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Showing papers on "Cobalt published in 1993"


Journal ArticleDOI
TL;DR: In this article, Ru atoms at the surface of Co crystallites increase the rate of removal of carbon and oxygen species during reaction and during regeneration of deactivated Co catalysts, leading to higher Co site density and enhanced readsorption of α-olefins.

398 citations


Journal ArticleDOI
TL;DR: In this paper, the authors showed that the combination of Co 2+, Mn 2+ and Ni 2+ with certain types of zeolites, e.g., ZSM-5 and mordenite, are active catalysts for NO x with methane in an oxidizing atmosphere.
Abstract: Catalytic reduction of NO x with methane in an oxidizing atmosphere was studied over metal exchanged zeolites. We found that the combinations of Co 2+ , Mn 2+ and Ni 2+ with certain types of zeolites, e.g., ZSM-5 and mordenite, are active catalysts for this reaction. For a Co-ZSM-5 catalyst, the nitric oxide conversion displays a volcano-shape curve as temperature increases, which is reversible upon decreasing temperature. The nitric oxide reduction activity is proportional to the level of Co 2+ exchanged into ZSM-5, but excess amounts of cobalt do not contribute to the activity. Mn-ZSM-5 is very similar to Co-ZSM-5 in the nitric oxide reduction activity, and Ni-ZSM-5 has slightly lower activity compared to Co-ZSM-5. Under an oxidizing conditions, Cu-ZSM-5, however, is ineffective for the nitric oxide reduction. Co-Y, which has much more Co 2+ , is much less active compared to Co-ZSM-5, or Co-mordenite. The amount of nitric oxide adsorbed, measured by TPD, on Co-Y is extremely small (NO/Co=0.06) compared to Co-ZSM-5 (NO/Co > 1.1) and Co-mordenite (NO/Co=0.8).

264 citations


Journal ArticleDOI
TL;DR: In this article, the effect of Co substitution on the Ni 3+ content and long-range order in Li x Ni 2− x O 2 (0.8≤ y ≤ 1) was investigated.

235 citations


Journal ArticleDOI
TL;DR: In this article, microscopic evidence is provided for the existence of an intrinsic defect, namely, twinned fcc crystallites and their associated grain boundaries, which may be the much sought cause of discrepancy on antiferromagnetic coupling data in Co/Cu(111) superlattices grown in ultrahigh vacuum.
Abstract: Cobalt grows initially on Cu(111) in the form of bilayer islands with the shape of triangles of alternate orientation. This is probably related to the initial stacking sequence of the Co layers. The islands do not coalesce upon further deposition and the resulting film, although epitaxial and crystalline to the extent tested by diffraction techniques, is, actually, granular. Thus, microscopic evidence is provided for the existence of an intrinsic defect, namely, twinned fcc crystallites and their associated grain boundaries, which may be the much sought cause of discrepancy on antiferromagnetic coupling data in Co/Cu(111) superlattices grown in ultrahigh vacuum.

183 citations


Journal ArticleDOI
TL;DR: The results of Stern-Gerlach-type magnetic deflection experiments on clusters of cobalt and gadolinium are reported, finding an internal magnetic moment per atom of 2.24±0.14μ B /atom for cobalt clusters containing 65-215 atoms at vibrational temperatures between 85 and 300 K.
Abstract: We report the results of Stern-Gerlach-type magnetic deflection experiments on clusters of cobalt and gadolinium. Cobalt clusters exhibit superparamagnetic behavior over a broad range of temperatures, applied magnetic fields, and cluster sizes. We find an internal magnetic moment per atom of 2.24\ifmmode\pm\else\textpm\fi{}0.14${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/atom for cobalt clusters containing 65--215 atoms at vibrational temperatures between 85 and 300 K, a value substantially in excess of the bulk value for cobalt. Over a similar temperature range, some gadolinium clusters exhibit superparamagnetic behavior while others exhibit behavior consistent with their moments being locked to their cluster lattices. In both cases, the internal magnetic moments per atom of gadolinium clusters are considerably reduced from the bulk value for gadolinium. The magnetic behaviors of many gadolinium clusters change qualitatively as their vibrational temperatures increase. We also address the current controversy concerning experimental cluster vibrational temperatures.

