Dynamic CO₂ sorption on MgO-based sorbent in the presence of CO and H₂O at elevated pressures

The presence of gas species other than the target adsorbate in practical conditions causes complications in implementing a sorption-based process because of synergistic or detrimental effects on the sorption mechanism. MgO-based sorbents have attracted massive attention for the pre-combustion CO₂ capture, where H₂O and CO co-exist in emission gas. Although H₂O has been reported to greatly enhance CO₂ sorption kinetics, CO₂ sorption behavior and mechanism under a large quantity of H₂O as in the practical condition remain unclear. Furthermore, CO₂ sorption behavior in the presence of CO has not been adequately examined. Here, the dynamic CO₂ sorption behavior of MgO-based sorbent was understood by coupling the breakthrough experiment under practically relevant conditions with in situ DRIFTS results. At elevated pressures, the sorption performance was considerably enhanced, whereas the influence by temperatures was insignificant. In addition, H₂O enhanced CO₂ sorption kinetics and initial CO₂ sorption on MgO-based sorbent, whereas CO hindered them. In situ DRIFTS analyses for the mechanism study revealed that OH groups generated from H₂O dissociation created highly basic sites that promoted the formation of monodentate carbonate, thereby enhancing the initial CO₂ sorption. In contrast, CO hampered CO₂ sorption through two mechanisms: (1) competitive sorption between CO₂ generated from the water–gas shift reaction and CO₂ in the feed; (2) interference of the promoted sorption by the molten nitrate salts. This study demonstrated that the practical condition of the pre-combustion CO₂ capture significantly alters the CO₂ sorption behavior of MgO, thereby providing insights for the ultimate implementation of MgO-based sorbents.