Effect of epitaxial growth on the formation of the cobalt catalysts of the Fischer-Tropsch synthesis

Mixed oxides Co_xAl_yO₄ with different Al/Co ratios applied as supports for the catalysts of the Fischer-Tropsch synthesis were prepared using the solid-state chemical reaction. The Co_xAl_yO₄ supports were prepared by modifying gibbsite with various cobalt salts (acetate, nitrate, and basic carbonate). The use of basic cobalt carbonate gives the Co(20%)/Co_xAl_yO₄ catalyst, which provides an increased yield of hydrocarbons C₅₊ and a decreased methane content compared to the impregnation catalyst Co(30%)/Al₂O₃. The introduction of small amounts of rhenium additives makes it possible to enhance the yield of hydrocarbons C₅₊ (179 g m⁻³) and also to increase the selectivity with respect to the C₅–C₁₈ fraction. The introduction of basic cobalt carbonate into the support, most likely, creates favorable conditions for the epitaxial growth of the precursor of the active phase. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1860, September, 2007.     

Effect of the composition and structure of the precursor compound on the catalytic properties of cobalt-aluminum catalysts in the Fischer-Tropsch synthesis

The effect of preparation procedure on the anionic composition and structure of hydroxo compounds as precursors of Co-Al catalysts and on their catalytic properties in the Fischer-Tropsch synthesis was studied. The dynamics of changes in the composition and structure of the hydroxide precursors of Co-Al catalysts during thermal treatment and subsequent activation was studied by thermal analysis, IR spectroscopy, XRD analysis, and in situ XRD analysis with the use of synchrotron radiation. It was found that the precursor compounds prepared by deposition-precipitation of cobalt cations on γ- and δ-Al₂O₃ under urea hydrolysis conditions, which had a hydrotalcite-type structure and contained nitrate, carbonate, and hydroxyl groups, turtned into the oxide compounds Co_{3 ? x} Al _x O₄ (0 < x < 2) with the spinel structure in the course of thermal treatment in an inert atmosphere. The hydrogen activation of an oxide precursor led to the formation of cobalt metal particles through the intermediate formation of a cobalt(II)-aluminum oxide phase. The catalyst was characterized by high activity and selectivity for C₅₊ hydrocarbons in the Fischer-Tropsch synthesis.     

Photoelectrochemical Study of Anodic Oxide Films on Titanium–Cobalt Alloys

Properties of anodic oxide films as a function of the composition of Ti _x –Co (x= 0, 10, 20, 30, 50, 67, 75 at. %) alloys in solutions of a borate buffer and sodium sulfate are studied by the voltammetric technique combined with photocurrent measurements. The oxide film on the alloys is shown to contain TiO₂and Co₂O₃. In a borate buffer, the oxide film presumably comprises two layers: an outer layer of cobalt oxides and an inner layer of a mixture of cobalt and titanium oxides.     

Biomimetic Synthesis of Metal Ion‐Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt‐Doped LiMn2O4 with Improved Electrochemical Properties through a Cobalt‐Doped MnCO3 Precursor

We have synthesized spinel type cobalt‐doped LiMn₂O₄ (LiMn_2?yCo_yO₄, 0≤y≤0.367), a cathode material for a lithium‐ion battery, with hierarchical sponge structures via the cobalt‐doped MnCO₃ (Mn_1‐xCo_xCO₃, 0≤x≤0.204) formed in an agar gel matrix. Biomimetic crystal growth in the gel matrix facilitates the generation of both an homogeneous solid solution and the hierarchical structures under ambient condition. The controlled composition and the hierarchical structure of the cobalt‐doped MnCO₃ precursor played an important role in the formation of the cobalt‐doped LiMn₂O₄. The charge–discharge reversible stability of the resultant LiMn_1.947Co_0.053O₄ was improved to ca. 12 % loss of the discharge capacity after 100 cycles, while pure LiMn₂O₄ showed 24 % loss of the discharge capacity after 100 cycles. The parallel control of the hierarchical structure and the composition in the precursor material through a biomimetic approach, promises the development of functional materials under mild conditions.     