183 citations


Book ChapterDOI
TL;DR: This chapter discusses the preparation and handling of cobalt enzymes and the nature of the information that can be obtained from spectroscopic measurements regarding the role of the metal center.
Abstract: Publisher Summary Cobalt ions exhibit characteristic spectra. When cobalt is introduced into proteins, the spectral properties become a desirable attribute to probe the environment of active enzymatic sites. Moreover, cobalt can be substituted for spectroscopically silent zinc when this is the native, catalytically active metal atom of enzymes. Such a metal exchange has been particularly fruitful in the study of these systems because the majority of cobalt substituted zinc enzymes retain their enzymatic activity. Hence, cobalt substitution for zinc has become an essential technique to address the structural basis of catalytic properties in zinc enzymes, as well as the coordination environment of structural zinc sites in proteins. This chapter discusses the preparation and handling of cobalt enzymes and the nature of the information that can be obtained from spectroscopic measurements regarding the role of the metal center. It evaluates the circumstances under which cobalt becomes a structural and functional substitute for zinc atoms. The existence of structural data for cobalt enzymes now makes possible such comparisons between cobalt and zinc in proteins.

173 citations


Journal ArticleDOI
TL;DR: In this article, a range of cobalt catalysts supported on kieselguhr, silica, alumina, bentonite, zeolite Y, mordenite and ZSM-5 was examined for catalytic activity and product selectivity in the Fischer-Tropsch reaction.
Abstract: A range of cobalt catalysts supported on kieselguhr, silica, alumina, bentonite, zeolite Y, mordenite and ZSM-5 was examined for catalytic activity and product selectivity in the Fischer-Tropsch reaction. These results were correlated with catalyst reducibility and adsorptive properties, as well as support acidity, surface area and structure. It was found that high surface area supports give high cobalt dispersions and tend to produce highly active Fischer-Tropsch catalysts, as long as the reducibility of the cobalt is not hindered by metal-support interactions or ion exchange, or that pore diffusion or blocking effects are not taking place. All supports produced catalysts with similar methane, carbon dioxide and higher hydrocarbon selectivities, with carbon dioxide selectivity being low in all cases. The nature of the higher hydrocarbons depended strongly upon support acidity, with the non-zeolitic, low acidity supports producing the classic straight chained Fischer-Tropsch product. Of the zeolite supported catalysts, the most strongly acidic ZSM-5 supported catalyst produced the most highly branched product, followed by the zeolite Y supported catalyst. The straight chained character of the product from the mordenite supported catalyst was explained by the inaccessibility of the primary Fischer-Tropsch products to the mordenite acid sites, due to the mordenite channel system and ion exchange properties, thereby preventing secondary reactions such as isomerisation from occurring.

164 citations


Journal ArticleDOI
TL;DR: The salen complexes ML (M II =Cu, Ni, Co) and the corresponding tetrahydrosalen complexes M[H 4 ]L were prepared and characterized by their vis absorption and EPR spectra, by their magnetic moments, and by cyclic voltammetry in acetonitrile as mentioned in this paper.
Abstract: The salen complexes ML (M II =Cu, Ni, Co) and the corresponding tetrahydrosalen complexes M[H 4 ]L (M II =Cu, Ni) were prepared and characterized by their vis absorption and EPR spectra, by their magnetic moments, and by cyclic voltammetry in acetonitrile

161 citations


Journal ArticleDOI
TL;DR: In this article, the growth morphologies produced during the electric arc-discharge between a graphite cathode and a composite cobalt-graphite anode, including the abundant formation of single-shell carbon nanotubes of 1-2 nm diameter, were reported.

