Cobalt oxidation kinetics

Hi) Cobalt formate. There is evidence that the kinetics of decomposition of cobalt formate [1026,1027] are similar to those of the nickel salt, considered in some detail below. A significant point of difference, however, is that metal production during reaction of the former is preceded by formation of cobalt oxides [1028]. 

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... 

Lanthanum cobaltate catalysts carbon monoxide oxidation, kinetics, 36 281-283... 

Steady state and transient experiments, the substantial though fragmented literature, and new interpretations are combined in an attempt to define and understand the catalytic kinetics for crrbon monoxide oxidation over cobalt oxide (C03O4) supported on alumina. The result is a rather coherent picture of oxidation-reduction catalysis by a metal oxide. It is shown that the dynamic methods yield vastly more information than steady state studies with significantly less experimental effort. 

N. Bahlawane, Kinetics of methane combustion over CVD-made cobalt oxide catalysts Appl. Catal. B-Environ., 2006, in press. 

The first surface challenge can be addressed by strong oxidation conditions [46] and careful hematite preparation, but the slow water oxidation kinetics are probably intrinsic to hematite. Nevertheless, methods have recently been found to increase the oxidation rate and thus reduce the overpotential. For example, the water oxidation by cobalt has been extensively studied and is known to be particularly rapid [114]. Indeed the treatment of Fe203 photoanodes (prepared by APCVD) with a monolayer of Co " resulted in a ca. 0.1 V reduction of the photocurrent onset potential [105]. Since this treatment also increased the plateau photocurrent it is good evidence that the reaction rate was increased, and the Co " did not just fill surface traps. Following the report of a remarkably effective cobalt-phosphate (Co-Pi)- based water oxidation catalyst [115], the overpotential was reduced even further on hematite photoanodes by Gamelin and coworkers [116]. Their results are shown in Fig. 4.11. 

Guesnet,P., Sabot,J.L. and D.Bauer. "Kinetics of cobalt oxidation in solvent extraction by 8-quinolinol and KELEX 100" (Proceedings of Int.Solvent Extraction Conf., ISEC 80, Belgium, 1980)... 

Figure 4.5.10. Experimental impedance spectra of Li-cobalt oxide (RC-41) and substituted Li-nickel oxide (FL-2) cathodes in the fully charged state and in the frequency range from 10 kHz to 200. uHz obtained by multifrequency FFT impedance measurement. Solid lines indicate the fit by Eqns (29) and (21) (a) and the fit with inclusion of the kinetics of phase formation by Eqns (29) and (30) is presented in part (b).

This mechanism includes the N2 formation via two parallel pathways with participation of N02 species located at the paired Co -QH sites (e.g., near acid sites) and nitrite-nitrate complexes formed on cobalt oxide clusters. The reaction turnover number (TON) over Co 4 -OH sites was ca. 20 times higher as compared with that over CoOx. The isotope studies were carried out in a wide range of feed gas compositions and temperatures [9]. This study allowed to reveal the kinetic equations for the key reaction steps and to determine their rate coefficients (Table 51.2). 

Ravdel BA (1994) Kinetics of Lithium Nickel Cobalt Oxide Electrode Material for Lithium-ion Batteries. Proceedings of the 186th Meeting of the Electrochem Soc. Miami Beach, Florida, Oct. 9-14, 1994. Abstract 638... 

FIGU RE 6.4 Kinetics of oxygen consumption of polyethylene containing 10 to 10 mol/mol PE of cobalt stearate (1), cobalt chloride (2), cobalt oxide C03O4 (3), cobalt sulfate C0SO4 (4), metallic cobalt (5), and PE without filler (6). 

As for pressurized reactors, no provision has to be made for adding a catalyst since the spent caustic almost always contains enough metallic oxides of iron, nickel or cobalt to achieve expected oxidation kinetics. 

Fiikuzumi and Cuo have very recently concluded that the termination reaction for oxidation of c miene with manganese dioxide or cobalt oxide supported on silica ( ) and during autoxidation of cumene initiated by reaction of cumene hydroperoxide with lead oxide ( ) is strictly first-order with respect to the concentration of cumylperoxy radicals. These workers proposed an unprecedented 1,3-methyl shift followed by 0-0 bond cleavage to account for these inusual kinetics. 

For Fe/Ni-based superalloys, a minimum of 20-25% chromium is required to ensure the formation of a protective Cr203 layer. Some cobalt-based alloys require 25-30% Cr203 and do not contain any aluminium. These alloys are resistant to high temperature and possess slower oxidation kinetics. Anyhow, their disadvantage is larger thermal CTE as compared to the iron-based alloys. 

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh . ... 

The decomposition of NO is a very slow catalytic reaction. Amirazmi, Benson, and Boudart recently studied the kinetics over platinum and over oxides of copper, cobalt, nickel, iron and zirconium from 450 to 900°C. They found that the kinetics is first order in NO with concentrations from 1.5 to 15%, and that oxygen has a strong inhibiting effect. Even at these temperatures, the kinetics is about a factor of 1000 too low for automotive usage (97). 

It is noteworthy that, as early as 1929, Shibata and Tsuchida reported a kinetic resolution of rac-3,4-dihydroxyphenylalanine by selective oxidation of one enantiomer using a chiral cobalt complex [Co(en)3NH3Cl]Br2 as a catalyst [46,47]. Figure 12 shows a highly enantioselective addition of diisopropy-Izinc to 2-(ferf-butylethynyl)pyrimidine-5-carbaldehyde via an autocatalytic process in the presence of a chiral octahedral cobalt complex with ethylenedi-... 

The oxidation of formate bound to cobalt(lll) ( captive formate ) has been examined by Candlin and Halpern . The kinetics are... 

Quite different kinetics are exhibited by the anaerobic oxidation of alkyl-benzenes by cobaltic acetate in a 95 % acetic acid medium , viz. 

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