A highly active and stable Fischer–Tropsch synthesis cobalt/silica catalyst with bimodal cobalt particle distribution

Silica-supported cobalt (20 wt%) catalysts were prepared by incipient wetness impregnation of silica with different cobalt nitrate solution. The catalyst prepared from dehydrated ethanol solution exhibited highest activity and very low methane selectivity. The catalyst prepared from cyclohexanol had the lowest activity and highest methane selectivity. The catalyst prepared from aqueous solution, a most conventional catalyst, exhibited moderate reaction behavior. The catalyst prepared from dehydrated ethanol had cobalt particles with two different size where the large particles showed low bulk density with cluster-like structure.     

Effects of thiourea and urea on zinc–cobalt electrodeposition under continuous current

The effect of thiourea and urea on zinc-cobalt alloys obtained from chloride baths under continuous current deposition are described and discussed. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and an X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. The use of additives does not refine the grain size of the Zn–Co alloy and an especially porous alloy was produced in the presence of urea. The preferred crystallographic orientations of zinc–cobalt alloys do not change in the presence additives. Zinc–cobalt alloys were without texture in the presence and absence of additives. Also, in the absence of additive and in the presence of urea, the XRD lines of the Zn–Co alloys are slightly shifted with respect to the pure zinc XRD lines, whereas, in the presence of thiourea, the XRD lines are not shifted. The alloy composition was examined using Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases slightly from 1.04 to 0.91 wt.% in the presence of urea and in the presence of thiourea it increases from 1.04 to 7.70 wt.%. Voltammetric studies show that thiourea increases the reduction rate of cobalt. This explains the increase in cobalt percentage in the alloy in the presence of thiourea.     

4′-(Oxodiphenylphosphino)-2,2′:6′,2′′-terpyridine – crystal structure and complexes of cobalt(II) and cobalt(III)

The complex [Co(2)₂]²⁺ (2 = 4^′-(oxodiphenylphosphino)-2,2^′:6^′,2^′′-terpyridine) has been prepared either by the direct reaction of 2 with Co(II) or by careful oxidation of [Co(1)₂]²⁺(1 = 4^′-(diphenylphosphino)-2,2^′:6^′,2^′′-terpyridine). Further oxidation with H₂O₂ leads to [Co(2)₂]³⁺. The ¹H NMR spectra of the paramagnetic and diamagnetic [Co(2)₂]²⁺ and [Co(2)₂]³⁺ are reported. The crystal structure of ligand 1 has been determined; in the solid-state, 1 exhibits extensive intermolecular π–π stacking.     

Nickel–molybdenum and cobalt–molybdenum sulfide hydrogenation and hydrodesulphurization catalysts synthesized in situ from bimetallic precursors

Unsupported nickel–molybdenum and cobalt–molybdenum sulfide catalysts are synthesized via the in situ decomposition of water-soluble bimetallic precursors in a hydrocarbon feedstock using nickel–molybdenum and cobalt–molybdenum complexes with citric, oxalic, succinic, glutaric, and tartaric acids as precursors. The sulfide catalysts are characterized by means of transmission electron microscopy and X-ray photoelectron spectroscopy. The catalyst activity in the hydrogenation of bicyclic aromatic hydrocarbons and the hydrodesulfurization of dibenzothiophene is studied. The effect the composition of the precursor solution in the hydrocarbon feedstock emulsion has on the activity of the resulting catalyst is determined. It is shown that the activity reaches high values even after 1 h of reaction. The hydrogenation of mono-, di-, and trimethylnaphthalenes and ethylnaphthalene is studied. The optimum promoter-to-molybdenum ratio (0.25: 1) is found. It is shown that the catalyst activity does not fall during recycling, due to the elimination of the negative effect of water contained in the emulsion, which results in oxidation of the catalyst surface. After the second reaction cycle, the catalyst particles are longer and have a greater number of MoS₂ layers than the respective parameters of the catalyst particles after the first cycle. XPS shows that the content of oxygen on the catalyst’s surface falls during recycling, while the fraction of metals in the sulfide environment and the sulfur in the sulfide state grows.     

