Fabrication of nanorattles with passive shell

This investigation describes the formation of a metal nanorattle with a pure metal shell by varying experimental parameters. The galvanic replacement reaction between silver and chloroauric acid was adopted to prepare hollow metal nanoparticles. This approach is extended to produce nanorattles of Au cores and Au shells by starting with Au(core)Ag(shell) nanoparticles as templates. The effect of temperature on the nanostructure of the final product is also considered. The composition of the shell in nanorattles can be controlled by varying the reaction temperature (to form pure gold or gold-silver alloy, for example). X-ray absorption fine structure spectroscopy is conducted to elucidate the fine structure of these nanoparticles. Partial alloying between the Au core and the Ag shell is observed by extended X-ray absorption fine structure (EXAFS).     

Colloidal gold nanoparticles as catalyst for carbon-carbon bond formation: application to aerobic homocoupling of phenylboronic acid in water

Gold nanoparticles (<2 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP NPs) were prepared by reduction of AuCl4- with NaBH4 in the presence of PVP and characterized via an array of methods including optical absorption spectroscopy, transmission electron microscopy, X-ray diffraction, X-ray absorption near-edge structure, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. We demonstrate for the first time that the Au:PVP NPs act as catalyst toward homocoupling of phenylboronic acid in water under aerobic conditions. Suppression of biphenyl formation under anaerobic conditions indicates that molecular oxygen dissolved in water is intimately involved in the coupling reactions. A mechanism of the aerobic homocoupling catalyzed by the Au:PVP NPs is proposed on the basis of a crucial role of dissolved oxygen, steric effects on the product yields, and the well-established mechanism for the Pd(II)-based catalysts.     

Synthesis and structural characterization of Se-modified carbon-supported Ru nanoparticles for the oxygen reduction reaction

This work is part of a continued research aimed at the understanding of the promoting role of Se in the enhancement of the electrocatalytic activity of Ru in the oxygen reduction reaction. The objective of this paper is to systematically investigate the transformation of Ru nanoparticles upon their modification with the increasing amounts of Se. The Se-modified Ru/C samples with Se:Ru ratio from 0 to 1 were prepared by reacting carbon-supported Ru nanoparticles with SeO2 followed by reductive annealing and characterized using high-resolution transmission electron microscopy, energy-dispersive X-ray, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure. The results suggest that Se strongly interacts with Ru, resulting in the chemical bond between Ru and Se and formation of Ru selenide clusters whose core at low Se content can be described as Ru2Se2O0.5. At Se:Ru = 1, high-resolution electron microscopy shows evidence of formation of core-shell particles, comprising a hexagonally packed Ru core and a Ru selenide shell with lamellar morphology. Modification of Ru nanoparticles with Se enhances their electrocatalytic activity in the oxygen reduction reaction, which is explained by the role of Se in inhibiting surface oxidation.     

Determination of CoSi2 self-aligned nanostructures with grazing incidence X-ray absorption spectroscopy

Self-aligned nanostructures (SAN) made by reacting Co nanoparticles with crystalline Si substrates at high temperatures were studied with grazing incidence X-ray absorption spectroscopy (GI-XAS). The results from extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES) were used to identify SAN as crystalline CoSi2. Theoretical calculations of EXAFS and XANES spectra of several crystalline cobalt silicides were performed with the FEFF8 package. On the basis of these studies, the SAN samples were determined to contain nearly pure CoSi2.     

镍铁氰化物纳米粒子的合成及其多相催化无溶剂条件下苯甲醇氧化的潜能(英文)

Nickel hexacyanoferrate nanoparticles were synthesized and characterized using elemental analysis, thermal analysis, infrared spectroscopy, and X-ray diffraction. A FE-SEM image of the nickel hexacyanoferrate showed that it consists of nearly spherical particles with sizes ranging from 30 to 70 nm. The synthesized material was found to be a heterogeneous catalyst useful for the solvent-free oxidation of benzyl alcohol with H2O2 as an oxidant. A 36% conversion of benzyl alcohol to benzaldehyde was achieved under optimized reaction conditions using specific parameters such as the amount of catalyst, the temperature, the benzyl alcohol to H2O2 molar ratio, and the reaction time.     

