Trisynergistic Catalytic Sites on Defect-Rich High-Entropy Oxide toward Solvent-Free Aerobic Oxidation of Aromatic Alcohols

Selective aerobic oxidation of aromatic alcohols is pivotal in valorization. However, current catalysts suffer from low aldehyde selectivity, which severely restricts their scalable application and sustainable utilization. High-entropy oxides (HEOs), endowed with flexible electronic structures and tunable defect chemistry, offer promising opportunities to surmount these limitations. However, the structure-activity relationships governing the selective conversion of alcohols-derived substrates remain poorly elucidated. Herein, we design a defect-rich spinel-type high-entropy oxide (HE-NiFe₂O₄) via a solvent-free mechanochemistry synthesis route, and demonstrate its high catalytic efficiency and excellent aldehyde selectivity in the solvent-free aerobic oxidation of benzyl alcohol-a typical representative of lignin-derived aromatic alcohols-as well as a series of alcohols -related substrates. Mechanistic investigations reveal a trisynergistic catalytic ensemble consisting of oxygen vacancies (Ov), electron-rich Mn sites and electron-deficient Fe sites; this active system cooperatively lowers the activation barriers for O-H and C-H bond cleavage and facilitates the preferential activation of O₂. As a result, HE-NiFe₂O₄ achieves an ultrahigh turnover frequency (TOF ≈ 7224 h⁻¹), nearly quantitative aldehyde selectivity, and remarkable recyclability over multiple catalytic cycles under solvent-free and base-free conditions. This work highlights a defect-driven active site design strategy for sustainable catalytic upgrading of forest-derived bioresources to high-value bioproducts.