First principles study on the adsorption of CO2 and H2O on the K2CO3 (001) surface

Potassium carbonate (K2CO3) is of interest as a CO2 absorbent. The molecular structure and properties of co-adsorption of CO2 and H2O on the K2CO3 (001) surface were investigated by density functional theory (DFT) methods. The DFT surface energies of K2CO3 low index planes were determined, and the (001) surface has the lowest surface energy. The calculated adsorption energies and Gibbʹs free energies indicate that H2O adsorbs much stronger than CO2, and their co-adsorption is repulsive on the K2CO3 (001) surface. The ab initio thermodynamics calculated coverage of CO2 under pre-combustion conditions is vanishingly small such that the net rate of bicarbonate formation is insignificant. This suggests that promoting bicarbonate formation requires a surface with stronger adsorption of CO2. This provides an indication that CO2 adsorption on the surface will be difficult in a wet stream, limiting the rate of conversion to the bicarbonate due to a low CO2 coverage. This is also in agreement with experimental results in the literature indicating that dry K2CO3 uptakes CO2 slowly, and that conversion to the bicarbonate proceeds initially through a hydrated structure.