Redox scheme

Unifying Mechanistic Redox Scheme for Standard and Fast SCR Reactions... 

When the components of the PS II reaction centre are drawn on a redox scale and compared in this way to those of the purple bacterial reaction centre, a remarkable similarity can be seen between the electron acceptors in each system (Fig. 4). The chemical natures of these components are extremely similar, being made up of a complex of two quinones, an iron atom and a pheophytin (a bacteriopheo-phytin in bacteria). The donor side of PS II in the redox scheme is, however, not comparable to that in bacteria. P-680 may appear to be structurally similar to P-870 in bacteria in that it is made up of chlorophyll (bacteriochlorophyll in bacteria) and that is acts as the primary electron donor however, the P-680/P-680+ redox couple is approximately 600-800 mV more oxidizing than the equivalent bacterial redox couple P-870/P-870, = +450 mV). In addition, PS II has an array of high-potential components which make up the 02-evolving enzyme and which are clearly unique to that system. 

Two-electron electrochemical reduction of [Mo 02(L-SO)2] to [Mo 0(L-SO)2] " is also observed, followed by comproportionation with starting material to form [Mo 0(L-SO)2]". In general, complexes of this type are reversibly reduced to corresponding Mo(IV) complexes but irreversibly oxidized. Several are capable of participating in the redox scheme of Eq, (24) 160, 165). 

These two reversible transfers of one electron per centre are evident from differences in peak potential values AE = 65 mV and the ratio /pa//pc 1.0. The following redox scheme containing a reversible formation of a mixed-valent Fe" -Ni> —Fe " species was ascribed to the electrochemical reduction processes ... 

Taking into account all the above mentioned results, a generalized Mars and van Krevelen model was considered for butane ODH over both catalysts. Consequently, the two steps mentioned above can be generally described by the following redox scheme ... 

Fig. 15. Redox scheme of glucose oxidation in the presence of glucose oxidase. SCE saturated calomel electrode, FAD flavin adenine dinucleotide.

Redox schemes illustrating proposed action of Fe hydrogenases (A) Clostridium pasteurianum hydrogenase I (B) Clostridium pasteurianum hydrogenase... 

The redox relationship of NO with other nitrogen oxides is shown in Fig. 3. As indicated, NO occupies a central and unique position in this redox scheme. The two-electron oxidation of ammonia (NH3) generates hydroxylamine (NH2OH) and a further two-electron oxidation of hydroxyl-amine generates nitroxyl (HNO). NO can then be generated by a single-... 

FIGURE 3 Redox scheme for the nitrogen oxides. Values in parentheses represent the formal nitrogen oxidation state. 

FIGURE 15.2 Redox scheme for polypyrrole, showing anion (A ) expulsion upon reduction. Typically n = 2-4, symbolizing a positive charge for every 2-4 monomer units. 

In order to first verify that modulation of oxygen potential in the vicinity of a metal or its oxide affects the morphological artefacts, small (25 mm X 12.5 mm) coupons cut from an Mo foil were subjected to several redox schemes and were characterized at the end of each treatment by XRD and SEM. 

A buffer gas mixture (CO/CO2 or Hj/HjO) of appropriate ratio provides a convenient environment for the proposed redox scheme from the point of view of experimental ease, CO/CO2 is a better buffer mixture. 

The transient kinetic model of the standard SCR reaction over a commercial V-based catalyst for vehicles reported in Reference (101) is the only treatment available so far accounting both for the redox nature of the SCR catalytic mechanism and for the ammonia inhibition effect. It relies on a dual-site redox scheme, whereby ammonia is first adsorbed onto acidic sites, but reacts with NO on different redox sites associated with the vanadium component. The redox sites can, however, be blocked by excess ammonia. Adopting a Mars-Van Krevelen formal approach, the following modified redox (MR) rate expression was derived (27) ... 

J.S., and Li, F. (2014) A hybrid solar-redox scheme for liquid fuel and hydrogen coproduction. Energy Environ. Set, 7, 2033-2042. 

Since the electronically excited states of metal complexes are good oxidants and reductants it is possible to envisage several redox schemes to achieve one or more of the above processes. 

Square-redox scheme for the CO-induced reductive elimination of hydride from an iron-hydride complex... 

Different from the above "cofeed" schemes is the "redox" scheme which has been suggested by researchers from ARCO [60]. Its advantage is certainly the use of air instead of pure oxygen which is usually applied in the "cofeed" processes for reasons of reducing separation expenditures (see Figure 31). 

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