Iron - promoter

Fischer-Tropsch ohgomerization of CO -1- H9 to make hydrocarbons and oxygenated compounds was originally catalyzed by cobalt, which forms the active carbonyl, but now iron promoted by potassium is favored. Dissociative chemisorption of CO has been observed in this process. 

Stainless steels each appear twice in the list. The more active potentials are those which the metal adopts when corroding as in a pit. The more cathodic potential is that adopted by the bare surface around the pit. The potential difference constitutes a significant driving force, analogous to the situation where the coupling of dissimilar metals such as copper and iron promotes the corrosion of the more anodic of the two (see below). 

Figure 2. I. Spatial distribution of the main orbitals of N2 involved in molecular chemisorption on iron promoted by potassium (K or K20). Arrows indicate the direction of transfer of electron density.5...

Scheme 29 Iron-promoted cyclization/halogenation of alkynyl diethyl acetals...

Gutteridge, J.M.C. (1986). Iron promoters of the Fenton reaction and lipid peroxidation can be released from haemoglobin by peroxides. FEBS Lett. 201, 291-298. 

Winyard, P.G., Blake, D.R., Chirco, S., Gutteridge, J.M.C. and Lunec, J. (1987a). Mechanism of exacerbation of rheumatoid synovitis by total-dose iron-dextran infusion in vivo demonstration of iron-promoted oxidant stress. Lancet i, 69-72. 

Ammonia synthesis N2 + h2 Iron promoted with A1203 and K nh3... 

Recently, the iron-promoted Barbier-type addition of alkyl halides to aromatic aldehydes has been reported (Equation (26)).326 According to the proposed mechanism, the initial step is the formation of an alkyl radical, which can be reduced to the corresponding carbanion. This carbanion nucleophile can react, while coordinated to the iron pentacarbonyl complex, with the corresponding aldehyde. This stoichiometric method is limited with respect to substrate scope and yield. The same authors have also developed the Reformatsky-type addition of cr-halosub-stituted carbonitriles to aldehydes and ketones in the presence of iron pentacarbonyl.3... 

Wiehnga B, Mizuba MM, Fendorf S. 2001. Iron promoted reduction of chromate by dis-similatory iron-reducing bacteria. Environmental Science and Technology 35 522-521. 

Y Inhibition of Hemoglobin- and Iron-Promoted Oxidation in Fish Microsomes by Natural Phenolics (from Pazos et ah, 2006)... 

An iron-promoted cobalt molybdate catalyst (Fe0 03Co0.9 7MoO4) was studied by Maksimov et al. [195,196] with respect to the role of iron in the transfer of charge. Iron strongly enhances the catalytic activity and at the same time increases the conductivity by a factor of 100. Mossbauer spectroscopy reveals that 4% of the iron ions are present as Fe2+ impurity . This fraction is doubled at steady state reaction conditions, and indicates participation of iron in the charge transfer process. 

A commercial, iron-promoted ammoxidation catalyst (Fe/Sn/Sb = 0.25/1/4) was investigated by Crozat and Germain [93] using a flow reactor at 350—480°C, atmospheric pressure and a C3H6/02 ratio of 1/10. The... 

A commercial iron-promoted catalyst (Sn/Sb/Fe = 1/4/0.25) was studied by Germain et al. [92,93,135,137]. Iron is reported to improve the ammoxidation qualities of the catalyst although it has no effect on the oxidation [93], The kinetics, determined in a flow reactor at 445°C and with a feed ratio C3H6/NH3/air = 1/1.2/10, are essentially similar for this catalyst and bismuth molybdate. The initial selectivity is 80% and the maximum yield is 65% (at 445°C). The initial selectivity markedly depends on the temperature (e.g. 91% at 415°C and 72% at 507°C). The effect of water is hardly significant for this catalyst the acrylonitrile formation is slightly inhibited, while some more acrolein is formed. Presumably, water and ammonia compete in the interaction with the catalyst, which is much less reactive with respect to ammonia than bismuth molybdate. The acrolein ammoxidation is very rapid (about six times the propene ammoxidation rate) and selective (86%). A comparison of the Sn—Sb—Fe—O catalyst with bismuth molybdate is presented in Table 14. 

Fischer-Tropsch oligomerization of CO + hydrogen to make hydrocarbons and oxygenated compounds. Iron promoted by potassium is favored, but the original catalyst was cobalt which formed a carbonyl in process. 

