Cobalt catalysts applications

In 1996, consumption in the western world was 14.2 tonnes of rhodium and 3.8 tonnes of iridium. Unquestionably the main uses of rhodium (over 90%) are now catalytic, e.g. for the control of exhaust emissions in the car (automobile) industry and, in the form of phosphine complexes, in hydrogenation and hydroformylation reactions where it is frequently more efficient than the more commonly used cobalt catalysts. Iridium is used in the coating of anodes in chloralkali plant and as a catalyst in the production of acetic acid. It also finds small-scale applications in specialist hard alloys. 

The rhodium catalyst has several distinct advantages over the cobalt catalyst it is much faster and far more selective. The higher rate is in process terms translated into much lower pressures (the cobalt catalyst is operated at pressures of 700 bar). Nickel- and palladium-based catalysts have also been reported, but no applications have resulted from these. The mechanism for group 10 metals has not been studied (see Section 9.3.2.3). 

Until recently, the hydroformylation using palladium had been scarcely explored as the activity of palladium stayed behind that of more active platinum complexes. The initiating reagents are often very similar to those of platinum, i.e., divalent palladium salts, which under the reaction conditions presumably form monohydrido complexes of palladium(II). A common precursor is (39). The mechanism for palladium catalysts is, therefore, thought to be the same as that for platinum. New cationic complexes of palladium that are highly active as hydroformylation catalysts were discovered by Drent and co-workers at Shell and commercial applications may be expected, involving replacement of cobalt catalysts. 

Ellis PR. and Bishop P.T. 2006. Supported cobalt catalysts for the Fischer-Tropsch synthesis. International Patent Application WO2006/136863. 

Also, nitrones can be formed by photochemical oxidation (X350 nm) of aldimines in acetonitrile, in the presence of O2 over a TiC>2 suspension (20, 21). Air oxidation of imines into oxaziridines with their subsequent transformation into nitrones, using cobalt catalysts, provides good yields. Utilization of molecular oxygen in the oxidation process seems highly promising due to its cost-effectiveness, availability, and the possibility of industrial application (22). 

Other methods for the preparation of acetic acid are partial oxidation of butane, oxidation of ethanal -obtained from Wacker oxidation of ethene-, biooxidation of ethanol for food applications, and we may add the same carbonylation reaction carried out with a cobalt catalyst or an iridium catalyst. The rhodium and iridium catalysts have several distinct advantages over the cobalt catalyst they are much fester and fer more selective. In process terms the higher rate is translated into much lower pressures (the cobalt catalyst is operated by BASF at pressures of 700 bar). For years now the Monsanto process (now owned by BP) has been the most attractive route for the preparation of acetic acid, but in recent years the iridium-based CATTVA process, developed by BP, has come on stream. 

Cobalt salts and their complexes have been widely used as homogeneous oxidation catalysts in organic syntheses as well as in the chemical industry [19]. Various complexes of cobalt are useful as catalysts for oxidative organic transformations [20-25]. In view of the ability of cobalt to cycle between the commonly encountered II and III oxidation states, complexes of cobalt find application as catalysts in the oxidation of a variety of substrates... 

Cobalt was the first catalyst used in commercial applications of the oxo-synthesis. In order to stabilize the HCo(CO)4 catalyst, high pressures are necessary with a maximum n/i ratio of 80/20. In the Shell process,324,325,393 cobalt catalysts modified with alkylphosphines e.g. ( )3 ( 4 9) are more selective towards linear products but exhibit high hydrogenation activity and are therefore mainly used for the direct synthesis of long chain alcohols. 

The application of hydroformylation is not limited to unfunctionalized petrochemicals. Also, renewables are of interest for industrial applications. One good available resource is oleocompounds which possess C=C-double bonds [16]. Ucciani and Lai first investigated the hydroformylation of unsaturated fatty acid esters using cobalt catalysts such as cobalt laurate or dicobalt octacarbonyl (Scheme 6) [17, 18]. 

Intramolecular Cyclopropanation with Chiral Rhodium(II) 2-Pyrroli-done-5-carboxylates. Applications of chiral copper and cobalt catalysts, including... 

A spectacular application allowed the synthesis of fenestranes by a three-step sequential action of cobalt nanoparticles and a palladium catalyst [131]. The cascade reaction started with a PKR of enyne 105, accomplished by the cobalt catalyst giving 106, followed by the formation of allyl-7r3 palladium complex 107 which reacted with a nucleophile derived from diethyl malonate, to give enyne 108. The final step was a second PKR that gave 109 in good yield. They used cobalt nanoparticles as with Co/charcoal the third step did not take place, apparently due to damage in this catalyst after the allylation step (Scheme 31). 

As early as 1938, Roelen discovered the cobalt-catalyzed hydroformylation of olefins, then known as the oxo reaction, which allowed the synthesis of aldehydes by addition of carbon monoxide and hydrogen to alkenes. Not long after this discovery it was found that cobalt, rhodium, ruthenium and platinum are also suitable as catalysts. However, because of the considerable price advantage for large scale applications in industry, cobalt catalysts are mostly used. Rhodium complexes, however, are... 

This reaciion was discovered in the late 1930s by Otto Roelen of Ruhrehemie, who was working on Fischer-Tropsch4ype chemistry. He found that alkencs can be converted to aldehydes by treatment with CO and H2 in the presence of a cobalt catalyst at elevated temperatures and pressures 12—14]. Today, in terms of product volume, hydroformylation represents one of the largest industrial applications of soluble transition metal catalysts. 

As mentioned above, most published papers and patent applications deal with ligands and their influence on activity and selectivity in the oxo synthesis. When alkylphosphine-modified cobalt catalysts were introduced by Shell [135], high n/i selectivities were reported. However, coordination of phosphine ligands makes the metal-hydrogen bond more hydridic, therefore leading to substantial formation of hydrogenation products. Hydroformylation of 1-pentene yielded hex-anol with 91 % linearity. 

In a technology involving two liquid phases, one of which contains the metal complex catalyst in solution, the idea of using water as one of the phases is not necessarily obvious. Hydroformylation, in 1972 - the time of Manasserfs idea -the most important application of homogeneous catalysis, utilized cobalt catalysts, whose handling sensitivity ruled out an aqueous phase. Or, as P. Cintas [20] wrote,... 

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