A composite catalyst of sugarcane-derived N-doped biochar and Fe(NO₃)₃ for improved electron transfer in stepwise oxidation of 5-hydroxymethylfurfuran under air

Flexible catalysts for the efficient oxidation of 5-hydroxymethylfurfuran (HMF) into valuable chemicals are in urgent demand. In this contribution, the sugarcane-derived N-doped biochar (Su-NCs) was prepared by MgCl2 activation in the presence of urea via a one-step pyrolysis method, which constructed a composite catalyst with Fe(NO3)(3) for HMF oxidation. The perfect combination of Su-NCs/Fe(NO3)(3) revealed remarkably enhanced catalytic performance and HMF conversion of ca. 100.0% with a 92.0% total yield in air. The effects of specific N-doping sites on the catalytic activity and role of Fe3+ were explored. The results disclosed the electron-rich pyridine-N and Fe3+ synergistically implemented the stepwise oxidation of alcohol to aldehyde and then carboxylic acid. Importantly, the Fe2+ came from electron transfer between the electron-rich N-doped sites and Fe3+ was the origin of reactive oxygen species (center dot O-2(-)), which further determined the reactivity and product distributions. The center dot O-2(-) was favorable for the oxidation of hydroxyl while the center dot OH evolved from center dot O-2(-) preferred to attack aldehyde on the furan ring. This work emphasizes the importance of surface electron transfer of Su-NCs on oxidation efficiency of HMF and creates an alternative chance to produce value-added chemicals from raw biomass.