Improved Fe/Mg-Al hydrotalcite catalyst for Baeyer–Villiger oxidation of ketones with molecular oxygen and benzaldehyde

Metal (Me: Fe, Co, Ni or Cu) containing Mg-Al hydrotalcite-type anionic clay catalysts have been prepared by adopting the “memory effect” of hydrotalcite and tested for Baeyer–Villiger oxidation of ketones. Mg-Al hydrotalcite was calcined to the mixed oxide and dipped in an aqueous solution of metal (Me) salt; metal species was incorporated by “memory effect” to form Me/Mg-Al hydrotalcite as the active phase on the surface of the Mg-Al mixed oxide. The activity and the structure of these catalysts have been compared with those of metal supported catalysts prepared by coprecipitation and impregnation. Among the metals tested, iron was the most effective and use of Fe(NH4)2(SO4)2·6H2O as the metal salt resulted in the highest activity. The activity of the catalyst was higher than those prepared by coprecipitation from the nitrates of Mg, Fe and Al. Judging from Mössbauer and Fe K-edge XAFS spectra, Fe species possess the Fe3+ valence state, are mainly octahedrally coordinated and form FeOFe cluster-type structure on the Mg-Al mixed oxides. This clearly indicates that the Fe3+OFe3+ cluster-type compounds are more active for the Baeyer–Villiger oxidation than well dispersed Fe3+ species formed on the hydrotalcite prepared by coprecipitation. Six-membered cyclic ketones, such as cyclohexanone, 2-norbornone and 2-adamantanone, were effectively oxidized to the corresponding lactones by using O2/benzaldehyde as an oxidizing agent.

Graphical abstractFe/Mg3Al prepared by the “memory effect” exhibited a high catalytic activity for Baeyer–Villiger oxidation of ketones using molecular oxygen and benzaldehyde. The Fe/Mg3Al catalyst showed higher activity than that prepared by copreciptation, and the prominent catalytic performance could be ascribed to cluster-like octahedrally coordinated Fe3+ species incorporated on the surface of Mg-Al mixed oxide. Figure optionsDownload full-size imageDownload as PowerPoint slide