Cobalt-Ceria Binary Oxide Nanojunctions for Aqueous-Phase Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid: The Role of Interfaces.

Cobalt-ceria binary oxide nanojunctions were prepared by a sol-gel method with various chelating agents. The formed interfaces among CeO2 and Co3O4 can promote the generation of nucleophilic •O2- from O2 and then tune the catalytic oxidizability of the as-prepared CoCe nanojunctions. Given the results of HMF oxidations, malic acid as a complexing agent during the preparation process of the cobalt-ceria binary oxide nanojunctions can lead to a good catalytic performance on HMF oxidations to FDCA, and a remarkable FDCA selectivity of 92.3% and almost 100% HMF conversion were obtained at 110 °C under O2 and alkali conditions. By comparing the catalytic performance of the nanojunctions and physical mixing of cobalt-ceria binary oxide on oxidations of HMF, 5-hydroxymethyl-2-furancarboxylic acid (HFCA), and 5-formyl-2-furancarboxylic acid (FFCA), the interfaces intrinsically enhanced the FDCA yield dominantly via boosting the HMF oxidation to HFCA with •O2- during the stepwise oxidation of HMF to FDCA. It can be enlightening that the introduction of the active sites for transforming O2 to •O2- to promote the transformation of HMF into HFCA is the key to boosting the selective aerobic oxidation of HMF to FDCA.