Characteristics of NaNO3-Promoted CdO as a Midtemperature CO2 Absorbent

In this study, we explored the reaction system CdO(s) + CO2(g) ⇄ CdCO3(s) as a model system for CO2 capture agent in the intermediate temperature range of 300–400 °C. While pure CdO does not react with CO2 at all up to 500 °C, CdO mixed with an appropriate amount of NaNO3 (optimal molar ratio NaNO3/CdO = 0.14) greatly enhances the conversion of CdO into CdCO3 up to ∼80% (5.68 mmol/g). These NaNO3-promoted CdO absorbents can undergo many cycles of absorption and desorption by temperature swing between 300 and 370 °C under a 100% CO2 condition. Details of how NaNO3 promotes the CO2 absorption of CdO have been delineated through various techniques using thermogravimetry, coupled with X-ray diffraction and electron microscopy. On the basis of the observed data, we propose a mechanism of CO2 absorption and desorption of NaNO3-promoted CdO. The absorption proceeds through a sequence of events of CO2 adsorption on the CdO surface covered by NaNO3, dissolution of so-formed CdCO3, and precipitation of CdCO3 partic...