Photochemically induced insertion of an olefin into the Co–Si bond; the key step for silylative coupling with vinylsubstituted organosilicon compounds

Co(SiEt₃)(CO)₄ (I) as an example of a Co–Si complex is shown to be a catalyst for silylative coupling of olefins (vinylsilanes, styrene) with vinylsilanes and dimerization of divinylsubstituted silicon compounds(although not as effective as previously reported Ru and Rh complexes). The catalytic and stoichiometric study on the insertion of styrene into the Co–Si bond of I confirms that the mechanism involves the first known β-silyl transfer (from β-silylethylcobalt(I)) to the cobalt atom.     

Strontium carbonate supported cobalt catalyst for dry reforming of methane under pressure

Catalytic performance of Co–SrO catalyst for dry reforming of methane was investigated at 1 MPa, 1023 K. The catalyst prepared by oxalate co-precipitation method or citric acid method showed a steady activity for dry reforming of methane under pressure. The importance and stability of cobalt metal with strontium carbonate were suggested for the Co–SrO catalyst, and thus it should be denoted as Co–SrCO₃. In addition, cobalt supported on strontium carbonate prepared by impregnation method (Co/SrCO₃) showed the comparable activity with high tolerance to oxidative atmosphere under reaction conditions.     

Products of combustion of mixtures of aluminum and tungsten nanopowders in air

It is experimentally found that intermediate products of combustion of mixtures of aluminum and tungsten nanopowders in air are aluminum nitrides, remainders of metallic tungsten and aluminum, complex oxides, and possibly tungsten nitrides. These products were obtained by terminating the combustion process when a temperature close to the maximum value is reached. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 59–65, July–August, 2007.     

Ammonia-treated carbon-supported cobalt tungsten as fuel cell cathode catalyst

The ammonia-treated carbon-supported cobalt tungsten (Co-W/C) was prepared by a reaction employing a temperature program in a stream of NH₃ between 773 and 1073 K. The effects of the NH₃ heat-treatment temperature, Co-W ratio and the preparation method were investigated. The activity of Co-W/C for the oxygen reduction reaction (ORR) was evaluated using a rotating disc electrode and single fuel cell measurements. The Co-W/C prepared by the impregnation method with the same atomic ratio of Co and W, and NH₃ heat treated at 823 K, exhibited the highest ORR activity with an onset potential of 0.74 V (vs. RHE at 5 μA cm⁻²). The XRD and temperature-programmed measurements revealed that the catalyst active species were ascribed to the presence of CoW oxynitride and Co nitride. The catalyst surface was characterized as nitrided metal (accommodation of the N-atom in the host Co-W lattice resulting from a sufficient distance between the Co-W atoms and N) and N-containing carbon (Co surrounded by N-atoms and attached to the C support) by X-ray photoelectron spectroscopy. The Co-W oxynitrides, Co nitride and pyrrolic-type nitrogen of the N-containing carbons are likely responsible for the good ORR activity.     

Cobalt–magnesia catalyst by oxalate co-precipitation method for dry reforming of methane under pressure

Catalytic performance of cobalt–magnesia catalyst prepared by oxalate co-precipitation method (Co–MgO) was investigated for dry reforming of methane at 1 MPa, 1023 K. Co–MgO (7 mol% Co) showed stable activity at such high space velocity as 400,000 cm³ h⁻¹ g⁻¹ whereas reactor was plugged during the reforming reaction with 10 mol% Co–MgO, and the activity of Co–MgO with Co content less than 6 mol% gradually decreased by the oxidation of cobalt species. Well-balanced cobalt content is essential for high and stable activity.     

Ultrafine Ni–Co–W–B amorphous alloys and their activities in benzene hydrogenation to cyclohexane

Quaternary Ni–Co–W–B amorphous alloys were prepared by chemical reduction of the aqueous solution of nickel and cobalt salts and sodium tungstate with potassium borohydride. The catalytic activities of the as-prepared materials were measured through liquid phase hydrogenation of benzene under moderate pressure. In comparison with Ni–Co–B, the as-prepared Ni–Co–W–B amorphous alloys showed superior activity, attributable to the promoting effect of tungsten on the microstructure of the alloys as revealed by XPS, XRD and DSC measurements.     

