Defect-Regulated Co/CeO2 Catalysts for Selective Hydrodeoxygenation of Lignin-Derived Phenolics: Unravelling the Interfacial Hydrogenation C–O Cleavage Synergy

Lignin-derived chemicals are important renewable building blocks for a sustainable chemical industry, and their selective hydrodeoxygenation (HDO) into cyclohexanol offers a promising route to high-value products; however, efficient C–O bond cleavage over non-noble-metal catalysts remains challenging. Herein, a series of oxygen-vacancy-regulated Co/CeO2 catalysts was prepared by supporting Co on hydrothermally synthesized CeO2 nanocubes, with the CeO2 calcination temperature (400–800 °C) used to tune the defect density and interfacial structure. Low-temperature calcination preserved the nanocubic morphology, high surface area, abundant Ce3+–OV sites, and highly dispersed reduced Co species, whereas higher calcination temperatures promoted crystallite growth, surface-area loss, oxygen-vacancy depletion, and Co aggregation. These structural changes directly governed guaiacol HDO performance. Under optimized conditions (160 °C, 2 MPa H2, 4 h, isopropanol), Co/CeO2-400 achieved nearly complete guaiacol conversion, with cyclohexanol accounting for approximately 99% of the relative GC–MS product distribution. Mechanistic studies indicate that metallic Co promotes H2 activation and aromatic-ring hydrogenation, while adjacent Ce3+–OV sites facilitate adsorption and cleavage of oxygen-containing groups. The resulting Co–CeO2 interfacial synergy drives a sequential hydrogenation–deoxygenation pathway and suppresses the accumulation of partially hydrogenated intermediates. Co/CeO2-400 also showed activity toward representative lignin-derived oxygenates and retained over 90% of its initial activity after five cycles. This work highlights oxygen-vacancy engineering as an effective strategy for designing robust non-noble-metal catalysts for selective lignin valorization.