Efficient C–O Bond Hydrogenolysis Over Polyoxometalate Catalysts in Mild Hydrodeoxygenation of Lignin-Derived Phenols to Cycloalkanes

Hydrodeoxygenation (HDO) plays a crucial role in the production of high-energy liquid fuels from lignin-derived phenols. Polyoxometalates (POMs), as strong acidic materials, are potential catalysts for liquid-phase HDO. In this study, we synthesized a series of Ru-based polyoxometalate catalysts (Ru/POMs) for the conversion of lignin-derived phenols to cycloalkanes. The optimization of Ru/POMs was achieved by controlling the ion types and ratios. The results indicated that the physiochemical properties of POMs were significantly influenced by the types of polyanions and metal cations, while the acidity related to the deoxygenation ability was greatly affected by the ion ratios of cations and polyanions. Additionally, the interaction between POMs and Ru varied depending on the type of POMs, leading to different Ru dispersions and hydrogenation ability. Among all catalysts tested, Ru/Cs_2.5SiW exhibited superior catalytic performance due to its high Ru dispersion and appropriate acidity. Under optimal conditions (160 °C, 4 h, and 3 MPa of H₂), guaiacol was completely converted to 93.7% cyclohexane in dodecane solvent. It was observed that Cs_2.5SiW displayed high activity in C–O bond hydrogenolysis. This work successfully achieved efficient HDO of lignin-derived phenols and provided a strategy for designing polyoxometalate catalysts.