Reduction Of Cobalt Research Articles

Reduction of aqueous cobalt(II) from acetate buffered solution by hydrogen under pressure

An investigation was made into the kinetics and mechanism of pressure reduction with hydrogen of aqueous cobalt(II) from acetate solution containing powdered aluminium. The effect was examined of temperature, initial pH of the feed solution, partial pressure of hydrogen, stirring rate, and total surface area of the powdered aluminium on the course of reduction and on the quality of the resultant Co(Al) composite powder. The reduction of cobalt(II) followed first order kinetics with regard to cobalt concentration and was kinetically controlled with an activation energy ( ΔE a) of 52 kJ/mol. The rate of reduction at pH values exceeding 3.7 was found to be proportional to the total surface area of the catalyst ( S A1), partial pressure of hydrogen P H2, initial concentration of acetates ([CH 3COO −] o), and was independent of the stirring rate ( v) in the range from 250 min −1 to 550 min −1. The following equation describes the course of reduction: - (d[Co(II)]/ d t)= k·[Co(II)], where: k=1.79·10 −2· S A1· P H2·[CH 3COO −] o· (pH o−3.7)·exp(− ΔE a/ RT). Optimum parameters of preparation of the cobalt-coated aluminum powder were established with regard to process rate, retardation of Co(II) hydrolysis and the quality of the cobalt coating.

Electrochemical aspects of pressure reduction of aqueous Cobalt(II) by hydrogen

The reduction of Co(II) by hydrogen on an aluminium electrode in acetate-sulphate aqueous solutions was examined using potentiostatic measurements in a three-electrode system. Measurements were performed at varying cobalt concentrations at 453 K and at varying temperatures at a cobalt concentration of 30 g/l. Thereafter, the oxidation of hydrogen on an aluminium electrode in acetate aqueous solutions was examined at 453 K and varying partial pressures of hydrogen and at varying temperatures at a hydrogen pressure of 3.0 MPa. Polarization curves were taken at an initial pH (pH o) of 6.2, mixing rate of 450 min −1, and a constant rate of potential change of 10 mV/s. From the resultant anodic and cathodic curves the exchange current density of the overall reaction was evaluated and found to correlate with the rate constants of pressure reduction of aqueous Co(II) by hydrogen determined in a previous kinetic study. The overall process was found to comprise two electrochemical half reactions on the aluminium surface: Co 2++2e −=Co and H 2−2e −=2H +.

Electrochromic Oxidation and Reduction of Cobalt and Zinc Naphthalocyanine Thin Films

Electrochromism of cobalt and zinc naphthalocyanines (, ) was investigated in thin films vacuum‐deposited on indium tin oxide substrates. The film exhibited color changes from original green to purple both upon reduction and oxidation, and the film exhibited a color change from green to brown only upon oxidation. The electrochromic reduction was a reversible process depending on an electroactivity of the central Co metal, and the electrochromism was attributed to a transition from a reduced state related to the Co(I) center to a π*‐state of the Nc‐ligand. On the other hand, the electrochromic oxidation irreversibly occurred at the Nc‐ring ligand. The ring‐oxidation was stably maintained by a retention of incorporated anions, which caused a film restructuring accompanied with a discorder of molecular stacking from the original α‐polymorphic form to an amorphous structure in the oxidized state.

Kinetic relationships of reduction of tungsten and cobalt in complicated oxide systems

Kinetic relationships of reduction of tungsten and cobalt in complicated oxide systems

Rate of Back-Extraction of Tris(acetylacetonato)cobalt(III) from Carbon Tetrachloride into Aqueous Acid Perchlorate Solutions

The rate of back-extraction of tris(acetylacetonato)cobalt(III), Co(acac)3, in carbon tetrachloride containing acetylacetone, Hacac, by washing with aqueous 4 mol dm−3 perchloric acid-sodium perchlorate solutions is studied. In the early stage, a rapid back-extraction which is due to the two-phase distribution of the complex is observed; the transient distribution equilibrium established is dependent on the acid concentration. This is explained in terms of the formation of protonated species, Co(acac)3H+ and Co(acac)3(H+)2. When the two phase agitation is continued, the back-extraction proceeds gradually. The rate is dependent on the acid concentration but it is not dependent on the Hacac concentration. Most cobalt back-extracted in this stage is found to be in the bivalent state. The rate-determining step is concluded to be the dissociation of the first acetylacetonate ion from the complex in the aqueous phase, which is followed by the reduction of cobalt(III) to cobalt(II). The rate constants of the dissociation of acetylacetonate ion from the Co(acac)3H+ and from the Co(acac)3(H+)2 are one and two orders higher than that from the Co(acac)3.