In situ extended X-ray absorption fine structure study during selective alcohol oxidation over Pd/Al2O3 in supercritical carbon dioxide

High-pressure in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are reported during the selective oxidation of benzyl alcohol to benzaldehyde in supercritical carbon dioxide over a Pd/Al(2)O(3) catalyst (shell impregnated). For this purpose, a continuous-flow system with a spectroscopic cell suitable for in situ X-ray absorption studies on heterogeneous catalysts up to 200 degrees C and 200 bar has been developed. Due to the high contribution of the dense fluid to the overall X-ray absorption, high stability of the process pressure is mandatory, particularly when recording EXAFS spectra. According to EXAFS and XANES results, the palladium particles were fully reduced after exposure to benzyl alcohol in scCO(2). In contrast to Pd-catalyzed liquid-phase oxidation, a higher oxygen tolerance of the catalyst was observed. Palladium was partially oxidized on the surface under typical reaction conditions (0.9 mol % benzyl alcohol/0.5 mol % O(2) in carbon dioxide), which gradually increased when the concentration of oxygen in the feed was raised. Both XANES and EXAFS data uncovered that palladium is mainly oxidized on the surface or within the outermost layers. These results are in accordance with simulations of the XANES data using the FEFF8.20 code (program for ab initio calculations on multiple scattering XAS) and EXAFS data fitting/simulation.     

The preparation of Pt nanoparticles by methanol and citrate

Platinum nanoparticles of 2-3 nm average size and ca. +/-2 nm distribution can be successfully prepared by methanol reduction while using sodium citrate as the stabilizer. Sol formation was investigated by UV-visible spectroscopy and EXAFS (extended X-ray absorption fine structure spectroscopy). The formation of Pt nanoparticles was confirmed by the presence of Pt-Pt bonding in the solution after a certain induction period in methanol-reduced sol with or without citrate. The possible two-step reduction of Pt(IV) was revealed by correlating EXAFS, UV-visible spectra and pH data. The presence of citrate resulted in a smaller Pt-Pt coordination number and a slower sol formation process. All these results prove that citrate acted as the stabilizer in this synthesis.     

Solvothermal preparation,and characterization,of Cu–Ag nanoparticles

Cu–Ag nanoparticles have been successfully synthesized by one-pot solvothermal treatment of a mixture of AgNO₃ and Cu(OAc)₂·H₂O in ethylene glycol solution at 180 °C for 10 h. The samples were characterized by UV–visible absorption, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The results showed that Cu–Ag nanoparticles and a small amount of phase-separated Cu–Ag alloy nanoparticles with an average diameter of 100 ± 30 nm were synthesized by the solvothermal treatment procedure. The mechanism of formation is discussed.     

Applications of X-ray absorption spectroscopy to biologically relevant metal-based chemistry

Recent developments in the understanding of the biosynthesis of the active site of the nitrogenase enzyme, the structure of the iron centre of [Fe]-hydrogenase and the structure and biomimetic chemistry of the [FeFe] hydrogenase H-cluster as deduced by application of X-ray spectroscopy are reviewed. The techniques central to this work include X-ray absorption spectroscopy either in the form of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) and nuclear resonant vibrational spectroscopy (NRVS). Examples of the advances in the understanding of the chemistry of the system through integration of a range of spectroscopic and computational techniques with X-ray spectroscopy are highlighted. The critical role played by ab initio calculation of structural and spectroscopic properties of transition-metal compounds using density functional theory (DFT) is illustrated both by the calculation of nuclear resonance vibrational spectroscopy (NRVS) spectra and the structures and spectra of intermediates through the catalytic reactions of hydrogenase model compounds.     

