Catalytic Hydrogenation of Lignin Ethers and Bio-Oil Using Non-Noble Cobalt Catalysts

The conversion of lignocellulosic biomass into lignin bio-oil and its subsequent upgrading into saturated cyclic products holds considerable promise for applications in the aviation industry. This study reports the synthesis of a defect-enriched monometallic CoO_x/Co-350-30 catalyst, which is utilized for hydrogenating lignin-derived molecules and lignin bio-oil obtained via reductive catalytic fractionation (RCF) of wheat straw. Under optimized conditions (180 °C, 2 MPa H₂, 2 h), benzyl phenyl ether (BPE) affords complete conversion, yielding ≈99% cyclohexanol and ≈98% methylcyclohexane. RCF of wheat straw (conducted at 230 °C and 3 MPa H₂ for 6 h) affords lignin bio-oil containing ≈43% alkyl-substituted phenols. Hydrogenation of the bio-oil using the CoO_x/Co-350-30 catalyst (at 250 °C for 2 h at 3 MPa H₂) results in ≈98% yield of cyclic aliphatic alcohols. Comparative studies with commercial 5%Ru/C reveal that the CoO_x/Co-350-30 catalyst produced products with lower oxygen functionalities and fewer native lignin linkages. Comprehensive catalyst characterizations and activity tests were conducted to propose a plausible reaction mechanism for BPE hydrogenation. The cobalt-based catalyst, devoid of noble metals, provides a sustainable and cost-effective method for biomass conversion into fuel-range products, addressing the growing industry demand for more efficient catalytic processes.