Dynamic solvent effect on the kinetics of the inner-sphere reduction of cobalt(III) anchored to a mercury electrode in mixtures of water with an organic solvent

Unimolecular rate constants have been measured for the electroreduction of two similar pentaamminecobalt(III) complexes in mixtures of water with acetone and acetonitrile. The reactants were attached to mercury via the bridging ligands 3-(2-thienyl)acrylocarboxylate and 3-(2-thienyl)propionocarboxylate. Only the reactant with a bridge featuring uninterrupted conjugation is known to undergo the adiabatic electron transfer in aqueous solutions. For this reactant, it has been found that the rate constant evidently decreases with the addition of organic solvent to the mixture. This observation is discussed in terms of a change in the longitudinal relaxation times for the mixtures.

Iron(II) reduction of halogenopyridinecarboxylatocobalt(III)-dioxime complexes: Kinetics and mechanism

The iron(II) reduction of cobalt(III)-dioxime complexes of the typetrans-[Co(DODOHbzo) (s-py)X]ClO4, where DODOHbzo=3,8-dimethyl-5,6-benzo-4,7-diazadeca-3,7-diene-2,9-dione dioximate (1−), s-py=pyridine (py), nicotinic acid (nic-COOH) or isonicotinic acid (isonic-COOH) and X−=Cl−, Br− or I−, was studied in 1% (v/v) DMSO-H2O at 27±0·1°C andI=0·25M (LiClO4) in the [H+] range 0·007–0·100M under pseudo-first-order conditions using an excess of the reductant. The inverse dependence of rate on [H+] suggests an equilibrium between the protonated and unprotonated forms of the complex, the protonated form reacting slower than the unprotonated one. The rate constants reflect the trend Cl−<Br−<I− and py<nic-COOH≃isonic-COOH for the axial ligands.

An IR study of the Ziegler system Co(acad)3/Mg(n-butyl)2 in THF

Applying IR spectroscopy for studying the Ziegler system Co(acac)3/Mg(Bu)2 (Bu=n-butyl) in tetrahydrofuran, it could be shown that the following reactions take place: reduction of cobalt (III), exchange of the acetylacetonate groups and their interaction with Mg(Bu)2.

Electrocatalysis of metalloporphyrins part 10. Electrochemical oxidation and reduction of water-soluble cobalt(III)-tetrakis(4-trimethyl-ammoniumphenyl

The aggregation of cobalt(III)-tetrakis(4-trimethylammoniumphenyl)porphyrin (CoTMAP) in acidic and neutral media has been investigated. CoTMAP obeys Be M at pH 1 (0.05 M H 2SO 4 + 0.25 M Na 2SO 4) and in the concentration range 10 −6-10 −4 M at pH 7 (0.1 M phosphate buffer). In vi electroreduction have been studied by means of cyclic voltammetry, the rotating ring disk electrode technique, computerized potential-step chronocoulom spectroelectrochemical method. In the presence of aggregating CoTMAP in aqueous solutions, its products generated during electro-oxidation will adsorb (I) state product will also adsorb cumulatively on the electrodes in both the presence and the absence of aggregation. Reaction mechanisms for the elec solutions in both the absence and the presence of aggregation are proposed.

