STUDIES ON BaF_2 PROMOTED PRASEODYMIUM OXIDE CATALYSIS FOR THE OXIDATIVE COUPLING OF METHANE

IntroductionTheoxidativecouplingofmethane(OCM)toetheneandethaneisanattractivereactiontoconvertnaturalgasintovaluablechemicals.SincethepioneeringworkbyKellerandBhasin[1],OCMhasbecomeasubjectofworldwideintenseresearchinrecentyears.Almostallofelementsinthepe…     

Facile-fabricated iron oxide nanorods as a catalyst for hydrogenation of nitrobenzene

Iron oxide nanorod catalysts were fabricated by wet chemistry method followed annealing. The facilefabricated FeOOH nanorods with an efficient catalytic performance for transfer hydrogenation of nitrobenzene with hydrazine hydrate are presented.     

Synthesis and Crystal Structure of a Novel Organolanthanide Schiff Base Complex[(η~5-C_5H_5)Pr(acac)_2(μ_3-OH)]_2·4THF

1 INTRODUCTION It is well known that lanthanide metals are quite oxophilic and the oxygen-stabilized organolanthanide complexes are tractable for exploring their physical and chemical properties. Organolanthanide complexes involving -diketonato chelate ligands have been largely prepared and characterized[1~5]. The Schiff base complexes are some of the most important stereochemical models in transition metal coordination chemistry; however, the organolanthanide Schiff base complexes are …     

稀土Pr6O11上CO和表面羟基反应的原位FT-IR研究

利用FT-IR原位考察了稀土氧化镨上CO和表面羟基的反应。在473K以下,未检测到CO和氧化镨表面反应的吸附物种;在CO气氛中,升温到473K,观察到甲酸根吸附物种的红外特征峰1578,1371和1367cm~(-1)。用同位素D_2部分还原的氧化镨吸附CO以及甲酸吸附证实了CO与氧化镨表面的羟基反应可生成表面甲酸根吸附物种。讨论了CO在氧化镨表面的反应机理及甲酸根的氧化过程。     

From layered double hydroxide to spinel nanostructures: facile synthesis and characterization of nanoplatelets and nanorods

Mg-Al spinel (MgAl2O4) nanorods and nanoplatelets transformed from Mg-Al layered double hydroxide (Mg-Al-LDHs) were synthesized via a combined hydrothermal method and calcination route using Al(NO3).9H2O and Mg(NO3)2.6H2O as raw materials. The nanorods and nanoplatelets were characterized by means of physical techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microcopy (HRTEM), selected-area electron diffraction (SAED), Fourier transform infrared spectra (FT-IR), thermogravimetric (TG), and nitrogen adsorption-desorption isotherms. XRD patterns reveal that the Mg-Al-LDHs nanostructures were obtained under a hydrothermal reaction temperature of 200 degrees C and Mg-Al spinel nanostructures were fabricated via calcination of the Mg-Al-LDHs nanostructures at 750 degrees C. It can be seen from TEM that the sizes of the Mg-Al-LDHs nanoplatelets were about 20-40 nm and the diameters of the MgAl2O4 nanorods were ca. 6 nm. The HRTEM images indicate that the crystal lattice spaces of the MgAl2O4 nanorods and nanoplatelets are 0.282 and 0.287 nm, respectively.     

CeO2 nanorods and gold nanocrystals supported on CeO2 nanorods as catalyst

The formation mechanism of uniform CeO2 structure at the nanometer scale via a wet-chemical reaction is of great interest in fundamental study as well as a variety of applications. In this work, large-scale well-crystallized CeO2 nanorods with uniform diameters in the range of 20-30 nm and lengths up to tens of micrometers are first synthesized through a hydrothermal synthetic route in 5 M KOH solution at 180 degrees C for 45 h without any templates and surfactants. The nanorod formation involves dehydration of CeO2 nanoparticles and orientation growth along the 110 direction in KOH solution. Subsequently, gold nanoparticles with crystallite sizes between 10 and 20 nm are loaded on the surface of CeO2 nanorods using HAuCl4 solution as the gold source and NaBH4 solution as a reducing agent. The synthesized Au/CeO2 nanorods demonstrate a higher catalytic activity in CO oxidation than the pure CeO2 nanorods.     

