First principles study on the adsorption of CO₂ and H ₂O 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 K₂CO ₃ (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 Gibb's free energies indicate that H ₂O 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.