Study on the mechanism of competitive adsorption on the surface of potassium carbonate during direct air capture process

Abstract

Direct air capture carbon dioxide (DAC) technology has the potential to achieve negative carbon emissions. Alkali metal-based absorbents (the active ingredient is mainly potassium carbonate or sodium carbonate) have a broad application prospect in DAC field. There is a paucity of reports on the competitive adsorption of major components of air on adsorbent surfaces. In this paper, the competitive adsorption behaviors of CO2, H2O, N2, and O2 on the surface of K2CO3 were investigated based on first principles and density functional theory (DFT), the synergic competition mechanism of each gas during adsorption was revealed by analyzing the parameters of adsorption energy, charge transfer, weak interactions and so on. The results showed that the maximum adsorption energy of CO2 by K2CO3 was 0.557 eV, and the relationship between the maximum adsorption energies of the four gases was O2 > H2O > CO2 > N2. The interaction between H2O and CO2 during co-adsorption inhibited their adsorption on the K2CO3 surface, especially weakening the adsorption effect of the surface O atoms on the H2O. Under CO2_N2_O2 gas composition, CO2 chemisorption occurred due to the strong oxidizing property of O2, the charge transfer effect commonly existed in the adsorption process of each gas, which contributed the most to O2 adsorption. The obtained results can further deepen the decarbonization mechanism of alkali metal-based adsorbents.