Solution structures of chromium(VI) complexes with glutathione and model thiols

Chromium(VI) complexes of the most abundant biological reductant, glutathione (gamma-Glu-Cys-Gly, I), are among the likely initial reactive intermediates formed during the cellular metabolism of carcinogenic and genotoxic Cr(VI). Detailed structural characterization of such complexes in solutions has been performed by a combination of X-ray absorption fine structure (XAFS) and X-ray absorption near-edge structure (XANES) spectroscopies, electrospray mass spectrometry (ESMS), UV-vis spectroscopy, and kinetic studies. The Cr(VI) complexes of two model thiols, N-acetyl-2-mercaptoethylamine (II) and 4-bromobenzenethiol (III), were used for comparison. The Cr(VI)-thiolato complexes were generated quantitatively in weakly acidic aqueous solutions (for I and II) or in DMF solutions (for II) or isolated as a pure solid (for III). Contrary to some claims in the literature, no evidence was found for the formation of relatively stable Cr(IV) intermediates during the reactions of Cr(VI) with I in acidic aqueous solutions. The Cr(VI) complexes of I-III exist as tetrahedral [CrO(3)(SR)](-) (IVa) species in the solid state, in solutions of aprotic solvents such as DMF, or in the gas phase (under ESMS conditions). In aqueous or alcohol solutions, reversible addition of a solvent molecule occurs, with the formation of five-coordinate species, [CrO(3)(SR)L](-) (IVb, probably of a trigonal bipyramidal structure, L = H(2)O or MeOH), with a Cr-L bond length of 1.97(1) A (determined by XAFS data modeling). Complex IVb (L = H(2)O) is also formed (in an equilibrium mixture with [CrO(4)](2)(-)) at the first stage of reduction of Cr(VI) by I in neutral aqueous solutions (as shown by global kinetic analysis of time-dependent UV-vis spectra). This is the first observation of a reversible ligand addition reaction in Cr(VI) complexes. The formation of IVb (rather than IVa, as thought before) during the reactions of Cr(VI) with I in aqueous solutions is likely to be important for the reactivity of Cr(VI) in cellular media, including DNA and protein damage and inhibition of protein tyrosine phosphatases.     

Mechanism of the Deaquation of Aquopentaaminocobalt(III) Bromide

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｓｏｌｉｄ ｐｈａｓｅｄｅａｑｕａｔｉｏｎ ａｎａｔｉｏｎｒｅａｃｔｉｏｎ[Ｍ(ＮＨ3 ) 5(Ｈ2 Ｏ) ]Ｘ3 → [Ｍ(ＮＨ3 ) 5Ｘ]Ｘ2 +Ｈ2 Ｏ(Ｍ =Ｃｏ3 + ,Ｃｒ3 + ｏｒＲｕ3 + ａｎｄＸ =Ｃｌ- ,Ｂｒ- ｏｒＮＣＳ- )ｈａｓｂｅｅｎｗｉｄｅｌｙｓｔｕｄｉｅｄｓｉｎｃｅｔｈｅｎｉｎｅｔｅｅｎｓｉｘｔｉｅｓ .Ｔｈｅｔｈｅｒｍａｌａｎｄｋｉｎｅｔｉｃｐａｒａｍｅｔｅｒｓｈａｖｅｂｅｅｎｃａｌｃｕｌａｔｅｄａｎｄｔｈｅｄｉｆｆｅｒｅｎｔｍｅｃｈａｎｉｓｍｈａｓｂｅｅｎｐｒｏｐｏｓｅｄａｎｄｄ…     

Catalysis by oxide-supported clusters of iridium and rhodium: hydrogenation of ethene, propene, and toluene

