Spinel cobalt

A clear advantage of alkaline electrolysers is the use of nickel-based electrodes, thus avoiding the use of precious metals. Catalytic research is aimed at the development of more active anodes and cathodes, primarily the development of high surface area, stable structures. Nickel-cobalt spinel electrodes for oxygen evolution and high surface area nickel and nickel cobalt electrodes for hydrogen evolution have been shown at the laboratory scale to lead to a decrease in electrolyzer cell voltage [47]. More active electrodes can lead to more compact electrolysers with lower overall systems cost. 

Keyser et al. studied Mn-Co F-T catalysts and found that, under industrial relevant conditions, the WGS activity of the catalysts increases with increasing Mn content, but decreases with increasing pressure. A lower olefin yield was also observed at high pressures. It was stated that structural changes in the cobalt spinel occur over a long period of time and are responsible for the increased hydrogenation activity and increased WGS activity. Mn seems in this... 

A/cm2, 90°C, 30 wt% KOH) with time during a batch experiment demonstrating in situ activation. Evidently the addition of only 10 mg/cnr of cobalt in the form of cobaltous nitrate, which is decomposed by generating soluble Co(OH)fand Co(OH)4 species, results in reduction of the anodic overpotential (+340 mV) by more than 50 mV. This is due to the anodic deposition of a thin film of electrocatalytically active cobalt spinell, C04O4, according to... 

Figure 1. XRD patterns of (A) CoAI-LDH and (B) CoAISn-LDH calcined at different temperatures for 5h CS - cobalt spinel, CT -Co2Sn04 inverse spinel... 

FIGURE 6.18 Linear scan voltammograms for (a) cobalt spinel, (b) a-cordierite, (c) P-cordierite, and (d) CoO, attached to paraffin-impregnated graphite electrodes immersed into 1.0 M HCl. Potential scan rate 20 mV/sec. 

Condom, S. et al.. Behaviour of cobalt spinel ultrali Ill ation membrane during salt filtration with different ionic strengths, J. Membr. Sci., 268, 175, 2006. 

Hydrotalcite-like compounds (HTlcs) have attracted much attention in recent years as catalyst precursors and catalyst support. This is due to (i) their ability to accommodate a large variety of bivalent and trivalent cations (ii) the homogeneous mixture of the cations on an atomic scale and (iii) the formation of thermostable mixed oxides, often denoted as ex-HTlcs, with high surface area upon decomposition. The first two properties are a result of the precursor while the last property appears to be related to the decomposition mechanism. The transitions in the structural properties of Co-based hydrotalcites upon high temperature treatments have been extensively studied in our group.15,16 In the first decomposition step, water is removed from the structure. This transition is followed by dehy-droxylation and decarbonation, as well as carbonate reorganization in the interlayer. Thermal treatment in air finally leads to a solid solution of cobalt spinels (Co(Co, A1)2C>4). Mixtures of CoO and C0AI2O4 are formed upon treatment in inert. 

This change in b can be either due to a change in the surface oxide-layer composition or due to a change in the active site characteristics caused by the surface interactions. Otherwise, the change in b reported for crystalline Ni-Co alloys in alkaline solutions has also been explained by the different nature of the surface oxides [27]. It is also important to say that the nickel and cobalt-spinel voltammetric behavior is attained after potential cycling at a low scan rate, where b = 0.04 V decade-1. However, a pre-anodization at 1.8 V vs. RHE led to a Co304 spinel electrode for which b = 0.06 V decade-1. 

Linde et al. (138) have studied propene oxidation under static conditions at low pressures over manganese-cobalt spinels. The reaction rate was found to be proportional to coverage of the surface with oxygen and independent of the hydrocarbon concentration. 

Klissurski et al. [87] have examined the combustion of acetone, toluene and styrene by zinc-cobalt spinel oxides supported on alumina. Catalysts were prepared by co-precipitation with sodium carbonate from a mixed zinc/cobalt nitrate solution at pH 9. The supported catalyst was prepared by deposition of the precursor on Y-AI2O3 from a suspension in dimethylformamide and water. The supported precursor was dried at 150°C and calcined at 300°C to produce the catalyst. The bulk and supported catalysts both showed the formation of zinc cobaltite spinel structures which were thermally stable. Microreactor studies at 15,000 h- space velocity showed that the components of a mix of acetone, toluene and styrene were destroyed at 225°C, 280°C and 350°C respectively. The VOC concentrations were not specifically expressed but it is assumed that they... 

Platinum and silver are aetive eatalysts in reaetion of electroreduction of oxygen. However wide use of such catalysts is limited by their high cost and deficiency. Several types of catalysts for oxygen (air) electrodes have been elaborated and investigated in Laboratory of Fuel Cells. They are activated by carbon (coal)-pure and modified, promoted by soot, complex oxides of transition metals, especially by nickel-cobalt spinel [3,4]. 

Advantages of oxygen (air) electrodes made of nickel-cobalt spinel are high electrochemical activity, relatively low cost and satisfactory thermodynamic stability. Life time reached 1000 hours at room temperature for air electrodes from nickel-cobalt spinel in alkaline electrolyte at a current density equal 100 mA/cm. Developed air (oxygen) electrodes ensure current density equal 100-150 mA/cm at polarization 0,2 V at room temperature. 

Several anode coatings not mentioned in Table 4.5.6 have been examined for use in chlor-alkali cells. The interesting compositions are Pt-Ir on titanium [114,115], cobalt spinels [116-118], PdO-based coatings [111], and platinates [119,120]. 

A. (2013) Rationales for the selection of the best precursor for potassium doping of cobalt spinel based deN20 catalyst AppL Catal B, 136-137,302-307. 

Stelmachowski, P Maniak, G., Kaezmarezyk, J., Zasada, F., Piskorz, W., Kotarba, A., and Sojka, Z. (2014) Mg and A1 substituted cobalt spinels as catalysts for low temperature deN20—evidence for octahedral cobalt active site. Appl. Catal... 

Tihay, F., Pourroy, G., Richard-Plouet, M., Roger, A.C., and Kiennemann, A. (2001) Effect of Fischer-Tropsch synthesis on the microstructure of Co-Fe based cobalt/ spinel composite materials. Appl Catal. A, 206, 29-49. 

Cobalt aluminium oxide does occur naturally as the rare blue gemstone, cobalt spinel. It is commonly referred to historically as cobalt blue q.v.), with various other common terms related to those who discovered and developed it in the late eighteenth and early nineteenth centuries. Interestingly, however, the compound appears to have been also known in Dynastic Egypt. 

C Liu, B Zou, AJ Rondinone, ZJ Zhang. Chemical control of supeiparamagnetic properties of magnesium and cobalt spinel ferrite nanoparticles through atomic level magnetic couplings. J Am Chem Soc 2000 122 6263. 

E. Manova, T. Tsoncheva, C. Estoumes, D. Ptmeva, K. Tenchev, I. Mitov, L. Petrov, Nanosized iron and iron-cobalt spinel oxides as catalysts for methanol decomposition. Appl. Catal. A Gen. 300, 170-180 (2006)... 

From experimental work with precipitated cobalt-iron catalysts it appeared that the cobalt reacted with alumina giving cobalt spinels, which helped to form smaller iron and cobalt crystallites during reduction and to increase the surface area to make the catalyst more stable and less sensitive to oxide forming poisons. In the presence of potash, cobalt was able to decrease the reduction temperature. 

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