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.