Base free HMF oxidation over Ru-MnO2 catalysts revisited: Evidence of Mn leaching to Mn-FDCA complexation and its implications on catalyst performance

Abstract

• Base free HMF oxidation with RuMn oxides revisited. • Substantial activity loss when catalyst reused at full oxidation level. • Acidic product (FDCA and FFCA) induced Mn leaching from MnO 2 based supports. • Formation of Mn-FDCA complexe and reduction Mn AOS responsible for missing mass balance and activity loss. • Weak bases can suppress Mn leaching, Mn-FDCA complexation and preserve Mn AOS. 2,5-furandicarboxylic acid (FDCA) is a high value bio-based chemical useful for the production of next generation renewable polymers, epoxy-resins and surfactants. Herein, we show that the performance and stability of MnO 2 based oxidation catalysts used in FDCA production are considerably influence by process conditions (especially initial HMF conc. and presence of base additives). Although, base free aerobic oxidation of HMF to FDCA is known to be highly effective over Ru modified MnO 2 catalysts, our experiments showed considerable leaching of MnO 2 phase under reaction conditions with the formation of insoluble Mn-FDCA complexes. The formation of Mn-FDCA complex and Mn leaching was also supported by control experiments between FDCA and various Mn oxides under hydrothermal conditions and its structure confirmed by single crystal XRD. Formation of Mn-FDCA and Mn leaching was also identified as the underlying reason for carbon balance deficit, catalyst mass loss and deactivation observed upon reuse.