Microstructure of single-phase cobalt and manganese oxide spinel Mn3−xCoxO4 ceramics

This paper reports microstructural studies of single-phase Mn_3−xCo_xO₄ (0.98 ≤ x ≤ 2.93) spinel ceramics using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). These ceramics were obtained by conventional sintering or by spark plasma sintering (SPS) of powders prepared by thermal decomposition of coprecipitated oxalate precursors. For x < 1.78 or x ≥ 1.78, the monophasic ceramics correspond respectively to quadratic (Q) or cubic (C) spinel structure. The ferroelastic character of the structural phase transition from C to Q is highlighted by specific microstructural features. The effect of chemical composition and heat treatment conditions on the microstructure and essentially on the presence and the characteristics of twins were investigated. The coherent twin interfaces are parallel to (1 1 2) planes in the Q cell. Twins can correspond to: tweeds, single lamellae (widths: 5–306 nm) arranged parallel to each other, large lamellae (widths: 69–928 nm) internally twinned and sometimes arranged in cyclic forms (triangular shapes).     

Impedance characteristics and electrical double-layer capacitance of composite polystyrene–cobalt–arsenate membrane

In continuation of our previous work with composite polystyrene–cobalt–arsenate (PS–Co–As), we further extended impedance measurements. All calculations reported were extracted from experiments carried out in the frequency range of 1–5 kHz and different concentrations (0.0001 ≤ c(M) ≤ 1) of KCl and NaCl at isothermal temperature (25 ± 0.1 °C). The membrane capacitance and resistance measurements were observed to depend on the concentration and the applied frequency of the electrolyte. The observed capacitances and resistances were used to calculate the membrane resistances (R_M), capacitance (C_M), reactance (X_X), and also derive the impedance (Z). At higher frequencies, the capacitances became low and the impedance decreased with increasing frequency with a corresponding increase in the measured phase angle. On the other hand at the highest frequencies attainable, the phase angle became low. At low frequencies, the phase angle was become independent of the cation, while the impedance showed a clear dependence. The diffused double-layer polarization charge on the geometric capacitor played important role by affecting the overall membrane capacitance. The applied frequencies affected the double-layer capacitance due to the movement of ions across the membrane. At the membrane–electrolyte interface, the electrical double-layer was influenced in addition to being controlled by the transport of ions.     

Charge–discharge curves and discharge capacities of LiNi1−yCoyO2 synthesized from lithium carbonate and nickel and cobalt oxides

LiNi_1?yCo_yO₂ (y=0.1, 0.3, and 0.5) were synthesized by a solid-state reaction method at 800 °C and 850 °C using Li₂CO₃, NiO, and Co₃O₄ as the starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were then investigated. For samples with the same composition, the particles synthesized at 850 °C were larger than those synthesized at 800 °C. The particles of all the samples synthesized at 850 °C were larger than those synthesized at 800 °C. LiNi_0.5Co_0.5O₂ synthesized at 850 °C had the largest first discharge capacity (159 mA h/g), followed in order by LiNi_0.7Co_0.3O₂ synthesized at 800 °C (158 mA h/g) and LiNi_0.9Co_0.1O₂ synthesized at 850 °C (151 mA h/g). LiNi_0.9Co_0.1O₂ synthesized at 850 °C had the best cycling performance with discharge capacities of 151 mA h/g at n=1 and 156 mA h/g at n=5.     

Simultaneous spectrophotometric determination of manganese,zinc and cobalt by kernel partial least–squares method

Simultaneous spectrophotometric determination of Mn, Zn and Co was studied by two methods, classical partial least-squares (PLS) and kernel partial least-squares (KPLS), with 2-(5-bromo-2- pyridylazo)-5-diethylaminephenol (5-Br-PADAP) and cetyl pyridinium bromide (CPB). Two programs, SPGRPLS and SPGRKPLS, were designed to perform the calculations. Eight error functions were calculated for deducing the number of factors. Data reductions were performed using principle component analysis. The KPLS method was applied for the rapid determination from a data matrix with many wavelengths and fewer numbers of samples. The relative standard errors of prediction (RSEP) for all components with KPLS and PLS methods were the same (0.0247). Experimental results showed both methods to be successful even where there was severe overlap of spectra.     

