铈锆铝复合氧化物的制备及其性能研究

以硝酸铈和硝酸锆为原料,氨水为沉淀剂,双氧水为氧化剂,采用共沉淀法将铈锆固溶体负载在固态铝源(拟薄水铝石、活性氧化铝和改性氧化铝)表面,制备了铈锆铝复合氧化物。通过XRD,TEM,BET,TPR等手段对铈锆铝复合氧化物进行了结构表征和性能分析。研究结果表明:铈锆固溶体负载在氧化铝上,颗粒明显变小,老化性能得到显著改善;不同形态固态铝源制备的铈锆铝复合氧化物性能各异,以拟薄水铝石为铝源制备的样品比表面积最大,以改性氧化铝为铝源制备的样品表现出最佳的储氧性能。     

固相反应-结构导向法合成铈锆固溶体

为获得结构和性能优化的铈锆固溶体,将固相反应-结构导向法引入制备过程,分别考察了NaOH添加量、铈锆比、晶化温度、晶化时间和表面活性剂加量等因素对固溶体结构的影响.结果表明,采用固相反应-结构导向法可以得到比表面较大的四方相铈锆固溶体,但其热稳定性还有待于进一步改善.OH-/Zr是影响固溶体结构的主导因素,它不仅影响着比表面的大小,还控制着晶相转化过程.     

Al的加入对CeZr固溶体催化剂结构及其乙苯脱氢活性的影响

为进一步提高铈锆固溶体储放氧性能,增强乙苯二氧化碳氧化脱氢反应性能,采用共沉淀法合成出氧化铝质量比为50%的铈锆铝氧化物催化剂。通过现代仪器分析表征技术,研究了Al加入对铈锆固溶体复合氧化物晶体结构、储放氧能力的影响。结果表明,Al的加入可起到"扩散阻碍"作用,且有效抑制铈锆固溶体晶粒长大,使得铈锆铝氧化物催化剂比表面积较铈锆固溶体增加了51.8 m~2/g,储放氧性OSC值提高了69.4μmol/g,将铈锆铝氧化物催化剂用在乙苯氧化脱氢5 h反应中,发现乙苯转化率提高了10%。     

铈锆固溶体制备方法的研究进展

铈锆固溶体具有优良的储释氧性能,在三效汽车尾气净化催化剂中起着重要作用,而铈锫固溶体的制备方法与其物化性质又有着密切联系.综述了近几年来国内外铈锆固溶体的制备方法(包括共沉淀法、模板剂法、溶胶-凝胶法、微乳液法等).讨论了晶相结构、比表面积、热稳定性等对固溶体储释氧性能的影响,通过分析固溶体的程序升温还原(TPR)谱图,解释了不同制备方法对所得铈锆固溶体氧化-还原能力的差异.结合文献结果,可以认为寻找工艺简单、性能稳定、重复性好的可控制备方法将是此类材料得到大规模应用的努力方向.     

还原热处理对铈锆铝复合氧化物性能的影响

采用共沉淀法制备铈锆铝复合氧化物(CeO2-ZrO2-Al2O3,CZA)和铈锆复合氧化物(CeO2-ZrO2,CZ),将样品分别在空气和10%H2/Ar气氛下进行热处理,利用X射线粉末衍射(XRD)、O2脉冲吸附、H2程序升温还原(H2-TPR)等手段研究了复合氧化物的结构及性能.结果表明:CZA样品经950℃还原热处理后出现CeAlO3晶相,热处理温度越高,越有利于CeAlO3物相生成.CZA储氧量(OSC)随着还原热处理温度升高逐渐增大,至900℃达到1270.3μmo·lg-1;温度继续升高,OSC减小,1100℃还原热处理后CZA的OSC仅为23.2μmo·lg-1.研究发现还原热处理中形成CeAlO3,其显著影响CZA样品的储氧性能和还原性能.     

制备方法对Ce0.5Zr0.5O2固溶体微观晶相结构及还原性能影响的研究

采用不同合成方法制备了4种组成为Ce0.5Zr0.5O2的铈锆固溶体.通过XRD,BET,H2-TPR,HREM以及SEAD等表征手段,研究了微观晶相结构对铈锆固溶体还原性能的影响规律,以及对固溶体储放氧能力的影响.分析结果表明,在同一组成下,不同制备方法得到截然不同的晶相组成,4种固溶体包含4种不同的晶相组合.通过对微观晶相结构的定量分析,发现立方相的形成对促进固溶体的还原性能起到重要作用.其中,反相微乳法制得的铈锆固溶体能够形成完整的立方相结构,在H2-TPR还原过程中耗氢量最大,表明其具有优良的可还原性及储放氧能力,适合作为TWC,POX等催化剂载体.     

