Folic Acid-Derived Nitrogen-Doped Carbon Catalyst for the Selective Catalytic Oxidation of <i>p</i> -Benzoquinone to Maleic Acid

Converting phenolic pollutants into value-added chemicals represents a sustainable yet challenging endeavor. Herein, we report a metal-free, nitrogen-doped carbon catalyst (NC-900) derived from a cost-effective folic acid precursor. The NC-900 catalyst, possessing a predominant graphitic nitrogen (N-Q) species (46.3% of total N) and abundant surface basic sites (195.6 μmol/g), achieved a remarkable 51.9% yield of maleic acid using H 2 O 2 as a green oxidant. Systematic characterization established a robust structure–activity correlation, unequivocally identifying N-Q as the primary active site. Electron paramagnetic resonance and quenching experiments elucidate a hydroxyl radical (HO • )-mediated pathway, which selectively drives the oxidative ring-opening while suppressing undesired reduction. This work provides a novel catalytic route for maleic acid production and offers fundamental insights into the rational design of carbon catalysts for selective oxidation.