Sustainable production of catechol derivatives from waste tung nutshell C/G-type lignin via heterogeneous Cu–NC catalytic oxidation

Abstract

The sustainable production of catechol derivatives is a challenging task. Catechyl (C) and guaiacyl (G) lignins coexisting in waste tung nutshells are promising feedstocks to form valuable catechol derivatives, but the depolymerization of C/G lignin typically involves a catalytic reductive process that cannot produce these oxidized aromatic chemicals. Herein, we demonstrated that the sustainable production of catechol derivative aldehydes and acids from C/G lignin could be achieved through a heterogeneous copper-catalyzed oxidative process. Under optimized conditions, the Cu–NC-800 catalyst affords a 43.5 mg g⁻¹ yield (8.9 wt%, based on Klason lignin) of aromatic aldehydes (protocatechuic aldehyde, vanillin) and acids (protocatechuic acid, vanillic acid). XRD and XPS analyses showed that CuO and Cu₂O may be the active species during the heterogeneous oxidation of the Cu–NC-800 catalyst. This study opens new opportunities for the sustainable production of catechol derivatives from C/G-type lignin.