Electrodeposition of noncrystalline cobalt–tungsten alloys from citrate electrolytes

Induced electrodeposition of Co–W alloys onto steel substrates from acid citrate baths has been investigated. The effects of some plating parameters, such as current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency of the alloy and the percentage tungsten in the alloy were studied. Highly adherent and compact Co–W alloys codeposited from citrate baths containing up to 28 mass % tungsten were obtained. The percentage W (w/w) in the alloy increases with increasing pH, bath temperature and Co²⁺ ion concentration. On the other hand, the percentage W in the alloy decreases with increasing current density. Anodic linear stripping voltammetry (ALSV) indicated that the alloy might consist of one phase solid solution. These alloys were determined to be noncrystalline by X-ray diffraction analysis.     

W-promoted Co–Mo–K/γ–Al2O3 catalysts for water–gas shift reaction

The effects of incorporating tungsten into the traditional Co–Mo–K/γ–Al₂O₃ catalysts on the catalytic performances for water–gas shift reaction were investigated. Activity tests showed that W-promoted Co–Mo–K/γ–Al₂O₃ catalysts exhibited higher activity than W-free Co–Mo–K/γ–Al₂O₃ catalyst. Raman and H₂-TPR studies indicated that part of the octahedrally coordinated Mo–O species on Co–Mo–K catalysts transformed into tetrahedrally coordinated Mo–O species in the presence of W promoter.     

Influence of additives on combustion of ultradisperse aluminum powder and chemical binding of air nitrogen

Experimental results are presented on combustion in air of ultradisperse aluminum powder with additives of ultradisperse powders of copper, nickel, iron, tin, silicon, graphite, boron, tungsten, and molybdenum.X-Ray diffraction and chemical analyses were used to study the composition of the end products. A tin additive has an inhibiting action on the chemical combining of air nitrogen as aluminum nitride and oxynitride, whereas iron, tungsten, and molybdenum additives favor an increase in nitrogen content. As is established, the influence of additives on the processes determining the duration of two combustion stages is greater than on the content of bound nitrogen in the products.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 2, pp. 108–110, March–April, 1996.     

Preparation of Cobalt Nitride from Co–Al Hydrotalcite and its Application in Hydrazine Decomposition

Alumina supported cobalt nitride [Co₄N–Al₂O₃ (HT)] with high cobalt loading has been prepared for the first time from Co–Al hydrotalcite precursors. The formation of the Co₄N phase was confirmed by XRD, H₂-TPR, and XPS. Compared with Co₄N/Al₂O₃ (IMP) prepared by conventional impregnation and nitriding, the hydrotalcite derived catalyst exhibited a much better activity for hydrazine decomposition as consequence of higher dispersion of active species.     

Dissolution from electrodeposited copper–cobalt–copper sandwiches

The electrochemical behaviour of electrodeposited Co–Cu/Cu multilayers from citrate electrolytes was investigated using cyclic voltammetry and stripping techniques at a rotating ring disc electrode. Copper and cobalt–copper alloy sandwiches were deposited from an electrolyte containing 0.0125 M CuSO₄, 0.250 M CoSO₄ and 0.265 M trisodium citrate at two different pHs, 1.7 and 6.0. The Cu/Co–Cu/Cu sandwich is representative of a single layer in a Co–Cu/Cu multilayer deposit, which is known to exhibit unusual physical and magnetic properties. Results from cyclic voltammetry and detection of dissolving species at the ring showed that cobalt is stripped from a Cu/Co–Cu/Cu sandwich even when a copper layer as thick as 600 nm covers the Co–Cu alloy. Scanning electron microscopy showed that cobalt can dissolve from the deposit easily because the copper layer covering the Co–Cu alloy is porous. A separate series of experiments with Cu/Co–Ni–Cu/Cu sandwich showed that cobalt does not dissolve from these deposits because the addition of nickel stabilises cobalt in the Co–Ni–Cu alloy.     

