(19b) The Adsorptions of the CO2 On Rumpled CaO (0 0 1) Surface and the Effect of Water Vapor Investigated by Density Functional Theory

Calcium oxide (CaO) is converted to calcium carbonate (CaCO3) by adsorbing carbon dioxide (CO2) to undergo carbonation in a reversible calcination process. There is enhanced adsorption in the presence of water vapor, which has been proven by experiment. While the CaO surface is widely used in industry as a highly reactive adsorbent and has been studied in many experiments, there is lack of theoretical studies to investigate the mechanism of CO2 adsorption on the CaO. In this study, the CaO surface was investigated for CO2 adsorption including the role of water molecules. The reaction rate constants and equilibrium constants for a CO2 gas molecule adsorption on a solid CaO cluster were calculated.

The adsorption of CO2 onto rumpled CaO (0 0 1) surfaces was investigated with density functional theory (DFT) methods. The surface was modeled using both a 5×5×2 cluster and a periodic slab designed with a 5×5×2 unit cell. Structures were optimized with the Perdew-Wang (PWC) functional with the local density approximation (LDA) using the Harris approximation in order to reduce the computational time. Adsorption energies of CO2 binding on the CaO surface were calculated with the gradient corrected (GGA) method with the BLYP functional using the optimized lower level geometries. The spin polarization effect was included in the calculations for higher quality results we. Furthermore, the adsorption of CO2 on rumpled CaO surface in the presence of water vapor was studied to investigate the effect of water vapor on the reaction. Results show how the carbonate was formed on the CaO surface by adsorbing carbon dioxide and the strong adsorption energy on the CaO surface. Water vapor as a catalyst will increase carbonation performance of the CaO surface.