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Showing papers on "Cobalt published in 1998"



Journal ArticleDOI
TL;DR: A new family of olefin polymerization catalysts, derived from iron and cobalt complexes bearing 2,6-bis(imino)pyridyl ligands, was described in this paper.

1,045 citations


Journal ArticleDOI
TL;DR: In this article, a flow-sheet of the hydrometallurgical process for the recovery of cobalt and lithium from the spent lithium-ion secondary batteries has been established based on the experimental results.

364 citations


Journal ArticleDOI
TL;DR: In this article, a self-organization of magnetic cobalt nanoparticles into 2D superlattices is reported, which can be used for data storage devices and sensors.
Abstract: The synthesis of nanoparticles, characterized by a low size distribution, is a new challenge in solid-state chemistry. Due to their small size, nanoparticles exhibit novel materials properties that differ considerably from those of the bulk solid state. In this emerging field, finely divided magnetic nanoparticles are desirable owing to their broad range of applications, especially in data storage devices and sensors. A great deal of work on large magnetic nanoparticles has been carried out, but, although the magnetic properties of isolated atoms are well understood, there are still questions about the development of magnetic order on a macroscopic scale. The creation of perfect nanometer-scale magnetic crystallites identically replicated with long-range order in a state that can be manipulated and understood in terms of a pure macromolecular substance is an ultimate challenge in present materials research and could help us to understand the formation of ferromagnetism. To develop this application, it is crucial to be able to control the spatial arrangement of these nanoparticles in 2D or 3D arrays. Recently, in our laboratory spontaneous arrangement of particles either into monolayer organized hexagonal networks or into 3D face-centered cubic (fcc) arrangements was observed with silver sulfide and silver nanosized clusters. Similar arrangements with metal particles such as gold or silver and CdSe semiconductors have been reported elsewhere. Here, we report, for the first time, self-organization of magnetic cobalt nanoparticles into 2D superlattices. The magnetic properties of isolated and organized particles are compared. Reverse micelles are water in oil droplets stabilized by a monolayer of surfactant (e.g., sodium bis(2-ethylhexyl)sulfosuccinate, usually called Na(AOT)). The diameter of the droplets is controlled by the volume of solubilized water and varies from 0.5 to 18 nm. In this liquid solution, as a result of Brownian motion, collision between droplets induces exchange between water pools. In a previous paper we demonstrated that nanosized cobalt particles can be produced by using reverse micelles as a microreactor. Cobalt particles are obtained by mixing two micellar solutions having the same diameter ([AOT] = 0.25 M): one contains 10 M Co(AOT)2 (cobalt bis(2-ethylhexyl)sulfosuccinate) and the other one 2 10 M sodium tetrahydroborate (NaBH4, sodium borohydride). After mixing, the micellar solution remains optically clear and its color immediately turns from pink to black, indicating the formation of colloidal particles. The synthesis is performed in 3 nm diameter reverse micelles. The average diameter of cobalt nanoparticles, determined by transmission electron microscopy (TEM), is 6.4 nm with a polydispersity of 21 % (Fig. 1a). The particles are very well dispersed and no aggregation occurs. However the particles are very readily oxidized. High-resolution TEM of the particles after synthesis shows a well-developed crystalline phase. The spacing distance of the lattice fringes is 2.15 Š which is consistent with the bulk value of fcc cobalt. No trace of oxide shell is observed on the surface. To form superlattices, the cobalt nanocrystallites are extracted from the reverse micelles. Trioctylphosphine (4 mL/ mL) is added to the micellar solution containing the cobalt nanoparticles. The solvent is then evaporated at 40 C under vacuum and a solid mixture of trioctylphosphine-coated nanoparticles and surfactant is obtained. The surfactant is removed by ethanol addition and a black solid remains, which is easily redispersed in pyridine. This surface treatment is carried out under nitrogen in a glove box to avoid oxidation. At the end of the process, the coating is thick enough to prevent the particles from being oxidized. The coated particles can be stored without taking any precautions for at least one week without any aggregation or oxidation. The size of the coated particles redispersed in pyridine can be determined by TEM (Fig. 1b). A size selection is made by extraction of the nanoparticles from reverse micelles (Fig. 1). The average size decreases from 6.4 nm to

264 citations



Journal ArticleDOI
TL;DR: In this paper, an extensive literature review of new experimental data on properties of Cu, Ni and Co and their precipitates in silicon with a discussion of experimental data recently obtained by the authors is presented.
Abstract: This article combines an extensive literature review of new experimental data on properties of Cu, Ni and Co and their precipitates in silicon with a discussion of experimental data recently obtained by the authors. Special attention is paid to the recombination activity of these metals. It is shown that the recombination activity of Cu, Ni, Co and their complexes is low in p-type Si, compared to that of other transition metals such as iron. However, it increases markedly upon formation of precipitates or decoration of existing lattice defects. This is explained by the formation of a precipitate-related defect band and of an attractive potential for minority charge carriers by the charged precipitates. The role of Cu, Ni and Co in the degradation of multicrystalline solar cells efficiency is discussed in a separate section. It is suggested that recently reported intragranular microdefects, which decrease the lifetime of solar cells, may be microprecipitates of these metals.