Iron oxide coated gold nanorods: synthesis, characterization, and magnetic manipulation

We report a simple process to generate iron oxide coated gold nanorods. Gold nanorods, synthesized by our three-step seed mediated protocol, were coated with a layer of polymer, poly(sodium 4-styrenesulfonate). The negatively charged polymer on the nanorod surface electrostatically attracted a mixture of aqueous iron(II) and iron(III) ions. Base-mediated coprecipitation of iron salts was used to form uniform coatings of iron oxide nanoparticles onto the surface of gold nanorods. The magnetic properties were studied using a superconducting quantum interference device (SQUID) magnetometer, which indicated superparamagnetic behavior of the composites. These iron oxide coated gold nanorods were studied for macroscopic magnetic manipulation and were found to be weakly magnetic. For comparison, premade iron oxide nanoparticles, attached to gold nanorods by electrostatic interactions, were also studied. Although control over uniform coating of the nanorods was difficult to achieve, magnetic manipulation was improved in the latter case. The products of both synthetic methods were monitored by UV-vis spectroscopy, zeta potential measurements, and transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the oxidation state of iron in the gold nanorod-iron oxide composites, which is consistent with Fe2O3 rather than Fe3O4. The simple method of iron oxide coating is general and applicable to different nanoparticles, and it enables magnetic field-assisted ordering of assemblies of nanoparticles for different applications.     

苯磺酰β-丙氨酸镨配合物的合成及晶体结构

合成了配合物{[Pr2 L6 (H2O)4]?H 2O}n (L = 苯磺酰b-丙氨酸), 并通过单晶X射线衍射确定了晶体结构。化合物(C27H41.21N3O17.6PrS3)属单斜晶系, 空间群P21 /n, 晶胞参数:a = 9.412(1), b = 18.019(2), c = 22.522(4) , b = 100.43(1), Z = 4, Mr = 926.59, Dc = 1.638 g/cm3, V = 3756.3(8) 3, F(000) = 1888, m = 1.540 mm1 。PrⅢ离子为9配位的单帽四方反棱柱结构, 羧基氧原子与镨原子间存在3种配位方式, 镨原子之间通过2种类型的羧基连接使配合物分子呈无限链状结构。     

稀土Pr_6O_(11)表面上低碳烃氧化反应的原位FT-IR研究

前文报道了CO与Pr_6O_(11)表面反应的结果.已发表的关于烃类与氧化物表面反应的研究,旨在了解烃类的活化和表面氧化机理,而且大部分工作都是在过渡金属氧化物上进行的.近年来的研究表明,稀土氧化物将是有潜力的甲烷氧化偶联制乙烯的催化剂,在消除环境污染的烃类完全氧化催化剂中,稀土氧化物也常被用作助剂或活性组分,但对于稀土氧化物本身的催化表面研究尚不多见.作者曾较系统地研究了CeO_2的表面催化性质,发现表面上存在多种氧物种,这些氧物种与烃类的反应活性差异很     

Homoleptic rare-earth metal(III) tetramethylaluminates: structural chemistry, reactivity, and performance in isoprene polymerization

