CO2 adsorption enhancement over alkaline metal-promoted MgO with SO2, O2, and H2O present: A theoretical study

Abstract

Protective effect of alkaline metals on CO 2 adsorption disturbed by SO 2 /O 2 /H 2 O. • SO 2 /O 2 /H 2 O adsorption on alkaline metal-promoted MgO is more intense than pure MgO. • SO 2 /O 2 /H 2 O aggregate around alkaline metals and save other adsorption sites for CO 2 . • Alkaline metals change surface potential fields of MgO in favor of CO 2 adsorption. • Involvement of alkaline metals helps to optimize electron transmission paths of CO 2 . • Desorption temperatures of CO 2 over promoted MgO increase due to strong adsorption. The oxidizing abilities of SO 2 /O 2 and molecular polarity of H 2 O severely hamper CO 2 adsorption on MgO via capturing surface electrons or occupying active sites. Therefore, it is crucial for MgO to gain better anti-SO 2 /O 2 /H 2 O features. In this study, alkaline metals are introduced as promoters for MgO to counter negative effects of SO 2 /O 2 /H 2 O. Through density functional theory (DFT) calculations, adsorption structures/energies, electron clouds/electron transfer, effects of temperatures are fully investigated to account for how adverse impacts of SO 2 /O 2 /H 2 O are counteracted. Based on DFT calculation results, the average adsorption energies of CO 2 on pure MgO are only 0.46, −6.54, and 2.41 kJ/mol with SO 2 , O 2 , and H 2 O present, respectively. For Li-promoted MgO, the average adsorption energy of CO 2 rises by about 65.51 kJ/mol with H 2 O present. As to Na-doped MgO, its average CO 2 adsorption energy is raised by around 200 % with SO 2 involved. As far as K-modified MgO is concerned, the average adsorption energy of CO 2 is almost 5.0 times as big as the counterpart with O 2 . Regarding Rb-amended MgO, its average adsorption strength of CO 2 is raised to about −38.55 kJ/mol when being affected by H 2 O/SO 2 /O 2 . What is more, it is proved that the desorption temperatures of CO 2 rise a lot over promoted MgO owing to stronger electronic interaction. The research results could provide meaningful information for applying promoted MgO as a CO 2 capturer in real industries.