Epoxidation Reaction - Involvement of Adsorbed Oxygen Species

Mechanism of the Epoxidation Reaction - Involvement of Adsorbed Oxygen Species. Herzog has reported that the use of nitrous oxide rather than oxygen as the oxidant for ethylene epoxidation results in a considerably reduced selectivity. Since nitrous oxide decomposition leads primarily to adsorbed atomic oxygen, Herzog concluded that molecular oxygen species are required for the partial oxidation reaction. More recently this experiment has been repeated in a closed recirculatory system the same result was obtained. When the reaction was carried out in the presence of both 02 and N2 0 the ethylene oxide contained 0 exclusively while was incorporated into the carbon dioxide. 

Seo and Sato have compared the heat and entropy of oxygen adsorption on three silver catalysts. The more selective the catalyst is for ethylene oxidation the lower the heat of oxygen adsorption and the higher the entropy of the adsorbed species. They argued 2 (ads) is the selective species since it has a lower heat of adsorption than 0 (ads) or 0 (ads) and it would be expected that 02 (ads) would have the higher entropy. 

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