Density functional theory analysis of the adsorption behaviors of H2O and CO2 on the CaCl2(110) surface

Abstract

The co-adsorption models of H₂O and CO₂ molecules on the CaCl₂(110) surface are established by the first-principles method based on the density functional theory. The adsorption structures, electron distribution, density of states, and reaction pathways are calculated and analyzed to reveal the reaction mechanism of H₂O and CO₂ molecules on the CaCl₂(110) surface. The results indicate that the adsorption site of the Ca_5c atom is more active than that of Ca_6c when H₂O is adsorbed on the CaCl₂(110) surface. The chemical co-adsorption processes of H₂O and CO₂ on the CaCl₂(110) surface are described via the Langmuir–Hinshelwood mechanism. Their adsorption energies are −0.903 eV and −1.284 eV, which were lower than that of a single H₂O molecule. The H₂O molecule loses electrons during the adsorption process and the Ca_5c atom bonded acts as the acceptor and transmitter of electrons. The energy required for the dissociation of H₂O is significantly reduced in the presence of co-adsorbed CO₂. Moreover, the dissociation of H₂O is promoted, and then the HCl molecule is formed by the OH⁻ bonded with the H atom on the CaCl₂(110) surface, and the reaction pathway requires only 1.03 eV when H₂O is bonded with chemisorbed CO₂ to form an HCO₃⁻ complex. In particular, this adsorption process follows a Langmuir–Rideal mechanism. The findings can lay a theoretical foundation for the chlorine liberation mechanism from CaCl₂ and also provides technical support for the pyro-hydrolysis of CaCl₂-containing solid wastes.