Designing of 3D Architecture Flower-like Mn-Promoted MgO and Its Application for CO₂ Adsorption and CO₂-Assisted Aerobic Oxidation of Alkylbenzenes

Abstract

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.

Selective Catalytic Oxidation of Ethylbenzene to Acetophenone: A Review of Catalyst Systems and Reaction Mechanisms

“…The characterization of Co/Mn/Br catalyst in the oxidation of EB using UV–visible spectroscopic technique showed easier generation of Mn­(III) when CO 2 is present, and such generation would be ascribed to the CO 2 enhancement effect. Recently, a 3D architecture flower-like Mn-promoted MgO catalyst with high CO 2 adsorption capacity, thanks to the basicity of MgO, was synthesized to simultaneously adsorb CO 2 and utilize it as co-oxidant for EB oxidation in the presence of O 2 to AP . Similarly, CO 2 /H 2 O 2 oxidant system has been used in the OEB-A over Keggin heteropolytungstate catalyst in a solvent-free reaction system .…”

“…Recently, a 3D architecture flower-like Mn-promoted MgO catalyst with high CO 2 adsorption capacity, thanks to the basicity of MgO, was synthesized to simultaneously adsorb CO 2 and utilize it as co-oxidant for EB oxidation in the presence of O 2 to AP. 257 Similarly, CO 2 /H 2 O 2 oxidant system has been used in the OEB-A over Keggin heteropolytungstate catalyst in a solvent-free reaction system. 258 Additionally, CO 2 (in the form of supercritical CO 2 ) has been explored as green solvent in the OEB-A reactions, and in addition to being environmentally benign solvent, the CO 2 acted as co-oxidant in the presence of tert-butyl hydroperoxide, thus improving selectivity to AP.…”

Additive- and base-free tandem aerobic oxidative cleavage of olefins to esters using bifunctional mesoporous copper-incorporated Al-SBA-15

“…Glycerol, cyclic carbonate, and γ-valerolactone (GVL) are examples of green solvents that have been investigated for use in oxidation reactions. 30–32 Therefore, the development of bifunctional catalysts has gained significant attention in recent years for enabling one-pot conversion of olefins to esters. The use of iron (Fe)-incorporated N-doped carbon nanoparticles as a bifunctional catalyst for the one-pot oxidative cleavage of olefins to esters is an interesting approach.…”

Base-Tailored Hierarchical MgO Microspheres as Efficient Catalysts for CO2 Fixation into Oxazolidinone at Atmospheric Pressure

“…Based on these drawbacks, we synthesized a broad-level applicable (for various organic transformations), nontoxic, easy-to-handle, and cost-efficient monometallic magnesium oxide (MgO) catalyst. 17,18 In contrast to other synthesis protocols, the simplest, low-cost, facile precipitation process assisted the hierarchical MgO microsphere catalyst synthesis using various metal carbonates as bases or precipitating agents. 19,20 This work described the one-pot synthesis of the oxazolidinone product through a three-component reaction between anthropogenic CO 2 , aniline, and styrene oxide at atmospheric pressure using the hierarchical MgO microsphere catalyst.…”

“…In earlier reports, catalyst synthesis procedures were little tedious, toxic solvents were used, and reactions were performed under high pressure and temperature, under solvent and cocatalyst conditions, and, more importantly, nonrecyclable featured catalysts. Based on these drawbacks, we synthesized a broad-level applicable (for various organic transformations), nontoxic, easy-to-handle, and cost-efficient monometallic magnesium oxide (MgO) catalyst. , In contrast to other synthesis protocols, the simplest, low-cost, facile precipitation process assisted the hierarchical MgO microsphere catalyst synthesis using various metal carbonates as bases or precipitating agents. , …”