Negatively Charged Metallacarborane Redox Couples with Both Members Stable to Air

The metallacarborane [3,3′‐Co(1,2‐closo‐C₂B₉H₁₁)₂]^? has been synthesized. This species allows the formation of redox couples in which both partners are negatively charged. The E_1/2 potential can be tuned by adjusting the nature and number of substituents on B and C. The octaiodinated species [3,3′‐Co(1,2‐closo‐C₂B₉H₇I₄)₂]^? is the most favorable, as it is isolatable and stable in air. A DFT study on stability and redox potentials of complexes has been performed.     

Cobalt Based Nanoparticles Embedded Reduced Graphene Oxide Aerogel for Hydrogen Evolution Electrocatalyst

Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS₂, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm^?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec^?1 and a charge transfer resistance (R_ct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer.     

Über die Magnetischen Eigenschaften der Cobaltate Na6CoS4, Na6CoSe4 und K6CoS4

Magnetic Properties of the Cobaltates Na₆CoS₄, Na₆CoSe₄, and K₆CoS₄ The alkali metal cobalt chalcogenides Na₆CoS₄, Na₆CoSe₄, and K₆CoS₄ crystallize in the space group P6₃mc with Z = 4. The structure is characterized by isolated [CoX₄]-tetrahedra. The magnetic susceptibilities show Curie-Weiss behaviour. The deviations at low temperatures are caused by antiferromagnetic interactions. The magnetic moments are discussed with regard to ligand-field parameters.     

Liquid phase oxidation of p-chlorotoluene to p-chlorobenzaldehyde over cobalt-doped mesoporous titania with a crystalline framework

Cobalt-doped mesoporous titania with a crystalline framework synthesized by surfactant templating method presented highly selective (99%) and reasonable conversion rate (49%) of catalytic oxidation of para-chlorotoluene to para-chlorobenzaldehyde in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. By contrast, cobalt-doped mesoporous titania without a crystalline structure and cobalt doped the commercial titania, Degussa P25 prepared by impregnation method with the similar concentration of cobalt were found inactive. The effects of catalyst concentration, reaction time, reaction temperature, and solvents on the performance of the catalyst were also investigated.     

Microwave absorption properties of composite powders with low density

The composites of barium ferrite coated on hollow ceramic microspheres were prepared using sol-gel technique. The crystal structure, morphology and microwave absorption properties of composite powders with different weight ratio of microspheres were studied with XRD, EDS, FESEM and vector network analyzer. The results show that the microwave absorption properties of composite powders are greatly improved. The maximum microwave loss of composite powders reaches 31 dB with an amount of 50 wt.% microspheres, and its density is only about 1.80 g/cm³. The effect of hollow ceramic microspheres on the microwave absorption property is also discussed.     

磁性钴纳米晶的二维自组装

在两种表面活性剂存在下，采用高温醇还原，合成出单分散、平均颗粒尺寸为14±19nm，直径标准偏差小(～18%)的磁性金属Co纳米晶.利用x射线衍射、紫外吸收光谱、x射线光电子能谱及透射电子显微镜对其结构和表面价态进行了分析.并将磁性金属Co纳米晶自组织形成有序的二维(2D)六方紧密堆积结构. 关键词： Co纳米晶 单分散 自组装     

钴（Ⅱ）—丁二酮单肟烟酰腙—亚硝酸盐体系的伏安行为及其应用

在氨性介质中(pH=9.0),钴(Ⅱ)-丁二酮单肟烟酰腙(DMNH)-亚硝酸盐体系可产生灵敏度很高的催化波。从体系的伏安行为可知,吸附于汞电极上的是混配的配盐NH_4[Co(Ⅱ)(DMNH)·(NO_2)_2],在-1.0 V(相对SCE)处,Co(Ⅱ)被还原至Co(0),DMNH被还原成自由基,由于NO_2~-的存在,自由基可参与再生反应而形成催化波。羟氨的存在可使产生催化波的最佳pH值移至8.2.用此体系进行了生物样品中钴的测定,其检出限为1×10~(-10)mol/L。     

Preparation and microwave absorption properties of electroless Co-Ni-P coated strontium ferrite powder

A new type of Co-Ni-P coated strontium ferrite nanocomposite was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The plating process was studied carefully. The morphology, crystal structure and microwave absorption properties of the Co-Ni-P coated powder were studied with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDX) and vector network analyzer. The results show that the strontium ferrite powder was successfully coated with Co-Ni-P alloy and possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −44.12 dB. The bandwidth with the loss above −10 dB exceeds 13.8 GHz.     

Microkinetic modelling of the formation of C1 and C2 products in the Fischer-Tropsch synthesis over cobalt catalysts

The heats of adsorption of different C₁ and C₂ molecules assumed to be present during the initial steps of the Fischer-Tropsch synthesis and activation energies for elementary steps envisioned to occur in the synthesis are calculated for Co by using the unity bond index-quadratic exponential potential (UBI-QEP) method. The preexponential factors for the elementary steps are calculated from transition-state theory, and the rate constants are calculated according to the Arrhenius equation. The activation barrier for hydrogenation of CO is found to be lower compared to hydrogen assisted dissociation of CO, which has a smaller activation barrier than direct dissociation of CO. The reaction steps with high activation barriers are eliminated. Based on this elimination two sets of elementary steps for formation of C₁ and C₂ alkenes and alkanes in the Fischer-Tropsch synthesis are established: one based on hydrogen assisted CO dissociation (carbide mechanism) and one based on CO hydrogenation (CO insertion mechanism). In addition, one mechanism of producing CO₂ from the water-gas shift reaction is proposed. The resulting mechanisms are combined and used in the microkinetic model, which are fitted to experimental results at methanation conditions (T = 483 K or 493 K, p = 1.85 bar and H₂/CO = 10) over a Co/Al₂O₃ Fischer-Tropsch catalyst. A good tuning is obtained by adjusting the C-Co and H-Co binding strengths. The microkinetic modelling based on these assumptions indicates that CO is mainly converted through hydrogenation of CO and that C₂ compounds are mainly produced by insertion of CO into a metal-methyl bond. Thus, from the surface coverages and reaction rates predicted by the microkinetic modelling the mechanism can be further reduced to only include the CO insertion mechanism. Hydrogenation of CHO to CH₂O is found to be the rate determining initiation step, and insertion of CO into a metal-methyl bond is found to be the rate determining step for chain growth. By using the UBI-QEP method for calculation of activation energies, the activation barriers for dissociation of CO and hydrogenation of surface carbon are found to be too large for the carbide mechanisms to occur. However, experimental data or another theoretical method is necessary in order to support or disprove the calculated activation energies in this work.