234 citations


Journal ArticleDOI
TL;DR: In this article, a critical overview is given of the spectroscopic tools used: (1) to decide about the cation sites of Co2+ and their occupancy; (2) to determine the spectral signatures of framework and extra-framework cobalt; (3) to calculate the amount of Co incorporated into the framework of molecular sieves; and (4) discuss local distortions of framework cobalt.

217 citations


Journal ArticleDOI
TL;DR: In this article, it was observed that limonite consists of aggregates of needle-like particles of goethite compacted together, and the grain model was finally proposed to best describe nickel dissolution kinetics.

213 citations


Journal ArticleDOI
TL;DR: In this paper, two series of transition metals (Co, Ni, Ru, Rh, Ir, Pt) based catalysts have been prepared using silica and γ-alumina.
Abstract: Two series of transition metals (Co, Ni, Ru, Rh, Ir, Pt) based catalysts have been prepared using silica and γ-alumina. Their activity and stability for the dry reforming of methane in the temperature interval from 673 up to 1023 K have been examined and compared. The obtained results show that the support exerts a great influence on the turnover frequency of a given metal but deactivation occurring under reaction conditions mainly depends on the nature of the active metallic phase. Some of the catalysts suffer deactivation processes at temperatures close to 1023 K, that can be ascribed to sintering, and in only some cases, also to carbon deposition. At low reaction temperatures, i.e. 723 K, deactivation was only observed over supported iridium. Among all tested catalysts, those based on nickel, cobalt and rhodium appear to be the most resistant to deactivation processes under our experimental conditions and for the whole temperature range up to 1023 K. Among them, supported rhodium catalysts show an excellent stability, though alumina supported rhodium exhibits a much higher turnover frequency.

211 citations


Journal ArticleDOI
TL;DR: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents.
Abstract: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

211 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between solid state chemistry, surface properties and electrocatalytical reactivities towards the reaction of oxygen is investigated on powder electrodes of cobalt and manganese spinel type oxides MnxCo3−xO4 (0≤x≤1).

Journal ArticleDOI
TL;DR: In this paper, a review of low-temperature synthesis and electrochemical properties of manganese, cobalt, nickel, iron, vanadium, chromium, titanium, molybdenum, and tin oxides is presented.
Abstract: The increasing demand for portable electronic devices has created significant activity in the development of compact lightweight batteries of high-energy density, and lithium batteries have become attractive in this regard. The commercial lithium cells use lithium cobalt oxide cathodes and the high cost and toxicity of cobalt has prompted the design and synthesis of alternate insertion hosts. Several low-temperature synthesis routes have been pursued during the past few years both to improve the properties of known oxide hosts as well as to access new insertion oxides, particularly metastable phases. This review, after providing a brief background to lithium batteries, lithium insertion compounds, and lithium ion batteries, presents the low-temperature synthesis and electrochemical properties of manganese, cobalt, nickel, iron, vanadium, chromium, titanium, molybdenum, and tin oxides. The use of soft chemistry methods such as sol−gel processing, ion-exchange reactions, hydrothermal reactions, and oxidatio...

Journal ArticleDOI
TL;DR: In this article, a completely hydrometallurgical process has been developed for the recovery of metal values such as cobalt, nickel and rare earths from spent nickel-metal hydride (Ni-MH) secondary batteries.

Journal ArticleDOI
TL;DR: In this article, perovskite-like mixed oxides of general formula La1−xA′xBO3 were prepared by the amorphous citrate method and tested for methane combustion within the 300-600°C temperature range.
Abstract: Some perovskite-like mixed oxides of general formula La1−xA′xBO3 were prepared by the amorphous citrate method and tested for methane combustion within the 300–600°C temperature range. Substitution at A-site with a bivalent (Eu, Sr) or tetravalent (Ce) metal cation led to a decrease or increase of catalytic activity, respectively. La0.9Ce0.1CoO3 proved to be the most active catalyst, showing complete conversion at 500°C. The nature of the metal cation introduced modifies the oxidation state of cobalt, which leads to the formation of cationic or anionic vacancies. TPD-MS analysis confirmed that the catalytic activity is related to the oxygen storage properties of the catalyst. The substitution at B-site (B=Fe, Co, Ni) allowed to find interesting correlations between catalytic activity and the temperature Tmax of maximum oxygen desorption rate.