The complexes [Ln(AlMe4)3] (Ln=Y, La, Ce, Pr, Nd, Sm, Ho, Lu) have been synthesized by an amide elimination route and the structures of [Lu{(micro-Me)2AlMe2}3], [Sm{(micro-Me)2AlMe2}3], [Pr{(micro-Me)2AlMe2}3], and [La{(micro-Me)2AlMe2}2{(micro-Me)3AlMe}] determined by X-ray crystallography. These structures reveal a distinct Ln3+ cation size-dependency. A comprehensive insight into the intrinsic properties and solution coordination phenomena of [Ln(AlMe4)3] complexes has been gained from extended dynamic 1H and 13C NMR spectroscopic studies, as well as 1D 89Y, 2D 1H/89Y, and 27Al NMR spectroscopic investigations. [Ce(AlMe4)3] and [Pr(AlMe4)3] have been used as alkyl precursors for the synthesis of heterobimetallic alkylated rare-earth metal complexes. Both carboxylate and siloxide ligands can be introduced by methane elimination reactions that give the heterobimetallic complexes [Ln{(O2CAriPr)2(micro-AlMe2)}2(AlMe4)(C6H14)n] and [Ln{OSi(OtBu)3}(AlMe3)(AlMe4)2], respectively. [Pr{OSi(OtBu)3}(AlMe3)(AlMe4)2] has been characterized by X-ray structure analysis. All of the cerium and praseodymium complexes are used as precatalysts in the stereospecific polymerization of isoprene (1-3 equivalents of Et2AlCl as co-catalyst) and compared to the corresponding neodymium-based initiators reported previously. The superior catalytic performance of the homoleptic complexes leads to quantitative yields of high-cis-1,4-polyisoprene (>98%) in almost all of the polymerization experiments. In the case of the binary catalyst mixtures derived from carboxylate or siloxide precatalysts quantitative formation of polyisoprene is only observed for nLn:nCl=1:2. The influence of the metal size is illustrated for the heterobimetallic lanthanum, cerium, praseodymium, neodymium, and gadolinium carboxylate complexes, and the highest activities are observed for praseodymium as a metal center in the presence of one equivalent of Et2AlCl.     

Synthesis of hexagonal BaTa2O6 nanorods and influence of defects on the photocatalytic activity

Hexagonal barium tantalate (BaTa2O6) nanorods were synthesized by a hydrothermal method based on the reaction of concentrated Ba(OH)2 solution and Ta2O5. BaTa2O6 samples show a uniform cylindrical structure with diameters of 5-30 nm and the lengths of 50-200 nm. The formation of BaTa2O6 nanorods follows a dissolution-recrystallization mechanism and is governed by hydrothermal temperature and time. BaTa2O6 nanorod samples prepared at 270 degrees C for 72 h have exhibited the highest photocatalytic activity in the degradation of Rhodamine B (RhB) in aqueous solution under UV radiation. Hydrogen-related defects were detected in BaTa2O6 nanorods, which originate from the oxygen octahedron. The number of defects was dependent on the hydrothermal temperature, and the photocatalytic activities of BaTa2O6 nanorods increase with the decrease of defect amounts. On the basis of the experiment results, the difference in photocatalytic activities for samples is mainly caused by lattice defects, which can act as inactivation centers.     

Aerosol assisted chemical vapor deposition using nanoparticle precursors: a route to nanocomposite thin films

Gold nanoparticle and gold/semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapor deposition (CVD). A preformed gold colloid in toluene was used as a precursor to deposit gold films onto silica glass. These nanoparticle films showed the characteristic plasmon absorption of Au nanoparticles at 537 nm, and scanning electron microscopic (SEM) imaging confirmed the presence of individual gold particles. Nanocomposite films were deposited from the colloid concurrently with conventional CVD precursors. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)(6)], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O(i)Pr)(4)]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. Titania/gold composite films were intensely colored and showed dichromism: blue in transmitted light and red in reflected light. They showed metal-like reflection spectra and plasmon absorption. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirmed the presence of metallic gold, and SEM imaging showed individual Au nanoparticles embedded in the films. X-ray diffraction detected crystalline gold in the composite films. This CVD technique can be readily extended to produce other nanocomposite films by varying the colloids and precursors used, and it offers a rapid, convenient route to nanoparticle and nanocomposite thin films.     

Lanthanum(III) and praseodymium(III) complexes with isatin thiosemicarbazones

Ten new lanthanum(III) and praseodymium(III) complexes of the general formula Na[La(L)2H2O] (Ln=La(III) or Pr(III); LH2=thiosemicarbazones) derived from the condensation of isatin with 4-phenyl thiosemicarbazide, 4-(4-chlorophenyl) thiosemicarbazide, 4-(2-nitrophenyl) thiosemicarbazide, 4-(2-bromophenyl) thiosemicarbazide and 4-(2-methylphenyl) thiosemicarbazide, have been synthesized in methanol in presence of sodium hydroxide. The XRD spectra of the complexes were monitored to verify complex formation. The complexes have also been characterized by elemental analysis, molar conductance, electronic absorption and fluorescence, infrared, far infrared, 1H and 13C NMR spectral studies. Thermal studies of these complexes have been carried out in the temperature range 25-800 degrees C using TG, DTG and DTA techniques. All these complexes decompose gradually with the formation of Ln2O3 as the end product. The Judd-ofelt intensity parameter, oscillator strength, transition probability, stimulated emission cross section for different transitions of Pr3+ for 4-phenyl thiosemicarbazones have been calculated.     

