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

Abstract

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.