Hydrodepolymerization of organosolv lignin over fumed silica-supported transition metal sulfide catalysts: Catalytic activity and distribution of bio-oil components

Lignin, due to its potential for depolymerization into valuable fine chemicals and liquid fuels, is viewed as a promising alternative to fossil fuels. In this research, three types of sulfide catalysts, Ni-S/SiO2, Ni-Mo-S/SiO2, and Mo-S/SiO2, were prepared using an ethanol low-temperature sulfidation method and the activity of hydrodeploymerization of lignin were investigated. The physicochemical properties of these catalysts were systematically examined through advanced equipment and technology. The hydrodepolymerization activity was assessed using organosolv lignin as the substrate, and the obtained bio-oils were analyzed. The composition of functional groups, chemical structure, and component distribution of the lignin-derived bio-oils was characterized and analyzed. The Ni-Mo-S/SiO2 catalyst possessed a higher density of defective sites within the structure. All three sulfide catalysts displayed typical IV-type isotherms of mesoporous materials, with a H2(b)-type hysteresis loop. All three sulfide catalysts effectively cleaved C-O ether bonds in lignin. The Ni-Mo-S/SiO2 catalyst demonstrated the best catalytic activity in the hydrodepolymerization reaction, achieving the highest lignin hydrodepolymerization product yield of 77.1% and a bio-oil yield of 71.2%. The proportion of monomers, dimers and trimers in the products reached 71.3%, which is higher than that achieved with Ni-S/SiO2 and Mo-S/SiO2 catalysts. This study demonstrates the effectiveness of the ethanol low-temperature sulfidation method in preparing highly efficient Ni-Mo bimetallic sulfide catalysts, providing a promising strategy for the valorization of lignin into valuable bio-oil and aromatic chemicals.