Iron-catalyzed water oxidation

Iron-catalyzed water oxidation was also developed by Lloret-Fillol and Costas, which reported a collection of iron(II) catalysts supported by different tetra- and penta-dentate N-donor hgands, including mcp, Pytacn, tmc, and Py2tacn (Fig. 25). By using sodium periodate as sacrificial oxidant at pH 2, the complex Fe(mcp)(OTf)2 evolves oxygen from water during more than 2 h, with a turnover number and frequency over 1000 and 200 h respectively. Kinetic studies based on the time evolution of UV—VIS hands... 

D. Quinonero, K. Morokuma, D. G. Musaev, R. Mas-Balleste, L. Que, Jr., Metal-peroxo versus metal-oxo oxidants in non-heme iron-catalyzed olefin oxidations Computational and experimental studies on the effect of water, J. Am. Chem. Soc. 127 (2005) 6548. 

Activated carbons are used as an adsorbent to remove methanethiol (methylmer-captan), CH3SH, from air [22]. CH3SH is used at low mass fractions in natural gas as an odorant for leak detection. Bashkova eta . [22] measured CH3SH capacities between 0.03 and 0.35 g per gram of adsorbent. Functional groups, such as iron, catalyze the oxidation of adsorbed methanethiol to disulfides. In wet gases, there is competitive adsorption between water and disulfides. 

Tubular Fixed-Bed Reactors. Bundles of downflow reactor tubes filled with catalyst and surrounded by heat-transfer media are tubular fixed-bed reactors. Such reactors are used most notably in steam reforming and phthaUc anhydride manufacture. Steam reforming is the reaction of light hydrocarbons, preferably natural gas or naphthas, with steam over a nickel-supported catalyst to form synthesis gas, which is primarily and CO with some CO2 and CH. Additional conversion to the primary products can be obtained by iron oxide-catalyzed water gas shift reactions, but these are carried out ia large-diameter, fixed-bed reactors rather than ia small-diameter tubes (65). The physical arrangement of a multitubular steam reformer ia a box-shaped furnace has been described (1). 

Recently, Nam, Fukuzumi, and coworkers succeed in an iron-catalyzed oxidation of alkanes using Ce(IV) and water. Here, the generation of the reactive nonheme iron (IV) 0x0 complex is proposed, which subsequently oxidized the respective alkane (Scheme 16) [104]. With the corresponding iron(II) complex of the pentadentate ligand 31, it was possible to achieve oxidation of ethylbenzene to acetophenone (9 TON). 0 labeling studies indicated that water is the oxygen source. 

The photocatalytic oxidation of organic and inorganic compounds and the photo-catalytic production of H202 occurs also at the surface of iron(III)(hydr)oxides. It has been proposed (e.g., Hoffmann, 1990 Faust and Hoffmann, 1986) that the oxidation of S(IV) by 02 in atmospheric water is catalyzed by iron(III)(hydr)oxide particles. It is assumed that the reductant (HSO3) is specifically adsorbed at the surface of an iron(III)(hydr)oxide, forming either a monodentate or a bidentate surface complex ... 

The iron cycle shown in Fig. 10.14 illustrates some redox processes typically observed in soils, sediments and waters, especially at oxic-anoxic boundaries. The cycle includes the reductive dissolution of iron(lll) hydr)oxides by organic ligands, which may also be photocatalyzed in surface waters, and the oxidation of Fe(II) by oxygen, which is catalyzed by surfaces. The oxidation of Fe(II) to Fe(III)(hydr)-oxides is accompanied by the binding of reactive compounds (heavy metals, phosphate, or organic compounds) to the surface, and the reduction of the ferric (hydr) oxides is accompanied by the release of these substances into the water column. 

The action nl catalysis cun he illustrated hy an cxample-the water gas shift reaction catalyzed by iron and chromium oxides. 

Membrane reactor models of various configurations, complexity, and ranges of applicability have been previously reported [Sun and Khang, 1988 Itoh and Govind, 1989 Liu et al., 1990], Several previous investigators have presented water-gas shift membrane reactor models. A model of the iron-chromium oxide catalyzed water-gas shift reaction at 673 K in a cylindrical, palladium membrane reactor was developed to demonstrate... 

Membranes can also be oxidized in the presence of iron, manganese, and other metals. These metals catalyze the oxidation of RO membranes. This type of oxidation tends to involve the entire RO skid rather than focus on the lead membranes. Again, when this type of degradation occurs, feed water passes into the permeate, resulting in an increase in permeate flow and a decrease in product quality. 

The chromia-promoted iron oxide catalyzed water-gas shift reaction ... 

Trimethylamine dehydrogenase is an iron-sulfur flavoprotein found in the methylotrophic bacterium Methylophilus methylotrophus W3A1. It catalyzes the oxidative N-demethylation of trimethylamine by water with formation of dimethylamine and formaldehyde (Steenkamp and Mallinson, 1976). The protein is a symmetrical dimer consisting of 166kDa subunits (Kasprzak et al., 1983 Lim et al., 1982). Each subunit contains one 4Fe-4S center and one FMN cofactor. The latter is bound covalently through the 6... 

Thiosulfate solutions are generally prepared from sodium thiosulfate penta-hydrate, NajSjOa SHjO, which under ordinary conditions is not a primary standard. The solutions should be prepared from water free of heavy-metal impurities to avoid catalytic air oxidation. Ordinary air oxidation is negligible in rate and proceeds through the slow decomposition of thiosulfate to sulfite, which is rapidly air-oxidized to sulfate. Catalyzed air oxidation, on the other hand, proceeds through the reduction of metals such as copper(II) or iron(III), present as thiosulfate complexes, followed by air oxidation of the lower oxidation state ... 

Figure 3. Diagram of a section through the cell wall of Acidithiobacillus ferrooxidans modified from Blake et al. (1992) showing the relationship between iron oxidation and pyrite dissolution. OM =outer membrane, P = periplasm, IM = inner or (cytoplasmic) membrane, cty = cytochrome, pmf = proton motive force. Passage of a proton (driven by proton motive force) into the cell catalyzes the conversion of ADP to ATP. Ferrous iron binds to a component of the electron transport chain, probably a cytochrome c, and is oxidized. The electrons are passed to a terminal reductase where they are combined with O2 and to form water, preventing acidification of the cytoplasm. Ferric iron can either oxidize pyrite (e.g. within the ore body) or form nanocrystalline iron oxyhydroxide minerals (often in surrounding groundwater or streams).

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