大比表面积铈锆氧化物固溶体的制备

采用共沉淀法制备铈、锆氧化物固溶体.发现以适当配比的(NH4)HCO3和NH3*H2O混合溶液作为沉淀剂,同时控制沉淀过成中的反应条件,所得到的沉淀在较低的温度(400 ℃)下焙烧即可形成铈、锆氧化物固溶体.该固溶体具有较大的比表面积和高的储氧能力.形成沉淀后添加适量表面活性剂,可进一步提高产品的比表面积而对其还原行为和储氧性能几乎无影响.对制得的氧化物以X-射线衍射、程序升温还原、氧的脉冲滴定和液氮物理吸附等方法进行了表征.     

烟草模板制备掺杂过渡金属铈锆固溶体及其催化氧化CO性能研究

以烟梗丝、烟叶片和烟梗条等材料为模板掺杂过渡金属合成了一系列铈锆固溶体材料.对合成的材料进行了扫描电子显微镜(SEM)、N2吸附-脱附、程序升温还原(H2-TPR)、X-射线衍射法(XRD)、储氧量(OSC)、X-射线光电子能谱(XPS)等表征.对铈锆固溶体材料进行CO氧化活性评价,结果表明不同烟草模板制备的铈锆固溶体性能不同.以烟叶片为模板制备的掺铜铈锆固溶体具有极高的储氧量,高达2961μmol/g,但该材料催化氧化CO的活性并非最强.以烟梗丝为模板制备的掺铜铈锆固溶体在铈锆比为45∶45∶10时,对CO氧化有着很好的催化活性,起燃活性温度(T50)为91℃.     

合成方法对纳米Ce-Zr-Al高温稳定性及储氧性能的影响

采用柠檬酸溶胶凝胶、溶胶辅助共沉淀和溶胶共沉淀3种方法合成了不同Al掺杂的纳米CexZr1-xO2与Al2O3的复合体Ce-Zr-Al.用XRD、BET和H2-TPR表征了纳米Ce-Zr-Al复合体的抗烧结性与储氧性能,与未掺杂的铈锆固溶体相比,Al掺杂的纳米铈锆复合体的抗烧结性与储氧性能均有显著改善,柠檬酸溶胶凝胶法的最佳掺杂量为5倍Al(Al与CexZr1-xO2摩尔比),溶胶辅助共沉淀法最佳掺杂量为10倍Al,溶胶共沉淀法最佳掺杂量为5倍Al,其中,柠檬酸溶胶凝胶法合成的Ce-Zr-Al纳米复合物储氧量最高,为717.5 μmol/g-CeO2,占理论储氧量(即储氧效率)的49.3％.     

铈锆固溶体的合成及其在CH_4和CO催化燃烧反应中的应用

分别利用固态反应和共沉淀法制备了铈锆固溶体,并以其为载体制备了车用三效催化剂,考察其在CH4和CO催化燃烧反应中的作用.研究发现固态反应法所得固溶体孔分布较宽,热稳定性较差,但表面较多的缺陷位贡献于其较高的储氧性能.而共沉淀法所得样品拥有较高的热稳定性和催化活性.固溶体的还原性质可以通过铈锆比调控.关联催化剂对CH4和CO的催化氧化性能发现,具有较大比表面积、集中孔径分布和较高储氧能力的固溶体显示了较低的催化剂起燃温度和较高的催化活性.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

KCl-KBO2-K2CO3, K2MoO4-KBO2-K2CO3, and K2WO4-KBO2-K2CO3 ternary systems

phase diagrams of KCl-KBO₂-K₂CO₃, K₂MoO₄-KBO₂-K₂CO₃, and K₂WO₄-KBO₂-K₂CO₃ ternary systems were studied by a calculation-experimental method and differential thermal analysis (DTA). The coordinates of ternary eutectics were determined to be E ₁: 622°C, 8.5 mol % KBO₂, 56.5 mol % KCl, and 35 mol % K₂CO₃; E ₂: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂MoO₄; E ₃: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂WO₄. The specific heats of melting of the eutectics were determined.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Solubility in the Na2Cr2O7-(NH4)2Cr2O7-K2Cr2O7-H2O system

Solubility in the Na₂Cr₂O₇-(NH₄)₂Cr₂O₇-K₂Cr₂O₇-H₂O four-component water-salt system at 25, 50, and 75°C was studied for the first time. Phase field boundaries for individual salts and potassium and ammonium dichromate solid solutions, monovariant lines, and invariant points were determined. Experimental data were used to optimize the looped isohydric process of potassium dichromate preparation involving additional salts.     