Journal ArticleDOI
TL;DR: In this paper, an analytical impedance model of the metal hydride electrode was used to calculate the diffusion coefficient of hydrogen in the metal alloy, and the impedance response of cobalt microencapsulated LaNi4.27Sn0.24 electrode was measured at different hydrogen contents.

Journal ArticleDOI
TL;DR: In this paper, X-ray diffraction shows that there is no phase transition during lithium deintercalation, contrary to what is observed for LixNiO2, in good agreement with the electrochemical behavior.

Journal ArticleDOI
24 Jun 1998-Langmuir
TL;DR: In this paper, four cobalt porphyrins were adsorbed on graphite electrodes and used to catalyze the electroreduction of O2 by four electron reduction.
Abstract: Four cobalt porphyrins were adsorbed on graphite electrodes and used to catalyze the electroreduction of O2. The two porphyrins without substituent groups in the meso positions of the porphyrin ring operated at the most positive potentials and catalyzed the reduction of O2 to both H2O2 and H2O, but the H2O did not result from significant reduction of H2O2. The porphyrins containing meso substituents catalyzed only the reduction of O2 to H2O2. The catalysts that accomplish the four-electron reduction of O2 are argued to consist of dimeric (or higher oligomeric) forms of the adsorbed porphyrins. The present results and those of two recent related studies1,2 indicate that the presence of only hydrogen or small alkyl groups in the meso positions of porphyrin rings facilitates the spontaneous formation of van der Waals dimers with greater catalytic activity for the reduction of O2 by four electrons. Such cobalt porphyrins were also found to be unusually active catalysts for the electro-oxidation of H2O2.

Journal Article
TL;DR: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents as discussed by the authors.
Abstract: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

Journal ArticleDOI
TL;DR: In this article, the rates of metal aluminate formation in MeOx/Al2O3 systems (Me=Ni, Co, Cu, Fe) at 500-1000°C in O2 or N2atmospheres were compared, using bothα-Al2 o3 andγ-Al 2 o3substrates.

Journal ArticleDOI
TL;DR: In this article, a two-step reduction of Co 3 O 4 to CoO and then to Co° is observed by EXAFS, consistent with surface and TPR or XRD studies.

Journal ArticleDOI
TL;DR: In this paper, an array of aligned, multi-walled carbon nanotubes were produced by catalytically pyrolyzing acetylene within the pores of an anodic aluminum oxide template.
Abstract: Arrays of aligned, multiwalled carbon nanotubes were produced by catalytically pyrolyzing acetylene within the pores of an anodic aluminum oxide template. Small cobalt catalyst particles were prede...

Journal ArticleDOI
TL;DR: In this paper, a new cobalt II succinate with an open framework, was prepared hydrothermally (180°C, 72 h, autogenous pressure) from a 2:3:8:120 mixture of Co(II) chloride, succinic acid, potassium hydroxide and water.
Abstract: Co 5 (OH) 2 (C 4 H 4 O 4 ) 4 , a new cobalt(II) succinate with an open framework, was prepared hydrothermally (180°C, 72 h, autogenous pressure) from a 2:3:8:120 mixture of Co(II) chloride, succinic acid, potassium hydroxide and water. Its monoclinic structure was solved by single crystal X-ray diffraction [space group P2 1 /c (no. 14) with a=9.5631(2) A, b=9.4538(2) A, c=12.5554(2) A, β=96.968(1)°, V=1126.72(4) A 3 , Z=4] from 3077 unique reflections [I≥2σ(I)], R1=0.020 and wR2=0.054. The three-dimensional structure is built up from layers of edge sharing octahedra pillared by succinate ions. Within the layers, cobalt octahedra form 12-membered ring windows. Below 10 K, Co 5 (OH) 2 (C 4 H 4 O 4 ) 4 , exhibits ferrimagnetic behavior.

Journal ArticleDOI
TL;DR: In this paper, the composition, crystal structure and deposition rate of NiCoB alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid).
Abstract: Fundamental aspects of electroless Ni–B, Co–B and Ni–Co–B alloys have been systematically examined. The composition, crystal structure and deposition rate of the alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid), bath pH and Ni2+/Co2+ ratio. Changes in the deposition rate and metallurgical features of the alloys induced by the change in plating parameters are discussed, based on electrochemical polarization data and the formation enthalpy of the nickel and cobalt borides.

