Research on the oxidation of furfural to maleic anhydride (MA) suffers from low efficiency, solvent corrosion, and harsh conditions. CuO_x/Nb₂O₅ was prepared as photocatalyst to catalyze furfural oxidation to MA and 5-hydroxy-2(5H)-furanone (HF) selectively, and can absorb visible light due to the ligand to metal charge transfer (LMCT) with adsorbed furfural molecules.

Abstract

Maleic anhydride (MA) is an important polyester monomer that can be produced from oxidizing renewable furfural derived from biomass. However, MA generation from furfural requires harsh reaction conditions, and suffers from low efficiency and solvent corrosion. Herein, we design a Nb₂O₅ photocatalyst loaded of highly dispersed CuO_x (CuO_x/Nb₂O₅), which selectively catalyzes furfural oxidation to MA and the precursor (5-hydroxy-2(5H)-furanone, HF). Due to CuO_x loading and forming a complex of ligand to metal charge transfer (LMCT) between the Nb₂O₅ surface and adsorbed furfural, the CuO_x/Nb₂O₅ absorbs visible light to activate furfural though Nb₂O₅ has a large band-gap energy (3.2 eV). Singlet oxygen (¹O₂) is the key active species for C−C bond cleavage and CO generation. MA and HF is produced with a combined yield of 59 % under optimized conditions. This work provides a mild way to provide renewable maleic anhydride via oxidative C−C bond cleavage.