Oxygen Vacancy-Rich TiO ₂ -Supported Single-Atom Ru Catalysts for Stable and Selective Demethoxylation of Lignin-Derived Phenolic Monomers

Design of a robust single-atom catalyst with high selectivity and thermal stability for the hydrodeoxygenation (HDO) of bio-oils is of great significance to the development of biorefining technology. In this study, an in situ doping method was adopted to prepare a series of single-atom Ru-modified mesoporous TiO 2 (Ru x /m-TiO 2 ) catalysts with abundant oxygen vacancies for selective demethoxylation of various phenolic monomers. In the HDO of guaiacol, the Ru 0.05 /m-TiO 2 with 0.05 wt % Ru loading maintained extraordinary catalytic activity (over 95% of both conversion and demethoxylation selectivity). Importantly, Ru single-atom identity was maintained even after 10 cycles under harsh conditions (300 °C, 2 MPa H 2 ). A combination of experimental data and density functional theory calculations unraveled that the isolated Ru was firmly anchored on the internal surface of m-TiO 2 and possibly stabilized by coordinatively unsaturated coordinated Ti centers, which facilitated the formation of Ru–O V –Ti sites. The cooperative interaction of the atomic Ru metal and the O V created an active domain with distinct electronic and geometric properties. With the assistance of phenolic hydroxyl groups, this domain selectively activated and cleaved the C Ar –OCH 3 bond at the ortho-position, thereby preserving the integrity of the aromatic ring. Moreover, this catalyst shows good versatility in catalyzing similar lignin-derived phenolic monomers. This work provides a facile synthetic strategy for constructing single-atom catalysts with abundant oxygen vacancies and valuable insights into the production route of high-value chemicals from biomass in the foreseeable future.