Sustainable Production of High-Value Chemicals from Selective Hydrogenolysis of Lignin Catalyzed by Co–Pd Bimetallic Supported on Nitrogen-Doped Carbon Spheres

The production of fuel and chemicals from renewable lignin supplies a sustainable chemical engineering process. In this study, Co–Pd bimetallic supported on porous polymer-derived nitrogen-doped carbon spheres (NDCS) was employed for the selective hydrogenolysis of organosolv lignin. Most of the products are phenolic monomers. At optimal conditions, 2.5 MPa H2, 280 °C for 5 h, 86.74% liquefaction of lignin and 36.38 wt % yield of phenolic monomers were obtained. Among these monomer products, 60.83% were identified as 4-hydroxy-3,5-dimethoxyphenylacetic acid (22.13 wt % yield), which is an important pharmaceutical intermediate. With the help of the characterization of catalysts and hydrogenolysis products, the reaction mechanism was proposed. The NDCS provided the prerequisites for metal anchoring and dispersion, and smaller metal particle sizes (2.56 nm) were obtained compared to those of undoped nitrogen carriers. Meanwhile, the synergistic interaction between Pd0 and Co0 promoted the conversion of active hydrogen. With active hydrogen, the C–C and C–O bonds in the lignin were cleaved, and then the active O was transferred to the Pd2+ and Co2+ sites and catalyzed the oxidation of 4-allyl-2,6-dimethoxyphenol to 4-hydroxy-3,5-dimethoxyphenylacetic acid. Lastly, cycling experiments demonstrated the remarkable stability of the catalyst.