Properties of electrodeposited silver–cobalt coatings

Silver–cobalt coatings were elecrodeposited from cyanide–pyrophosphate electrolytes with and without additives (diammonium oxalate monohydrate and 2-Butyne-1,4-diol). The deposition rate, the alloy composition, as well as some physicomechanical (internal stress, microhardness, plug-in forces, abrasion resistance) and electrical properties (contact resistance, magnetoresistance) of the obtained coatings, depending upon the applied current density or the cobalt content, respectively, were investigated. The increase in current density led to the increase in the Co content of the coatings and to a decrease in the grain size of both silver and cobalt phases. Granular structural type of deposits with a magnetoresistance of about 4% ratio was shown. The tensile stress observed in pure Ag deposits increased in the presence of Co and with an increase in its content in the alloy. The increase in the microhardness, abrasion resistance and electrical resistance of the Ag–Co coatings depended almost linearly on the Co content. The performed high speed electroplating showed significant increase in the deposition rate and smoothness of the coatings.     

Detection and characterization of molybdenum oxides formed during the initial stages of cobalt–molybdenum electrodeposition

The initial stages of cobalt–molybdenum electrodeposition on a vitreous carbon electrode were studied to obtain information about the mechanism of cobalt–molybdenum induced codeposition. Solutions containing cobalt sulphate, sodium molybdate and sodium citrate at pH 6.6 were used. A first step in the mechanism of alloy deposition is proposed. This step takes into account the formation of molybdenum(IV) oxides over which Co–Mo alloy may be only deposited if sufficient potential is applied. Co–Mo electrodeposition occurs through an early stage involving low reduction current, related to the formation of molybdenum oxides, followed by a later stage in which the reduction current suddenly increases, corresponding to alloy codeposition. When a low potential is applied, a continuous coloured molybdenum oxide film is formed on the electrode and Co–Mo is not deposited. To induce the alloy deposition on the oxide film it is necessary to apply more negative potentials than a threshold value, which depends on the composition of the electrolytic bath. By increasing molybdate concentration in solution, the threshold potential shifts to more negative values. Intermediate molybdenum oxides were characterized using scanning electron microscopy (SEM), compositional analysis, Raman measurements and Auger and X-ray photoelectron spectroscopies.     

Synthesis of lithium LiNi1−yCoyO2 from lithium carbonate,nickel oxide and cobalt carbonate and their electrochemical properties

LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from Li₂CO₃, NiO and CoCO₃ as starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. Among LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) synthesized at 850 °C, LiNi_0.7Co_0.3O₂ has the largest intercalated and deintercalated Li quantity Δx at the first charge–discharge cycle, followed in order by LiNi_0.9Co_0.1O₂ and LiNi_0.5Co_0.5O₂. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (142 mAh/g), followed in order by LiNi_0.9Co_0.1O₂ synthesized at 850 °C (113 mAh/g), and LiNi_0.5Co_0.5O₂ synthesized at 800 °C (109 mAh/g).     

Cinetique electrochimique du couple cobalt(III)—cobalt(II) en milieu acide phosphorique concentre

The electrochemical behaviour of the cobalt(III)—cobalt(II) couple in 96.5% and 85 wt% H₃PO₄ have been studied at a stationary gold electrode by using chronopotentiometry and triangular voltamperometry. The results have shown that the Co(III)—Co(II) system is reversible and the electrode reaction involves a single electron. The Co(II) ions' diffusion coefficient in the two phosphoric acid solutions was determined as 4.3 × 10⁻⁸ cm².s⁻ in 96.5% wt % H₃PO₄ and 1.2 × 10⁻⁷ cm².s⁻¹ in 85 wt % H₃PO₄. The stabillity of the Co(III) ion in 96.5 wt % H₃PO₄ media was also investigated.     