Convenient and Mild Epoxidation of Alkenes Using Heterogeneous Cobalt Oxide Catalysts

A general epoxidation of aromatic and aliphatic olefins has been developed under mild conditions using heterogeneous Co_xO_y–N/C (x=1,3; y=1,4) catalysts and tert‐butyl hydroperoxide as the terminal oxidant. Various stilbenes and aliphatic alkenes, including renewable olefins, and vitamin and cholesterol derivatives, were successfully transformed into the corresponding epoxides with high selectivity and often good yields. The cobalt oxide catalyst can be recycled up to five times without significant loss of activity or change in structure. Characterization of the catalyst by XRD, TEM, XPS, and EPR analysis revealed the formation of cobalt oxide nanoparticles with varying size (Co₃O₄ with some CoO) and very few large particles with a metallic Co core and an oxidic shell. During the pyrolysis process the nitrogen ligand forms graphene‐type layers, in which selected carbon atoms are substituted by nitrogen.     

Recent advances in layered LiNi x CoyMn1−x−y O2 cathode materials for lithium ion batteries

Lithium cobalt oxide, LiCoO₂, has been the most widely used cathode material in commercial lithium ion batteries. Nevertheless, cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials, among which LiNi _x Co_yMn_{1 − x − y} O₂ may have improved performances, such as thermal stability, due to the synergistic effect of the three ions. Recently, intensive effort has been directed towards the development of LiNi _x Co _y Mn_{1 − x − y} O₂ as a possible replacement for LiCoO₂. Recent advances in layered LiNi _x Co_yMn_{1 − x − y} O₂ cathode materials are summarized in this paper. The preparation and the performance are reviewed, and the future promising cathode materials are also prospected.     

Preparation of hierarchical LiNixCoyMnzO2 from solvothermal [NixCoyMnz](OH)2 via regulating the ratio of Ni,Co, and Mn and its excellent properties for lithium-ion battery cathode

The ternary-layered oxide (LiNi_xCo_yMn_zO₂) has become the most promising cathode material for lithium-ion batteries due to the advantages of higher discharge platform, better conductivity, and higher theoretical capacity. The [Ni_xCo_yMn_z](OH)₂ with different ratios of nickel, cobalt, and manganese (NCM) was prepared by solvothermal method, and then ternary cathode material LiNi_xCo_yMn_zO₂ was obtained by mixing lithium and calcining. In this paper, ternary cathode materials with different ratios of NCM were prepared by the solvothermal method. The structure and morphology of the materials were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The effects of the ratio on the electrochemical properties of the materials were investigated by constant current charge and discharge test and electrochemical impedance spectroscopy test. The synthesized lithium-nickel-cobalt-manganese oxide belongs to the hexagonal system and has an α-NaFeO₂ layered structure, which is an R-3m space group. The NCM ternary cathode materials with different morphologies were obtained by changing the ratio of NCM. The sample with NCM ratio of 5:3:2 has a unique sheet-like spherical shape and has the best rate performance.     

Carbon black and propylene oxidation over Ru/CoxMgyAl2Oz catalysts

The effects of Co_xMg_yAl₂O_z mixed oxides composition and ruthenium addition on the oxidation of propylene and carbon black (CB) were investigated. Different reactive cobalt and ruthenium oxide species were formed following calcination at 600 °C. The addition of ruthenium was beneficial for the CB oxidation under “loose contact” conditions and for propylene oxidation when the cobalt content was intermediate to low. The calculated activation energy for CB oxidation was decreased from 151 kJ mol⁻¹ for the uncatalyzed reaction to 111 kJ mol⁻¹ over the best catalyst.     

Thermal behavior of Co<Subscript>x</Subscript>Fe<Subscript>3−x</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites obtained by a modified sol–gel method

The thermal behavior of Co_xFe_3?xO₄/SiO₂ nanocomposites obtained by direct synthesis starting from nonahydrate ferric nitrate and hexahydrate cobalt nitrate in different ratios with and without the addition of 1,4-butanediol was studied. For the synthesis of Co_xFe_3?xO₄ (x = 0.5–2.5) dispersed in the silica matrix a wide Co/Fe molar ratio was used. The decomposition processes, formation of crystalline phases, gases evolvement and mass changes during gels annealing at different temperatures were assessed by thermal analysis. The absence of succinate precursor and a low mass loss were observed in the case of the gel obtained in the absence of 1,4-butanediol. In case of gels obtained using a stoichiometric ratio of Co/Fe, no clear delimitation between Co and Fe succinates was observed, while for samples with a Fe or Co excess, the formation of the two succinates was observed. The evolution of the crystalline phase after annealing (673, 973 and 1273 K) investigated by X-ray diffraction analysis and Fourier transformed infrared spectrometry revealed that in samples with Fe excess, stoichiometric Fe/Co ratio or low Co excess, the cobalt ferrite (CoFe₂O₄) was obtained as a single phase, while in samples with higher cobalt excess, olivine (Co₂SiO₄) as a main phase, cobalt oxide and CoFe₂O₄ as secondary phases were obtained after annealing at 1273 K. The SEM images confirmed the nanoparticles embedding in the silica matrix, while the TEM and X-ray diffraction data showed that the obtained nanoparticles’ size was below 10 nm in most samples.     

