Activity cobalt catalyst solutions

Cobalt-on-alumina catalysts with increased dispersion and catalytic activity are prepared by addition of mannitol to the cobalt nitrate solution prior to impregnation. Thermogravimetric analysis (TGA) and in situ visible microscopy of the impregnation solution show that the organic compound reacts with cobalt nitrate, forming a foam. The foam forms because significant amounts of gas are released through a viscous liquid. The structure of the foam is retained in the final calcined product. It is this effect that is responsible for the increased dispersion. 

The [YCo] systems catalyze this reaction only above 130°C, and hence, the reaction must be carried out in dilute benzene or toluene solutions to keep the TON values below —500. Only very active catalysts can be used for the reaction of Eq.(13) when carried out in pure acrylonitrile. Every cobalt catalyst sufficiently active below 125°C was tested in a batch reactor. A solution of the catalyst in pure acrylonitrile was saturated with acetylene at —2.0 MPa and then heated to 130°C (for experimental procedures, see 84MI5). The TON values after 2 hrs are summarized in Table II. The best results were obtained with the i7 -phenylborininato complex (9), which produced 2.78 kg VP/g Co. 

The solvent is a sine qua non of a homogeneous catalyst system. Solvent properties are indeed very important in determining the activity, selectivity, and stability of a catalyst. Solvent stability is also essential, if the catalytic system as a whole is to be stable. As described above, several solvents have been employed in studies of cobalt-catalyzed CO reduction. Keim et al. (39) noted a substantial difference in activity and selectivity between catalyst solutions in toluene and W-methylpyrrolidone (Table I). Most of the information in this area again comes from the work of Feder and Rathke (36). Listed in Table IV are their results showing changes in the activity of the cobalt catalyst corresponding to changes in solvent polarity. The rates... 

Activated aziridines should be as useful as epoxides for carbon-carbon bond formation, with the advantage that the product will already incorporated the desired secondary aminated stercocentcr. To date, a general enantioselective method for the aziridination of alkcncs has not been developed. Eric Jacobsen of Harvard University (Angew. Chem. hit. Ed. 2004,43, 3952) has explored an interim solution, based on the resolution of racemic epoxides such as I. The cobalt catalyst that selectively hydrolyzes one enantiomer of the epoxide also promotes the addition of the imidc to the remaining enantiomerically-enriched epoxide. As expected, the aziridine 4 is opened smoothly with dialkyl cuprates. 

Catalysts from Group VIII metals have given unsatisfactory results. In the polymerization of butadiene with soluble cobalt catalysts tritium is not incorporated when dry active methanol is employed [115], although it is combined when it has not been specially dried [117, 118]. Alkoxyl groups have been found when using dry alcohol [115, 119] but the reaction is apparently slow and not suited to quantitative work [119]. Side reactions result in the incorporation of tritium into the polymer other than by termination of active chains [118], probably from the addition of hydrogen chloride produced by reaction of the alcohol with the aluminium diethyl chloride [108], Complexes of nickel, rhodium and ruthenium will polymerize butadiene in alcohol solution [7, 120], and with these it has not been possible to determine active site concentrations directly. 

The life of the Cr-promoted sponge cobalt catalyst also was tested. As shown in Fig. 3, a small initial decrease in activity was observed between the first and second uses, then the activity remained essentially constant for the next six cycles. In contrast to the results obtained from the Cr-promoted sponge nickel catalyst, washing the catalyst with NaOH solution between uses appears to be unnecessary. This result may indicate that the nickel catalyst is more susceptible than the cobalt catalyst to poisoning by reaction intermediates and/or products. 

The catalyzed oxidation of ethanol to acetic accompanied by acetaldehyde oxidation may be accomplished by use of acetic acid solutions with a cobalt acetate catalyst. In an example, 252 g of acetaldehyde is fed to the catalyst solution for activation, and then 85.4 g of 100 per cent ethanol together with air is introduced. Conversion of ethanol is 94.2 per cent to acetic acid, 3.5 per cent unchanged, and 2.3 per cent to ethyl acetate. Temperatures below 145°C were used. Various other metal acetates have been patented for the above process, including the salts of alkali and alkaline-earth groups, salts of the platinum metals group, and salts of the chromium metals group. A solid palladium-on-alumina catalyst is active in promoting air oxidation of ethanol to acetic acid. ... 

The first of these new cobalt catalysts were made in 1986 by coprecipitation techniques using aqueous solutions with ammonium bicarbonate as the precipitant in a similar way to the methods used for methanol synthesis catalysts. The new catalysts were immediately found to be very active and selective catalysts for the conversion of syngas into hydrocarbons. A particularly attractive feature was their low methane make and tolerance of CO2 The CO2 tolerance was ascribed to the interplay between the support and the cobalt phase both in the oxidized and reduced forms. The general belief is that the support stabilizes the cobalt phase such that the catalyst can be operated at the higher temperatures, required to maintain activity despite competitive adsorption by CO2, without any loss in stability. Other investigators e.g. Shell have used similar strategies [2]. 

The active carbon-supported cobalt catalyst was prepared by impregnation of cobalt nitrate aqueous solution onto active carbon (Kanto Chemical Co., specific surface 1071.7 mVg, pore volume 0.43 mVg, pellet size 20-40 mesh). The noble metal promoted Co/A.C. catalysts were prepared by co-impregnation of cobalt nitrate and aqueous solution of noble metal coordinated compounds with different noble metal loading. The cobalt loading of all of catalysts was 10 wt%. The noble metal promoted catalysts were named as lOCo+XM, where X was noble metal loading and M was symbol of noble metal. The details of catalyst preparation were described elsewhere [7]. 

Activity and stability are strongly dependent on the nature of the B cation. In the case that the B cation is cobalt, AC0O3 perovskite oxides will be very active ORR catalysts but they are not stable chemically in concentrated alkaline solution. In contrast, AFeOs perovskite oxides whose B cation is iron are very stable but not active catalysts. 

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