Metal Ion Cages: Capping Reactions With Bifunctional Methylene Compounds and Formaldehyde

[(1,1,1-Tris(4-amino-2-azabutyl)ethane)cobalt(III)](3+) ([co(sen)]3+) and [(tris(4-amino-2- azabutyl)amine)cobalt(III)](3+) ([Co(azasen)]3+) react with formaldehyde and diethyl malonate or cyanoacetic acid ethyl ester in the presence of base to form macrobicyclic cages [ox- osarcophagine (oxosar) and oxoazasarcophagine (azaoxosar)] about the metal ion. The cage structure of the complexes has been established by an X-ray crystallographic analysis of [(1-carboxy-8-methyl-2-oxo-3,6,10,13, 16,19-hexaazabicyclo[6.6.6]icosanato)cobalt(III)] diperchlorate [Co(Me,CO2H-oxosar- H)]2+ which crystallizes in the orthorhombic space group Pbcn, with cell parameters a 33.61, b 10.42, c 13.743 � , and V 4813 � 3 , and Z 8. The chiral cobalt(III) complex is characteristically inert to substitution and racemization, but the cobalt(II) complex, obtained by reduction of the appropriate cobalt(III) compound, is surprisingly stable both to loss of Co2+ ion and to racemization at 25°C (pH 7.1, t½4.5 days). The syntheses, spectroscopic and chemical properties are reported. The kinetics of the electron self exchange for the cage system [Co(Me,CO2Et-oxosar-H)]+/2+, and of H2O2 formation from [coII(Me,co2Et-oxosar - H)]+ and O2 are reported. Similar syntheses have been carried out to half-cap the [co(en)3]3+ ion (en = ethane-1,2-diamine). These and related reactions have allowed substituents such as COOR, COOH, CN, COCl, CONR2, NH2 and NO2 to be placed on the bridgehead carbon atoms, and have altered the redox potentials of the systems by at least 0.3 V. The oxosar COII ions are useful as powerful reducing agents [from c. -0.3 to -0.6 V (v. n.h.e.)], and the cages are capable of further derivatization to build larger macromolecules.

Hydrocarbon synthesis from carbon monoxide + hydrogen on impregnated cobalt catalysts

Abstract The physicochemical properties of 10% Co/silica-alumina catalysts prepared by impregnation were studied by TPR, thermoanalysis and carbon monoxide adsorption. The temperature at which the catalyst was pretreated was found to have a great influence on its adsorption capacity for carbon monoxide. Both reduced and unreduced samples calcined in air at relatively high temperatures adsorbed carbon monoxide, but the reduced ones adsorbed much larger amounts. The adsorption capacity tended to increase with increasing pretreatment temperature. The character of carbon monoxide TPD profiles and the proportions of the individual adsorption forms were found to depend on the pretreatment temperature and the degree of cobalt reduction. Carbon monoxide was found to be adsorbed in three forms on species originating in cobalt-support interactions, metallic cobalt and on Co 3 O 4 . Calcination in air was found to cause a decrease of both cobalt reduction and the activity in hydrocarbon synthesis. While the yield of gaseous products remained constant, that of the liquid ones decreased substantially with increasing pretreatment temperature, reaching a maximum value when the degree of cobalt reduction was ca. 40–50%. The average carbon number decreased with increasing cobalt reduction. The catalytic properties of Co/silica-alumina are more similar to those of Co/SiO 2 than of Co/Al 2 O 3 , but Co/silica-alumina catalysts are less efficient in polymerization than either Co/SiO 2 or Co/Al 2 O 3 . The hypothesis, suggesting that the adsorption centres of weakly bonded carbon monoxide were involved in the production of liquid hydrocarbons and that the cobalt oxide species act directly in this synthesis, was confirmed.

Reduction mechanism of cobalt(II)-malonate and -succinate complexes at a dropping mercury electrode

The reduction of cobalt(II) in the presence of malonate and succinate ios was examined polarographically. The species reduced at the dropping mercury electrode, their electrokinetic parameters and the stability constants of complexes were determined at ionic strength 0.5 mol dm −3 (NaClO 4) and 25°C.

