Abstract
Exo-electron emission from a silver catalyst during partial oxidation of ethylene has been studied by measuring simultaneously the exo-electron emission rate and the rate of ethylene oxide formation. The silver catalyst emits exo-electron continuously in a temperature range 150–210 °C and its emission rate is proportional to the rate of ethylene oxide formation. The temperature dependence of the exo-electron emission obeys the Richardson relation for thermo-electron emission from semiconductor, whereas the rate of ethylene oxide formation fits to the Arrhenius equation. This continuous exo-electron emission is discussed using a schematic diagram of electronic levels of the silver surface with conclusions that the exo-electron emission from the silver catalyst during partial oxidation of ethylene is regarded as a thermo-electron emission from a thin semiconducting oxide layer on silver, the work function of which is reduced by adsorption of ethylene in the form of ethylene oxide. No exo-electron emission and no ethylene oxide formation are shown to occur from metallic copper, nickel oxide and iron oxide, with which only complete oxidation of ethylene proceeds.
Published Version
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