158 citations


Journal ArticleDOI
TL;DR: In this paper, a ligand-field multiplet model was used to analyze the cobalt 2p X-ray absorption spectra of CoO, Li-doped CoO and LiCoO2 with 0.1 eV resolution.
Abstract: The oxygen 1s and cobalt 2p X-ray absorption spectra of CoO, Li-doped CoO and LiCoO2 have been measured with 0.1 eV resolution. The cobalt 2p spectra are analysed with a ligand-field multiplet model and the inclusion of chase-transfer effects is discussed. The oxygen 1s spectra are interpreted as transitions to empty oxygen p states and it is concluded that the effects of correlations in the 3d band possibly are too small to be detectable. The symmetries and the electronic configurations of the cobalt ions in the oxides are determined. It is concluded that, in contrast to for example NiO and La2CuO4, the doping-induced states are possibly of 1A1 symmetry, which would imply that the quasi-particles have spin 3/2 and are most likely trapped.

143 citations


Journal ArticleDOI
TL;DR: In this article, the synthesis and characterization of (meso-tetraphenylporphyrinato)cobalt(II) complexes containing six, seven, or eight Br groups at the β-pyrrole positions of the macrocycle is reported.
Abstract: The synthesis and characterization of (meso-tetraphenylporphyrinato)cobalt(II) complexes containing six, seven, or eight Br groups at the β-pyrrole positions of the macrocycle is reported. Each compound undergoes three one-electron oxidations and up to nine one-electron reductions depending upon the degree of Br substitution. The first oxidation yields [(TPPBr x )Co III ] + while the first reduction gives [(TPPBr x )Co I ] - where TPPBrx is the dianion of the brominated tetraphenylporphyrin

Patent
19 Nov 1993
TL;DR: In this paper, the authors proposed a lithium secondary battery comprising a positive electrode composed of a positive active material comprising at least one member selected from the group consisting of lithium phosphate, lithium-cobalt phosphate, cobalt oxide, and lithium cobalt oxide.
Abstract: A lithium secondary battery comprising a positive electrode composed of a positive electrode active material comprising at least one member selected from the group consisting of lithium phosphate, lithium-cobalt phosphate, cobalt oxide, and lithium-cobalt oxide, such that the molar ratio of cobalt:phosphorus: lithium is more than 0.1:more than 0.2:1, a negative electrode, and an electrolyte. The lithium secondary battery of the invention has high energy density leading to high discharge capacity, high electromotive force, and high discharge voltage, and excellent cycle properties.

Journal ArticleDOI
TL;DR: In this article, a new solvent polymeric membrane electrode based on Schitt base complexes of Co(II) is described, which demonstrates excellent selectivity toward the iodide ion.
Abstract: A new solvent polymeric membrane electrode based on Schitt base complexes of Co(II) is described which demonstrates excellent selectivity toward the iodide ion. The resulting electrode exhibits fairly low detection limits and good selectivity properties. The selectivity sequence observed is iodide>thiocyanate∼nitrite> perchlorate∼bromide>nitrate>chloride> sultate. The excellent selectivity for iodide is related to the unique interaction between the central Co(II) ion and iodide. The response mechanism of the electrode was also studied with the ac impedance and spectroscopic techniques

Journal ArticleDOI
TL;DR: In this paper, the microstructures formed during powder processing and spraying were analyzed using several analytical techniques, including X-ray diffraction, Auger electron spectroscopy and energy-dispersive spectrograms in a transmission electron microscope.
Abstract: Sand erosion tests were performed on WC-Co and WC-CoCr coatings deposited by the high velocity oxy-fuel spraying method. Several analytical techniques, including X-ray diffraction, Auger electron spectroscopy and energy-dispersive spectroscopy in a transmission electron microscope were used to characterize the microstructures formed during powder processing and spraying. It was found that a substantial fraction of WC decomposed into W2C or reacted with the cobalt matrix to form ternary carbides such as Co3W3C and other mixed compounds. In both cases the binder phase had a nanocrystalline structure of size 4-8 nm containing tungsten, cobalt, carbon and chromium elements. The addition of chromium inhibits to a large extent the decomposition of WC and avoids the formation of metallic tungsten. In addition, chromium improved the erosion resistance by several times compared with the WC-Co coating. Scanning electron microscopy showed that the CoCr matrix binds carbides better than the cobalt matrix, thereby inhibiting carbide loss at the spray particle boundaries. The hydroabrasive wear behaviour of coatings and the mechanisms for material removal are discussed with respect to the microstructures formed during spraying.