Ammonia, Hydrogen, and Methanol Production The ammonia synthesis catalyst is metallic iron promoted with AljO,. K 0. MgO. and CaO. The hydrogen-producing (methane reforming) catalyst is supported nickel. The methanol synthesis catalyst is ZnO promoted with Cr Oj or Cu(l>—ZnO promoted with CrjOl or AUOi. The respective reactions are cited as follows. 

It is well known, even from old literature data (ref. 1) that the presence of metal promotors like molybdenum and chromium in Raney-nickel catalysts increases their activity in hydrogenation reactions. Recently Court et al (ref. 2) reported that Mo, Or and Fe-promoted Raney-nickel catalysts are more active for glucose hydrogenation than unpromoted catalysts. However the effects of metal promotors on the catalytic activity after repeated recycling of the catalyst have not been studied so far. Indeed, catalysts used in industrial operation are recycled many times, stability is then an essential criterion for their selection. From a more fundamental standpoint, the various causes of Raney-nickel deactivation have not been established. This work was intended to address two essential questions pertinent to the stability of Raney-nickel in glucose hydrogenation namely what are the respective activity losses experienced by unpromoted or by molybdenum, chromium and iron-promoted catalysts after recycling and what are the causes for their deactivation ... 

Promoter. In some cases, a relatively small quantity of one or more substances, the promoter or promoters, when added to a catalyst improves the activity, the selectivity, or the useful lifetime of the catalyst. In general, a promoter may either augment a desired reaction or suppress an undesired one. There is no formal system of nomenclature for designating promoted catalysts. One may, however, for example, employ the phase iron promoted with alumina and potassium oxide. ... 

Chuang, F., Larson, R.A., and Wessman, M.S., Zero-valent iron-promoted dechlorination of polychlorinated biphenyls, Environ. Sci. Technol., 29, 2460-2463, 1995. 

Evidence is now accumulating to show that reactions involving metals might be the common denominator underlying AD and PD. In these disorders, an abnormal reaction between a protein and a redox-active metal ion (copper or iron) promotes the formation of ROS. It is especially intriguing how the antioxidant Cu/Zn-SOD activity can convert into a pro-oxidant activity, a theme echoed in the recent proposal that Ap and PrP, the proteins respectively involved in AD and prion diseases, possess similar redox properties [Bush, 2002],... 

Bromooctane (12) is reported to give high yields of coupling products 13 from an electrochemically generated iron promoter (equation 8). Moderate yields of coupled prod-... 

Lee J, Kim J, Choi W. Oxidation on zerovalent iron promoted by polyoxometalate as an electron shuttle. Environ Sci Technol 2007 41 3335-40. 

Keywords alkanes-isomerization iron-promoter n-pentane-isomerization platinum-promoter selectivity tungsten oxide zirconia-tungstated-acidity zirconia-tungstated-redox properties... 

X. Carrier, P. Lukinskas, S. Kuba, L. Stievano, F. E. Wagner, M. Che, and H. Knozinger, The State of the Iron Promoter in Tungstated Zirconia Catalysts, Chem. Phys. Chem. 5, 1191-1199 (2004). 

Moglie, Y., Alonso, F., Vitale, C., Yus, M. and Radivoy, G. (2006) Active-iron-promoted hydrode-halogenation of organic halides. Appl. Catal. A General 313, 94-100. 

Stratz compared Raney Ni without inhibitor with the Raney Ni poisoned by dicy-andiamide in the hydrogenation of o-chloronitrobenzene in methanol below 120°C and 1 MPa H2. Proportion of dechlorination decreased from 44.3% without inhibitor to 0.3% in the presence of the inhibitor, and the yield of o-chloroaniline increased from 54.5% without inhibitor to 98.8% with the inhibitor. The dechlorination decreased further to 0.2%, and the yield of o-chloroaniline increased to 99.3% over a Raney Ni promoted with chromium and iron (eq. 9.50).114 Similarly, dehalogenation over the chromium- and iron-promoted Raney Ni was only 0.6% with m-chloroni-trobenzene, 0.2% with 3,4-dichloronitrobenzene, and 0.5% with p-bromonitroben-zene. 

Scheme 5 Proposed radical mechanism for the iron-promoted oxidative dehydrogenation of a coordinated secondary...

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