Efficient Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran over Fe₂O₃-Promoted MnO₂ Catalyst

It is challenging to effectively convert 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF), a flexible biobased building-block, over non-noble metal catalysts. In this contribution, Mn-Fe oxides were prepared and served as highly active catalysts for the selective oxidation of HMF to DFF. Among Mn-Fe oxides with varied Mn-Fe molar ratios, Mn₆Fe₁O_x showed the best catalytic activity and offered HMF conversion up to 97% with a DFF selectivity of 98% (110 °C, 5 h, and 1.5 MPa O₂). It is revealed that the introduction of α-Fe₂O₃ resulted in significant enhancement in the amount of catalytic active sites (Mn⁴⁺-O^2- pairs) and their activity in Mn₆Fe₁O_x for the dehydrogenation of HMF to DFF. Mn₆Fe₁O_x also was a robust catalyst that could be successively used at least six times without substantial loss in its catalytic activity. Furthermore, a facile two-step process for the conversion of fructose to DFF with a yield up to 80% was developed by the integration of dehydration and oxidation over Amberlyst-15 and Mn₆Fe₁O_x, respectively.