Redox dynamics

Hu and Ruckenstein s results (130) showed that on the reduced nickel-containing catalyst, the reaction took place by a Langmuir-Hinshelwood mechanism involving adsorbed CH4 and oxygen species. Furthermore, they indicated that a slow dynamic redox process consisting of lattice oxygen formation and its reduction by carbon species was at least partly responsible for the CO formation. 

As discussed at length in this review. Mo isotope variations are now known to be pervasive. This finding was not rmexpected. First, the Mo isotope system spans a mass range of 8% (Fig. 1), which compares favorably with many other stable isotope systems. Second, the dynamic redox chemistry of Mo, and the fact that Mo-ligand interactions have strong covalent character, lends itself to chemical isotope effects. Finally, with seven stable isotopes of relative abundance -10-25%, high-precision Mo isotope analyses are analytically tractable. 

Direct observation of dynamic redox processes in C3H6 02 (or air) mixtures behaviour of surface defect structures... 

Figure 3.8. Dynamic redox experiments in propylene oxygen mixtures around the same sample area m (a) fresh catalyst (b) domains (c) bulk domains with CS nucleation (arrowed) and (d) CS planes. The domains and CS planes are formed even in the presence of oxygen gas (after Gai 1981).

Depending on the water composition other radical species are formed, such as carbonate and chloride radicals. This imposes net oxidizing conditions at the water—fuel interface because the generated oxidants, molecular oxygen and hydrogen peroxide, predominate under a radiation, and other radical species like OH- or CQf- are more active than the generated reductants, mainly molecular hydrogen. This is why we propose that the spent fuel-water interface is a dynamic redox system, independently of the conditions imposed on the near field (Merino et al. 2001). 

Sivan, O., Y. Erel, D. Mandler, and A. Mishri. 1998. The dynamic redox chemistry of iron in the epilimnion of Lake Kinneret. Sea of Galilee. Geochimica et Cosmochimica Acta 62 565-576. 

Dooley CT, Dore TM, Hanson GT, Jackson WC, Remington SJ, Tsien RY. Imaging dynamic redox changes in mammalian... 

Pierre, C. (1985) Isotopic evidence for the dynamic redox cycle of dissolved sulphur compounds between free and interstitial solutions in marine salt pans. Chemical Geology 53, 191-196. 

These results Indicate that a variety of reactions may lead to Cu(I)/Cu(II) Interconversions In seawater. The results are summarised schematically In Figure 3 to demonstrate how copper redox cycling probably occurs. The basic features are a dynamic redox cycle Involving the relatively minor but klnetlcally reactive species which react with oxygen and hydrogen peroxide as described previously. They are probably reactive with ohter photochemlcally... 

Ishigaki Y, Suzuki T, Nishida J et al (2011) Hysteietic tricolor electrochromic systems based on the dynamic redox properties of imsymmetrically substituted dihydrophenanthrenes and biphenyl-2,2 -diyl dications efficient precursor synthesis by a flow micTOTeactor method. Materials 4 1906-1926... 

Hay S, Brenner S, Khara B, Quinn AM, Rigby SE, Scrutton NS (2010) Nature of the energy landscape for gated electron transfer in a dynamic redox protein. J Am Chem Soc 132 9738-9745... 

Actually, the question is complex, because in the reactors there are both reductive (CH4, H2, CO) and oxidative (CO2, H2O) species, so there is a kind of dynamic redox process (Ruckenstein Wang, 2002). When the reductive compounds dominate, there is a massive deposition of coke that is prevented when the concentration of oxidative species is higher, so a catalyst is stable when a kind of balance is reached. 

The largest division of interfacial electrochemical methods is the group of dynamic methods, in which current flows and concentrations change as the result of a redox reaction. Dynamic methods are further subdivided by whether we choose to control the current or the potential. In controlled-current coulometry, which is covered in Section IIC, we completely oxidize or reduce the analyte by passing a fixed current through the analytical solution. Controlled-potential methods are subdivided further into controlled-potential coulometry and amperometry, in which a constant potential is applied during the analysis, and voltammetry, in which the potential is systematically varied. Controlled-potential coulometry is discussed in Section IIC, and amperometry and voltammetry are discussed in Section IID. 

RB Yelle, N-S Park, T Ichiye. Molecular dynamics simulations of rubredoxm from Clostridium pasteurianum Changes m structure and electrostatic potential during redox reactions. Proteins 22 154-167, 1995. 

Stationary microwave electrochemical measurements can be performed like stationary photoelectrochemical measurements simultaneously with the dynamic plot of photocurrents as a function of the voltage. The reflected photoinduced microwave power is recorded. A simultaneous plot of both photocurrents and microwave conductivity makes sense because the technique allows, as we will see, the determination of interfacial rate constants, flatband potential measurements, and the determination of a variety of interfacial and solid-state parameters. The accuracy increases when the photocurrent and the microwave conductivity are simultaneously determined for the same system. As in ordinary photoelectrochemistry, many parameters (light intensity, concentration of redox systems, temperature, the rotation speed of an electrode, or the pretreatment of an electrode) may be changed to obtain additional information. 

It is also often taken for granted that many of the Earth s subsystems are exposed to free oxygen (O2), leading to a range of one-way reactions of reduced materials (such as organic carbon or metal sulfides) to an oxidized form. As pointed out many times in earlier chapters, the oxidation-reduction status of the planet is the consequence of the dynamic interactions of biogeochemical cycles. As is the case with the acid-base balances, there is considerable sensitivity to perturbations of "redox" conditions, sometimes dramatically as in the case of bodies of water that suddenly become anaerobic because of eutrophication. Another extreme... 

Fedurco M. 2000. Redox reactions of heme-containing metalloproteins Dynamic effects of self-assemhled monolayers on thermod3mamics and kinetics of c)dochrome c electron-transfer reactions. Coord Chem Rev 209 263-331. 

As illustrated in Fig. 9.40, progressively more complex models for the environment of Fe in oxidized or reduced rubredoxin produce better simulations of the NIS pattern. A simple Fe(SCH3)4 model (21 atoms) predicts a division of the spectrum into Fe-S stretch and S-Fe-S/Fe-S-C bend regions, but at least a model with 49 atoms is needed to reproduce the splitting of the stretch region and to capture some of the features between 10 and 30 meV. These results confirm the delocalization of the dynamic properties of the redox-active Fe site far beyond the immediate Fe-S4 coordination sphere. 

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