Cobalt inactive

Deactivation is a common and important phenomenon in FTS. Deactivation effects of water are recorded on all commonly used supports. The suggested mechanisms include oxidation, sintering and solid state reactions rendering cobalt inactive. 

It was observed by Gleu that chlorate ions can be rapidly reduced by arsenic-(III) during the reaction between arsenic(III) and cerium(IV). Csanyi and Szabo have established that induced reduction can be carried out by other 1-equivalent reagents, e.g. cobalt(III), manganese(III), permanganate while 2-equivalent reagents, e.g. bromine, chlorine, periodate, proved to be inactive. 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

The first catalysts reported for the electroreduction of C02 were metallophthalocyanines (M-Pc).126 In aqueous solutions of tetraalkylammonium salts, current-potential curves at a cobalt phthalocyanine (Co-Pc)-coated graphite electrode showed a reduction current peak whose height was proportional to the C02 concentration and to the square root of the potential sweep rate at a given C02 concentration. On electrolysis, oxalic acid and glycolic acid were detected, but formic acid was not. Mn and Pd phthalocyanines were inactive, while Cu and Fe phthalocyanines were slightly active. At the potentials used for C02 reduction, M-Pc catalysts would be in their dinegative state, and the occupied dz2 orbital of the metal ion in the metallophthalocyanine was suggested to play an important role in the catalytic activity. 

Mechanism 3 involves NiOH in at least three reactions, and Ni(OH)2 as the active Ni reactant in solution. Since increasing the concentration of the complex-ant(s) in solution will reduce the concentration of both unhydrolyzed and hydrolyzed metal ions, arguments of complexation cannot be readily employed to either support or discount this mechanism. However, it has been this author s experience in formulating electroless Co-P solutions with various complexants for Co2+ that improper complexation which results in even a faint precipitate of hydrolyzed cobalt ions yields an inactive electroless Co-P solution. Furthermore, anodic oxidation of hypo-phosphite at Ni anodes does not proceed at a significant rate under conditions where the surface is most probably covered with a passive film of nickel oxide [48], e.g. NiO.H20, which would be expected to oxidize the reducing agent via a cyclic redox mechanism. 

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... 

Knowledge of the coenzyme forms of vitamin Bi2 has increased steadily. The first coenzyme of Bi2 isolated from bacteria had similarities to pseudovitamin Bi2 it contained adenylic acid instead of 5,6-dimethyl-benzimidazole, but differed in lacking cyanide and having an extra molecule of adenine which was assumed to be bound to the cobalt atom by the coordination site, often occupied by cyanide (B24). This coenzyme, adenylcobamide, was completely inactive for Ochromonas malhamensis, but active for Escherichia coli 113-3. 

The trianionic cobalt catalyst has been successfully employed in the hydrogenation of 1,3-butadiene in [bmim][BF4] [10], The product from this reaction is 1-butene which is formed with 100% selectivity. Unfortunately the catalyst undergoes a transformation to an inactive species during the course of the reaction and reuse is not possible. The cationic rhodium catalyst together with related derivatives have been used for numerous reductions, including the hydrogenation of 1,3-cyclohexadiene to cyclohexane in [bmim][SbF6] [11],... 

High-pressure in-situ NMR spectroscopy have been reported about reactions of carbon monoxide with cobalt complexes of the type, [Co(CO)3L]2. For L=P(n-C4H9)3, high pressures of carbon monoxide cause CO addition and disproportionation of the catalyst to produce a catalytically inactive cobalt(I) salt with the composition [Co(CO)3L2]+[Co(CO)4] . Salt formation is favoured by polar solvents [13],... 

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

Spectra of four catalysts of cobalt on activated carbon. Inactive catalysts 2 are in metallic state active catalysts B-1 and B-2 appear to be CoO. 

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

The iodide content of the catalyst formulation is the key to avoiding these problems of competing reactions and achieving maximum acetic acid selectivity. The addition of iodide ensures that any initially formed methanol (7) is rapidly (H) converted to the more electrophilic methyl iodide. However, further increases in the quantities of iodide beyond that needed for methanol conversion to methyl iodide may lead to a portion, or all, of the catalytic-ally active cobalt carbonyl reverting to catalytically inactive cobalt iodide species - e.g. the [Col4] anion identified in this work, or possibly the cationic [Co(MeOH) (CO) I species (9). 

Careful studies by Doyle et al. (163) have also shown that soluble ruthenium species are inactive for hydrocarbon formation. A soluble system could be maintained in heptane solvent at 250°C under 100 atm of 1 1 H2/CO for many hours by taking precautions to avoid the possible introduction of impurities into the system and by slowly raising the temperature. No hydrocarbon formation was observed in this reaction. Only upon heating to about 260°C was the disappearance of soluble ruthenium complexes noted, along with the formation of linear alkanes. These results may suggest that metastable homogeneous ruthenium solutions can be formed, as has been reported for cobalt complexes (56) precipitation of the metal may be an autocatalytic process. 

A point which has not been examined is the nature of the surface during exchange reactions carried out at high temperatures such as those required for the exchange of methane. Surface carbides may be formed under these conditions. The inactivity of iron films and the comparatively small activity of cobalt films at 300° for the exchange of ethane 19) may possibly be due to the tendency of these metals to form not only surface but also bulk carbides. 

This formula he afterwards modified to (2) in order to explain the fact that if two ammonia molecules fewer are present in the molecule, two acid residues become inactive and therefore must be directly linked to cobalt. Removing two ammonia molecules from scheme (2) yields the formula at that time given to the pcntanunino-salts, namely, in the ease of chloro-pentammino-cobaltic chloride,... 

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