Journal ArticleDOI
TL;DR: The structures of LT-LiCoO2 (synthesised by reaction of Li2CO3 and CoCO3 at 400°C) and its delithiated product LT-LCoO 2 have been reinvestigated by neutron powder diffraction as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the reduction of CoBr 2 with NaBH, in diglyme solution has been studied as a method of preparing ultrafine Co particles, where the primary products are Co, H 2, and B 2 H6.
Abstract: The reduction of CoBr 2 with NaBH, in diglyme solution has been studied as a method of preparing ultrafine Co particles. The primary products are Co, H 2 , and B 2 H6. However, in the presence of the catalytic cobalt particles, B 2 H 6 is decomposed to boron and H 2 . These results are quite different from aqueous reductions of CoX 2 with NaBH 4 , where Co 2 B is the primary product (in the form of ultrafine particles).

Journal ArticleDOI
TL;DR: Ruthenium-cobalt catalysts effectively catalyze the oxidation of alcohols by O(sub 2 ) as discussed by the authors, which is attractive for a number of pragmatic reasons and has previously been limited to activated systems.
Abstract: Ruthenium-cobalt catalysts effectively catalyze the oxidation of alcohols by O{sub 2}. The aerobic oxidation method is attractive for a number of pragmatic reasons and has previously been limited to activated systems. 1 tab.

Journal ArticleDOI
TL;DR: In this paper, the interplay between sulfur adsorption and carbon deposition reactions was investigated by monitoring not only the gas-phase products but also the amount of filamentous carbon deposited from the interaction of sulfur-contaminated cobalt particles with ethylene/hydrogen mixtures.

Journal ArticleDOI
TL;DR: The first direct evidence of oscillatory coupling in Co/Au(111)/Co trilayers grown in ultrahigh vacuum is reported and is in good agreement with theoretical predictions.
Abstract: The first direct evidence of oscillatory coupling in Co/Au(111)/Co trilayers grown in ultrahigh vacuum is reported. For samples with identical cobalt layer thicknesses, up to three peaks of magnetoresistance, corresponding to antiferromagnetic coupling between the cobalt layers, are observed with increasing gold spacer layer thickness, t Au . By growing trilayers with different cobalt coercive fields, a direct measurement of both ferromagnetic and antiferromagnetic coupling as a function of t Au was possible. The experimental data are in good agreement with theoretical predictions

Journal ArticleDOI
TL;DR: Binary and ternary palladium alloys with manganese, cobalt, ruthenium, tin and lead were obtained in the form of continuous thin films on asymmetric polymer membranes, porous metal sheets and oxide plates.
Abstract: Binary and ternary palladium alloys with manganese, cobalt, ruthenium, tin and lead were obtained in the form of continuous thin films on asymmetric polymer membranes, porous metal sheets and oxide plates. All of these compositions proved to be permeable for hydrogen only. Compositions on polyarilyde (polydiphenylenephtalide ) were stable in air up to 473 K and did not swell in hydrocarbons. A metallised polyarilyde membrane had a hydrogen permeability of 13.8 m 3 /m 2 h at 473 K and pressure drop of 1 MPa. Productivity and selectivity for pentadiene vapour phase hydrogenation to pentenes of these compositions are the same as for the palladium alloy foil but contained 180 times less palladium than the foil. The selectivity of palladium-ruthenium foil for ethene and propene synthesis by carbon monoxide hydrogenation increased drastically after coverage of this foil with islands of cobalt. Hydrogen permability of a stainless steel porous sheet deposited with a 10 μm thick film of palladium-ruthenium alloy by magnetron sputtering decreased twofold after a 1000 h test at 1073 K. Introduction of a 0.8 μm thick intermediate layer of tungsten into this composition maintained its hydrogen permeability at high temperatures. Magnesia and zirconia intermediate layers were effective as well. A porous plate made of magnesia and 15% yttria covered with a 10 μm film of palladium alloy with 6% of ruthenium had a hydrogen permeability of 108 m 3 /m 2 h (at 973 K and a pressure drop of 2 MPa) which was constant for 1000 h. Palladium-lead clusters implanted in the pores of a stainless steel sheet had 96% selectivity for the liquid phase hydrogenation of dehydrolinalool to linalool at 423 K with a productivity of 9 mol/m 2 h. A membrane catalyst for acetone condensation to 2-methylpentanone-4 was prepared by introduction of active alumina particles into the porous surface of palladium alloy foil.

