Reactivity of silver oxide in the absorption of carbon dioxide

Abstract

Silver carbonate prepared by precipitation from very dilute solutions of AgNO3 and NaHCO3 decomposes at 170 °C to yield Ag2O which is particularly active for the uptake of CO2. In contrast to other oxide adsorbents prepared from carbonates, the high activity is not a consequence of the development of a high surface area. The decomposition of Ag2CO3 leads to only a small increase in surface area, the oxide product having an area less than 1 m2 g–1. The activity in this system is linked instead with the presence of water. Co2 absorption depends upon the continuing availability of water at the reacting interface. Ag2O rapidly loses activity towards CO2 uptake in absorption–regeneration cycles if dry CO2 is employed. There is, in addition, a slow loss of activity during cycling which is independent of the presence of water. The results are discussed by use of a model in which water is considered to be incorporated in the oxide as OH– and in the carbonated solid as OH– and HCO3– ions.