CO2 capture of manganese oxides in multiple oxidation states: correlating surface basicity, recyclability, kinetics, and thermodynamics study

Developing efficient and regenerable adsorbents for CO2 capture is critical for mitigating anthropogenic emissions. This study investigates the CO2 capture performance of manganese oxides with different oxidation states (MnO, Mn2O3, MnO2, and Mn3O4), focusing on structural, recyclability, kinetic, and thermodynamic characteristics. Characterization using XRD, FTIR, FESEM–EDX, and TPD–CO/CO2 revealed MnO as the most promising candidate, exhibiting a physisorption capacity of 0.85 mg/g and chemisorption of 56.7 mg/g at 25 °C. This is attributed to its accessible surface area (1.7 m2/g) and moderate basicity (20.0 mg/g). Isotherm modeling indicated the Freundlich model (R2 = 0.9922) best fit the data, suggesting multilayer adsorption on a heterogeneous surface. Recyclability over five cycles showed only 6% capacity loss. CO2 exposure studies (0–48 h) confirmed carbonate formation, with new IR bands (1980–2180 and 1450–1650 cm–1) emerging after 6 h, intensifying at 12 h, alongside morphological changes observed by FESEM. Kinetic analysis followed a pseudo-second-order model, indicating chemisorption dominance. Thermodynamic parameters (ΔH‡ = −34.45 kJ/mol, ΔS‡ = −372.89 J/mol·K, ΔG‡ = +76.67 kJ/mol at 298 K) and activation energy (Ea = 31.92 kJ/mol) confirm an exothermic but kinetically controlled process with a well-ordered transition state. These findings position MnO as a robust, regenerable CO2 adsorbent, offering insight into the role of oxidation states in enhancing CO2 binding and guiding the development of advanced metal oxide-based carbon capture materials.

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