Journal ArticleDOI
TL;DR: The reaction of Ru(NH[sub 3])[sub 5]OH[sub 2][sup 2+] with the pyridine sites in (5-(4-pyridyl)-10,15,20-triphenylporphyrinato)cobalt(II), (5,10-bis(4-polycyclic polygonal polycyclic acid)15, 20-diphenyl polycyclohexyl polyphenyl polymorphic acid (PDPPA) cobalt (CPA) as mentioned in this paper
Abstract: The reactions of Ru(NH[sub 3])[sub 5]OH[sub 2][sup 2+] with the pyridine sites in (5-(4-pyridyl)-10,15,20-triphenylporphyrinato)cobalt(II), (5,10-bis(4-pyridyl)-15,20-diphenylporphyrinato)cobalt(II), (5,10-bis(4-pyridyl)-15,20-bis(4-(trifluoromethyl)phenyl)porphyrinato)cobalt(II), (5,15-bis(4-pyridyl)-10,20-diphenylporphyrinato)cobalt(II), and (5,10,15-tris(4-pyridyl)-20-phenylporphyrinato)cobalt(II) adsorbed on pyrolytic graphite electrodes produce the mono-, di-, and triruthenated complexes. The adsorbed complexes act as catalysts for the reduction of dioxygen. The mono- and diruthenated complexes catalyze the two-electron reduction of dioxygen to hydrogen peroxide, whereas the triruthenated complex catalyzes the four-electron reduction to water. The preparation and electrocatalytic behavior of the catalysts are described. A comparison of the catalysts has provided additional insight into the mechanisms by which they operate in catalyzing the electroreduction of dioxygen. 20 refs., 9 figs., 2 tabs.


Journal ArticleDOI
TL;DR: In this article, the effects of cobalt content, BET surface area and dissolved cobalt ions and the kinetics of the reaction were investigated at 5-15 kg/cm2 and 115-135°C in a semi-batch autoclave reactor.
Abstract: In this study, CoAPO-5 was found to be an effective heterogeneous catalyst for the liquid-phase oxi- dation of cyclohexane with glacial acetic acid as the solvent without any promotors being added to the reaction mixture. The effects of cobalt content, BET surface area and dissolved cobalt ions and the kinetics of the reaction were investigated at 5–15 kg/cm2 and 115–135°C in a semi-batch autoclave reactor. Under these reaction conditions, no induction period was observed. The products of reaction were cyclohexanone, cyclohexanol, dibasic acids, and caprolactone, etc. The ratio of the concentration of adipic acid to succinic acid had a maximum value at the middle stage of reaction. The initial rate of reaction was found to be proportional to the 2.0 power of the cyclohexane concentration and to the 0.5 power of the catalyst loading. The effects of oxygen pressure on the reaction rate depended on the cobalt content and the reaction conditions. The cobalt ions of CoAPO-5 are mainly in the lattice positions and they can transform reversibly between the oxidizing states of CoII and CoIII. Reaction mechanism and rate expressions were proposed. Since the conversion and selectivity reported in this study were mod- erately good, and because CoAPO-5 has the advantage of being a durable heterogeneous catalyst, it could prove useful as a catalyst for the one-step liquid-phase oxidation of cyclohexane.

