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

Abstract 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 TiO 2 . TiO 2 synthesis involves the hydrolysis of titanium alkoxide followed by modification with H 3 PO 4 :HNO 3 . TiO 2 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 NH 3 Temperature-Programmed Desorption (NH 3 –TPD), N 2 physisorption, XRF, XRD, H 2 –TPR, and SEM analyses. XRD confirmed the presence of anatase TiO 2 at 2 θ = 25.28°, 38.02°, and 38.33°, while Ru was dispersed in TiO 2 , as supported by the SEM and XRF results. N 2 physisorption showed a decrease in the surface area by 20.1–40.3 m 2 /g, with mesoporous characteristics (pore size: 1.7-24.4 nm) after impregnation. NH 3 -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 Ru 4 Ni 1 /TiO 2 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.