Alkanes iron catalysts

There are many bi- and polynuclear iron(III) complexes where bridging oxide is supported by carboxylates. Combinations of Fe—O—Fe plus carboxylate bridges occur in model compounds for proteins and in biomineralization. Electronic spectra of [Fe(/u-0)(//-02CR)2Fe] complexes have been reviewed briefly. [Fe2(//-0)(M-02CMe)2(bipy)2Cl2] is both an alkane activation catalyst and a bio-model. ... 

The metal-catalysed hydrogenation of cyclopropane has been extensively studied. Although the reaction was first reported in 1907 [242], it was not until some 50 years later that the first kinetic studies were reported by Bond et al. [26,243—245] who used pumice-supported nickel, rhodium, palladium, iridium and platinum, by Hayes and Taylor [246] who used K20-promoted iron catalysts, and by Benson and Kwan [247] who used nickel on silica—alumina. From these studies, it was concluded that the behaviour of cyclopropane was intermediate between that of alkenes and alkanes. With iron and nickel catalysts, the initial rate law is... 

S. Ruba, B. C. Gates, P. Vijayanand, R. R. Grasselli, and H. Rnozinger, An active and selective alkane isomerization catalyst iron - and platinum - promoted tungstated zirconia, J. Chem. Soc. Chem. Commun. 321-322 (2001). 

The effects of introducing halogens in the 2 and 6 position of phenyl imine catalysts was also studied in diimine pyridine iron dichloride/MAO systems [13]. These catalysts afford linear products with a low olefin content, generally less than one (olefin) functionality per chain. The latter is due to a fast transfer of iron bound alkyl groups to the aluminum compounds that are present in excess. After hydrolysis, alkanes are obtained. When a high ratio of aluminum alkyl to iron catalyst is used, polyethene waxes are obtained due to the statistically favored alkyl group exchange between the metal species. 

K. Chen, L. Que, Jr., Evidence for the participation of a high-valent iron-oxo species in stereospecific alkane hydroxylation by a non-heme iron catalyst, Chem. Commun. (1999) 1375. 

Iron Catalysts. - The addition to the feed stream of a labeled molecule that is a potential intermediate in the reaction network has been utilized in many studies. The reaction network for the FTS can be written as in Scheme 1. Hydrocarbon (alkene and alkane) and oxygenate (alcohol) products are shown for illustration in this simplified reaction network the actual products for each carbon number may be more complex than shown. C-labeled ethanol is shown in Scheme 1 to illustrate the labeled molecule technique. Thus, a small amount of " C-labeled ethanol would be added to the synthesis gas and this mixture would be passed over the catalyst. The products are collected and then each carbon number product is analyzed to determine the amount of C-label that it contains. 

With the iron catalyst, C-propene gave a somewhat higher splitting than C-ethene. The [l- C]-propene transformation to C3+ -hydrocarbons is low the principal selectivity was for lower carbon compounds (Figure 35). Dimerization of [l- C]-propene occurred to produce 2-methylpentane with a much higher activity than either the /-C5 or /-C7 alkane. For normal hydrocarbons, butane has a much higher activity than the higher carbon number alkanes. 

Costas M, Chen K, Que L (2000) Biomimetic nonheme iron catalysts for alkane hydroxyl-atlon. Coord Chem Rev 200-202 517-544... 

In summary, periodic operation has an influence on the selectivity of the products from FTS. First, there is a decrease in the alpha value of FTS with increasing period. Secondly, the alkane/alkene ratio increases with an increase in the period. There did not appear to be a change in CO2 selectivity that could not be attributed to a change in CO converesion. Finally, the fraction of the hydrocarbon product that was methane increased with increasing length of the period, as previously reported. In general, the periodic operation with the iron catalyst does not appear to provide effects in selectivity or activity that are desirable. 

Fischer-Tropsch (FT) processes can operate at either low-temperature (LTFT), 190-260 °C, or high-temperature (HTFT), 300-350 With iron catalysts, HTFT processes are used for the production of petroleum-compatible alkanes and low molecular weight alkenes, while low-temperature (LTFT) processes are typically used to generate longer-chain hydrocarbons that can be refined into diesel and waxes. ... 

This review will deal with the direct and indirect anodic oxidation of unactivated CH bonds in alkanes, and of remote CH bonds in substrates with various functional groups. The conversion of CH bonds activated by vinyl, aryl, amino or alkoxy groups will not be dealt with in this chapter. However, the catalytic oxidation of alkanes in fuel cells and the oxidation of alkanes with molecular oxygen and iron catalysts are included. 

An illustrative example of tripodal ligand is tpa. As mentioned above, the combination of [Fe(tpa)(CH3CN)2] ( 104)2 with H2O2 proved to oxidize alkanes effectively. The oxidation is highly stereospecific (>99% retention of configuration for the oxidation of cis- and frans-l,2-dimethylcyclohexane (DMCH)), this being the first example of non-heme iron catalysts capable of stereospecific alkane oxidation [42, 43]. Studies with [Fe(OTf)2(tpa)] (OTf = trifluoromethylsulfonate anion) and derivatives where pyridine heterocycles were later systematically replaced by aliphatic amines (Scheme 4) were performed by Britovsek and coworkers [44]. These studies showed that at least two pyridine donors were needed... 

Scheme 26 Benzyl-modified mcp iron catalysts for efficient alkane oxidation reactions...

Compositional modulation has been practiced for the FT synthesis in catalytic reactors [126]. It was found that the cyclic feeding of synthesis gas (CO/IT2) had an influence on the selectivity of the FT products. In the early studies, only low conversions could be utilized due to the exothermic nature of the reaction. It was concluded that for an iron catalyst, the methane selectivity increased with periodic operation as did the molar ratio of alkene/alkane. Higher conversion studies were conducted in a CSTR, and it was found that periodic operation had an influence on the selectivity of the products from the FT synthesis using an iron catalyst [127]. First, there was a decrease in the alpha value for synthesis with increasing period. In addition, the alkane/alkene ratio increased with an increase in the period. There was a change in the CO2 production but this could be attributed to the change in CO conversion and not the... 

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