Layered cobalt hydroxides

Layered Cobalt Hydroxides. The above results demonstrate the importance of the interlayer Co rather than the framework cobalt, in forming the required metallic Co catalyst. A structure with optimal catalytic activity would consist of one where there were only Co/Al hydroxide sheets, a structure closely approximated to by the hydrotalcite series of double layered hydroxides. 

Lotmar and Feitknecht investigated variations in ionic distances of bivalent basic metal halogenides with layered structures of the Cdl2 type. In this context they needed the unit cell dimensions of nickel hydroxide as well as cobalt hydroxide. 

PREPARATION AND CHARACTERISATION OF COBALT CONTAINING LAYERED DOUBLE HYDROXIDES... 

In addition to the exclusion of carbon dioxide, it is necessary to exclude oxygen from reactions where cations of the metal hydroxide layer are easily oxidized under basic conditions. LDHs of this type include manganese, cobalt (131) and iron in the divalent oxidation state, and vanadium in the trivalent state. Reactions involving these metal ions have formed LDHs with, for instance, Co " /Co and Fe " /Fe metal content, with the latter, known as green rust, being discussed earlier in Section II.J. 

Nickel hydroxide active material is provided by reacting nickel sulfate solution and an alkaline solution. A part of nickel of nickel hydroxide is substituted for Zn and Co for the improvement of the battery performance. The theory capacity of nickel hydroxide is 289 mAh/g by supposing one electron reaction. The utilization of nickel hydroxide of a sintered-type electrode is approximately 100 %, but that of a pasted-type electrode without a conductive additive is around 65 %. The improvement of the utilization is enabled by forming CoOOH conductive networks between nickel hydroxide particles. The cobalt compound (Co, CoO, Co(OH>2) is filled into the formed nickel substrate with nickel hydroxide as an additive. The Co compounds form a conductive network as CoOOH by charging. To improve the conductivity of the cobalt conductive layer, Co(OH)2 layer coating to the surface of nickel hydroxide particles and the oxidation treatment in an alkaline solution of this coated powder are suggested. 

Impedance analysis is a powerful thermoelectrochemical instrument. It proved useful to study the capacity of cobalt hydroxide film formation in double-layer electrolyte capacitors [56]. Also, experiments with the capacity of electrodes in solid state electrolytes have been published, e.g. with silver hahde/graphite... 

Anionic complexes can easily be prepared by the sulfonation of the aromatic rings in the complexes. Sulfonated cobalt phthalocyanine intercalated in a layered double hydroxide host was a stable catalyst for the oxidation of thiols162,163 and phenol derivatives.164 It was concluded that the complex has been intercalated with the plane of the phthalocyanine ring perpendicular to the sheet of the host (edge-on orientation) (Fig. 7.2). 

There are probably several mineral phases, particularly for the highly alkaline systems, that remain to be discovered. Mixed hydroxides may control solubility. Calcium zincate (CaZn2(OH)6), for example, is thermodynamically more stable than Zn(OH)2 above pH 11.5 and may be important in cementitious systems. Another group of minerals is that of the hydrotalcite-like minerals, the layered double hydroxides (LDH, M2+2M3+l/yXy (OH)6 where X is an anion). Cobalt, Ni and Zn can form such minerals (Johnson Glasser 2003) under neutral to alkaline conditions. For the majority of species, however, solubility-limiting phases do not appear to control dissolved concentrations. 

Recently, the cobalt(II)-tetrasulfonatophthalocyanine system was reinvestigated for its catalytic activity while intercalated into a Mg5Al2 -layered double hydroxide. The intercalate exhibited catalytic properties in the activation of atmospheric dioxygen for the oxidation of a thiolate to a disulfide (97a) and for the oxidation of 2,6-di-tert-butylbenzene to (nearly exclusively) the 2,6,2, 6 -tetra-tert-butyldiphe-noquinone (97b). In marked contrast to the results reported for the homogeneous catalyst, this intercalated catalyst remained active for... 

Ukrainczyk, L., Chibwe, M., Pinnavaia, T.J. Boyd, S. A. (1994). ESR study of cobalt(II) tetrakis(N-methyl-4-pyridiniumyl)porphyrin and cobalt(II) tetrasulfophthalocyanine intercalated in layered aluminosilicates and a layered double hydroxide. Journal of Physical Chemistry, 98, 2668-76. 

Table 1 shows the properties of smectite-type materials prepared. Smectite materials prepared at lower pH had fewer sodium ions, higher surface areas, and larger pore volumes for a series of samples containing the same divalent cation species (nickel and cobalt) in the octahedral sheet. The adsorption of methylene blue on all the synthetic smectites shows that the smectite fragments are negatively charged. The Si M ratios of synthetic smectites were about 8 6, indicating that most of divalent cations exist in octahedral layers and small amount of divalent cations would exist as hydroxide or oxide cluster in smectite materials. However, the amounts of the hydroxide or oxide cluster were small, because only smectite structures were observed in XRD patterns and EXAFS Fourier transforms of synthetic smectites calcined at 873 K. 

Impregnation of cobalt and molybdenum (without sodium) increases largely the isomerizing activity of the catalyst the /3-pinene is then completely converted. The catalysts prepared with sodium molybdate and sodium hydroxide (Co-Mo-Na and Na-Co-Mo-Na) have lower isomerizing activities while their HDS activities are significantly increased. As in the case of alumina supported catalysts the sulfided CoMo phase protected by a double layer of alkaline ions on the carbon support gives the best results in HDS of /3-pinene. The behaviour of this catalyst was examined in desulfurization of the turpentine oil (40% a-pinene, 25% /3-pinene, 25% A -carene and 10% camphene + dipentene + myrcene, 1500 ppm S). The results are recorded in Table 6. 

A hydroxide suppression model first proposed by Dahms and Croll (2) explains anomalous codeposition behavior of zinc-iron group alloys. This explanation was later supported by a number of workers (3) who measured a rise in pH near the cathode surface during the deposition of Zn-Co alloy. In this model it was assumed that the Zn(OH)2 was formed during deposition as a consequence of hydrogen evolution, thus raising pH in the vicinity of the cathode. Zinc would deposit via the Zn(OH)2 layer, while cobalt deposition took place by discharge of Co2+ ions... 

Perez Bernal, M. E., Ruano Casero, R. and Pinnavaia, T. J. (1991). Catalytic autoxidation of 1-decanethiol by cobalt(II) phthalocyaninetetrasulfonate intercalated in a layered double hydroxide. Catal. Lett. 11, 55. 

Chibwe, M. and Pinnavaia, T. J. (1993). Stabilization of a cobalt(II) phthalocyanine oxidation catalyst by intercalation in a layered double hydroxide host. J. Chem. Soc., Chem. Commun., 278. 

Cobalt Clays and Double-Layered Hydroxides as Fischer—Tropsch Catalysts... 

BRUCEETAL. Cobalt Clays Double-Layered Hydroxides... 

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