Journal ArticleDOI
TL;DR: In this paper, the catalytic properties of cobalt containing ZSM-5 zeolites prepared by various methods were compared, including TPR, XRD, N 2 -BET, XPS, FTIR and UV-vis spectroscopy were used for characterizing the samples.
Abstract: The catalytic properties of cobalt containing ZSM-5 zeolites prepared by various methods were compared. TPR, XRD, N 2 -BET, XPS, FTIR and UV–vis spectroscopy were used for characterizing the samples. Well-dispersed cobalt oxide-like species and isolated Co 2+ ions in charge compensation positions were found in the zeolite. Catalysts prepared using a single step cation exchange method showed high activity for N 2 O decomposition in a temperature range 300–550°C, in the presence of 0–5% O 2 , and high stability in the presence of 10% H 2 O to the feed. UV–vis spectra and TPR experiments indicated the presence of some cobalt oxides, not detected by DRX, in a Co-ZSM-5 catalyst containing 3.76 wt% Co, prepared by a solid-state reaction procedure. The N 2 O conversion over this catalyst was strongly affected by addition of both O 2 and H 2 O to the feed.

Journal ArticleDOI
TL;DR: In this article, a new phase of hydrotalcite-like Co hydroxide with mixed valent states has been synthesized, along with preparations of known α and β phases.
Abstract: Through an atmosphere-controlled method, a new phase of hydrotalcite-like Co hydroxide with mixed valent states has been synthesised, along with preparations of known α and β phases. Structural and thermal behaviours of all the Co hydroxides have been compared. Three major stages of decomposition are found: (i) 149-164°C for dehydration of interlayer water, (ii) 185-197°C and (iii) 219-222°C for dehydroxylation of hydrotalcite- and brucite-like phases, respectively. Intercalated nitrate anions in hydrotalcite-like phases decompose largely during stage (ii). The oxide Co 3 O 4 starts to form at temperatures as low as 165°C especially for hydrotalcite-like phases. An intermediate compound, HCoO 2 , which is formed thermally, decomposes at 258-270°C. The Co 3 O 4 oxide converts into CoO at 842-858 and 935-948°C respectively in nitrogen and air, which is much lower than the previously reported range of 1000-1200°C. Surface areas of calcined samples are found to be proportional to the intercalated anion content. The catalytic activity of the resultant Co 3 O 4 oxides with nitrous oxide is 7.2-8.2 mmol N 2 O g –1 h –1 at 375°C, which is comparable to some reported active catalyst systems.

Journal ArticleDOI
TL;DR: In this article, cobalt and nickel were extracted from cobalt-free raffinate in two stages at equal phase ratio with PC 88A and Cyanex 272 followed by their stripping with 0.02 M H 2 SO 4 at O:A ratio of 4:3 and 2:1, respectively.

Journal ArticleDOI
TL;DR: In this article, Oxidized and reduced cobalt(II) hexacyanoferrates were fabricated and characterized in the presence of alkali metal (Li+, Na+, K+, Cs+) and Co2+ countercations.
Abstract: Oxidized and reduced cobalt(II) hexacyanoferrates were fabricated and characterized in the presence of alkali metal (Li+, Na+, K+, Cs+) and Co2+ countercations. Formal potentials of hexacyanoferrat...

Journal ArticleDOI
16 Oct 1998-Science
TL;DR: The results suggest that only a few atoms forming a 2D in-plane magnetized dot may provide a stable elementary bit for nanorecording.
Abstract: Single two-dimensional (2D) atomically thick magnetic particles of cobalt and iron with variable size and shape were fabricated by combining a mask technique with standard molecular beam epitaxy. Reduction of the lateral size of in-plane magnetized 2D cobalt films down to about 100 nanometers did not essentially modify their magnetic properties; although the separation of boundaries decreased greatly, neither domain penetrated the particle, nor was any sizable shape anisotropy observed. The mutual interaction of 2D cobalt particles was negligible, and the magnetic state of a single particle could be switched without modifying the state of the neighbors. Perpendicularly magnetized iron particles did not exhibit such responses. These results suggest that only a few atoms forming a 2D in-plane magnetized dot may provide a stable elementary bit for nanorecording.

Patent
28 Dec 1998
TL;DR: In this article, a process for the preparation of a cobalt-containing catalyst or catalyst precursor is described, which is at least partially insoluble in the amount of liquid used.
Abstract: A process for the preparation of a cobalt-containing catalyst or catalyst precursor, comprising (a) mixing (1) titania or a titania precursor, (2) a liquid, and (3) a cobalt compound, which is at least partially insoluble in the amount of liquid used, to form a mixture, (b) shaping and drying of the mixture thus-obtained, and (c) calcination of the composition thus-obtained. A catalyst or catalyst precursor obtainable by the process as defined, and a process for the preparation of hydrocarbons comprising contacting a mixture of carbon monoxide and hydrogen with the catalyst as defined.

Journal ArticleDOI
TL;DR: The different functions of nickel in catalysis are highlighted by describing the active sites of six nickel enzymes - methyl-coenyzme M reductase, urease, hydrogenase, superoxide dismutase, carbon monoxide dehydrogenase and acetyl-coenzyme A synthase.