Erbium substituted nickel–cobalt spinel ferrite nanoparticles: Tailoring the structural,magnetic and electrical parameters

In this article, we have reported an effective, rapid as well as economical Er³⁺ substituted Ni_0.4Co_0.6Fe₂O₄ ferrite nanoparticles synthesized via surfactant-assisted co-precipitation route. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), dielectric properties, current-voltage (I–V) measurements, and vibrating sample magnetometry (VSM). XRD and FTIR confirmed the face-centered (FCC) spinel structure of all compositions of the synthesized spinel ferrite nanoparticles. The deviations in the lattice constant granted with the variation in size of the guest (Er³⁺) and host (Fe³⁺) cations. These ferrites were also subjected for electrical, magnetic and dielectric investigations. I–V measurements showed that resistivity values decreased from 6.20 × 10⁷ Ω cm to 0.03 × 10⁷ Ω cm with the increased Er³⁺ contents. Saturation magnetization increased from 35.99 to 39.95 emu/g. This high value of saturation magnetization suggested the possible utilization of such ferrites for practical applications such as microwave and recording devices fabrication. Interestingly, the magnetic and dielectric properties of nickel-cobalt ferrite nanoparticles showed ample improvement upon Er³⁺ substitution. The results clearly indicate the potential of Er⁺³ substituted spinel ferrite particles in various advanced technological devices fabrication.     

Structure and catalytic performance of Pt-promoted alumina-supported cobalt catalysts under realistic conditions of Fischer–Tropsch synthesis

The structure of alumina-supported cobalt catalysts promoted with platinum and their catalytic performance in Fischer–Tropsch synthesis were investigated under realistic reaction conditions (P = 20 bar, T = 493 K) using in situ time-resolved X-ray diffraction with simultaneous analysis of reaction products. The catalysts were prepared via incipient wetness impregnation and characterized by a wide range of ex situ techniques. Direct in situ measurements were indicative of considerable versatility of alumina-supported cobalt catalysts during Fischer–Tropsch synthesis. Cobalt sintering occurred at the first hours of the reaction and resulted in a significant drop of the catalytic activity. In addition to sintering, partially oxidized catalysts containing smaller cobalt particles (mean particle size <5 nm) were slowly reducing during Fischer–Tropsch reaction. Treatment of cobalt catalysts in pure carbon monoxide led to selective transformation of cobalt metallic phases to Co₂C cobalt carbide. Cobalt carbidization followed by hydrogenation selectively led to cobalt hcp metallic phase, which seems to be more active in Fischer–Tropsch synthesis than cobalt fcc phase. Cobalt oxidation by water was not significant in the catalysts with metal particles larger than 5 nm even at high water concentrations.     

Electrochemical and structural influence on BaZr0.8Y0.2O3-δ from manganese,cobalt, and iron oxide additives

Proton conductive BaZr_0.8Y_0.2O_3−δ (BZY20) is a promising electrolyte candidate with perspective application in electrochemical devices, including fuel cells, electrolyzer cells. Mn, Fe, and Co are commonly incorporated into BZY20, to improve the sinterability (CoO), or due to possible inter-diffusion by calcining with cathode materials (eg, La_1−xSr_xMnO_3−δ, La_1−xSr_xCo_1−yFe_yO_3−δ) for cell preparation. This work was performed to investigate the influence of Mn, Fe, and Co on the structural and electrochemical properties of BZY20. As reported in literature, the sinterability of BZY20 was improved by adding CoO. XANES analysis shows that Mn, Fe, and Co are possibly incorporated into the perovskite crystal structure of BZY20, and are partially reduced when the samples were exposed to hydrogen at 600°C for 24 hours. However, through electrochemical analysis, we found that all these three elements decrease both the proton conductivity and transport numbers of proton conduction of BZY20. Therefore, the BZY20 electrolyte should be carefully handled to avoid the incorporation of these transition metal elements, to fabricate the cells with high performance.     

