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Solid CaO-based sorbents for CO2capture represent a promising alternative technology compared to traditional amine scrubbing methods. However, CaO-based sorbents are rapidly sinter and easily decrease CO2uptake capacity with regenerated carbonation–calcination cycle. Thus, in this study, doping CaO with CeO2make it an excellent candidate for improving stability and facilitating CO2capture efficiency. The dual function of CaO bio-based sorbents with varying ratios of cerium (Ce) were derived from naturally occurring blood clam using the gel-combustion method. Their nanostructures and physicochemical properties were characterized through the specific methods, including in situXAS, CO2chemisorption and physisorption, XPS, XRD, and SEM. An in-depth understanding of CO2adsorption mechanism was further emphasized using a density functional theory (DFT) simulation. The results demonstrate that nanosized CeO2-CaO, with a mole ratio of 1:9, exhibited the highest performance for CO2capture (6.44 mmol CO2/g sorbent). It is postulated that Ce serves as a physical barrier, effectively partitioning adjacent CaO grains and thereby diminishing the sintering rate. CaO is identified as the primary adsorption site, in contrast to CeO2. Mixing the Ce-Ca dual oxide initiates the electron-rich O at the O’ site. The electron localization at the O’ active site improves the activity of O’, making the performance CeCa(200) for capturing CO2capture dominant. This discovery suggests that CeO2-CaO holds promise as a sustainable alternative sorbent for future CO2capture applications.