Cobalt oxide, commercial preparation

The microstructure of commercial varistors is extremely complex, and commercial preparations also contain other dopants, mainly oxides of cobalt, manganese, chromium, and antimony, that are used to fine tune the varistor characteristics. The transition-metal dopants are chemically similar to Zn2+ and mainly form substitutional defects within the ZnO grains, such as CoZn, that modify the n-type behavior of the grain interior. (See also Chapter 8 for further discussion of the electronic... 

Cobalt(ll) oxide is used as a pigment for ceramics and paints for drying paints, varnishes and oils for coloring glass as a catalyst and for preparation of other cobalt salts. The commercial product is a mixture of cobalt oxides. 

Tricobalt tetroxide is a minor component of commercial cobalt oxides. It is used in ceramics, pigments, and enamels. Other applications are in grinding wheels, in semiconductors, and for preparing cobalt metal. 

Coball(lI) hydroxide exists in two allolropic forms, a blue or-Co (OH) and a pink /l-Co(OH) . The hydroxide is prepared by precipitation from u cobaltous salt solution by an alkali hydroxide. When the alkali is in excess the pink ft form is produced—the blue a-furni is produced when the cobalt salt is in excess. The salt slowly oxidizes in air at mom temperature and changes to hydrated cobaltic oxide, Co-Oi - H 0. The hydroxide is practically insoluble in H 0 and in bases, but highly soluble in mineral and organic acids. The commercial salt is used as Ihe starting material in the preparation of drying agents. 

A total of206 mg [119] of commercial Cu/Zn catalyst from SiidChemie (G-66MR) ground to the nanometer range was coated into the channel system at 5 pm thickness to promote the steam reforming reaction. A cobalt oxide catalyst was prepared by impregnating the corundum layer (see above) with cobalt nitrate and calcining at 350 °C for 2 h 434 mg [119] of the CoO catalyst were applied for the combustion reaction (see Section 2.5). 

Silica-supported cobalt catalysts were prepared from cobalt nitrate (Co(N03)2), lanthanum nitrate (La(N03)3) and commercially available silica gel (Fuji Davison, ID gel, 270 m /g) using conventional methods of impregnation [14]. The composition of the catalyst was Co La Si02 = 20 6 87 by weight. The catalyst precursor was dried in air at 120°C and then calcined at 450 °C for 3 h to form supported metal oxides. It was then exposed to hydrogen at 400 °C for 12 h. The mean pore diameter of the catalyst was 8.7 nm. 

Preparing LiNi02 with an excess amount of Li was found to be one of the methods to produce stoichiometric cathode material. Another, even more effective method for stabihzing the lithium nickel oxide structure was the introduction of cobalt and thus formation of the hthiated nickel cobalt oxide derivatives of LiNi02 material. These findings led to laboratory development and commercial production of various derivatives of lithium nickel oxide, summarized in Table 1.4. 

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

Many perfluoroaUphatic ethers and tertiary amines have been prepared by electrochemical fluorination (1 6), direct fluorination using elemental fluorine (7—9), or, in a few cases, by fluorination using cobalt trifluoride (10). Examples of lower molecular weight materials are shown in Table 1. In addition to these, there are three commercial classes of perfluoropolyethers prepared by anionic polymerization of hexafluoropropene oxide [428-59-1] (11,12), photooxidation of hexafluoropropene [116-15-4] or tetrafluoroethene [116-14-3] (13,14), or by anionic ring-opening polymeriza tion of tetrafluorooxetane [765-63-9] followed by direct fluorination (15). 

F-T Catalysts The patent literature is replete with recipes for the production of F-T catalysts, with most formulations being based on iron, cobalt, or ruthenium, typically with the addition of some pro-moter(s). Nickel is sometimes listed as a F-T catalyst, but nickel has too much hydrogenation activity and produces mainly methane. In practice, because of the cost of ruthenium, commercial plants use either cobalt-based or iron-based catalysts. Cobalt is usually deposited on a refractory oxide support, such as alumina, silica, titania, or zirconia. Iron is typically not supported and may be prepared by precipitation. 

The cobalt carbonate basic salt is the commercially-used cobalt carbonate. It is used primarily for manufacturing cobalt pigments. It also is used to prepare cobalt(II) oxide and other cobalt salts. 

The catalysis of the selective oxidation of alkanes is a commercially important process that utilizes cobalt carboxylate catalysts at elevated (165°C, 10 atm air) temperatures and pressures (98). Recently, it has been demonstrated that [Co(NCCH3)4][(PF6)2], prepared in situ from CoCl2 and AgPF6 in acetonitrile, was active in the selective oxidation of alkanes (adamantane and cyclohexane) under somewhat milder conditions (75°C, 3 atm air) (99). Further, under these milder conditions, the commercial catalyst system exhibited no measurable activity. Experiments were reported that indicated that the mechanism of the reaction involves a free radical chain mechanism in which the cobalt complex acts both as a chain initiator and as a hydroperoxide decomposition catalyst. 

Cobaltous carbonate, C0CO1. is found almost pure in the mineral sphaerocobaltile in the Republic of Zaire and less extensively in Zambia. The pale-red anhydrous salt is obtained by reaction in solution of an alkaline carbonate and a cobaltous salt under a slight pressure of carbon dioxide (up 10 I atmosphere) and subsequent heating at 140 C The commercial salt is violet-red in color, partially hydrolyzed with an indeterminate composition. It is insoluble in H 0 and alcohol, bul dissolves easily in inorganic and organic acids, and is often used for the preparation of other salts. According to the thermal conditions it decomposes to the different types of oxides. 

Preparation of Cobalt.—The metallurgy of cobalt is complicated by the fact that cobalt ores invariably contain a certain amount of nickel. Since these two metals closely resemble one another in their chemical properties it will be evident that their complete separation on a commercial scale is a matter of considerable difficulty. It is not usually required, however. The details of the actual methods employed in the commercial production of cobalt are kept fairly secret, more particularly as regards the initial stages of the preparation of the crude oxide. We shall, therefore, content ourselves by giving in outline accounts of a few different methods that may be employed. It is convenient to discuss the subject in three sections, namely ... 

The chromium carbonyl linkers 1.40 (98) and 1.41 (99) were prepared from commercial triphenylphospine resin and respectively from pre-formed p-arene chromium carbenes and Fischer chromium amino carbenes. Their SP elaboration is followed by cleavage with pyridine at reflux for 2 h (1.40) and with iodine in DCM for 1 h at rt (1.41) both linkers produce the desired compounds in good yields. A similar cobalt carbonyl linker 1.42 (100) was prepared as a mixmre of mono- (1.42a) and bis- (1.42b) phosphine complex, either from pre-formed alkyne complexes on triphenylphosphine resin or by direct alkyne loading on the bisphosphine cobalt complex traceless cleavage was obtained after SP transformations by aerial oxidation (DCM, O2, hp, 72 h, rt) and modified alkynes were released with good yields and... 

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