Cobalt catalysts structure

The isomerization of an allylic amine to an enamine by means of a formal 1,3-hydrogen shift constitutes a relatively small structural change. However, this transformation could be extremely valuable if it could be rendered stereoselective. In important early studies, Otsuka and Tani showed that a chiral cobalt catalyst, prepared in situ from a Co(ii) salt, a chiral phosphine, and diisobutylaluminum hydride (Dibal-H), can bring about the conversion of certain pro-chiral olefins to chiral, isomeric olefins by double bond migra-... 

Ma, W.P., Jacobs, G., Sparks, D.E., Spicer, R.L., Graham, U.M., and Davis, B. H. 2008. Comparison of the kinetics of the Fischer-Tropsch synthesis reaction between structured alumina supported cobalt catalysts with different pore size. Prepr. Am. Chem. Soc. Div. Petro. Chem. 53 99-102. (see Chapter 8 of this book.)... 

Carbon deposition from CO on a cobalt catalyst at low pressures is known to be a structure-sensitive process. CO is adsorbed molecularly on the low index surfaces (Co (0001)), but its dissociation occurs on the Co (1012), Co (1120), and polycrystalline surfaces.5762 Deposition of carbon on Co (1012) and the probable formation of Co3C have been established by Auger emission spectroscopy (AES) and low-energy electron diffraction (LEED) techniques.66... 

Additives such as rare earth or noble metals are generally introduced into industrial cobalt FTS catalysts as structural or reduction promoters.92 The addition of various promoters to cobalt catalysts has also been shown to decrease the amount of carbon produced during the FTS.84 87 93 94 Also, the addition of promoter elements may decrease the temperature of regeneration, preventing the possible sintering of supported cobalt particles during such treatments.92... 

We undertook this investigation in order to examine the relationship of physical structure and composition of cobalt catalysts to catalytic activity. Several different cobalt species have been detected on supported cobalt catalysts ( lj 7 ) the type, amount, and reactivity of the cobalt species varied with support, metal loading, and preparation procedures. For this investigation, the supports were varied and the other parameters were held constant. Si02> Ti02, AI2O3, and K-AI2O3 were used as... 

Heavy metals are widely used as catalysts in the manufacture of anthraquinonoid dyes. Mercury is used when sulphonating anthraquinones and copper when reacting arylamines with bromoanthraquinones. Much effort has been devoted to minimising the trace metal content of such colorants and in effluents from dyemaking plants. Metal salts are used as reactants in dye synthesis, particularly in the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. These structures are described in detail in Chapter 5, where the implications in terms of environmental problems are also discussed. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. The environmental impact of the heavy metal salts used in dye application processes is dealt with in Volume 2. 

Zeolites have attracted much attention as cobalt catalyst supports ]151-155]. Co2(CO)8 reacts rapidly from the vapor phase with X and Y faujasite type zeolites Co4(CO)i2, subcarbonyl species and [Co(CO)4] species form inside the pores. Further migration of Co4(CO)i2 carbonyl is inhibited because of pore size hmita-tions, and subsequent decarbonylation can take place only above 150 °C. In contrast, the reaction of Co2(CO)g with an A-type zeolite is limited to the surface due to the inability of the carbonyl precursors to pass through the apertures of the cavities of the structure. 

The structure-activity relationship for cobalt catalysts in the pyridine synthesis can be summarized in the following manner If the substituent R is a donor, the Co-NMR signals are shifted to higher field and the catalytic activity decreases. If R is an acceptor, the Co-NMR signal is shifted to lower field and the activity increases. Donor substituents are oriented orthogonal to complexed cod in the catalyst precursors acceptors are oriented parallel. The deformation of the spherical charge distribution about cobalt is also dependent on the nature of R. 

The addition of promoter elements to cobalt-based Fischer-Tropsch catalysts can affect (1) directly the formation and stability of the active cobalt phase structural promotion) by altering the cobalt-support interfacial chemistry, (2) directly affect the elementary steps involved in the turnover of the cobalt active site by altering the electronic properties of the cobalt nanoparticles electronic promotion) and (3) indirectly the behaviour of the active cobalt phase, by changing the local reaction environment of the active site as a result of chemical reactions performed by the promoter element itself synergistic promotion). 

The oxo reaction (31) is carried out in the liquid phase at high pressure using a cobalt catalyst. A mixture of aldehyde isomers is always produced, each isomer being one carbon number higher than the starting olefin. As a group the oxygenated products of the hydrocarbon synthesis (Fischer-Tropsch) process and the oxo process are primary compounds and thus (except, of course, the methyl and ethyl derivatives) differ fundamentally from the products based on alcohols made by the hydration of olefins, which are always secondary or tertiary in structure. 

In 1943, A. C. Byrns et al. (7), of Union Oil of California published the first study showing under semi-industrial conditions the relative activities of Mo03 and CoO and the mechanical mixture of these two oxides, which they compared to C0M0O4 supported on bentonite. These authors demonstrated that a mixture of molybdenum and cobalt in their oxidic state should be chemically associated in order to be very active, while the simple mechanical mixture only showed the additive activities of the individual oxides. However, these authors mainly emphasized the behavior of these catalysts under different industrial conditions and reduced their discussion of catalyst structure and characterization to a few lines of speculation. 

Syndiotactic 1.2 polybutadiene has also been made by Longiave and Castelli (49) using an anionic cobalt catalyst made from oxygenated aluminum compounds. Less amounts of 1.2-structure were found in polymerizations in hydrocarbon media. Alkyllithium produced only 6.8% 1.2-structure with the remainder being 1.4 cis and trans. 

The enantiomeric purity of the 3-pinanecarbaldehyde corresponds to the a-pinane utilized (70-85%). Enantiomerically pure aldehyde can be obtained by the acid-catalyzed trimerization of the aldehyde, with only one enantiomer being preferentially cyclotrimerized to a crystalline compound.2311 Cleavage of the trimer results in enantiomerically pure aldehyde. If cobalt catalysts are employed in the cyclization, rearrangement to the bomane structure takes place (equation 9).25... 

The obvious choice (at least from the standpoint of availability) to test the role of the salen ligand chelating Co(II) was to buy Jacobsen s cobalt catalyst, 2330 (Scheme 12). This species would introduce several new structural and stereoelectronic factors at the same time (relative to the... 

Donors have been added to the cobalt catalysts used to polymerize butadiene (20). Cobalt chloride-pyridine complexes gave a soluble catalyst with AlEt2Cl which was effective for cis polymerization of butadiene, but at the low concentrations of pyridine employed (Al/Co/py = 1000/1/1 to 4), there was no effect on the polymer structure. However, it was observed that the molecular weight fell as the ratio of pyridine to cobalt was increased. Isopropyl ether in the cobalt octoate-methylaluminum sesquichloride catalyst had a similar effect, although at the highest ether concentrations (typical ratios employed were Al/Co/iPr20 = 160/1/3.5 to 8), a reduction in cis content and polymerization... 

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