Catalytic Lignin Depolymerization to Aromatic Chemicals

consumption, maintaining the aromatic structure and preparing high-value aromatic chemicals from renewable lignin is more profitable. Therefore, lignin depolymerization to easy-to-handle aromatic monomers with acceptable conversion and selectivity is of great importance. In this article, we present our recent studies on lignin's catalytic conversion to aromatic chemicals. First, we introduce our research on protolignin depolymerization via a fragmentation-hydrogenolysis process in alcohol solvents. Then, focusing on the catalytic cleavage of lignin C-C and C-O bonds, we shed light on a recapitulative adjacent functional group modification (AFGM) strategy for the conversion of lignin models. AFGM strategy begins with the adjacent functional group modification of the target C-C or C-O bond to directly decrease the bond dissociation enthalpy (BDE) of targeted bonds or generate new substrate sites to introduce the cleavage reagent for further conversion. Subsequently, on the basis of these two concepts from AFGM, we summarize our strategies on lignin depolymerization, which highlight the effects of lignin structure, catalyst character, and reaction conditions on the efficiency of strategies. In short, the key point for lignin depolymerization to aromatics is promoting the lignin conversion and restraining the condensation. Compared with the complex research on direct lignin conversion, this bottom-up research approach, beginning with lignin model research, can make the conversion mechanism study clear and provide potential methods for the protolignin/technical lignin conversion. In addition, one of our perspectives for lignin utilization is that the products from lignin conversion can be used as monomers for artificial polymerization, such as the simple phenol (PhOH) and other potential acid compounds, or that lignin derivative molecules can be used to synthesize high-value synthetic building blocks.