Effect of K + and Ca 2+ Cations on Structural Manganese(IV) Oxide for the Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid.

The promising influences of K + and Ca 2+ ions in the development of effective MnO 2 for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid (FDCA) were studied for the catalytic performance under a high-pressure reaction of aqueous O 2 (0.5 MPa) in a basic system. Various oxidation states of manganese in MnO 2 were able to accelerate the oxidation of 5-formyl-2-furancarboxylic acid to FDCA in the rate-determining step. The results were in good agreement that Ca 2+ played a key role in the highest FDCA yield up to 85% due to the associated cations on the local coordination to enhance the high surface area and the electronic effect on the manganese ion. Both K-MnO 2 and Ca-MnO 2 catalysts showed excellent catalytic activities without a significant change in the efficiency in the reusability experiments.