SiO2-CeO2复合氧化物的制备及抛光性能

采用正硅酸乙酯溶胶-凝胶法制备纳米SiO₂，并与氯化铈溶液混合，用氨水沉淀法制备了SiO₂-CeO₂复合氧化物。利用XRD、SEM等手段对其物相类型、外观形貌、颗粒大小、表面电位等物理性能进行了表征，测定了它们对3种光学玻璃的抛光速率。结果表明：合成复合氧化物具有立方萤石型结构，由Sherrer方程计算的晶粒D_XRD(200)小于100 nm甚至10 nm。随着SiO₂复配量的增加和煅烧温度的降低，晶粒度减小，比表面增大；激光粒度分析仪测定的中位粒径D₅₀在2～3 μm之间，且随SiO₂复配量的增加呈增大趋势，但随煅烧温度的变化在800 ℃时出现极小值，而此时的ζ电位的负值最大，对3种玻璃的抛光速率也最大。证明抛光速率与表面电位及相应的悬浮性、颗粒大小有直接关系。随着SiO₂复配量的增加，复合氧化物的ζ电位负值及对3种玻璃的抛光速率均增大。因此，在CeO₂中复配SiO₂是提高抛光速率的有效方法，此时，最佳的煅烧温度为800 ℃。     

硫中毒对Co3O4/CeO2复合氧化物上炭黑催化燃烧的影响

采用共沉淀法制备了CeO₂,Co₃O₄和一系列Co₃O₄/CeO₂复合氧化物催化剂,在400 ℃下含SO₂的氧化气氛中对催化剂进行了硫中毒处理,通过原位红外光谱、X射线衍射、程序升温脱附和X射线光电子能谱对新鲜和硫中毒的样品进行了表征. 结果表明,所有测试的硫中毒样品上均形成了硫酸盐,CeO₂上累积的硫酸盐明显比Co₃O₄上的多,Co₃O₄/CeO₂复合氧化物在硫中毒过程中形成了硫酸钴和硫酸铈. 对新鲜和硫化样品在NO/O₂气氛下进行了催化炭黑燃烧实验,发现Co₃O₄/CeO₂复合氧化物的活性和抗硫性能优于CeO₂,但抗硫性能低于Co₃O₄.     

水热法制备核壳结构的纳米Ag-Fe2O3复合氧化物

在PVP(聚乙烯吡咯烷酮)辅助下用水热法制备Ag Fe2O3核壳结构的纳米复合粒子,利用XRD、TEM、磁性测量系统对产品进行了表征,研究了水热温度、时间及表面活性剂等因素对产品形貌的影响.结果表明:在水热温度为120℃时,粒子直径约为60 nm,温度升高和反应时间增加都使粒子直径增大;产品在120℃和180℃时,剩磁量分别为0.0022和0.0034 emu/g,矫顽力分别为245.16和313.98 Oe.     

K2NiF4型希土复合氧化物Eu2-xSrxNiO4+δ的合成、结构及还原性能

利用柠檬酸配合物分解法合成了单相的K₂NiF₄型希土复合氧化物Eu_2-xSr_xNiO_4+δ(0.5≤x≤1.2),粉末X射线衍射分析表明,在x为0.6～0.7的范围内,物相从空间群为Fmmm的正交相转变成空间群为I4/mmm的四方相,随着Sr²⁺的加入,部分Ni²⁺转变为Ni³⁺,其转变量与理论值接近。反映结构稳定性的高温还原峰温与晶胞参数c有对应关系,表明化合物的结构稳定性取决于AO层与ABO₃层的层间距离。     

SrFe1.5-xCoxO3.25+δ体系结构、相组成和电导研究

利用碘量法测定了SrFe_1.5-xCo_xO_3.25+δ系列样品在不同温度下的金属平均价态,结合XRD谱图研究了温度、钴含量对其结构、相组成的变化的影响规律。研究发现:随钻含量增加,体系由层状相过渡到钙钛矿相,并伴随有尖晶石相的出现。此外,由交流四端子法测量了SrFe_1.5-xCo_xO_3.25+δ系列样品的总电导率随钴含量的变化关系,总电导率随钻含量和温度的升高而增大,但对于钻     

SEELFS对Mg-Al复合氧化物结构的研究

应用EXAFS类似原理,对MgO和Mg-Al复合氧化物[Mg(Al)O]中Mgk-边的SEELFS(SurfaceExtendedenergyLossFineStructure)一阶微分谱进行数据处理,得到了Mg近邻原子的配位距离。研究发现,同MgO比较,由于Al^3^+的引入,使[Mg(Al)O]中的Mg－mg配位距离增加,配位数降低,而Mg－O的配位环境基本不变。     

