Selective and stable production of furoic acid by furfural aerobic oxidation at controlled mild-pH conditions

Abstract

This study proposes a new and sustainable approach for the aerobic oxidation of furfural to furoic acid, the precursor of 2,5-furandicarboxylic acid (FDCA), a key monomer in the development of green polyethylene terephthalate substitutes. This work presents an alternative method for conducting this reaction utilizing a buffer solution to maintain a constant pH of 8. Au/TiO2 is identified as the optimal catalyst, its high capacity to activate oxygen being the key factor to explain the favorable results obtained. The mechanistic and kinetic study of experimental results corroborates that the Cannizzaro route (which co-produces furfuryl alcohol) is suppressed. Thus, furoic acid is the only compound detected in the liquid phase when working at temperatures below 120ºC and 20 bar O2. The pH control has also a double positive effect on the stability, with a significant reduction in the humins formation and preventing the catalytic deactivation observed in base-free reactions by the permanent adsorption of the acids obtained. To sum up, this new approach represents a significant improvement in terms of activity, selectivity, and stability. These three aspects are crucial to ensure sustainability and to facilitate the process scale-up.