The hydrogenation reactions of ethene, propene, and toluene were used as probes of the catalytic properties of small clusters of rhodium (Rh6) and of iridium (Ir4 and Ir6) (as well as of larger aggregates of these metals) on oxide supports (gamma-Al2O3, MgO, and La2O3). The catalysts were characterized in the working state by extended X-ray absorption fine structure (EXAFS) spectroscopy, providing evidence of the cluster structures and cluster-support interactions; by infrared spectroscopy, providing evidence of hydrocarbon adsorbates and possible reaction intermediates on the clusters; and by kinetics of the hydrogenation reactions. The EXAFS data indicate that the metal clusters, while remaining intact and maintaining their bonding to the support during catalysis, underwent slight rearrangements to accommodate reactive intermediates. As the concentrations of reactive intermediates such as pi-bonded alkenes and alkyls on the clusters increased, the cluster frames swelled, and the clusters flexed away from the support. The data indicate self-inhibition of reaction by adsorbed hydrocarbons and differences between ethene hydrogenation and propene hydrogenation that may arise primarily from different adsorbate-adsorbate interactions.     

聚苯并噁嗪固载钯基纳米催化剂在芳香醇氧化反应中的应用

以球状聚苯并噁嗪为载体, 采用浸渍热解法合成了钯炭纳米催化剂. 通过透射电子显微镜观察发现, 钯纳米粒子几乎全部均匀分布在载体上, 且尺寸均一, 平均直径约为3.5 nm. 结果表明, 载体表面含有丰富的含氮含氧官能团, 氮和氧原子与钯之间存在相互作用, 从而使聚苯并噁嗪能够有效固载钯纳米粒子. 采用相同的方法进一步合成Pd-Au/C和Pd-Pt/C双金属催化剂, Pd-Au和Pd-Pt纳米粒子也展现出良好的分散性, 无明显团聚现象, 平均直径分别为4.3和4.2 nm, 进一步说明聚苯并噁嗪对金属活性组分的有效固载. 将催化剂应用于苯甲醇氧化反应, 其中Pd₁-Au₁/C在2 h的转化率为98%, 对产物苯甲醛的选择性大于99%, 该催化剂经过焙烧可恢复催化活性, 表现出良好的循环稳定性, 并能将不同取代基的芳香醇氧化为相应的醛, 是一种良好的醇氧化催化剂.     

Investigation on mechanism of catalysis by Pt-LiCoO2 for hydrolysis of sodium borohydride using X-ray absorption

The synthesis of platinum nanoparticle loaded LiCoO2 (Pt-LiCoO2) was carried out successfully by an impregnation method followed by sintering at different temperatures. The catalytic role of Pt-LiCoO2 composite in hydrogen generation during hydrolysis of sodium borohydride (NaBH4) was studied for fuel cell applications. X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) have been used to elucidate the structural and catalytic properties of Pt-LiCoO2. It was found that the 15 wt % of Pt nanoparticles on LiCoO2 sintered at 450 degrees C support showed the maximum efficiency for the catalysis reaction of hydrogen production. X-ray absorption near edge structure (XANES) analysis and extended X-ray absorption fine structure (EXAFS) analysis using a synchrotron radiation source were performed to carry out ex situ measurements in order to understand the mechanism of the catalytic process for the production of hydrogen during the hydrolysis of NaBH4. Co K-edge XANES showed a small percentage of cobalt in the metallic form after hydrogen generation which suggests the reduction of the cobalt during the hydrolysis of NaBH4.     

Formation and oxidation mechanisms of Pd-Zn nanoparticles on a ZnO supported Pd catalyst studied by in situ time-resolved QXAFS and DXAFS

Formation and oxidation processes of PdZn nanoparticles on ZnO were successfully observed by means of in situ time-resolved X-ray absorption fine structure spectroscopy (XAFS), and the analysis of data on near-edge (XANES) and extended (EXAFS) structures revealed detailed changes in Pd during both processes. PdZn nanoparticles were formed on ZnO through a two-step scheme under a hydrogen atmosphere. The first process was the formation of metallic Pd nanoparticles, which was quickly finished within 1 s. The second process was the formation of PdZn nanoparticles, which took several tens of minutes. Oxidation of the PdZn nanoparticles also consisted of two processes. Zn atoms were oxidized prior to Pd atoms and the metallic Pd nanoparticles surrounded by ZnO were formed afterwards. Oxidation of the metallic Pd nanoparticles was scarce and very slow. According to the results of kinetic analyses, the metallic Pd surrounded by ZnO was a stable species under the oxidative atmosphere.     

