Experimental and density functional theory study of the synergistic effect between steam and SO2 on CO2 capture of calcium-based sorbents

•Detrimental effect of sulfation on CO2-capturing capacity in presence of steam.•Understanding of the competitive adsorption mechanism between CO2 and SO2.•Detailed reaction paths of carbonation and sulfation when H2O molecules exist.•Comparison of CO2 and SO2 adsorption energies on various sites of CaO (100) surface. Calcium looping is a fast-developing second generation CO2 capture technology. In practical looping of Ca-based sorbents, steam and SO2 are naturally present in the flue gas subjected to CO2 capture, due to the combustion of fossil fuels. Until now, the single effect of steam or SO2 has been reported to have a significant impact on the CO2 capture of sorbents. However, there are few studies on the synergistic effect of steam and SO2 on the CO2 sorption characteristics of sorbents, and it is poorly understood. In this study, experiments and DFT calculation are employed to clearly understand the synergistic effect of steam and SO2 on the carbonation behaviors of sorbents. Tests were first performed under typical calcium looping (CaL) conditions with and without the presence of steam and SO2 during the carbonation process. Results indicated that the enhancement of steam on the sulfation is obviously stronger than that on the carbonation as the CaL cycles increased, which is then verified by a series of characterization methods. According to quantitative analysis through DFT calculation, the adsorption energy of SO2 on CaO (100) surface was found to be more than that of CO2 in the presence of steam, indicating the preferential adsorption of SO2 in the presence of H2O molecules on the CaO (100) surface. Therefore, the experimental results were verified and the competitive adsorption mechanism of SO2 and CO2 in the presence of steam during the carbonation process was further understood from microscopic aspect.