Ba调变复合氧化物LaxBa1-xNiAl11O19-δ催化剂的制备和性能表征

制备了Ba调变Ni基复合氧化物催化剂LaxBa1-xNiAl11O19-δ,并通过XRD、XPS、TPR、TEM、BET和TGA等技术对催化剂的结构、性质和对甲烷二氧化碳重整制合成气反应的催化性能以及催化剂表面积炭情况进行了表征.结果表明,Ba调变后复合氧化物的微观结构随Ba调变量发生规律性变化,但结构的改变对催化剂的理化性质和催化性能均无明显影响,该系列Ni基复合氧化物都具有较好的催化活性以及较高的抗烧结和抗积炭性能,是甲烷二氧化碳重整制合成气反应选择氧化的良好催化剂.     

稀土氧化物催化和表面化学：I.CeO2和Pr6O11的表面羟基及其反应活…

利用ＦＴ－ＩＲ、同位素技术和内循环反应等方法考察了ＣｅＯ２和Ｐ６Ｏ１１的表面羟基及其与ＣＯ反应的活性。ＣｅＯ２和Ｐｒ６Ｏ１１经高温脱气处理后表面大量的碳酸基和羟基脱附。但部分残留的表面羟基反应活性很高，在２００℃甚至更低温度可与ＣＯ反应形成表面甲酸基物种。当温度超过３００℃时，表面甲酸基物种被表面晶格氧进一步氧化为表面碳酸基物种，但部分表面羟基又复原。认为经高温脱气处理后造成表面配位不饱和中心并使     

XANES研究Al2O3包覆LiNi0.4Co0.2Mn0.4O2材料的稳定性

采用溶胶凝胶水解法在LiNi0.4Co0.2Mn0.4O2(NCM)表面包覆了0.5 wt%Al2O3.透射电镜(TEM)表明在NCM表面形成了均匀的Al2O3包覆层;分别采用恒电位极化及热重分析(TG)研究了包覆前后NCM的析氧特性;采用X射线吸收近边结构谱(XANES)研究了包覆前后O的电子结构.结果表明,包覆后的NCM析氧量更少;Al2O3包覆使得NCM表面层中与金属3d轨道杂化的O比例减少,而更稳定的、与金属4sp轨道杂化的O比例增加.这些因素导致Al2O3包覆后的NCM更加稳定、安全性更高.     

温度对Mg-Al-O复合氧化物催化剂体相和表面酸碱性质的影响

用ＮＨ３和ＣＯ２作探针分子,采用红外光谱,真空原位测定Ｍｇ－Ａｌ－Ｏ复合氧化物表面酸碱中心的类型结果表明,主要存在Ｌ酸,碱中心是氧阴离子,而焙烧温度对样品表面碱中心的类型几乎没有影响,在６７３、８７３和１０７８Ｋ焙烧样品的固态ＭＡＳ＾２７Ａｌ核磁共振结果显示,样品呈现显著的物相转变,炽的过渡态对确定它们碱性质显得非常重要。ＸＰＳ测定样品中Ａｌ２ａ和Ｏ１ａ结合能与样品表面酸碱中心的强度相关。     

Growth and Electronic Properties of Ag Nanoparticles on Reduced CeO2-x(111) Films

Ag nanoparticles grown on reduced CeO_2-x thin films have been studied by X-ray photoelec-tron spectroscopy and resonant photoelectron spectroscopy of the valence band to understand the effect of oxygen vacancies in the CeO_2-x thin films on the growth and interfacial elec-tronic properties of Ag. Ag grows as three-dimensional particles on the CeO_2-x(111) surface at 300 K. Compared to the fully oxidized ceria substrate surface, Ag favors the growth of smaller particles with a larger particle density on the reduced ceria substrate surface, which can be attributed to the nucleation of Ag on oxygen vacancies. The binding energy of Ag3d increases when the Ag particle size decreases, which is mainly attributed to the final-state screening. The interfacial interaction between Ag and CeO_2-x(111) is weak. The resonant enhancement of the 4f level of Ce³⁺ species in RPES indicates a partial Ce⁴⁺→Ce³⁺ re-duction after Ag deposited on reduced ceria surface. The sintering temperature of Ag on CeO_1.85(111) surface during annealing is a little higher than that of Ag on CeO₂(111) surface, indicating that Ag nanoparticles are more stable on the reduced ceria surface.     