二氧化钛与碳化钨纳米复合材料制备及其对甲醇的电催化氧化活性

以市售纳米二氧化钛(TiO2)为载体,六氯化钨为钨源,将浸渍法与原位还原碳化技术相结合制备了核壳结构碳化钨(WC)/TiO2纳米复合材料;应用X射线衍射分析、透射电子显微镜、高分辨扫描透射成像和X射线能量散射谱等手段对样品晶相、形貌、微结构和化学组成等特征进行了表征.结果表明,样品的晶相由金红石型TiO2、Ti4O7、WC、W2C和WxC构成,钨碳化物负载于钛氧化物外表面,构成比较典型的核壳结构.采用三电极体系和循环伏安法测试了样品在碱性溶液中对甲醇的电催化氧化活性,结果表明,相比于纯碳化钨和二氧化钛,复合材料的电催化活性得到了明显的提升.样品电催化活性的提升与前驱体钨钛摩尔比、还原碳化时间、核壳结构壳层的完整性和晶相组成以及核壳结构中二氧化钛和碳化钨之间的协同效应有关.这说明金红石是能够提升碳化钨电催化氧化活性的载体材料之一.     

Local structural characterization of Au/Pt bimetallic nanoparticles

In this study, we examined the amount-dependent change in morphology for a series of Au/Pt bimetallic nanoparticles synthesized using chemical reduction. The Au/Pt molar ratio was varied from 1/1 to 1/4 to synthesize Pt shell layers with different thicknesses. We have obtained that these bimetallic nanoparticles can form flower-like nanoparticles. Moreover, an extended X-ray absorption fine structure (EXAFS) analysis was used to demonstrate the structure of Au/Pt bimetallic nanoparticles. The EXAFS results confirmed the formation of a core–shell structure and inter-diffusion between Au and Pt atoms. The composition of the shell layer was found to be Pt-enriched Au/Pt alloy.     

氧化铁磁性纳米粒子的表面配体交换及相转移

以苯甲醇为单一溶剂, 通过常压、高温热解乙酰丙酮铁, 制备了尺寸单分散的四氧化三铁磁性纳米粒子. 采用透射电镜(TEM), X射线衍射(XRD), 动态光散射(DLS)等方法对粒子形貌和结构进行了表征. 利用傅里叶变换红外(FT-IR)光谱和热重分析(TGA)研究了所制备纳米粒子的表面化学, 结果表明稳定四氧化三铁粒子的是苯甲酸分子, 且表面覆盖度小于20%. 所制备的磁性纳米粒子可以在室温下方便地进行表面配体交换, 从而为氧化铁磁性纳米粒子的功能化提供新的途径.     

Mechanistic study on adsorptive removal of tert-butanethiol on Ag-Y zeolite under ambient conditions

The dynamics and surface chemistry of tert-butanethiol (TBT) adsorptive removal over silver-exchanged Y zeolite (Ag-Y) were studied under ambient conditions. Saturation uptake on Ag-Y was higher than that on H-Y and Na-Y. The structural analyses by a combination of X-ray diffraction, Ag K-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structures (EXAFS), Ag L(III)-edge XANES, S K-edge XANES, and in situ UV-vis show that the AgSH molecule, Ag(2)S monomer, and Ag(4)S(2) cluster are the dominant silver species in TBT-saturated Ag-Y. Dynamic changes in adsorbed intermediates, gas-phase products, and the silver sulfides were followed by in situ FTIR, mass spectroscopy and in situ UV-vis, respectively. The results show the following reaction mechanism: (1) formation of iso-butene and adsorbed H(2)S on the Ag(+) site via C-S cleavage of hydrogen-bonded TBT initially adsorbed on the Ag(+) site; (2) conversion of the adsorbed H(2)S to AgSH and H(+) on zeolite; (3) the reaction of two Ag-SH species to yield Ag(2)S and H(+) on zeolite.