Hydrocarbon synthesis from carbon monoxide and hydrogen on impregnated cobalt catalysts Part I. Physico-chemical properties of 10% cobalt/alumina and 10% cobalt/silica

The physico-chemical properties of impregnated cobalt catalysts were found to depend on the nature of the support and on the temperature of pretreatment. The decomposition of dried 10% cobalt/alumina and 10% cobalt/silica in an inert gas was found to proceed in two steps (the crystal water evolution and the total decomposition of cobalt nitrate) . In a reducing atmosphere, the endothermic decomposition was accompanied by exothermic reduction of cobalt nitrate, and the whole process depended strongly on the nature of the support. On silica, the formation of cobalt surface compounds with the support was much more limited than on alumina. The amount of adsorbed carbon monoxide was found to increase with the temperature of calcination, while both the degree of cobalt reduction and the cobalt dispersion decrease. Carbon monoxide was found to be adsorbed in four different states on the 10% cobalt/alumina catalyst (linear forms on Co 2+, Co δ+ and Co 0, bridged form on Co 0). Their relative amounts depended on the temperature of pretreatment. Catalyst pretreatment with a carbon monoxide and hydrogen mixture under hydrocarbon synthesis conditions causes a certain modification of the metal surface which leads to variations of the carbon monoxide adsorption states.

Activation of carbon-supported cobalt-molybdenum catalysts in thiophene hydrodesulfurization

Thiophene hydrodesulfurization (HDS) activities and product distributions of impregnated Co/C, CoMo/C and Mo/C catalysts were studied at 673 K and atmospheric pressure. Two kinds of pretreatments (prereduction by hydrogen or presulfidation by H 2/H 2S mixture) were carried out on Co and/or Mo catalysts supported on three kinds of carbon (non-activated, activated by CO 2 for 1 h and 10 h). These catalysts were tested in thiophene HDS. Characteristic synergistic effects were not observed, either in thiophene conversions (CONV) or in hydrogenation selectivities (HYD) of butene products of the HDS reaction. The latter values were similar for Co/C and Mo/C catalysts, in contrast to alumina-supported samples. CONV and HYD values of Co/C catalysts were more stable with increasing reaction time than those of Mo-containing samples, and these values decreased in most cases in the following order: presulfided ‘non-pretreated’ prereduced catalysts. The above order and the gradual decrease in CONV and HYD values with increasing Co content of prereduced samples show that reduction of cobalt is not favourable to high CONV and HYD values, because this reduced Co cannot be sulfided by the hydrogen/thiophene reaction mixture and oxidic Co (in non-pretreated samples) cannot be sulflded efficiently in the HDS reaction. High 1-butene and trans-2-butene excesses over thermodynamic equilibrium ratios of butene isomers were found on non-activated and 1 h-activated carbon-supported catalysts, which indicate the predominance of the reaction route producing 1-butene over these supports. Higher specific surface areas of the activated support seem likely to result in higher surface areas of active phase, too, but it presumably cannot prevent the segregation of metallic Co during prereduction. Widening of micropores and the increasing number of mesopores during activation of the support also contribute to the increasing HDS activities and HYD selectivities.

Reactive Deposition of Cobalt Electrodes: I . Experimental

Reactive deposition is a novel method for producing highly porous, high‐surface‐area metal structures. The process involves the electrodeposition of metal in the presence of bubbling oxygen and Cl− ions in solution. The cobalt electrodes produced by the reactive deposition technique have grain and pore size of less than one micron. In this paper, the processes of reactive deposition of Co electrodes were investigated by using both galvanostatic and potentiostatic techniques. In the presence of bubbling oxygen, the deposition processes of Co metal are the results of competition of direct electrodeposition of Co2+ ions and the reduction of cobalt oxides/hydroxides. It has been found that the reduction of cobalt oxides, particularly at the electrode surface, is the predominant process. The presence of Cl− ions in the solution also plays an important role, possibly by activating and increasing the dissolution processes of freshly formed cobalt/cobalt oxides.

