The interaction between silver and N₂O in relation to the oxidative dehydrogenation of methanol

The interaction of N₂O with pure silver at temperatures up to 900 °C has been studied using temperature-programmed reduction and desorption; the interaction is compared with that of oxygen with silver. The effect of addition of N₂O, as well as of the complete replacement of oxygen by N₂O, on the oxidative dehydrogenation of methanol on a silver catalyst has also been studied. It was found that the interaction of silver with N₂O was much slower than that of O₂; no atomic surface oxygen species were observed, probably because the formation of subsurface species was not complete; selective adsorption appears to take place on the surface defects and grain boundaries involved in the formation of the subsurface species. Addition of small amounts of N₂O to the reaction mixture (CH₃OH + O₂) for the oxidative dehydrogenation of methanol had almost no influence on the conversion or on the product distribution measured. However, the conversions were considerably lower when oxygen was totally replaced by N₂O; only above 600 °C was the N₂O exhausted. At the same level of conversion of the methanol, the amount of CO₂ produced was lowered compared to the case of O₂. This is in agreement with the suggestion that CO₂ is formed via weakly bound surface oxygen.