Eco-CaMnOx: A Greener Generation of Eco-catalysts for Eco-friendly Oxidation Processes

Abstract

Owing to the alarming problems of depletion of mineral resources and ever-growing pollution by metallic elements, biosourced catalysts were prepared from Mn-accumulating plant species from a large-scale program of ecological rehabilitation of mining sites. This new generation of catalysts, "Eco-CaMnOx" catalysts, were obtained directly from a controlled thermal treatment of four species of Grevillea genus, a Mn-rich biomass, and without any further chemical treatment. Eco-CaMnOx catalysts were characterized by microwave plasma-atomic emission spectrometer, X-ray powder diffraction spectroscopy, high-resolution transmission electron microscopy, and scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy. These analyses revealed a natural richness in two unusual and valuable mixed calcium-manganese oxides: Ca2Mn3O8 and CaMnO3. The high efficiency of Eco-CaMnOx catalysts was demonstrated via the epoxidation of various biosourced terpenes and lipids, using the mixture H2O2/NaHCO3 as a green co-oxidant. This study demonstrated not only the high potential of Eco-CaMnOx catalysts as alternatives to oxidative reagents prohibited by REACH regulation but also the efficient synthesis of biosourced epoxides, which can be used as monomers for the preparation of biodegradable polymers. Finally, the original composition of Eco-CaMnOx catalysts led to distinctive catalytic behaviors compared to previously studied Eco-Mn and Pyr-Mn, allowing the preparation of sensitive epoxides such as linalool epoxide.