Electrochemical behavior of ‘costa-type’ organocobalt coenzyme B 12 models

The cathodic reduction of nine ‘Costa-type’ organocobalt B 12 model compounds, [RCo(III)L]C1O 4 (where R = alkyl ligand; L = N 2, N 2′-propanediylbis- (2,3-butanedione 2-imine 3-oxime) and a neutral base), was studied in acetonitrile solvent, using cyclic voltammetry, controlled potential coulometry, and spectroelectrochemical techniques. The effect of the alkyl substituents, namely i-C 3H 7, neo-C 5H 11, i-C 4H 9, CH 3CH 2, C 6H 5CH 2, CH 3, HO(CH 2) 2, CH 3- COOCH 2 and CF 3CH 2, on the relevant cobalt reduction mechanisms and potentials was investigated. A marked infiuence of axial group bulk on the reactivity of the low oxidation state cobalt derivatives formed in the reduction process has been evidentiated. The reactivity of these electrogenerated compounds is conditioned for the most part by their ability to form stable bisalkyl complexes.

Acylcobalt salophen reagents. Precursors to acyl radical intermediates for use in carbon-to-carbon bond-forming reactions to alkenes

Acylcobalt salophen reagents (6) are conveniently synthesised from carboxylic acid chlorides following treatment with the sodium derivative (5) produced from reduction of cobalt(II) salophen with sodium amalgam in tetrahydrofuran at room temperature. The acylcobalt salophens (6) undergo homolytic cleavage in the presence of light from a conventional 300 W sunlamp to give acyl radicals (24) which then undergo additions to activated carbon-to-carbon double bonds, leading to enones, viz.(26)[following dehydrocobaltation from presumed organocobalt intermediates (25)], or saturated ketones, viz.(34)[following H-quenching of intermediates (25)]. Intramolecular cyclisations of the acylcobalt salophens (42a) and (42b) lead to the ylidenecyclopentanones (43) and (45), respectively.

Reduction mechanism of cobalt(II)-ammonia complexes on a dropping mercury electrode

The mechanism of the polarographic reduction of cobalt(II) complexes with ammonia at a dropping mercury electrode over a wide ligand concentration range was investigated. It was shown that the Co(II) aquo ion and the Co(NH3)2+ and Co(NH32+2 complexes participate in the electrode process. Transfer coefficients, α, for these species and the electrode reaction rates were evaluated. Stability constants of Co(II) complexes with ammonia in 0.5 M ammonium perchlorate were determined on the basis of the polarographic wave equation of totally irreversible reduction of complex specie.

Reactions of metal-substituted myoglobins with excess electrons studied by pulse radiolysis and low-temperature gamma-radiolysis

Reactions of metal-substituted myoglobins with excess electrons in electron-pulse-irradiated aqueous solutions at room temperature and γ-irradiated aqueous matrices at 77 K were studied for the purpose of probing the functional role of heme iron. The rate constants for the reactions of various myoglobins with hydrated electrons were not much different from each other, and were close to those of diffusion-controlled reactions. In contrast, the reduction rates of myoglobins with dithionite depended markedly on the kind of central metals in the myoglobins. The difference was interpreted in terms of Marcus' theory for electron-transfer reactions. Effects of the 6-coordinate structure of the cobalt(III) species on the reaction with dithionite was also discussed. The steady-state optical-absorption measurements of γ-irradiated matrices containing cobaltimyoglobin at 77 K demonstrated the reduction of cobalt(III) species by excess electrons produced by the action of ionizing radiation. It was shown, by electron-spin resonance spectroscopy, that a 6-coordinated cobalt(II) species produced at 77 K transformed to a 5-coordinate one at higher temperatures, as reported previously. However, structural relaxation was not observed by optical spectroscopy either in the solutions or in the low-temperature matrices. It was concluded, therefore, that the intermediate 6-coordinate cobalt(II) species gave an optical absorption spectrum which was indistinguishable from that of the relaxed 5-coordinate cobalt(II) species.

Kinetics of cobalt(III) reduction. 2. Reaction in p-xylene solution of p-toluic acid

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of cobalt(III) reduction. 2. Reaction in p-xylene solution of p-toluic acidJaroslav Novotny, Milan Hronec, and Jan IlavskyCite this: Ind. Eng. Chem. Res. 1989, 28, 10, 1471–1473Publication Date (Print):October 1, 1989Publication History Published online1 May 2002Published inissue 1 October 1989https://doi.org/10.1021/ie00094a006RIGHTS & PERMISSIONSArticle Views82Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (348 KB) Get e-Alerts Get e-Alerts