Journal ArticleDOI
12 Mar 1993-Science
TL;DR: In the present study, diamond was synthesized from graphite in the presence of elemental phosphorus at high pressure and temperature (7.7 gigapascals and 1800C) and single-crystal diamond was grown on a diamond seed crystal.
Abstract: As diamond-producing catalysts, 12 transition metals such as iron, cobalt, and nickel were first reported by General Electric researchers more than 30 years ago. Since then, no additional elemental catalyst has been reported. An investigation of the catalytic action of group V elements is of great interest from the viewpoint of producing an n-type semiconducting diamond crystal. In the present study, diamond was synthesized from graphite in the presence of elemental phosphorus at high pressure and temperature (7.7 gigapascals and 1800 degrees C). Furthermore, single-crystal diamond was grown on a diamond seed crystal.

Journal ArticleDOI
TL;DR: In this paper, correlations between structural and magnetic properties of two layered parent compounds, Co(OH) 2 and Co 2 (NO 3 ) (OH) 3, which mainly differ by their interlayer distances are investigated.
Abstract: This paper deals with correlations between structural and magnetic properties of two layered parent compounds, Co(OH) 2 and Co 2 (NO 3 )(OH) 3 , which mainly differ by their interlayer distances. Measurements of magnetization, magnetic susceptibility, and specific heat show the occurrence of phase transitions at nearly the same temperatures, and this is explained by strong anisotropic in-plane interactions between cobalt(II) ions. Using HTS expansion for a triangular 2D lattice and numerical computations, the in-plane ferromagnetic interactions are shown to be J=9.2 K for Co(OH) 2 and 7.4 K for Co 2 (NO 3 )(OH) 3

Journal ArticleDOI
TL;DR: In this paper, the authors observed that diamond nucleation occurred only after the substrate and its surface had been carbon saturated, and the length of the interval until saturation was reached depended on the substrate thickness.

Journal ArticleDOI
TL;DR: In this paper, the effect of trace elements on the methanogenesis from methanol and acetate was studied utilizing granular sludge obtained from an anaerobic wastewater treatment plant.

Journal ArticleDOI
TL;DR: In this paper, the crystal structures of the cobalt and nickel derivatives have been determined by refinement of X-ray powder diffraction data, and they have been synthesized through soft hydrothermal treatments.
Abstract: Crystalline microporous phosphites of transition metal ions, have been synthesized through soft hydrothermal treatments. The crystal structures of the cobalt and nickel derivatives have been determined by refinement of X-ray powder diffraction data.

Patent
05 Oct 1993
TL;DR: In this paper, a process for separating nitrogen from gas mixtures containing nitrogen and less strongly adsorbed components such as oxygen, hydrogen, argon or helium by use of an at least binary exchanged X-zeolite having lithium and a divalent cation selected from the group consisting of barium, cobalt, copper, chromium, iron, magnesium, manganese, nickel, zinc and mixtures thereof in a ratio of preferably 5% to 50% of the divalent Cation and 50% to 95% lithium.
Abstract: The present invention is directed to a process for separating nitrogen from gas mixtures containing nitrogen and less strongly adsorbed components such as oxygen, hydrogen, argon or helium by use of an at least binary exchanged X-zeolite having lithium and a divalent cation selected from the group consisting of barium, cobalt, copper, chromium, iron, magnesium, manganese, nickel, zinc and mixtures thereof in a ratio of preferably 5% to 50% of the divalent cation and 50% to 95% lithium.

Journal ArticleDOI
TL;DR: In this article, thin films of cobalt ranging from 1 ML up to 10 ML have been grown on a Cu(100) substrate and characterized by LEED, adopting a slight tetragonal distortion of its high-temperature FCC phase.
Abstract: Epitaxial thin films of cobalt ranging from 1 ML up to 10 ML have been grown on a Cu(100) substrate and characterized by LEED. The cobalt is found to grow, adopting a slight tetragonal distortion of its high-temperature FCC phase. Further growth of 5 ML Cu on top of a 5 ML Co film results in an almost perfect Cu(100) surface.