2)-NCs due to an increase in the number of oxygen vacancies, which results from the substitution of Ce(4+) species with Sm(3+) ions. In contrast, Gd doping had a negative effect on the CO catalytic oxidation due to the special electron configuration of Gd(3+) (4f(7)). Our work demonstrates that the oxygen vacancies in pure CeO(2) and the electron configuration of the dopants in doped CeO(2) play an important role in CO oxidation.