Vapor phase reduction of cyclohexanone to cyclohexanol on CexZr1-xO2 solid solutions

Reduction of cyclohexanone to cyclohexanol using propane-2-ol as hydrogen donor has been carried out in vapor phase on Ce_xZr_1-xO₂ solid solutions synthesized by ombustion synthesized at 302°C. The solid solutions around 0.4 mol% cerium content show better catalytic activity compared to pure ZrO₂ and the selectivity to cyclohexanol is 98%. A moderate acid-base and good redox properties of Ce_xZr_1-xO₂ solid solutions are seen to be responsible for the catalytic activity. A possible mechanism of hydride transfer has been proposed with cerium ions as promoters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Crystal structures and phase transitions of Sr2CrSbO6

Sr₂CrSbO₆ was synthesized by the conventional solid-state reaction process. X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) has been used to reinvestigate the structure at room temperature and to study the phase transitions at high- and low-temperature. Rietveld analysis revealed that Sr₂CrSbO₆ crystallizes at room temperature in a monoclinic system having a space group I2/m, with a=5.5574(1) Å; b=5.5782(1) Å; c=7.8506(2) Å and β=90.06(2), no P2₁/n space group as was previously reported. The high-temperature study (300-870 K) has shown that the compound presents the following temperature induced phase-transition sequence: I2/m-I4/m-Fm-3m. The low-temperature study (100-300 K) demonstrated that the room-temperature I2/m monoclinic symmetry seems to be stable down to 100 K.     

Synthesis and crystal structures of CaY2Ge3O10 and CaY2Ge4O12

New compounds CaY₂Ge₃O₁₀ and CaY₂Ge₄O₁₂ were prepared by heating mixtures of CaCO₃, Y₂O₃ and GeO₂ at 1200 °C. CaY₂Ge₃O₁₀ is stable at 1300 °C, while CaY₂Ge₄O₁₂ decomposes into a melt and CaY₂Ge₃O₁₀ at approximately 1250 °C. We obtained single crystals of CaY₂Ge₃O₁₀ by cooling a sample with an initial composition of Ca:Y:Ge=1:2:8 from 1300 °C with a rate of −6 °C/h. The crystal structure of CaY₂Ge₃O₁₀ was determined by single crystal X-ray diffraction. CaY₂Ge₃O₁₀ crystallizes in the monoclinic space group P2₁/c with a=6.0906(8), b=6.8329(8), and β=109.140(3)°, Z=4, and R₁=0.029 for I>2σ(I). In the structure of CaY₂Ge₃O₁₀, Ca and Y atoms are situated disorderly in three 7-fold coordination sites between isolated germanate groups of triple GeO₄ tetrahedra, Ge₃O₁₀. The structural formula of CaY₂Ge₃O₁₀ is expressed as (Ca_0.45Y_0.55)(Ca_0.46Y_0.54)(Ca_0.09Y_0.91)Ge₃O₁₀. The crystal structure of CaY₂Ge₄O₁₂ was analyzed by the Rietveld method for the X-ray powder diffraction pattern. CaY₂Ge₄O₁₂ is isotypic with SrNa₂P₄O₁₂, crystallizing in the orthorhombic space group P4/nbm, a=9.99282(6), , Z=2, R_wp=0.092, R_p=0.067. CaY₂Ge₄O₁₂ contains four-membered GeO₄-tetrahedra rings, Ge₄O₁₂. Eight-fold coordinated square-anitiprism sites and 6-fold octahedral sites between the layers of the Ge₄O₁₂ rings are occupied by Y atom and Ca/Y atoms, respectively The structural formula is Y(Ca_0.5Y_0.5)₂Ge₄O₁₂.     

Synthesis, structure and magnetic properties of A2MnB′O6 (A=Ca, Sr; B′=Sb, Ta) double perovskites

A₂MnB′O₆ (A=Ca, Sr; B=Sb, Ta) double perovskites have been synthesized and their structural and magnetic properties have been investigated. Rietveld refinement of the powder X-ray diffraction data for Sr₂MnSbO₆ indicated significant ordering of Mn and Sb at the B-site while all other phases showed mostly a random distribution of the B-site cations. X-ray absorption spectroscopic data established the presence of Mn in the 3+ and Sb/Ta in the 5+ oxidation states in all the phases. Magnetic susceptibility data indicated ferromagnetic correlations for all the A₂MnB′O₆ phases with Weiss temperatures varying from 64 to 107 K.     

Li2Si3O7: Crystal structure and Raman spectroscopy

The crystal structure of metastable Li₂Si₃O₇ was determined from single crystal X-ray diffraction data. The orthorhombic crystals were found to adopt space group Pmca with unit cell parameters of , and . The content of the cell is Z=4. The obtained structural model was refined to a R-value of 0.035. The structure exhibits silicate sheets, which can be classified as [Si₆O₁₄] using the silicate nomenclature of Liebau. The layers are build up from zweier single chains running parallel to c. Raman spectra are presented and compared with other silicates. Furthermore, the structure is discussed versus Na₂Si₃O₇.     

