Oxygen in acidic media

The oxidation of metal carbonyl compounds by atmospheric oxygen in acid media, or alternatively with an oxidizing acid, have only been reported in a few instances. 

Hiroyoshi et al. (1997) monitored the oxygen consumption, sulfur formation, total iron, and Fe(II) concentrations at different pH levels during the oxidation of chalcopyrite. On the basis of the reaction products formed, it was concluded that ferrous ions catalyzed the oxidation by dissolved oxygen in acidic media ... 

The standard reduction potentials of the most relevant half-reactions involved in the four- and two-electron reduction of dioxygen in acid and alkaline aqueous media are listed in Table 3.1. It follows from these values, that, under full thermodynamic control, the equilibrium concentration of peroxide at the reversible potential for the four-electron reduction of oxygen in acid media, that is, 1.23 V, is of the order of 10 18 M. Hence, a stepwise reduction of dioxygen to yield currents of about 1A cm 2 will require values for the standard heterogeneous rate constants for... 

J Gierer, N-O Nilvebrant. Studies on the degradation of lignin by oxygen in acidic media. 2nd International Symposium on Wood and Pulping Chemistry, Tsukuba, Japan. Proceedings, Vol. 4, pp. 109-112, 1983. 

Franke, R., D. Ohms, and K. Wiesener (1989). Investigation of the influence of thermal treatment on the properties of carbon materials modified by N4-chelates for the reduction of oxygen in acidic media. J. Electwanal. Chem. 260, 63—73. 

Richards G, Swavey S (2009) Electrooxidation of Fe, Co, Ni and Cu metalloporphyrins on edge-plane pyrolytic graphite electrodes and their electrocatalytic ability towards the reduction of molecular oxygen in acidic media. Eur J Inorg Chem 35 5367-5376... 

The preparation of triaryknethane dyes proceeds through several stages formation of the colorless leuco base in acid media, conversion to the colorless carbinol base by using an oxidising agent, eg, lead dioxide, manganese dioxide, or alkah dichromates, and formation of the dye by treatment with acid (Fig. 1). The oxidation of the leuco base can also be accompHshed with atmospheric oxygen in the presence of catalysts. 

Subsequent steps of the process involve the decomposition of ammonium peroxometalates, (NH4)3Ta08 and (NH4)3Ta08, which takes place according to a hydrolytic mechanism. Belov et al. [512] presents the following interactions as occurring by different mechanisms in different media. Hydrolysis in acidic media at pH < 3 appears to occur with the separation of oxygen, as shown in Equation (152) ... 

Bron M, Bogdanoff P, Fiechter S, Hilgendorff M, Radnik J, Dorbandt I, Schulenburg H, Tributsch HJ (2001) Carbon supported catalysts for oxygen reduction in acidic media prepared by thermolysis of Ru3(CO)i2. Electroanal Chem 517 85-94... 

In acidic media, the reactivity of ethanol on Au electrodes is much lower than in alkaline media. The main product of the oxidation of ethanol on Au in an acidic electrolyte was found to be acetaldehyde, with small amounts of acetic acid [Tremiliosi-FiUio et al., 1998]. The different reactivities and the product distributions in different media were explained by considering the interactions between the active sites on Au, ethanol, and active oxygen species absorbed on or near the electrode surface. In acidic media, surface hydroxide concentrations are low, leading to relatively slow dehydrogenation of ethanol to form acetaldehyde as the main oxidation pathway. In contrast, in alkaline media, ethanol, adsorbed as an ethoxy species, reacts with a surface hydroxide, forming adsorbed acetate, leading to acetate (acetic acid) as the main reaction product. 

Wang JX, Zhang JL, Adzic RR. 2007. Double-trap kinetic equation for the oxygen reduction reaction on Pt(lll) in acidic media. J Phys Chem A 111 12702-12710. 

Solid alkaline membrane fuel cells (SAMECs) can be a good alternative to PEMFCs. The activation of the oxidation of alcohols and reduction of oxygen occurring in fuel cells is easier in alkaline media than in acid media [Wang et al., 2003 Yang, 2004]. Therefore, less Pt or even non-noble metals can be used owing to the improved electrode kinetics. Eor example, Ag/C catalytic powder can be used as an efficient cathode material [Demarconnay et al., 2004 Lamy et al., 2006]. It has also... 

Kuzume A, Herrero E, Feliu JM. 2007. Oxygen reduction on stepped platinum surfaces in acidic media. J Electroanal Chem 599 333-343. 

Au has recently received less attention than Pt as a supported catalyst because of its lower impact in PEMFC energy conversion technology, since the ORR is dominated by a two-electron reduction process, at what is a high overpotential, in acidic media. Nevertheless, it is an important oxygen reduction catalyst in alkaline media, and, in contrast to Pt, is oxide-free in the potential range where oxygen reduction occurs. 

Komanicky V, Menzel A, You H. 2005. Investigation of oxygen reduction kinetics at (111)-(100) nanofaceted platinum surfaces in acidic media. J Phys Chem B 109 23550-23557. 

Macia MD, Campina JM, Fehu JM. 2004. On the kinetics of oxygen reduction on platinum stepped surfaces in acidic media. J Electroanal Chem 564 141 -150. 

The catalytic cycle in Fig. 18.20 also rationalizes the potential-dependent av of series 2 catalysts (Fig. 18.19). The primary partially reduced oxygen species was determined to be superoxide, 02, by using 02 scavengers incorporated in catalytic films. Superoxide is produced by autoxidation, i.e., heterolysis of the Fe-O bond in the ferric-superoxo intermediate [Shikama, 1998], probably induced by protonation of the terminal O atom in bound O2. The hypothesis of protonation-assisted autoxidation was supported by the observation that av at the rising part of catalytic curves was smaller in acidic media (more superoxide was produced), whereas no partially reduced oxygen species were detected at any potentials in basic (pH > 8) electrolytes. The autoxidation rate constant at pH 7 was estimated to be 0.03 s (for the Fe-only forms of series 2 catalysts) and <0.01 s for the FeCu forms. 

Jeon, S., D. Kim, and M. Ahmed, Different length linkages of graphene modified with metal nanoparticles for oxygen reduction in acidic media. Journal of Materials Chemistry, 2012. 22(32) p. 16353-16360. 

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