Catalytic Depolymerization of Lignin into Aromatic Monomers over Ru-Ni/TiO2 Catalysts

Lignin, a natural hydrocarbon polymer, can be converted into aromatic monomers via catalytic depolymerization. This study focuses on the lignin depolymerization into aromatic monomers through hydrogenolysis using bimetallic Ru-Ni supported on TiO2. TiO2 synthesis involves the hydrolysis of titanium alkoxide followed by modification with H3PO4:HNO3. TiO2 was impregnated with Ru and Ni at various ratios (5:0, 4:1, 2.5:2.5, 1:4, and 0:5). The characterization was performed using NH3 Temperature-Programmed Desorption (NH3–TPD), N2 physisorption, XRF, XRD, H2–TPR, and SEM analyses. XRD confirmed the presence of anatase TiO2 at 2θ = 25.28°, 38.02°, and 38.33°, while Ru was dispersed in TiO2, as supported by the SEM and XRF results. N2 physisorption showed a decrease in the surface area by 20.1–40.3 m2/g, with mesoporous characteristics (pore size: 1.7-24.4 nm) after impregnation. NH3-TPD results indicate that the metals ratio influences the acidity of the catalyst. GC-MS analysis of the depolymerization reaction for aromatic monomers showed optimal results over the Ru4Ni1/TiO2 catalyst, demonstrating selectivity and yield of 42.2% and 71 mg/g, respectively. This study highlights a promising avenue for lignin depolymerization through efficient catalyst design and process optimization.