Carboxylation of Bio-Based 2-Furoic Acid with CO2 to 2,5-Furandicarboxylic Acid over CuAlO x Catalysts

Abstract

Direct C–H carboxylation with CO2 as a renewable C1 source stands out as an atom-economical strategy for CO2 utilization. However, the low reactivity of C–H bond and intrinsic inertness of CO2 limit carboxylation efficiency. This work presents a cooperative CuAlOx-Cs2CO3 catalytic system for the C–H carboxylation of 2-furoic acid (FA) with CO2 to produce 2,5-furandicarboxylic acid (2,5-FDCA), a key bio-based monomer for polyethylene furanoate (PEF). By integrating a hydrotalcite-derived Cu2AlOx catalyst into a Cs2CO3-promoted system, the 2,5-FDCA yield increases from 13% to 91% at 190 °C under 2 MPa CO2 with 1.33 equiv Cs2CO3, with a reduction of 61 kJ·mol–1 in apparent activation energy. The high Cu-normalized apparent activity (33.2 mmolFA gCu–1 h–1) with 96.8% selectivity to 2,5-FDCA is achieved. Mechanistic and theoretical analyses reveal that Cu2AlOx promotes the activation of both FA and CO2. The interaction of Cu2AlOx with the carboxylate group of FA elongates the C5-H bond and facilitates Cs2CO3-promoted deprotonation, while Cu2AlOx activates CO2 mainly via bidentate carbonate species that enhance the electrophilicity of the carbon center, thereby lowering the C–C coupling barrier. The resulting 2,5-FDCA is a viable monomer for producing PEF with rigid furan-based backbones, underscoring its potential for engineering plastic applications. This synergistic strategy offers an atom-economical route to bio-based 2,5-FDCA and provides mechanistic insights into substrate and CO2 activation in direct C–H carboxylation.