Explaining steam-enhanced carbonation of CaO based on first principles

Calcium-based sorbents have been regarded as effective agents for capturing CO2 from industrial flue gas. Recent studies have shown that steam can enhance the carbonation performance of calcium-based sorbents. In this paper, a CaO (001) surface was made to investigate the micro-level mechanism of steam-enhanced carbonation based on first principles calculations. Charge transfer and bond population were calculated to evaluate an interaction effect between adsorbates and the CaO (001) surface. Individual adsorption of CO2 and H2O was compared with binary adsorption and co-adsorption of the two molecules on the CaO (001) surface, based on dispersion-corrected density functional theory (DFT-D) calculations. First, the predicted adsorption energies suggest the O-top site is the best site. It forms carbonate-like structure and hydroxyl-like structure for the individual adsorption of CO2 and H2O. Binary adsorption calculations indicate that H2O is more easily adsorbed by the CaO (001) surface than CO2. The adsorption of H2O and CO2 adsorption are promoted in comparison with their individual adsorption on the CaO (001) surface. Moreover, the analysis of adsorption energies and partial density of states (PDOS) suggests that a H2O-CaO (001) surface (CaO (001) surface that has already adsorbed H2O) is more reactive than the clean CaO (001) surface for CO2 adsorption, which further supports the idea that the steam-enhanced mechanism is an Eley-Rideal (E-R) mechanism, which means H2O is adsorbed on the CaO surface, and then CO2 is adsorbed. (c) 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.