Magnetically recoverable MFe₁₂O₁₉ nanoparticles as efficient and environmentally benign catalysts for gram-scale selective oxidation of olefins

Catalytic oxidation is an efficient route for synthesizing oxygenated compounds such as epoxides and aldehydes. However, developing cost-effective, environmentally friendly and selective gram-scale catalysts, in full agreement with circular economy and green chemistry principles, remains a significant challenge. Herein, we report on MFe₁₂O₁₉ magnetic nanoparticles (MNPs) as a novel, magnetically recoverable and selective catalyst for the oxidation of olefins. Three different MFe₁₂O₁₉ (M = Cu, Sn and Sr) MNPs were synthesized using the coprecipitation method and characterized by XRD, FTIR, Raman, XPS, SEM-EDX, TEM, BET, zeta potential and ⁵⁷Fe Mössbauer spectroscopy. XRD analysis demonstrates that the patterns of SnFe₁₂O₁₉ and CuFe₁₂O₁₉ are totally different from those of the magnetoplumbite hexaferrite structure due to the confirmed coexistence by Rietveld refinements of SnO₂-Fe₂O₃ and CuFe₂O₄-Fe₂O₃ as composite structures, respectively. In good agreement, Raman studies exclusively confirms the coexistence of MO _<i>x</i> -Fe₂O₃ as a composite structure in MFe₁₂O₁₉, due to the presence of α-Fe₂O₃ and γ-Fe₂O₃ as intermediate phases during the formation process of the hexaferrite structure. Moreover, the XPS and Mössbauer results are consistent with the experimental evidence and spectroscopic characterizations. Subsequently, the catalytic activity of the as-synthesized MNPs was evaluated for the oxidation of styrene as a model olefinic substrate. Among the as-prepared MFe₁₂O₁₉ MNPs, the composite structure CuFe₂O₄-Fe₂O₃ in CuFe₁₂O₁₉ effectively enhances catalytic activity, selectivity and reusability due to the synergistic catalytic effect within a single magnetically recoverable nanostructure. Overall, MFe₁₂O₁₉ MNPs present a facile and greener approach using magnetically recyclable hexaferrites for selective catalytic oxidation reactions.