Additive-free photo-assisted selective partial oxidation at ambient conditions of 5-hydroxymethylfurfural by manganese (IV) oxide nanorods

The valorization of natural and renewable resources, like lignocellulosic biomass, towards value-added chemicals by low energy and economically viable processes still remains a global research and technological challenge. 5-hydroxymethylfurfural (HMF) is an important platform chemical that can be easily derived from biomass, and it can be further used as a feedstock for the production of building blocks for polymers or fuels. In this context, the partial oxidation of the hydroxyl group on the HMF molecule leads to the formation of the corresponding aldehyde, 2,5-diformylfuran (DFF), which may find multiple applications in bio-chemical industries. Herein, we present the synthesis and characterization of novel manganese (IV) oxide nanorods as catalyst for the HMF to DFF partial oxidation at ambient conditions. This 1D nanocatalyst operates at low energy light irradiation and without the addition of chemicals (bases or oxidants) as a highly selective photo-assisted catalyst. Under optimized experimental conditions, the HMF conversion was found to be above 99%, while the DFF selectivity was almost 100%. The presence of molecular O-2 played a key role in triggering the selective oxidation, while the use of an aprotic and less polar organic solvent, such as acetonitrile, compared to water, further enhanced the reactivity of the catalyst.