Manganese-Biochar Catalyst for Sustainable Glycolic Acid Production from Biomass-Derived Glucose and Oligosaccharides

Production of glycolic acid from renewable resources is a significant challenge considering its extensive market and the depletion of fossil resources. This study accomplished sustainable glycolic acid production from biomass-derived saccharides using a microwave-assisted aerobic oxidation system. Various Mn-biochar catalysts were synthesized using different precursors (MnCl₂ and KMnO₄) and synthesis temperatures (400–850 °C). Glycolic acid yield from glucose could reach 62.8 Cmol % within 20 min at 180 °C over MnBC-VII-700 (i.e., catalyst derived from Mn(VII) precursor and synthesized at 700 °C). Mn(III) was identified as the catalytically active state by correlation with the catalytic performance. Biochar support is vital for reactant adsorption, electron transfer, and microwave absorption. Transformation from glucose to glycolic acid would experience retro-aldol and oxidation reactions, while oxidation-hydrolysis of the glycosidic bond could be achieved for one-pot oligosaccharide conversion. The yields of glycolic acid reached 43.1, 29.2, and 33.3 Cmol % within 30 min, when the substrates were cellobiose, maltose, and maltotriose, respectively. This study developed a low-cost Mn-biochar catalyst for biomass valorization. The study presents valuable mechanistic insights that can serve as a critical reference for the sustainable production of chemical building blocks in heterogeneous catalysis.