Highly Efficient Conversion of Carbohydrates into Formic Acid with a Heterogeneous MgO Catalyst at Near-Ambient Temperatures

The conversion of carbohydrate biomass to formic acid (FA) is drawing increasing research attention in the pursuit for more sustainable and greener synthesis of chemicals/fuels; however, only a few studies have achieved this conversion near ambient temperatures, which relies heavily on the unrecyclable homogeneous catalysts. Herein, a simple but efficient MgO-H2O2 system without adding any extra homogeneous base was established, achieving the highest 78.6% FA yield with 90.5% glucose conversion within 4 h at 323 K in water as a green medium. The catalyst MgO could be recycled five times without decline in activity with a simple regeneration procedure, which occupied only 2.3% of the total operation cost based on an ex ante life cycle assessment, and it is much cheaper than its homogeneous counterparts such as LiOH. A mechanistic study with in situ Fourier transform infrared spectroscopy (FTIR) analysis revealed that the oxidation started from the -CHO end of glucose, which more importantly found that the pronounced synergetic effects of the solid base catalyst and the oxidant promoted the formation of an active MgII species Mg(OH)(OOH), acting as a key intermediate for glucose oxidation at the -CHO group and C-C cleavage. This work advances efficient oxidation of glucose into FA near ambient temperatures with a heterogeneous catalyst, establishing a possible approach to produce FA from renewable biomass resources in real application.