Infrared Study of Carbon Dioxide Adsorbed on Magnesium and Calcium Oxides

Abstract The infrared absorption spectra of CO2 adsorbed on MgO and GaO were measured in the wide region 700–4000 cm−1 at various amounts of adsorbed CO2 and temperatures of adsorption and desorption. It has been found that both uni- and bidentate carbonates are formed on MgO when a small amount of CO2 is adsorbed and that unidentate carbonates predominate as the amount of adsorbed CO2 is increased. On the other hand, only unidentate species were formed on CaO at room temperature independently of the amount of adsorbed CO2, but bidentate species were also formed on CaO when the temperature of adsorption was high. The unidentate carbonates formed on both MgO and CaO at room temperature partially changed to bidentate carbonates upon evacuation at higher temperatures. The correlation between Δv=|v1–v5| and the partial charge on oxygen atoms of various oxides, which corresponds to basic strength on the surface, was examined.