DFT study of CO2 adsorption across a CaO/Ca12Al14O33 sorbent in the presence of H2O under calcium looping conditions.

• The adsorption of CO 2 and H 2 O by CaO/Ca 12 Al 14 O 33 was studied by DFT calculations. • The chemical adsorption of CO 2 and H 2 O on Ca 12 Al 14 O 33 -supported CaO is competitive. • The adsorption of CO 2 on Ca 12 Al 14 O 33 -supported CaO is stronger than that of H 2 O. • The adsorbed H 2 O activates adjacent O atoms of CaO, which benefits CO 2 adsorption. • The DFT can predict the CO 2 adsorption performance of different CaO-based sorbents. The synthetic CaO/Ca 12 Al 14 O 33 sorbent has been regarded as an efficient CO 2 sorbent during the calcium looping cycles. In this work, the CO 2 adsorption performance of the synthetic CaO/Ca 12 Al 14 O 33 sorbent in the presence of H 2 O was investigated by density functional theory (DFT) calculations. DFT was used to analyze the adsorption of CO 2 and H 2 O on the synthetic sorbent. Both structural parameters (atomic layout and electronic configuration) and the adsorption parameters (energy, bond lengths, angles, bond population and charge transfer) of CO 2 and H 2 O on the synthetic sorbent were determined. To confirm the feasibility of DFT analysis, the CO 2 capture performance of the synthetic sorbent in the presence of steam was examined in a dual fixed bed reactor. The results indicate strong interactions between the C atom and the O atom in CaO and interactions between the H atom and the O atom in CaO. The higher adsorption energy of CO 2 than H 2 O on pristine CaO and Ca 12 Al 14 O 33 -supported CaO suggests that the adsorptions of CO 2 and H 2 O are competitive and that the adsorption of CO 2 is stronger than that of H 2 O. The adsorption of H 2 O leads to the activation of adjacent O atoms of CaO and thus stronger CO 2 adsorption on the O atom with H 2 O adsorbed. The electrons in the p orbital of the O atom near the Fermi level play important roles in CO 2 adsorption by CaO. The presence of Ca 12 Al 14 O 33 hinders CO 2 adsorption by CaO. A low Ca 12 Al 14 O 33 content in synthetic sorbents should be maintained to ensure high CO 2 capture capacity and sintering resistance of synthetic sorbents. DFT calculations can predict the CO 2 adsorption performance of CaO-based sorbents with additives under different reaction atmospheres. [ABSTRACT FROM AUTHOR]