Oxides of cobalt

Impure C0O2 (oxidizing agent on alkaline Co(ll)) and some mixed oxides of cobalt(lV) and (V), e.g. K.3C0O4, are known. 

For this reaction, charcoal is a catalyst if this is omitted and hydrogen peroxide is used as the oxidant, a red aquopentammino-cobalt(lll) chloride, [Co(NH3)jH20]Cl3, is formed and treatment of this with concentrated hydrochloric acid gives the red chloro-p0itatnmino-coba. t(lll) chloride, [Co(NH3)5Cl]Cl2. In these latter two compounds, one ammonia ligand is replaced by one water molecule or one chloride ion it is a peculiarity of cobalt that these replacements are so easy and the pure products so readily isolated. In the examples quoted, the complex cobalt(III) state is easily obtained by oxidation of cobalt(II) in presence of ammonia, since... 

Cobalt(II) acetylacetonate [14024-48-7] cobalt(II) ethyUiexanoate [136-52-7] cobalt(II) oleate [14666-94-5] cobalt(II) linoleate [14666-96-7] cobalt(II) formate [6424-20-0], and cobalt(II) resinate can be produced by metathesis reaction of cobalt salt solutions and the sodium salt of the organic acid, by oxidation of cobalt metal in the presence of the acid, and by neutralization of the acid using cobalt carbonate or cobalt hydroxide. 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

Metal oxides, sulfides, and hydrides form a transition between acid/base and metal catalysts. They catalyze hydrogenation/dehydro-genation as well as many of the reactions catalyzed by acids, such as cracking and isomerization. Their oxidation activity is related to the possibility of two valence states which allow oxygen to be released and reabsorbed alternately. Common examples are oxides of cobalt, iron, zinc, and chromium and hydrides of precious metals that can release hydrogen readily. Sulfide catalysts are more resistant than metals to the formation of coke deposits and to poisoning by sulfur compounds their main application is in hydrodesulfurization. 

In the preparation of a)balt(III) hexaammine salts by ihe aerial oxidation of cobalt(II) in aqueous ammonia it is possible, in the absence... 

Zaffer, m. zaffer, zaffre (impure oxide of cobalt). Zaffetika, /. asafetida. 

The advantage is an oxidation temperature of 500°F compared to non-catalytic combustion of 1500°F. The active ingredients used were platinum, as well as the base metal oxides of cobalt, nickel, manganese, chromium, and iron. The support material included nickel-chromium ribbons, ceramics rods, beads, and pellets (13-17). 

Murray J.W., Dillard J.G. The oxidation of cobalt (II) adsorbed on manganese oxide. Geochim Cosmochim Acta 1979 43 781-787. 

Only two oxides of cobalt have been characterized, CoO and Co304 (which is actually ConConl04). The latter has a structure in which Co2+ ions are located in tetrahedral holes and Co3+ ions are located in octahedral holes of a spinel structure. Decomposition of either Co(OH)2 or CoC03 produces CoO, and decomposition of Co(N03)2 can be used to produce Co304. 

The oxidation of cobalt metal to inactive cobalt oxide by product water has long been postulated to be a major cause of deactivation of supported cobalt FTS catalysts.6 10 Recent work has shown that the oxidation of cobalt metal to the inactive cobalt oxide phase can be prevented by the correct tailoring of the ratio Ph2cJPh2 and the cobalt crystallite size.11 Using a combination of model systems, industrial catalyst, and thermodynamic calculations, it was concluded that Co crystallites > 6 nm will not undergo any oxidation during realistic FTS, i.e., Pi[,()/I)i,2 = 1-1.5.11-14 Deactivation may also result from the formation of inactive cobalt support compounds (e.g., aluminate). Cobalt aluminate formation, which likely proceeds via the reaction of CoO with the support, is thermodynamically favorable but kinetically restricted under typical FTS conditions.6... 

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... 

There seems to be several mechanisms leading to the activity loss oxidation of cobalt metal, sintering of cobalt metal particles as well as sintering of the support and formation of stable cobalt-support metal oxides (silicates or aluminates). Oxidation by water is a key issue, possibly occurring on all supports and on unsupported cobalt. A thermodynamic analysis of this effect was reported by van Steen et al.,40 and they describe the FTS reaction system in terms of reactions (1) and (2) below ... 

In terms of the effect of water on the deactivation, several mechanisms have been identified, and they will influence the stability of the catalyst depending on the conditions and the support used. At high partial pressures of water oxidation is always a possibility, but the various reports are less clear to whether this is mainly surface oxidation of cobalt particles irrespective of particle size, or if small particles... 

P. J. van Berge, J. van de Loosdrecht, S. Barradas and A. M. van der Kraan, Oxidation of cobalt based Fischer-Tropsch catalysts as a deactivation mechanism, Catal. Today, 2000, 58, 321-334. 

The oxidation of cobalt(II) in the organic phase can be minimized by the addition of donor molecules, such as the solvating extractants. 

Spectra of the oxides of cobalt CoO and C08O4 are shown in Fig. 14. Locations of the principal peak, at 18 and 24 ev., respectively, correlate with the valences. The extension of the fine structure throughout the 200 ev. range studied is in line with the simple crystal structures of these oxides. 

It is oxidized by air or weak oxidizing agents, forming cobalt(III) carbonate, Co2(C03)3. It decomposes on heating, forming the oxides of cobalt with the evolution of CO2. 

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