Turning oxygen vacancies in Zn-doped CeO2-x/HZSM-5 for hydrothermal oxidation of lignin.

Hydrothermal oxidation is a promising route for converting enzymatic hydrolysis lignin into value-added liquid products, yet regulating depolymerization and oxidation pathways remains challenging. Herein, Zn-doped CeO2-X/HZSM-5 catalysts were prepared to investigate the role of Zn-Ce interfacial oxygen vacancies in lignin hydrothermal oxidation using water as the reaction medium. Zn incorporation modified the CeO2-X/HZSM-5 interface, promoted Ce3+ formation, and enhanced the oxygen-vacancy-related defect response, thereby improving oxygen activation and regulating the transformation of lignin-derived intermediates. Among the catalysts, 15Ce/HZSM-5 exhibited the highest lignin conversion and total bio-oil yield, whereas 7.5Zn-7.5Ce/HZSM-5 showed a more favorable effect on conversion-pathway regulation and bio-oil quality. Compared with 15Zn/HZSM-5, the bimetallic catalyst produced a higher light-oil yield and increased the relative abundance of aldehyde- and ketone-type compounds. The light oil obtained over 7.5Zn-7.5Ce/HZSM-5 exhibited a higher heating value of 27.75 MJ·kg-1, while the corresponding heavy oil reached 27.98 MJ·kg-1. Control experiments under Ar atmosphere and with TBA and p-BQ further suggested the participation of molecular oxygen and oxygen-derived active species. This work clarifies the role of Zn-Ce interfacial oxygen vacancies in regulating lignin hydrothermal oxidation and provides a feasible strategy for upgrading enzymatic hydrolysis lignin into bio-oil and oxygen-containing aromatic intermediates.