Catalytic Hydrogenolysis\nof Lignin into Propenyl-monophenol\nover Ru Single Atoms Supported on CeO<sub>2</sub> with Rich Oxygen\nVacancies

Lignin is the most abundant aromatic source of natural\nproducts,\nbut developing efficient catalysts to depolymerize it into valuable\nmonophenol with high yield and unique selectivity remains a challenge.\nHerein, we report a Ru single-atom catalyst (SAC) supported on rod\nCeO<sub>2</sub> with oxygen vacancies (Ov) for the depolymerization\nof birch dioxane acidolysis lignin (DAL). A near-theoretical maximum\nmonophenol yield (14.8 wt %) with good selectivity to 4-<i>n</i>-propenyl guaiacol (51.4%), as well as high catalyst stability, was\nachieved. The calculated turnover (TON) was 387 mol<sub>aromatics</sub>/mol<sub>Ru</sub>, which is 55× higher than that of the Ru/C\ncatalyst. The possible reaction for this catalyst was proposed by\nstudying a series of lignin model compounds and in situ DRIFT measurements.\nThe mechanism involves the cleavage of C<sub>α</sub>–OH\nand C<sub>β</sub>–O bonds to produce coniferyl alcohol,\nfollowed by the removal of γ-OH to generate 4-<i>n</i>-propenyl guaiacol. The effects of some key parameters like solvent,\nRu content, temperature, reaction time, and H<sub>2</sub> pressure\nwere also investigated in terms of monophenol yields and average molecular\nweight. This work provides an economically feasible method for the\ndepolymerization of lignin into highly valuable monophenols.