Transformation of organosolv lignin into sustainable aromatics: Catalytic hydrodeoxygenation using carbon-supported bimetallic MoRu catalyst

While lignin holds potential as a sustainable source for fuels and chemicals, it faces hurdles due to its large molecular size, low heating values, and high oxygen content. In this study, the reductive depolymerization of organosolv lignin was investigated using mono-/bimetallic carbon-supported catalysts. At 340 °C, the MoRu/AC catalyst significantly reduced organosolv lignin feed's molecular weight from 2600 to 460 g/mol, yielding ∼70 % depolymerized organosolv lignin with a higher heating value of 32.92 MJ/kg, mainly composed of substituted phenolic compounds/aromatic hydrocarbons. Conversely, the MoRu/ACP catalyst underperformed, possibly due to residual acidity triggering undesirable side reactions like condensation. Thorough investigations revealed that introducing Mo into Ru catalysts significantly influences the hydrodeoxygenation process, resulting in H/C and O/C ratios of 1.29 and 0.20, contrasting with the initial feed's 1.05 and 0.35 ratios. Furthermore, density functional theory calculations showed lower energy barriers for breaking Caryl−OH/Caryl−O* bonds in guaiacol, a model compound, due to MoRu interactions, implying a promising deoxygenation potential for organosolv lignin transformation. The successful production of high-value bio-oil from technical lignin using the MoRu catalyst showcases its potential to pave the way toward carbon neutrality by offering eco-friendly alternatives to traditional fossil fuels and chemicals.