Pt/γ-Al2O3/CexZr1-xO2催化剂低温催化燃烧去除饮食油烟

以CexZr1-xO2固溶体做载体, 制备了系列Pt/γ-Al2O3/CexZr1-xO2催化剂(x=1, 0.75, 0.5, 0.25, 0). 应用Brunauer-Emmet-Teller (BET)比表面积分析、X射线衍射(XRD)和H2程序升温还原(H2-TPR)等手段对催化剂进行相关表征, 并系统研究了催化剂在饮食油烟催化燃烧中的催化活性. BET结果表明催化剂的比表面积随Ce/Zr摩尔比的减小而减小. XRD结果表明贵金属Pt很好地分散在氧化铝和CexZr1-xO2固溶体上. H2-TPR结果发现催化剂Pt/γ-Al2O3/Ce0.5Zr0.5O2的还原峰面积最大且氧离子的流动性最好. 催化活性研究结果表明Pt负载在CexZr1-xO2固溶体上有利于油烟的催化燃烧, 降低了反应温度. 随着CexZr1-xO2固溶体中Ce/Zr摩尔比的变化, 催化剂的活性顺序为Pt/γ-Al2O3/Ce0.5Zr0.5O2>Pt/γ-Al2O3/Ce0.25Zr0.75O2>Pt/γ-Al2O3/Ce0.75Zr0.25O2>Pt/γ-Al2O3/CeO2>Pt/γ-Al2O3/ZrO2.     

Ionic conductivity, structural and thermal properties of pure and Sr doped Y2Ti2O7 pyrochlores for SOFC

In the present study, SrO doped Yttrium titanate pyrochlore was synthesized using solid state reaction technique. The sintering characteristics, crystal structure, thermal and conductivity behavior of doped and undoped pyrochlores have been studied to find their suitability in solid oxide fuel cells (SOFC). The as-prepared samples were characterized using X-ray diffraction (XRD), Fourier-Transform-Infrared spectroscopy (FT-IR), thermal-gravimetric analysis (TGA) and ac conductivity up to 900 °C. The results are discussed in light of oxygen vacancy formation and structural disordering. Undoped and doped yttrium titanate with SrO (x = 0.1) exhibits single Y₂Ti₂O₇ phase with relative density of 94%. It was observed that further doping of SrO (x = 0.2–0.4) leads to formation of Y₂Ti₂O₇ phase along with SrTiO₃ phase. Excessive SrO (x = 0.4) results in increase in ionic conductivity to 1.50 × 10⁻¹ S cm⁻¹ whereas it impedes the densification process with relative density of 85%.     

Pt/CexZr1-xO2 催化剂在含硫合成气中催化水煤气变换反应活性

 采用浸渍法制备了 Pt/Ce_xZr_1-xO₂ 催化剂, 通过 X 射线衍射和程序升温还原等方法对催化剂进行了表征, 并在固定床反应器中评价了催化剂在合成气和含硫合成气中的水煤气变换活性. 结果表明, 铈锆固溶体的氧化还原能力强于 CeO₂, Zr 的掺杂明显改善了 CeO₂ 的孔道结构, 其担载的 Pt 催化剂具有更高的金属分散度, 因而活性更高. 两种催化剂在含硫合成气中的催化活性较无硫合成气中的均有所降低, 且 H₂S 浓度越大, 催化剂活性下降越多, 但这种因吸附硫而引起的失活是可逆的, 即催化剂重新暴露在无 H₂S 重整气的还原性气氛下活性能基本恢复.     

Raman, XRD and microscopic investigations on CeO2-Lu2O3 and CeO2-Sc2O3 systems: A sub-solidus phase evolution study

A sub-solidus phase evolution study was done in CeO₂-Sc₂O₃ and CeO₂-Lu₂O₃ systems under slow-cooled conditions from 1400 °C. Long-range order probing of X-ray diffraction technique is utilized in conjunction with the ability of Raman spectroscopy to detect the changes in local co-ordination. Lu₂O₃ showed solubility of 30 mol% in CeO₂, thus forming an anion deficient fluorite-type (F-type) solid solution, whereas Sc₂O₃ did not show any discernible solubility. A biphasic region (F+C) was unequivocally detected by Raman spectroscopy in Ce_1−xLu_xO_2−x/2 (0.4?x?0.9) and in Ce_1−xSc_xO_2−x/2 (0.1?x?0.9) systems. Raman spectroscopy was valuable in studying these systems since oxygen vacancies are created on doping RE₂O₃ into ceria and Raman spectroscopy is very much sensitive to oxygen polarizability and local coordination. Back scattered images collected on representative compositions support the above-mentioned results.