Cobalt metal, reactions

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

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. 

When permanganate ions in aqueous solution react with cobalt metal in strong add, the equation for the reaction that takes place is... 

Calciothermic reduction of samarium oxide, in the presence of cobalt powder, yields samarium-cobalt alloys in the powder form. The process is popularly known as reduction diffusion. Samarium oxide, mixed with cobalt powder and calcium hydride powder or calcium particles, is heated at 1200 °C under 1 atm hydrogen pressure to produce the alloys. Cobalt oxide sometimes partly replaces the cobalt metal in the charge for alloy preparation. This presents no difficulty because calcium can easily reduce cobalt oxide. A pelletized mixture of oxides of samarium and cobalt, cobalt and calcium, with the components taken in stoichiometric quantities, is heated at 1100-1200 °C in vacuum for 2 to 3 h. This process is called coreduction. In reduction diffusion as well as in coreduction, the metals samarium and/or cobalt form by reduction rather quickly but they need time to form the alloy by diffusion, which warrants holding the charge at the reaction temperature for 4 to 5 h. The yield of alloy in these processes ranges from 97 to 99%. Reduction diffusion is the method by which most of the 500 to 600 t of the magnetic samarium-cobalt alloy (SmCOs) are produced every year. 

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... 

It was concluded that in this case an equilibrium existed which gave 100 ppm of soluble cobalt at reaction temperature. The polymer support acted as a reservoir for furnishing soluble metal at reaction temperature and reabsorbing it after completion (about 10 ppm in the product after cooling to ambient temperature). The rate approximated that obtained in a standard cobalt reaction with 100 ppm of cobalt catalyst. 

Two aspects of porphyrin electrosynthesis will be discussed in this paper. The first is the use of controlled potential electroreduction to produce metal-carbon a-bonded porphyrins of rhodium and cobalt. This electrosynthetic method is more selective than conventional chemical synthetic methods for rhodium and cobalt metal-carbon complexes and, when coupled with cyclic voltammetry, can be used to determine the various reaction pathways involved in the synthesis. The electrosynthetic method can also lead to a simultaneous or stepwise formation of different products and several examples of this will be presented. 

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 ... 

The above value of k4 1 s for bpy loss from Rh(bpy)3 + may be compared with k4 - 3 s for bpy loss from the formally related Co(bpy)32+ (13,14) Recently obtained results indicate that the rate constant for addition of bpy to Rh(bpy)2(H2O)2 (k 4 s 0.2 x lO Ms"1) is greater than that for the comparable cobalt(II) reaction (13,14) The more-or-less comparable labilities of Rh(bpy)3 T and Co(bpy)3 + are not unexpected in light of data for rates of ammonia loss from the two metal centers which are also available ammonia loss from rhodium(II) is quite rapid (10 s 1 to 10 s l with loss from Rh(NH3)5 H20 + being much faster than from Rh(NH3)4 +, etc ) W t>ut somewhat slower than the comparable process for cobalt(II) (15) Of course, here the relative affinities of the two metals for NH3 are not known and so cannot be taken into account A further reason these comparisons lack great validity is that, although these Co(II) complexes contain 3d metal centers, Co(bpy)3 + and Co(NH3)n + are high-spin complexes i.e. the ground states are (t2g) (eg) whereas 4d species are expected to be low spin, (t2g) (eg)1. Furthermore, as will be seen shortly it is not clear that even "low spin 4d " is an adequate description of the... 

Cobalt octacarbonyl is used as a catalyst in the Oxo process (see Carbon Monoxide). It also is used as a catalyst for hydrogenation, isomerization, hydrosilation and polymerization reactions. The compound is also a source of producing pure cobalt metal and its purified salts. 

Metal-Nitrogen Compounds The cobalt catalyzed reaction of primary and secondary amines with carbon monoxide leads to the formation of formamide derivatives. Dimethylamine, for example, gives iV,i T-dimethvlformamide in 60% yield (90, 91). Very likely cobalt-nitrogen compounds are intermediates which undergo a CO insertion and then reduction. The following mechanism has been suggested for the reaction (90). 

Scope of the Review Paper. - From the above reasoning it is clear that over the past decades a large number of studies have been reported on supported cobalt F-T catalysts. All these studies indicate that the number of available surface cobalt metal atoms determines the catalyst activity and attempts to enhance the catalytic activity have been focusing on two interconnected issues (1) to reduce the cobalt-support oxide interaction and (2) to enhance the number of accessible cobalt atoms available for F-T reaction. It has been shown that the number of catalytically active cobalt atoms as well as their selectivity can be largely enhanced by the addition of small amounts of various elements, called promoters, to the catalyst material. The exact role of these promoters - as is the case for many other heterogeneous catalysts as well -remains often, however, unclear. 

The partial pressure of CO necessary to maintain Co2(CO)8 in solution rises rapidly with temperature. The decomposition of Co2(CO)g may, however, be kinetically slow in the absence of compounds which could catalyze this conversion (56), and the decomposition process is reported to be autocatalytic (59). Thus, a catalytic reaction was possible in an unstable temperature-pressure region for some time before cobalt metal precipitation became noticeable. Although operation with a metastable catalyst may be possible in short batch experiments, it would be undesirable in a continuous reaction where stability over extended periods is essential. 

Fahey presents the products of (17) as uncomplexed formaldehyde and HCo(CO)3 rather than a bound-formaldehyde species (43). Free formaldehyde is a thermodynamically unfavorable product from H2 and CO (8), and significant stabilization may be expected as the result of coordination in a metal complex. However, thermodynamic calculations are presented which indicate that small equilibrium concentrations of formaldehyde could be present under the conditions of these cobalt-catalyzed reactions (43). Although small amounts of uncoordinated formaldehyde are indeed expected as a result of the following endothermic (36, 37) equilibrium ... 

CoH(CO)4], formed in situ when cobalt metal or cobalt(II) salts are reacted with synthesis gas at elevated temperature under pressure, is the active species in the cobalt-catalyzed reaction.14,17,18 It is also capable of stoichiometric... 

In the nickel- and cobalt-catalysed reactions [166,207] it was observed that the butene distribution depended upon the temperature of reduction of the catalyst. For both powders and alumina-supported catalysts prepared by reduction of the oxides, reduction at temperatures below ca. 330° C gave catalysts which exhibited so-called Type A behaviour where but-2-ene was the major product and the frans-but-2-ene/cis-but-2-ene ratio was around unity. Reduction above 360° C (Ni) or 440° C (Co) yielded catalysts which gave frans-but-2-ene as the major product (Type B behaviour). It is of interest to note that the yield of cis-but-2-ene was not significantly dependent upon the catalyst reduction temperature with either metal. 

The Ojima group has extended their studies of silylformylation to include more complex substrates, such as alkenyne, dialkyne, alkynyl nitrile, and ethynyl pyrrolidinone. Use of rhodium or rhodium-cobalt metal complexes catalyzes the silylformylation of these substrates with high chemoselectivity, as the other functionalities present are inert to the reaction.122b,c d... 

Aldridge and Jonassen (7) have attempted to distinguish between the similar poisoning effects of thiophene and heavy metals on metal carbonyls and fresh metal surfaces. They concluded that Eq. (64) was heterogeneously catalyzed by cobalt metal. This is a point which is difficult to prove unequivocally, however. Attempts to vindicate the early assumption that the hydroformylation reaction is heterogeneously catalyzed (5, 6) have received no further support in recent years. 

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