Second-generation biofuel has been widely considered as a renewable and sustainable energy source, from which the utilization and valorization process remain challenging. Among the plant sources for these biofuels, lignin is the most under-utilized bioenergy source in lignocellulosic biomass, due to its highly complex and aromatic-rich structure. Lignin extraction following Organosolv pretreatment has been shown to produce the lignin with high quality. One effective route for breaking down the lignin into value-added products is to use copper porous metal oxide catalysts (CuPMO) for heterogenous catalysis. Despite valid information from current characterization technologies, there is only limited information about low molecular weight compounds with lower abundance and only general information of depolymerization products. In this work, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) was used to characterize Organosolv poplar lignin depolymerization via the catalytic process by CuPMO in either MeOH or MeOH-dimethyl carbonate (MeOH-DMC) solvents. Synergistic data analysis including Van Krevelen (VK) diagrams, SHAP (Shapley additive explanations), double bond equivalent (DBE), nominal oxidation state of carbon (NOSC) and Kendrick mass defect (KMD) were used to elucidate the lignin reaction mechanism and insights occurring under different depolymerization conditions. The results show that Organosolv treated lignin exhibited greater selectivity during the heterogenous catalytic depolymerization than noncatalytic depolymerization, and substantially higher yield of aromatic products with DMC involved solvent system. Our work advances the understanding of both the molecular-level structures comprising the larger lignin oligomer fractions and the mechanism by which these structures form during biomass heterogenous catalysis and complex lignin valorization, which provides additional insights to guide towards future biofuel production from natural biomass.
