Carbon—hydrogen activation hydrocarbons

Table I. Carbon-Hydrogen Activation of Hydrocarbons Using Compounds 1 and 2 as Catalysts and Iodosylbenzene as the Monooxygen Transfer Agent4...

Table m. Carbon-Hydrogen Activation of C1-C3 Hydrocarbons with a Manganese-Substituted Keggin Ion Catalyst Using t-Butyl Hydroperoxide as the Monooxygen Transfer Reagent in Benzene a... 

Fendrick CM, Marks TJ. ThermochemicaUy based strategies for carbon-hydrogen activation on saturated hydrocarbon molecules. Ring-opening reactions of a thoracyclobutane with tetramethylsilane and methane. J Am Chem Soc. 1984 106 2214-2216. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Ruthenium is a known active catalyst for the hydrogenation of carbon monoxide to hydrocarbons (the Fischer-Tropsch synthesis). It was shown that on rathenized electrodes, methane can form in the electroreduction of carbon dioxide as weU. At temperatures of 45 to 80°C in acidihed solutions of Na2S04 (pH 3 to 4), faradaic yields for methane formation up to 40% were reported. On a molybdenium electrode in a similar solution, a yield of 50% for methanol formation was observed, but the yield dropped sharply during electrolysis, due to progressive poisoning of the electrode. 

Carbonaceous species on metal surfaces can be formed as a result of interaction of metals with carbon monoxide or hydrocarbons. In the FTS, where CO and H2 are converted to various hydrocarbons, it is generally accepted that an elementary step in the reaction is the dissociation of CO to form surface carbidic carbon and oxygen.1 The latter is removed from the surface through the formation of gaseous H20 and C02 (mostly in the case of Fe catalysts). The surface carbon, if it remains in its carbidic form, is an intermediate in the FTS and can be hydrogenated to form hydrocarbons. However, the surface carbidic carbon may also be converted to other less reactive forms of carbon, which may build up over time and influence the activity of the catalyst.15... 

The metals known to be active for hydrogenating carbon monoxide to hydrocarbons and alcohols are Fe, Ni, Co and Ru. Rhodium is also receiving considerable attention by many research workers for the production of alcohols. The relative prices of these metals are given in Table I. 

Burger. P. and Bergman, R.G. (1993) Facile intermolecular activation of carbon-hydrogen bonds in methane and other hydrocarbons and silicon-hydrogen bonds in silanes with the iridium(III) complex Cp (PMe3)Ir (CH3)(OTf). J. Am. Chem. Soc., 115 (22). 10462-10463. 

Much effort has been devoted to activate hydrocarbons, particularly saturated compounds, through the formation of organometallic compounds and transformation of the latter to substituted derivatives. A number of transition-metal complexes have been found to insert into carbon-hydrogen bonds leading to stable alkyl metal hydrides ... 

The influence of a number of chemical substances on these limits is known and has been studied in extraordinary detail the most active influence is exerted by the halides, whose admixture in small amounts makes mixtures of carbon monoxide, hydrogen and hydrocarbons with air incombustible. Yet the thermal properties of the mixtures change comparatively little. In our laboratory it was shown that the influence of admixtures on the limits is a result of their influence on the flame velocity the addition of tetrachloride stannic to hydrogen-air mixtures (Sadovnikov), or the addition of chlorine or tetrachloride carbon to mixtures of carbon monoxide with air and oxygen (Barskii, Drozdov) in amounts insufficient to fully flegmatize the mixture significantly decrease the flame velocity. 

A few decades later in 1968, Halpem formulated the need for new approaches to the activation of C-H bonds with a particular focus on saturated hydrocarbons. C-H bond activation, equated with dissociation of carbon-hydrogen bonds by metal complexes , was identified as one of the most important challenges in catalysis [4]. Perhaps the most influential discovery in this area was made in the late 1960s by Hodges and Garnett, who demonstrated that a homogeneous aqueous so-... 

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