Room-Temperature Synthesis of Magnesium Incorporated Into OMS-2 Enables Highly Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran.

Selective oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) remains a challenge. Herein, we prepared magnesium intercalated into cryptomelane-type OMS-2 to achieve ultrafine Mg-OMS-2 nanorods via room-temperature coprecipitation. The results confirm that Mg2+ cations are incorporated into the MnO6 octahedral lattice of OMS-2. The Mg9%-OMS-2 with 9 wt% Mg exhibits high catalytic activity for aerobic oxidation of HMF with 91% conversion and 99.9% DFF selectivity at 120 °C within 1 h. Experimental results and characterization demonstrate that the reaction follows the Mars-van Krevelen redox mechanism. It involves a redox cycle by a reduction of high valence state of Mn ions combined with the participation of lattice oxygen, whereas surficial oxygen vacancies (Ovac) are continuously replenished by aerial soluble oxygen. The reaction rate equation of HMF oxidation is expressed dependent on O2 pressure and HMF concentration. Moreover, the predicted activities agree well with the measured activities in wide ranges of HMF concentrations and O2 pressures. Therefore, the ultrafine Mg9%-OMS-2 nanorods, featuring efficient catalytic performance, facile regeneration, insightful mechanism, and kinetics descriptions present a significant potential toward practical applications.