Photofading of azo dyes: a theoretical study

The light fastness of a number of azo dyes has been investigated using all-valence molecular orbital methods, AM1 and PM3. The results of molecular orbital calculations are used to obtain both highest occupied molecular orbital and lowest unoccupied molecular orbital frontier electron density, which, respectively, can account for the propensity of the electrophilic and nucleophilic attack at a particular atom in a molecule. The highest occupied molecular orbital and lowest unoccupied molecular orbital superdelocalisability have also been obtained to explain the order of light fastness values in different dyes of a particular series. In addition, attempts have been made to correlate the light fastness values with the difference in energy of the highest occupied molecular orbital of the dye and the lowest unoccupied molecular orbital of the singlet oxygen.     

Electrolytic oxygen evolution on Ni-Co-P alloys

Electrolytically obtained Ni–Co–P alloys exhibit amorphous structure. On heating these alloys to 773 K crystalline nickel and cobalt phosphide phases, and also nickel crystallites, are formed. After cathode-anode polarization of the amorphous and crystalline Ni–Co–P alloys in 5m KOH for 18 h, oxygen-cobalt compounds together with crystalline or amorphous nickel phosphides appear on the electrode surface. The evolution of oxygen from 5m KOH was studied on Ni–Co–P alloys prepared in this way. The Tafel parameters were determined and it was ascertained that the values of directional coefficients of the Tafel lines are comparable with those obtained for spinel NiCo₂O₄ oxides, while calculated values of the exchange currents for the oxygen evolution reaction are dependent on the chemical composition of the alloy. The rate of electrolytic oxygen evolution is virtually identical for amorphous and crystalline Ni–Co–P alloys of the same chemical composition. The highest rate of oxygen evolution was found for the alloy containing 15–20% Ni, 66–73% Co and 12–14% P.     

Stability of silicon nitride heated in air and in carbon monoxide

Conclusions Silicon nitride oxidizes in air at 1100–1500°C mainly with the formation of silica. An addition of NaF contributes to oxidation of the silicon nitride to silicon oxynitride.In a coke filling silicon nitride decomposes at 1450–1550°C into oxynitride and cubic silicon carbide.Additions of CaF₂ and MgO contribute to the conversion of the silicon nitride in a carbon monoxide atmosphere into the silicon oxynitride at 1550°C.Translated from Ogneupory, No.6, pp. 33–39, June, 1967.     

Co–SiO2 aerogel-coated catalytic walls for the generation of hydrogen

Cobalt–silica (Co–SiO₂) aerogel coatings were successfully grown on the walls of ceramic monolith channels, thus resulting in structured catalytic wall materials useful for gas–solid reactions. The preparation involved the synthesis in situ of SiO₂ gels by the sol–gel hydrolysis and condensation of tetraethylorthosilicate (TEOS), quenching at the gelation point, incorporation of Co by impregnation, and extraction of the solvent by supercritical drying. Characterization of the aerogel-coated monoliths revealed an excellent dispersion and homogeneity of the aerogel and good adherence properties. The catalytic performance of these materials in the ethanol steam reforming reaction addressed to obtain hydrogen was studied at atmospheric pressure by carrying out consecutive cycles at 473–773–473 K with a C₂H₅OH:H₂O  1:3 (molar) mixture and stability tests, and the results were compared with those obtained over monoliths prepared by conventional washcoating methods from Co–SiO₂ xerogel. Co–SiO₂ aerogel catalytic walls were about four times more active for hydrogen generation at 623 K than conventional monoliths. An unusual rapid activation of aerogel-coated monoliths was attained at 580–590 K, even after several cycles and oxidation treatments at 563–613 K, which was attributed to highly dispersed cobalt particles and higher effective diffusivity of reaction species due to high porosity and larger average pore size. The reproducible low-temperature activation of Co–SiO₂ aerogels supported on ceramic monoliths may be useful for the practical application of fuel reformers to the on-site generation of hydrogen from ethanol.     

