Sustainable chemistry research prioritizes reducing atmospheric carbon dioxide, and one logical solution is to develop adsorbents suitable for carbon capture and utilization. In this work, a new family of three-dimensional (3D) flower-like Mn-promoted MgO was synthesized by the coprecipitation method and used as an adsorbent for CO2 capture and a catalyst for CO2 utilization. The scanning electron microscopy (SEM) analysis of the samples shows a 3D architecture composed of thin nanosheets. The X-ray diffraction (XRD) analysis confirms the presence of the MgO with a cubic structure, while X-ray photoelectron spectroscopy (XPS) reveals the existence of Mn particles as a combination of Mn3+ and Mn4+ ions on MgO. N2 adsorption–desorption experiments highlight the beneficial contribution of Mn particles to surface area enhancement and reveal the existence of mesopores. Furthermore, the designed 3D Mn-doped MgO as an adsorbent demonstrates its capability to improve the ability of MgO to adsorb CO2 (from 0.28 mmol/g for pure MgO to 0.74 mmol/g) in ambient conditions and it is regenerable up to 9 cycles with a slight variation after the third cycle. Moreover, Mn-doped MgO shows good catalyst activity for the oxidation of ethylbenzene derivatives to carbonyl compounds in the presence of CO2 and O2. Mn-15/MgO shows excellent catalytic behavior with a conversion of 97.4 and 100% selectivity. Also, it is regenerable with an insignificant decrease in conversion (∼11.63%) after seven cycles, while the selectivity of acetophenone remains stable. The analyses of the recycled sample suggest that the chemical compositions of Mn and Mg influence the catalytic activity of those Mn-promoted MgO materials. The role of CO2 gas in the aerobic oxidation of ethylbenzene to acetophenone has also been proved. Finally, the control experiments and EPR studies reveal that the reaction takes place through the formation of radicals.

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