Cobalt activations

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Although the FTS is considered a carbon in-sensitive reaction,30 deactivation of the cobalt active phase by carbon deposition during FTS has been widely postulated.31-38 This mechanism, however, is hard to prove during realistic synthesis conditions due to the presence of heavy hydrocarbon wax product and the potential spillover and buildup of inert carbon on the catalyst support. Also, studies on supported cobalt catalysts have been conducted that suggest deactivation by pore plugging of narrow catalyst pores by the heavy (> 40) wax product.39,40 Very often, regeneration treatments that remove these carbonaceous phases from the catalyst result in reactivation of the catalyst.32 Many of the companies with experience in cobalt-based FTS research report that these catalysts are negatively influenced by carbon (Table 4.1). 

H2/CO = 2 small amounts of inert carbon species on the cobalt active phase regeneration required to maintain activity ... 

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 characterization tools to investigate cobalt-based Fischer-Tropsch catalysts are mostly used to study the catalyst materials under conditions far from industrially relevant reaction conditions i.e., in the presence of CO and H2, as well as of the reaction products, including H2O at reaction temperatures and at high pressures. Since catalytic solids are dynamic materials undergoing major changes under reaction conditions it can be anticipated that the currently obtained information on the active site is at least incomplete. This holds also for the active state and location of the promoter element under reaction conditions. For example, an electronic elfect on the cobalt active phase induced by a promoter element can maybe exist only at high pressures and will remain -due to the lack of the appropriate instrumentation - unnoticed to the catalyst... 

In the presence of a large excess of Co2+, both native (97) and cobalt (92) carboxypeptidase A show an approximately two-fold activity increase. The kinetics of the enzyme are very complex at moderate or high substrate concentrations and involve both apparent activation and inhibition by substrate (95). Under the standard assay conditions used in connection with the observed cobalt activation, all these complicating factors contribute significantly. The additional Co2+ possibly interferes with these secondary effects rather than being a participant in catalysis. Further experimentation is needed to clarify this detail. 

The argentic oxide catalyst may also be activated by the addition of a small amount of cobaltic oxide, CO2O3, about 0.2% of cobalt being effective for this purpose. However, cobalt activated preparations are not very stable, readily lose oxygen on storage, and absorb CO2. With... 

Food-grade sodium metabisulfite that is free of impurities should be used in RO systems. The compound must not be cobalt-activated, as cobalt can catalyze the oxidation of the polyamide composite membrane in a manner similar to iron and manganese (see Chapter 7.6). Further, while the shelf life of solid sodium metabisulfite is 4-6 months, in solution, the shelf life depends on the concentration, as shown in Table 8.9.9... 

Cobalt-activated acylase e-Aminopentyl-o-hydroxy-isocaproyl-DL-tyrosine ethyl ester Sepharose 4B 157... 

Systems in which the behavior of cobalt would be expected to follow Equation 15 most closely would be diflBcult to reproduce in the laboratory, in a form that permitted good control of conditions and sampling access. However, some field evidence has been obtained that indicates that Equation 15 is useful as a predictor of cobalt activity where manganese oxides are known to be forming in the system, and where reliable measurements of dissolved manganese and pH are available. Analyses for ten small mountain streams in Colorado that were affected by drain-... 

Mechanisms for coprecipitation of lead and cobalt with manganese oxide can be derived based on thermodynamic calculations. They can explain the increased oxidation state of manganese reached in the mixed oxide precipitates, and they provide a potential control of the solubility of the accessory metals. The effectiveness of the control has been evaluated in a preliminary way by laboratory experiments described here, and by some fleld observations. Cobalt activity seems to be controlled by manganese coprecipitation in many natural systems. Although more testing by both laboratory experiments and fleld studies is needed, the proposed mechanisms appear to be applicable to many coupled oxidation-reduction processes. 

Mixture of Si02 and polyphosphoric acid 1970 Cobalt-activated coal... 

The contribution of Ru loading for cobalt active carbon catalyst. 

Stelmachowski, P Maniak, G., Kaezmarezyk, J., Zasada, F., Piskorz, W., Kotarba, A., and Sojka, Z. (2014) Mg and A1 substituted cobalt spinels as catalysts for low temperature deN20—evidence for octahedral cobalt active site. Appl. Catal... 

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