Voltammetric study of plating baths for electrodeposition of Co-W amorphous alloys

Cyclic voltammetry and chronoamperometry at glassy carbon and platinum microdisc electrodes have been used to study the electrodeposition of Co–W amorphous alloys. Voltammetric results show that cathodic deposition of Co–W alloy is accompanied by hydrogen evolution and the efficiency of Co–W electrodeposition does not exceed 20%. Voltammetric behaviour of cobalt (II) and tungstate in ammonium citrate solution depend strongly on composition of the plating bath. The concentration of Co(II) ions can be monitoredin situ during electroplating by means of anodic stripping voltammetry at a platinum microelectrode. The deposit of the alloy on the microelectrode is stable in the atmosphere and thus can be stored for subsequent comparison with a deposit obtained later in the life of the working bath.     

CVD preparation of alumina-supported niobium nitride and its activity for thiophene hydrodesulfurization

Niobium nitride was synthesized on a Si(400) substrate and a γ-alumina pellet using a CVD method with a stream of NbCl₅/Ar, NH₃, and H₂ gases at 723–973 K under reduced pressure. The composition and surface properties of the deposited niobium nitride were analyzed using XRD and XPS measurements. The activity of alumina-supported niobium nitrides for the hydrodesulfurization (HDS) of thiophene at 673 K and atmospheric pressure was determined. The alumina had a surface area of 177 m² g⁻¹ and the alumina-supported niobium nitride catalyst had surface areas of 179–190 m² g⁻¹. Although the catalysts had low activity in the initial stages, the activity increased after 200–300 min started to about three times the initial activities. XPS analysis indicated that the activity of the niobium nitride catalysts was decreased by sulfur accumulation on the surface and nitrogen released from niobium nitride. The relationship between the surface properties of the niobium nitride catalysts and the activities for thiophene HDS is discussed.     

Activity of alumina-supported molybdenum nitride for carbazole hydrodenitrogenation

The alumina-supported molybdenum nitride catalyst was extremely active in the hydrodenitrogenation of carbazole at 553–633 K and 10.1 MPa total pressure when compared with the sulfided and reduced catalysts.     

Catalytic reduction of nitrous oxide with carbon monoxide over calcined Co–Mn–Al hydrotalcite

The N₂O catalytic reduction by carbon monoxide over Co–Mn–Al calcined hydrotalcite was studied. The effect of oxygen and that of CO/N₂O molar ratio on the rate of N₂O decomposition was examined. CO strongly enhanced N₂O conversion when O₂ was absent in the feed gas. In the presence of oxygen, carbon monoxide acts as a non-selective reductant thereby inhibiting N₂O destruction. Continuing excess of CO over N₂O without presence of O₂ led to a very slow reduction of the catalyst, which caused noticeable N₂O conversion decrease with progressing catalyst reduction. The simultaneous reduction of N₂O by CO and direct N₂O decomposition took place when CO was limiting reactant (CO/N₂O < 1) but only at temperatures, at which the direct decomposition is possible without presence of reductant. Simple reduction was observed when reactants ratio was CO/N₂O ≥ 1.     

Raman, FTIR and Theoretical Evidence for Dynamic Structural Rearrangements of Vanadia/Titania DeNOx Catalysts

Insight into the selective catalytic reduction (SCR) of NO by NH₃ over vanadia/titania catalysts is obtained from a combination of Raman and FTIR spectroscopic investigations and density functional theory (DFT) calculations. Studies of the V–OH and V=O functional groups under different conditions coupled with calculations of the stability and mobility of H atoms provide evidence that dynamic structural rearrangements may occur during the SCR reaction. Hydrogen atoms are bonded more strongly to oxygen atoms that are coordinated to a single vanadium atom (V=O species), compared to bonding at oxygen atoms that are coordinated to multiple vanadium atoms (e.g., V–O–V species); and, activation energy barriers for hydrogen transfer from a V=O species to another V=O species and to a V–O–V species are estimated from DFT calculations to be 60 and 130 kJ/mol, respectively. This dynamic nature of hydrogen transfer between oxygen atoms having different coordination environments also appears to explain some of the spectroscopic changes observed for vanadia/titania catalysts having different vanadia loadings.