Insights into the mechanism of the capture of CO2 by K2CO3 sorbent: a DFT study.

ABSTRACT

The adsorption and reactions of CO2 and H2O on both monoclinic and hexagonal crystal K2CO3 were investigated using the density functional theory (DFT) approach. The calculated adsorption energies showed that adsorption of H2O molecules was clearly substantially stronger on the K2CO3 surface than the adsorption of CO2, except on the (001)-1 surface of hexagonal K2CO3, where CO2 is competitively adsorbed with H2O. Carbonation reactions easily occur on pure K2CO3 and involve two parallel paths one is where adsorbed H2O reacts with molecular CO2 in gas to form the bicarbonate, while the other is where H2O dissociates into OH and H before bicarbonate formation, and then OH reacts with gaseous CO2 to form a bicarbonate. Our results indicate that adding a support or promoter or using a special technique to expose more (001)-1 surfaces in hexagonal K2CO3 may improve the conversion of CO2 to the bicarbonate, which provides a theoretical direction for the experimental preparation of the K2CO3 sorbent to capture CO2.