Oxidative Catalytic Fractionation of Lignocellulose to High-Yield Aromatic Aldehyde Monomers and Pure Cellulose

Facile oxidation is a promising technology to valorize lignocellulosic biomass toward high-value chemicals and cellulose. However, the carbon efficiency is restricted by inevitable dissolution and conversion of carbohydrates and the condensation and degradation of lignin and monophenolics. Herein, we report the use of CuO nanoparticles (NPs) to oxidatively fractionate lignocellulose with O2 in aqueous NaOH under mild conditions, achieving over 80% carbon efficiency. Lignin was converted to aromatic aldehyde monomers (up to 48.6 wt %, mainly vanillin and syringaldehyde), and the yield can surpass the theoretical value (on the basis of the β-O-4 bond content) due to cleavage of other bonds. This was proven by several model compounds with different interlinkages. All hemicelluloses were transformed toward water-soluble small acids (mainly oxalic acid). As it was protected by the complexation of Cu cations, up to 80% cellulose was obtained as a white crystalline residue with high purity (>95%), which has potential applications in the production of materials and chemicals.