Synthesis and Electrochemical Characterization of Gradient Composite LiNi1-yCoyO2 Used as Cathode Materials in Lithium-ion Battery

Gradient composites, LiNi1-yCoyO2, are synthesized from coated spherical Ni(OH)2 precursor. These composites could be applied as new cathode materials in lithium-ion batteries because they have low cobalt content (y≤0.2)and exhibit excellent properties during high-rate charge/discharge cycles. The initial discharge capacity of coated composite of LiNio.95Co0.05O2 is 186 mAh/g, and the decreasing rate of the capacity is 3.2% in 50 cycles at 1C rate. It has been verified by TEM and EDX experiments that a core-shell structure of the composite particles develops because of the cobalt enrichment near the surfaces, and the formation of the cobalt enrichment layer is sensitive to sintering temperature. High cobalt surface concentration may reduce the undesired reactions and stabilize the structure of the particles.     

Effect of CeO<Subscript>2</Subscript> on the properties of the Pd/Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/cordierite catalyst in the conversion of CO,NO, and hydrocarbons

The effect of CeO₂ on the properties of the Pd/Co₃O₄-CeO₂/cordierite catalyst is a function of the method of its preparation. The catalyst obtained by the simultaneous deposition of cerium oxide and cobalt oxide showed high activity in the oxidation of CO (CO + O₂, CO + NO) and extensive oxidation of hexane (C₆H₁₄ + O₂). This behavior is due to the increased mobility of surface oxygen and increased dispersion of the catalyst components.     

A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation

In regard to earth‐abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt‐substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low‐temperature solvolysis of molecular heterobimetallic Co_4?xZn_xO₄ (x=1–3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self‐supported water‐oxidation electrocatalyst, which was observed by HR‐TEM on FIB lamellas of the EPD layers. The Co‐rich hydroxide‐oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours.     

Microwave hydrothermal flash synthesis of nanocomposites Fe-Co alloy/cobalt ferrite

The present article presents, for the first time, the last developments reported for an original microwave hydrothermal flash synthesis of Fe-Co alloys (Fe_yCo_1−y)/cobalt ferrite (Fe_3−xCo_xO₄) nanocomposites. Synthesis was performed in alcoholic solutions of ferrous chloride, cobalt chloride and sodium ethoxide (EtONa) using a microwave autoclave (The RAMO system) specially designed by authors. Compared with conventional synthesis, smaller grains (100 nm compared to 1 μm) can be produced in a short period (e.g. 10 s) using a less basic medium. In all the cases, the microstructure and the amount of metal inside the composite particles are very different from the product obtained via a classical route. Indeed, 20% of metal was routinely obtained using the microwave flash synthesis. Nevertheless, this mean of production is more efficient and much faster than the ones commonly used to produce this type of nanocomposites.     

Urchin-like cobalt incorporated manganese oxide OMS-2 hollow spheres: Synthesis,characterization and catalytic degradation of RhB dye

Urchin-like K_xCo_yMn_8−yO₁₆ hollow spheres assembled from nanoplate building blocks were successfully fabricated via a one-pot hydrothermal route using cobalt acetate and potassium permanganate as raw material. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrometer, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) measurement. The thermal stability and surface areas of cobalt ion in the manganese sites of KMn₈O₁₆ structures were clearly evidenced by TGA and N₂ adsorption–desorption isotherms curves. Based on time depended experiment results, a possible formation mechanism for this structures was proposed. The catalytic degradation of Rhodamine B (RhB) on K_xCo_yMn_8−yO₁₆ materials has, therefore been dependent for the molar precursor ratio and specific surface area of the as-fabricated products. UV–vis, LC–MS and barium hydroxide methods were utilized to monitor the temporal course of the catalytic reaction.     

Formation of nanosized oxide films via thermal oxidation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/InP heterostructures

Modification of InP film with magnetron-deposited 30 nm nanolayer of Co₃O₄ has resulted in the transit mechanism of thermal oxidation of the semiconductor and formation of nanosized oxide-phosphate films. Efficient transit interactions of Co₃O₄ with the semiconductor due to fast chemical binding of indium has led to the suppression of its diffusion inside the films. Secondary interactions of the oxides result in the formation of phosphate scaffold in the inner film regions, whereas the surface layer contains cobalt and indium oxides.     

