Density Functional Theory Study on CO2 Adsorption by Ce-Promoted CaO in the Presence of Steam

Calcium looping is one of the most promising technologies for large-scale CO(2 )capture, while CaO-based materials suffer from the deactivation in CO(2 )capture capacity in the multiple carbonation/calcination cycles as a result of sintering. Ce-promoted CaO is considered as an effective CO2 sorbent during calcium looping cycles. In this paper, the CO2 adsorption performance of Ce-promoted CaO in the presence of steam was investigated using density functional theory (DFT) calculations. The cyclic CO2 capture performance of Ce-promoted CaO in the presence of steam was tested to confirm the feasibility of DFT calculations. Moreover, the structural and adsorption parameters, including atomic layout, energy, bond length, and charge transfer of CO2 and H2O molecules on Ce-promoted CaO, were determined. The DFT calculation results indicate that the surface O atoms in Ce-promoted CaO are activated by the Ce atom; therefore, the CO2 adsorption performance is improved on Ce-promoted CaO. When the H2O molecule is pre-adsorbed on Ce-promoted CaO and CaO, the adsorption of CO2 is enhanced. The CO(2 )adsorption energies on Ce-promoted CaO and CaO in the presence of H2O are -1.99 and -1.53 eV, respectively, which are larger than those in the absence of H 2 O. The co-adsorption of CO2 and H2O molecules appears feasible on Ce-promoted CaO, while CaO exhibits obvious inhibition on the co-adsorption. The experimental results indicate that the Ce species in Ce-promoted CaO exist in the form of CeO2, which leads to higher CO(2 )capture activity and sintering resistance than those of CaO. The presence of steam in carbonation improves the CO(2 )capture capacity of Ce-promoted CaO; therefore, the experimental results agree well with DFT calculations. The cost of makeup flow of Ce-promoted CaO is 20.3% lower than that of CaO. Therefore, Ce-promoted CaO appears promising in calcium looping.