Catalytic Aerobic Oxidation of Renewable Furfural with Phosphomolybdic Acid Catalyst: an Alternative Route to Maleic Acid

Developing new technologies to obtain chemicals from biomass in place of the fossil feedstock have attracted attention in academic and industrial communities. In this work, using renewable furfural as the feedstock, catalytic aerobic oxidation of furfural to maleic acid was investigated with phosphomolybdic acid catalyst in the aqueous/organic biphase system. The oxidation happens in the aqueous phase, and the organic phase serves as the reservoir to release the substrate gradually through phase equilibrium. Under the optimized conditions, 34.5% yield of maleic acid could be obtained with 68.6% of selectivity, and the conversion of furfural is 50.4%. Because furfural and maleic acid dominantly exist in two different phases, the product separation and reactant recycle would be very simple in its potential application. The FT-IR and 31P NMR technologies were applied to characterize the phosphomolybdic acid catalyst, and the pathway of maleic acid formation was also discussed based on obtained mechanistic information. This work demonstrates an alternative, renewable route to maleic acid, and the mechanistic information from this study also provides clues to improve the catalyst for efficient oxidation of furfural to maleic acid.