DFT and in situ EXAFS investigation of gold/ceria-zirconia low-temperature water gas shift catalysts: identification of the nature of the active form of gold

A combined experimental and theoretical investigation of the nature of the active form of gold in oxide-supported gold catalysts for the water gas shift reaction has been performed. In situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) experiments have shown that in the fresh catalysts the gold is in the form of highly dispersed gold ions. However, under water gas shift reaction conditions, even at temperatures as low as 100 degrees C, the evidence from EXAFS and XANES is only consistent with rapid, and essentially complete, reduction of the gold to form metallic clusters containing about 50 atoms. The presence of Au-Ce distances in the EXAFS spectra, and the fact that about 15% of the gold atoms can be reoxidized after exposure to air at 150 degrees C, is indicative of a close interaction between a fraction (ca. 15%) of the gold atoms and the oxide support. Density functional theory (DFT) calculations are entirely consistent with this model and suggest that an important aspect of the active and stable form of gold under water gas shift reaction conditions is the location of a partially oxidized gold (Audelta+) species at a cerium cation vacancy in the surface of the oxide support. It is found that even with a low loading gold catalysts (0.2%) the fraction of ionic gold under water gas shift conditions is below the limit of detection by XANES (<5%). It is concluded that under water gas shift reaction conditions the active form of gold comprises small metallic gold clusters in intimate contact with the oxide support.     

Mild benzene-thermal route to GaP nanorods and nanospheres

GaP nanorods and nanospheres were synthesized from a mild benzene-thermal route at 240 and 300 degrees C, respectively, using Na, P, and GaCl(3) as the starting materials. The structure of the products was identified as zinc blende phase by X-ray powder diffraction (XRD). Transmission electron microscopy (TEM) images showed that, when the reaction temperature was 240 degrees C, the products were nanorods with widths of 20-40 nm and lengths of 200-500 nm and nanospheres with diameters of 20-40 nm. However, when the reaction temperature was increased to 300 degrees C, the products were only nanospheres, and the diameters increased to 40-60 nm. The reaction proceeded through a metallic gallium intermediate, and a solution-liquid-solid (SLS) mechanism was proposed for the one-dimensional growth. The products were also investigated by UV-vis absorption and X-ray photoelectron spectroscopy.     

金修饰ZnO纳米棒阵列制备及对甲醛气敏性能

通过两步溶液法在氧化铝陶瓷管上先制备出ZnO纳米棒阵列,再用真空蒸镀法在ZnO纳米棒表面形成一层均匀Au膜,于500℃下热处理得到Au纳米颗粒修饰的ZnO(Au-ZnO)纳米棒阵列体系。通过场发射扫描电子显微镜(FE-SEM)和X射线衍射仪(XRD)对ZnO纳米棒阵列和Au-ZnO纳米复合体系进行表面形貌表征和结构分析。气敏性能测试结果表明,Au-ZnO纳米复合体系在300℃下对1000μL·L-1甲醛的灵敏度为41.5,而在200℃下灵敏度仍能达到10.3,表明可以制备低工作温度下气敏性能良好的甲醛气敏传感器。     

Synthesis, structure, texture, and CO sensing behavior of nanocrystalline tin oxide doped with scandia

