System silver-oxygen

Figure 4 Selectivity in epoxidation for a range of substrates plotted against the dissociation enthalpy of the weakest C-H bond in the olefin (m) TS-1 peroxide system (u) silver-oxygen system. 1. 1-octene, 2. 1-butane, 3. 2-butane, 4. gropene, 5. 4-unyltoluene, 6. 1-3 butadiene, 7. styrene, 8. 4-vinylpyridine, 9. ethylene.2...

Raveau, B. 1967. Studies in the systems vanadium-silver-oxygen and vanadium-copper-oxygen. Rev. Chim. Min. 4 729-758. 

Unlike monovalent silver oxide systems, additives such as graphite or manganese dioxide cannot be added to the divalent silver oxide. Graphite enhances the decomposition of AgO to AgjO and oxygen. Manganese dioxide is readily oxidized by AgO to alkali-soluble man-ganate compounds. 

The decomposition equilibria of metal oxides were investigated in 1916 by Treadwell in the region of 1000°C with quartz and porcelain as solid electrolytes and with a silver/oxygen electrode as the reference system [29]. After these investigations, Baur and Treadwell filed a patent on fuel cells with metal oxide electrodes and a molten salt, held in a porous ceramic, electrolyte [30]. Only after many fruitless experiments with liquid electrolytes of different types, Baur in 1937 came to the conclusion that fuel cells have to be made completely solid [31], But the extensive empirical search by Baur [18,32,33] and other authors... 

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.

The poor efficiencies of coal-fired power plants in 1896 (2.6 percent on average compared with over forty percent one hundred years later) prompted W. W. Jacques to invent the high temperature (500°C to 600°C [900°F to 1100°F]) fuel cell, and then build a lOO-cell battery to produce electricity from coal combustion. The battery operated intermittently for six months, but with diminishing performance, the carbon dioxide generated and present in the air reacted with and consumed its molten potassium hydroxide electrolyte. In 1910, E. Bauer substituted molten salts (e.g., carbonates, silicates, and borates) and used molten silver as the oxygen electrode. Numerous molten salt batteiy systems have since evolved to handle peak loads in electric power plants, and for electric vehicle propulsion. Of particular note is the sodium and nickel chloride couple in a molten chloroalumi-nate salt electrolyte for electric vehicle propulsion. One special feature is the use of a semi-permeable aluminum oxide ceramic separator to prevent lithium ions from diffusing to the sodium electrode, but still allow the opposing flow of sodium ions. 

Figure 9.16. Ethylene hardly adsorbs on clean silver, but it does interact with preadsorbed oxygen atoms. At low coverages, the O atoms preferably interact with the C-H bond of ethylene, leading to its decomposition into fragments that oxidize to CO2 and H2O but at higher coverages the oxygen atoms become electrophilic and interact with the n-system of ethylene to form the epoxide. [After R.A. van Santen and H.P.C.E. Kuipers, Ac/v, Catal. 35 (1987) 265.]...

GP 2] [R 3a] A Shell Series catalyst was measured in a fixed-bed configuration and deposited in micro channels electrophoretically (20 vol.-% ethylene, 80 vol.-% oxygen 0.3 MPa 230 °C) [101]. The selectivity was lower in the micro channels (51%) than in the fixed bed (57%) at a conversion of 17%. In a further investigation, a sputtered silver catalyst (cesium promoted) was better than both systems (68%) at higher conversion (25%). 

Similar size effects have been observed in some other electrochemical systems, but by far not in all of them. At platinized platinum, the rate of hydrogen ionization and evolution is approximately an order of magnitude lower than at smooth platinum. Yet in the literature, examples can be found where such a size effect is absent or where it is in the opposite direction. In cathodic oxygen reduction at platinum and at silver, there is little difference in the reaction rates between smooth and disperse electrodes. In methanol oxidation at nickel electrodes in alkaline solution, the reaction rate increases markedly with increasing degree of dispersion of the nickel powders. Such size effects have been reported in many papers and were the subject of reviews (Kinoshita, 1982 Mukerjee, 1990). 

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