Magnesium oxide (MgO) is an interesting material with tunable acido-basic properties. MgO-based composite sorbents (MgAl2O4, MgSiO3, and MgTiO3) have drawn much attention based on their high temperature CO2 sorption. In this study, a theoretical and experimental investigation by phonon calculations and high-pressure CO2 sorption was conducted to identify a potential candidate to achieve CO2 capture under pre-combustion conditions. The divergence of the physico-chemical properties of the various sample materials was found to be the determining factor for the enhanced CO2 sorption. From the high-pressure CO2 sorption experiment at 200 °C, MgAl2O4 shows high chemisorption capacity of CO2 compared to the other systems such as MgO, MgSiO3 and MgTiO3. However, the thermodynamic properties of MgAl2O4 for CO2 capture were found to be less favorable than those of other compounds in our phonon calculations. Thus, the carbonation of MgAl2O4, producing MgCO3 is not a favorable reaction at the experimental condition in our phonon calculations due to the formation of Al2O3 as a byproduct. On the other hand, MgO was experimentally found to have low adsorption capacity under similar conditions. Contrarily, the carbonation of MgO, which has a large number of basic sites at pre-combustion conditions and produces MgCO3, is found to be favorable in our calculations clearly defining the existence of tradeoff properties under practical CO2 sorption conditions.