氧化钴和氮掺杂碳纳米管纳米复合物的催化与容量性质(英文)

The nanocomposites based on cobalt oxide and nitrogen-doped carbon nanofibers (N-CNFs) with cobalt oxide contents of 10–90 wt% were examined as catalysts in the CO oxidation and supercapacity electrodes. Depending on Со3О4 content, such nanocomposites have different morphologies of cobalt oxide nanoparticles, distributions over the bulk, and ratios of Со3+/Co2+ cations. The 90%Со3О4-N-CNFs nanocomposite showed the best activity because of the increased concentration of defects in N-CNFs. The capacitance of electrodes containing 10%Со3О4-N-CNFs was 95 F/g, which is 1.7 times higher than electrodes made from N-CNFs.     

Characterization and thermal stability of cobalt-modified 1-D nanostructured trititanates

One-dimensional (1-D) nanostructured sodium trititanates were obtained via alkali hydrothermal method and modified with cobalt via ion exchange at different Co concentrations. The resulting cobalt-modified trititanate nanostructures (Co-TTNS) were characterized by TGA, XRD, TEM/SAED, DRS-UV-Vis and N₂ adsorption techniques. Their general chemical formula was estimated as Na_xCo_y/2H_2−x−yTi₃O₇·nH₂O and they maintained the same nanostructured and multilayered nature of the sodium precursor, with the growth direction of nanowires and nanotubes along [010]. As a consequence of the Co²⁺ incorporation replacing sodium between trititanate layers, two new diffraction lines became prominent and the interlayer distance was reduced with respect to that of the precursor sodium trititanate. Surface area was slightly increased with cobalt intake whereas pore size distribution was hardly affected. Besides, Co²⁺ incorporation in trititanate crystal structure also resulted in enhanced visible light photon absorption as indicated by a strong band-gap narrowing. Morphological and structural thermal transformations of Co-TTNS started nearly 400 °C in air and the final products after calcination at 800 °C were found to be composed of TiO₂-rutile, CoTiO₃ and a bronze-like phase with general formula Na_2xTi_1−xCo_xO₂.     

NixCo3-xO4表面修饰对CdSe/TiO2纳米管阵列光电化学氧化水活性的影响

利用氨挥发诱导法在CdSe/TiO2纳米管阵列表面负载一层NixCo3-xO4。采用SEM、XRD、XPS、UV-Vis对样品进行表征,通过线性扫描伏安法测定光阳极的释氧电势来评价其光电水氧化活性。结果表明:表面NixCo3-xO4是尖晶石结构;相对于CdSe/TiO2纳米管阵列光阳极,NixCo3-xO4/CdSe/TiO2光阳极能将光电氧化水的过电势降低430 mV。Ni离子的引入使得NixCo3-xO4表面富含三价阳离子(Ni3+,Co3+),从而促进CdSe/TiO2光阳极光电水氧化的进行。     

Interface characterization of PICVD-coated polymer substrates

The binding structure in the interface region oxide film/polymer has been investigated by means of XPS and is correlated with the adhesion obtained by a Pull Test. Polycarbonate (PC) and diethyleneglycol-bisallylcarbonate (CR39) are employed as substrate and SiO_xC_yH_z-films are deposited by using a pulsed microwave plasma deposition process (PICVD). Best adhesion is obtained by pretreatment of the substrate surface with an O₂-plasma which increases the O/C ratio, in combination with a PICVD-process with low precursor content. Received: 27 July 1996 / Revised: 13 January 1997 / Accepted: 18 January 1997     

Mesoporous Co3O4 Nanobundle Electrocatalysts

Tailoring metal oxide nanostructures with mesoporous architectures is vital to improve their electrocatalytic performance. Herein, we demonstrate the synthesis of 2D mesoporous Co₃O₄ (meso‐Co₃O₄) nanobundles with uniform shape and size by employing a hard‐template method. In this study, the incipient wetness impregnation technique has been chosen for loading metal precursor into the silica hard template (SBA‐15). The results reveal that the concentration of a saturated precursor solution plays a vital role in mesostructured ordering, as well as the size and shape of the final meso‐Co₃O₄ product. The optimized precursor concentration allows us to synthesize ordered meso‐Co₃O₄ with four to seven nanowires in each particle. The meso‐Co₃O₄ structure exhibits excellent electrocatalytic activity for both glucose and water oxidation reactions.