Formation of Adsorbed Oxygen and Its Reactivity with Ethylene over Silver Catalysts

Article abstract of DOI:10.1021/j150604a023

The temperature-programmed desorption of oxygen from silver catalysts showed a single peak in the range 413-573 K with a maximum around 503 K.This temperature was not affected by the differences in the methods of preparation of silver samples.The amount of adsorbed oxygen increased in proportion to the logarithm of the adsorption pressure.This oxygen adsorbate led to the formation of ethylene oxide and carbon dioxide by reaction with ethylene, which were desorbed at 298-393 and 373-573 K, respectively.Both the amounts of produced ethylene oxide and carbon dioxide showed a bell-shaped dependence on the concentration of adsorbed oxygen; that is, the excess amount of adsorbed oxygen inhibited the productions of both ethylene oxide and carbon dioxide.In a similar manner the adsorption of carbon dioxide or ethylene oxide on oxygen-preadsorbed silver was investigated.On the basis of the results obtained, it was concluded that ethylene and oxygen adsorb competitively on silver atoms on which a slightly positive charge had been induced by the neighbor oxygen adsorbates.The mechanism for the oxidation of ethylene to ethylene oxide is also suggested, including the reaction of molecular oxygen adsorbates with ethylene adsorbed linearly on a silver atom.