Alternating copolymerization of carbonyl sulfide and Cyclohexene Oxide catalyzed by zinc–cobalt double metal cyanide complex

This paper describes the first example of alternating copolymerization of carbonyl sulfide (COS) with cyclohexene oxide (CHO) via heterogenous catalysis of a nano-lamellar zinc–cobalt(III) double metal cyanide complex (Zn–Co(III) DMCC), providing an efficient method for converting COS to poly(cyclohexene monothiocarbonate) (PCHMTC) with an alternating degree up to 93%. The number-average molecular weight (M_n) of PCHMTC was 6.5–25.0 kg/mol with polydispersities (PDIs) of 1.6–2.1. The productivity of the catalyst was up to 970 g polymer/g catalyst (5.0 h). The oxygen–sulfur exchange reaction (O/S ER) caused by Zn–Co(III) DMCC was largely suppressed when the reaction was performed at 100–110 °C in the presence of THF or CH₂Cl₂, and thus the selectivity of the monothiocarbonate over carbonate linkages was up to 98%. The mechanisms of the copolymerization and O/S ER were proposed based on the ESI-MS, GC–MS and FT-IR spectra. The obtained PCHMTC is highly transparent and exhibits good solubility in various organic solvents, high T_g of 112 °C, initial decomposition temperature of 214 °C and high refractive index of 1.705.     

Ruthenium promoted cobalt–alumina catalysts for the synthesis of high-molecular-weight solid hydrocarbons from CO and hydrogen

The effect of the ruthenium promotion of Fischer–Tropsch (FT) cobalt–alumina catalysts on the temperature of catalyst activation reduction and catalytic properties in the FT process is studied. The addition of 0.2–1 wt % of ruthenium reduces the temperature of reduction activation from 500 to 330–350°C while preserving the catalytic activity and selectivity toward C₅₊ products in FT synthesis. FT ruthenium-promoted Co–Al catalysts are more selective toward higher hydrocarbons; the experimental value of parameter α_ASF of the distribution of paraffinic products for ruthenium-promoted catalysts is 0.93–0.94, allowing us to estimate the selectivity toward C₂₀₊ synthetic waxes to be 48 wt %, and the selectivity toward C₃₅₊ waxes to be 23 wt %. Ruthenium-promoted catalysts also exhibit high selectivity toward olefins.     

Copper–cobalt heterobimetallic ceramic oxide thin film deposition: Synthesis,characterization and application of precursor

Thin films of halide free Cu–Co mixed metal oxide have been prepared at 390 °C from the heterobimetallic complex Co₄(THF)₄(TFA)₈(μ-OH)₂Cu₂(dmae)₂ · 0.5C₇H₈ (1) [dmae = N,N-dimethylaminoethanol ((CH₃)₂NCH₂CH₂O⁻), TFA = triflouroacetate (CF₃COO⁻), THF = tetrahydrofurane (C₄H₈O)] which was prepared by the reaction of [Cu(dmae)Cl]₄ and Co(TFA)₂ · 4H₂O. The precursor was characterized for its melting point, elemental composition, FTIR and X-ray single crystal structure determination. Thin films grown on glass substrate by using AACVD out of complex 1 were characterized by XRD and SEM. TGA and AACVD experiments reveal it to be a suitable precursor for the deposition of halide free Cu–Co mixed-metal oxide thin films at relatively low temperatures.     

Analytical approaches for the determination of cobalt,nickel and copper by aeration-assisted homogeneous liquid–liquid microextraction and flame atomic absorption spectrometry

A new aeration-assisted homogeneous liquid–liquid microextraction using high-density solvent for determination of copper, nickel and cobalt, as a prior step to their determination, coupled to flame atomic absorption spectrometry is presented. Under the optimum conditions, the calibration graphs were linear in the range of 5.0–600.0 ng/mL for copper, 10.0–450.0 ng/mL for nickel and 8.0–500.0 ng/mL for cobalt. The limits of detection were 1.3, 3.6 and 2.7 ng/mL and the enrichment factor estimated to be 350, 340 and 360, for copper, nickel and cobalt, respectively. The proposed method was successfully applied for the determination of these cations in different samples.