Weakly agglomerated nanocrystalline scandia doped tin oxide powders with high surface area (170-220 m(2)/g) and uniform size (3-4 nm) were synthesized for the first time by a two-step hydrothermal process in the presence of urea, followed by the calcination between 500 and 1200 degrees C. The structure and texture of the binary oxide system were characterized by thermogravimetry and differential thermal analysis, Brunauer-Emmett-Teller-specific surface area analysis, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. A metastable scandium tin oxide solid solution in tetragonal structure was formed for the scandia content lower than 6 mol % as the samples were calcined at 800 degrees C, and the excess Sc atoms were dispersed at the surface of the crystallites above this limit. The solid solution was metastable, so scandium migrated toward the surface region of the crystallites and produced a second phase of Sc(4)Sn(3)O(12) during calcining at high temperatures over 1000-1200 degrees C. In the case of the samples with higher dopant concentration (>15 mol %), the calcination at the temperature between 500 and 800 degrees C caused the precipitation of Sc(2)O(3), and the calcination over 1000-1200 degrees C led to the formation of more Sc(4)Sn(3)O(12). Textural analysis showed that doping an appropriate amount of Sc(2)O(3) into nanosized SnO(2) could effectively inhibit the grain growth and stabilize the surface area against high-temperature calcinations below 1000 degrees C. CO gas-sensing property measurements revealed that the dispersion of Sc at the surfaces of the SnO(2) nanocrystallites could improve the CO sensitivity significantly, and the pellet sample with scandia content of 10 mol % sintered at 800 degrees C showed the best CO gas-sensing property in the operation temperature range of 300-400 degrees C. On the basis of the structural and textural analysis, the correlation between the structure/texture and the sensitivity to CO for the as-calcined (SnO(2))(1-x)(Sc(2)O(3))(x) nanocrystallites has been established and explained.     

In situ surface oxidation study of a planar Co/SiO2/Si(100) model catalyst with nanosized cobalt crystallites under model Fischer-Tropsch synthesis conditions

The oxidation of nanosized metallic cobalt to cobalt oxide during Fischer-Tropsch synthesis (FTS) has long been postulated as a major deactivation mechanism. In this study a planar Co/SiO(2)/Si(100) model catalyst with well-defined cobalt crystallites, close to the threshold value reported for oxidation in the literature (4-10 nm), was prepared by the spin coating method. The planar Co/SiO(2)/Si(100) model catalyst was characterized with atomic force microscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering. The surface oxidation behavior of the nanosized metallic cobalt crystallites of 4-5 nm was studied using in situ near-edge X-ray absorption fine structure under model FTS conditions, i.e., H(2)/H(2)O = 1, P(Total) = 0.4 mbar, and 150-450 degrees C. No surface oxidation of metallic cobalt was observed under these model FTS conditions over a wide temperature range, i.e., 150-400 degrees C.     

四价镨化合物的研究(Ⅰ)——铈镨杂多核氧化物的制备及四价镨在不同溶液中的稳定性

在常温常压下,从近中性的混合铈、镨硝酸盐水溶液中,采用臭氧(或氧气)氧化,制得了红棕色的四价铈镨杂多核氧化物,这种在铈的存在下镨的氧化,拟称为"带同氧化"。通过化学分析,X射线衍射物相分析以及与二氧化锰作用的研究,证明了杂多核氧化物中四价镨的存在。该杂多核氧化物溶于浓硝酸、浓盐酸和冰醋酸中,生成血红色的溶液。通过颜色的变化和紫外可见光谱的研究,考察了四价镨在这些溶液中的稳定性。四价镨在冰醋酸中相当稳定,浓硝酸中一小时内逐渐消失,浓盐酸和硫酸(1:1)中则极不稳定。含四价镨的浓硝酸和冰醋酸溶液的吸收光谱,分别在460nm和440nm处呈现宽带特征吸收峰。通过与不含四价镨的纯铈(Ⅳ)、纯错(Ⅲ)及铈钕混合氧化物等光谱的比较,初步认为这两个特征吸收峰与四价镨的存在有关。     

Influence of pH on the synthesis ZnO nanorods and photocatalytic hydrogen production from glycerol solution

Photocatalytic oxidation of glycerol at ambient conditions has been investigated with the use of Zinc oxide photocatalysts. Zinc oxide nanorods were prepared via a simple hydrothermal method using zinc nitrate and sodium hydroxide in the solution pH of 7, 8 and 9. The samples prepared in this way were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET) and ultraviolet–visible spectroscopy (UV–vis). The pH of the solution is 7, the sample contains zinc hydroxide nitrate hydrated. When the pH of solution was adjusted to 8 and 9, the samples consisted of pure hexagonal wurtzite ZnO without impurity detection. The influence of solution pH on hydrogen formation was investigated. The wurtzite ZnO nanorods synthesized in a solution with pH 9 are considered promising photocatalysts for hydrogen production under xenon radiation.