System manganese-oxygen

Labeling and kinetic studies indicate that imino transfer proceeds from a [(tpfc)Mn (=NTs) N(Ts)LAr ] complex, and thus this catalyst operates in a fashion that is reminiscent of the manganese oxygenating system reported by Goldberg [52]. Hydrogen atom abstraction from hydroanthracene (to form anthracene), however, can occur upon reactions with an intermediate [(tpfc)Mn N(Ts)rAr ] species [83]. 

The aluminum-oxygen system. The high electrochemical potential and low equivalent weight of aluminum combine to produce a theoretical energy density of 2.6 kWh/kg and make it an attractive candidate as an anode material in metal/air electrochemical cells. The development of aluminum-based cells dates back to 1855 when M. Hulot described a voltaic cell containing aluminum with an acid electrolyte. Since then, many attempts to substitute aluminum for zinc in zinc/carbon and zinc/manganese dioxide cells have been reported. Zaromb first proposed its use in combination with air diffusion electrodes in 1962. Three types of AI-O2 cells have been developed to date ... 

Fig. 1. Schematic representation of a battery system also known as an electrochemical transducer where the anode, also known as electron state 1, may be comprised of lithium, magnesium, zinc, cadmium, lead, or hydrogen, and the cathode, or electron state 11, depending on the composition of the anode, may be lead dioxide, manganese dioxide, nickel oxide, iron disulfide, oxygen, silver oxide, or iodine.

Soon it became evident that the zinc anode, working in both cases under capacity-limiting conditions, causes severe troubles too. Whereas in the zinc/air system the anode automatically limits the discharge (because access to oxygen from the air is practically unlimited), the anode limitation in zinc/manganese dioxide cells has another reason Kordesch and co-workers... 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

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