Water oxidation mechanisms

Details of the water oxidation mechanism are unavailable however, it is likely that one could generate an intermediate HOCl that could go on, under acid conditions in a second step, to form 02. This is reminiscent... 

Fig. 4. A schematic depiction of hetero neous water oxidation mechanism...

R4. T Wydrzynski, W Flillier and J Messinger (1996) On the functionai significance of substrate accessibiiity in the photosynthetic water oxidation mechanism. Physiol Plant 96 342-350... 

Wang, H., Lindgren, T., He, J., Hagfeldt, A., Lindquist, S.-E. Photolelectrochemistry of nanostructured WO3 thin film electrodes for water oxidation mechanism of election transport. J. Phys. Chem. B 104, 5686 (2000)... 

Fig. 9 Key equilibrium and 0-0 forming transition state in the water oxidation mechanisms with the McKenzie catalyst.

The water oxidation mechanism was explored in detail by Baik for the Llobet s catalyst. Calculations were carried out with the broken-symmetry DFT approach using the hybrid B3LYP functional. Two different basis sets of double- and triple- quahty, including ECP, were used to optimize the geometries (gas phase) and refine the energies (water continuum). The full... 

Liao RZ, Karkas MD, Lee BL, Akermark B, Siegbahn PEM. Photosystem II like water oxidation mechanism in a bioinspired tetranuclear manganese complex. Inorg Chem. 2015 54 342-351. 

Acuna-Par F, Costas M, LuisJM, Lloret-FUlolJ. Theoretical study of the water oxidation mechanism with nonheme Fe(pytacn) iron complexes. Evidence that the Fe (0)(pytacn) species cannot react with the water molecule to form the 0-0 bond. Inorg Chem. 2014 53 5474-5485. 

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

The biodegradation of poly(alkylene glycols) is hindered by their lack of water solubiUty, and only the low oligomers of poly(propylene glycol) are biodegradable with any certainty (179—181), as are those of poly(tetramethylene glycol) (182). A similar xo-oxidation mechanism to that reported for poly(ethylene glycol) has been proposed. 

Rusting of iron consists of the formation of hydrated oxide, Fe(OH)3 or FeO(OH), and is evidently an electrochemical process which requires the presence of water, oxygen and an electrolyte — in the absence of any one of these rusting does not occur to any significant extent. In air, a relative humidity of over 50% provides the necessary amount of water. The mechanism is complex and will depend in detail on the prevailing conditions, but may be summarized as ... 

The behaviour of uranium has been well characterised for a variety of environments of importance in the nuclear industry. The corrosion is governed by the constitution and physical character of the solid reaction products which in turn are determined mainly by the oxygen potential of the environment, the temperature and the presence of water. The mechanisms of attack are known in broad outline. A major area in need of more detailed study is the influence of irradiation both prior to and during oxidation. 

The reason for the exponential increase in the electron transfer rate with increasing electrode potential at the ZnO/electrolyte interface must be further explored. A possible explanation is provided in a recent study on water photoelectrolysis which describes the mechanism of water oxidation to molecular oxygen as one of strong molecular interaction with nonisoenergetic electron transfer subject to irreversible thermodynamics.48 Under such conditions, the rate of electron transfer will depend on the thermodynamic force in the semiconductor/electrolyte interface to... 

In the present article the photocatalytic reaction of water oxidation is examined from the standpoint of the electronic theory. We shall analyze here one of the possible mechanisms of the reaction [see reference (7[Pg.197]

McEvoy, J.P. and Brudvig, G.W. (2004). Structure-based mechanisms of photosynthetic water oxidation. Phys. Chem. Chem. Phys., 6, 4754 1763... 

In contrast the oxo-ruthenium complex c ,c -[ (bpy)2Runl(0H2) 2(//-0)]4+ and some of its derivatives are known to be active catalysts for the chemical or electrochemical oxidation of water to dioxygen.464-472 Many studies have been reported473 181 on the redox and structural chemistry of this complex for understanding the mechanism of water oxidation. Based on the results of pH-dependent electrochemical measurements, the basic structural unit is retained in the successive oxidation states from Rum-0 Ru111 to Ruv O Ruv.466... 

Traube [15,16] performed the next important step in understanding of the oxidation mechanism. He studied the oxidation of metals in water and proposed hydrogen peroxide as the primary product of oxidation. Traube proposed the following scheme of metal oxidation ... 

In terms of the effect of water on the deactivation, several mechanisms have been identified, and they will influence the stability of the catalyst depending on the conditions and the support used. At high partial pressures of water oxidation is always a possibility, but the various reports are less clear to whether this is mainly surface oxidation of cobalt particles irrespective of particle size, or if small particles... 

From the above it is clear that DMPO can undergo the addition-oxidation mechanism with water as the nucleophile, provided a suitable oxidant is present. With a primary alcohol competing, the O-connected alkoxy spin adduct is formed in addition to HO-DMPO". On the other hand, with a hydroxyl radical source a competing alcohol will undergo hydrogen abstraction by HO" and form an a-hydroxyalkyl radical which forms a C-connected spin adduct. This criterion clearly can distinguish between the two mechanisms at least in model systems (for recent examples, see Reszka and Chignell, 1995 Janzen et al., 1995 Thomas et al., 1996). 

The low-temperature hydrocarbon oxidation mechanism discussed in the previous section is incomplete because the reactions leading to CO were not included. Water formation is primarily by reaction (3.56). The CO forms by the conversion of aldehydes and their acetyl (and formyl) radicals, RCO. The same type of conversion takes place at high temperatures thus, it is appropriate, prior to considering high-temperature hydrocarbon oxidation schemes, to develop an understanding of the aldehyde conversion process. 

In the absence of more easily oxidized substrates, residual water in aprotic solvents will undergo oxidation at platinum anodes. However, the mechanism of proton formation is not necessarily by simple water oxidation with the evolution of O2 but may involve radical reactions of the solvent or oxidation of supporting electrolyte anions [6, 7]. The protons produced, together with the most basic species in solution, form... 

However, with different pretreatment of the carbon, a different spatial arrangement of the groups seems to result during oxidation. These relationships deserve further studies. The effect of oxidation catalysts or inhibitors on the formation of the functional groups has not been studied yet. A definite influence is to be expected since the oxidation mechanism is certainly changed by additives such as water vapor or chlorine (87,88). 

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