Li2SO4-Na2SO4-H2O和Li2SO4- K2SO4-H2O溶液的体积性质

本文用高精度数字式振荡管密度计测定了288K至318K温度范围内Li₂SO₄ + Na₂SO₄ + H₂O和 Li₂SO₄ + K₂SO₄ + H₂O三元体系的密度。混合溶液的离子强度范围从0.1到4.5 mol.kg_–1,混合溶液中Na₂SO₄和K₂SO₄的离子强度分数为0.2,0.4,0.6和0.8。用密度实验值拟合得到了不同温度下Pitzer离子相互作用模型混合参数θ_V和 ψ_V,模型的计算值与实验值的偏差在±0.002 g.cm_–3以内。用Pitzer模型计算了不同离子强度下三元体系的混合体积。     

NaBO2-NaCl-Na2CO3, NaBO2- Na2CO3-NaMoO4, NaBO2- Na2CO3-NaWO4, and NaBO2-NaCl-Na2WO4 ternary systems

The phase diagrams of the NaBO₂-NaCl-Na₂CO₃, NaBO₂-Na₂CO₃-Na₂MoO₄, NaBO₂- Na₂CO₃-Na₂WO₄, and NaBO₂-NaCl-Na₂WO₄ ternary systems were studied by a calculation-experimental method and differential thermal analysis. The coordinates of ternary eutectics were determined: E ₁: 612°C, 16 mol % NaBO₂, 42 mol % NaCl, and 42 mol % Na₂CO₃; E ₂: 568°C, 12 mol % NaBO₂, 28 mol % Na₂CO₃, and 60 mol % Na₂MoO₄; E ₃: 575°C, 12 mol % NaBO₂, 32 mol % Na₂CO₃, and 56 mol % Na₂WO₄; E ₄: 628°C, 8 mol % NaBO₂, 20 mol % NaCl, and 72 mol % Na₂WO₄; and E ₅: 655°C, 9 mol % NaBO₂, 53 mol % NaCl, and 38 mol % Na₂WO₄.     

Theoretical study of polyoxide clusters B20O30, Al20O30, V20O50, Si20O30H20, and Si20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters B₂₀O₃₀, Al₂₀O₃₀, V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀ and their complexes with the H⁻ ion and ammonia complexes Al₂₀O₃₀ · nNH₃ have been calculated by the density functional theory B3LYP method with different basis sets. The computation results show that the symmetric closo structure I _h with oxygen bridges located above the centers of the faces of an empty [M₂₀] dodecahedron is more favorable for V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀. For B₂₀O₃₀, the cage closo isomer is also more favorable than the other isomers, but its structure is severely distorted as compared to a dodecahedron and has a symmetry close to C ₃ . For Al₂₀O₃₀, the I _h structure corresponds to a high-lying local minimum of the potential energy surface. For Al₂₀O₃₀, a set of unusual puckshaped isomers of symmetry C _i , with different numbers of four-coordinate atoms ^IVAl and three-coordinate atoms ^IIIO, was localized; these structures are more than 90 kcal/mol more favorable than the dodecahedron I _h . The most favorable isomer of Al₂₀O₃₀ contains twelve four-coordinate atoms ^IVAl and four five-coordinate atoms ^VAl. The energies of dissociation of the most favorable M₂₀O₃₀ clusters into the M₂O₃ (C _2v ) and M₄O₆ (T _d ) fragments and, in the case of Al₂₀O₃₀, also into the Al₈O₁₂ (O _h ) and Al₁₂O₁₈ (D _3d ) fragments, have been estimated. The conclusion has been drawn that these clusters can, in principle, exist and can be experimentally detected in the isolated state. Analogous calculations have been performed for ammonia complexes Al₂₀O₃₀ · nNH₃ with n varying from 1 to 20. The effect of solvation on the relative stability of the dodecahedral and puckshaped isomers of the Al₂₀O₃₀ cluster is observed. The isomers with ammonia molecules in their first coordination sphere become much closer to one another on the energy scale; however, the dodecahedron remains a considerably less favorable intermediate. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 4, pp. 624–635.     

Structural chemistry of Sr3Cr2WO9, Ca3Cr2WO9, and Ba3Cr2WO9

We have studied the preparation and crystallographic structure of three perovskite-type compounds: Sr₃Cr₂WO₉, cubic, the lattice parameter of which is a = 7.812Å; Ca₃Cr₂WO₉, tetragonal, the lattice parameters of which are a = 5.408 Å and c = 7.635Å; and Ba₃Cr₂WO₉, hexagonal, the lattice parameters of which are a = 5.691 Å and c = 13.957Å. We have compared these three structures and shown the relationship between the dimensions of the alkaline-earth metal and the existence of the different structures.     

SnSbBiS4-SnS and SnSbBiS4-Sn2Sb6S11 sections of the SnS-Sb2S3-Bi2S3 ternary system

SnSbBiS₄-SnS and SnSbBiS₄-Sn₂Sb₆S₁₁ sections were studied by physicochemical methods (DTA, X-ray powder diffraction, microstructure observation, and microhardness measurements). These sections were found to be eutectic quasi-binary sections of the SnS-Sb₂S₃-Bi₂S₃ ternary system. Solid solution regions based on the initial components were found on either side of the sections. Alloys in the solid solution region are p-type semiconductors.     

Extension of the La7Mo7O30 structural type with La7Nb3W4O30 and La7Ta3W4O30 compounds

Two compounds of formula La₇A₃W₄O₃₀ (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490 °C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: , and , . The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La₇Mo₇O₃₀, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.