Formation and Change Mechanisms of CO₂ Adsorption Structure in Zeolites with Different Cations

CO₂ molecule can interact with cation(M)and framework oxygen atom in zeolites,forming an adsorption structure like M-O=C=O⊥O_z.Theoretical calculations show that with the increase of radius and polarizability of cation,the M-O distance in the minimum energy structure of a single cation-CO₂ interaction is increase with the order of 0.200,0.241,0.281 nm for Li⁺,Na⁺,and K⁺,and its minimum potential energies decrease.Molecular simulations suggest that in different loadings,the M-O distance following the trend that LiX< NaX< KX,and the M-O distance derived from the radial distribution function are 0.205,0.248,and 0.289 nm,while the adsorption structure energies are-57.9,-53.1,and-41.3 kJ/mol,for LiX,NaX,and KX,respectively.The good agreement between theoretical calculation and molecular simulation suggests that the adsorption structure characteristics could be reflected by the minimum potential energy position of a sin-gle cation-CO₂ interaction.Furthermore,the trend of simulated CO₂ loading that LiX> NaX> KX is consistent with the trend of the adsorption structure energy formed in those zeolites,indicating that the cation in zeolite could influence the CO₂ adsorption capacity by affecting the adsorption structure energy by changing its M-O distance.