Accelerating oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid by high entropy alloy catalyst design under base-free conditions

Abstract

In the process of air oxidation of (benzyl-) alcohols, aldehydes, amines and bio-furan derivates, a soluble alkali is often needed to guarantee the oxidation rate and selectivity of desired products. The addition of a soluble alkali results in high cost for the subsequent product purification and generation of many low-value salts. The slow kinetics of air oxidation under non-alkali conditions becomes the key to solve this problem. In the preparation of 2,5-furandicarboxylic acid (FDCA) by non-basic catalytic oxidation of 5-hydroxymethylfurfural (HMF), the oxidation of 5-formyl-2-furoic acid (FFCA) to FDCA is the rate-determining step. In this work, it is hypothesized that the O₂ activation pathway and generated oxidation species can be regulated by rational design of the metal atom coordination structure and the electronic structure of catalytic centers, thus promoting the oxidation of FFCA to FDCA. Based on this, a FeCoNiCuPt high entropy alloy catalyst supported over activated carbon (HEA/C) was prepared. The catalytic results show that HEA/C has high catalytic activity and FDCA selectivity in the non-basic catalytic oxidation of HMF in water. Free radical quenching experiments suggest that free radicals may be involved in this process. This work shows that it is a feasible strategy to increase the oxidation rate and desired product selectivity by rational fabrication of the catalytic center atomic structure.