Review of the Application of Bimetallic Catalysts Coupled with Internal Hydrogen Donor for Catalytic Hydrogenolysis of Lignin to Produce Phenolic Fine Chemicals

Lignocellulosic biomass contains lignin, an aromatic and oxygenated substance and a potential method for lignin utilization is achieved through catalytic conversion into useful phenolic and aromatic monomers. The application of monometallic catalysts for lignin hydrogenolysis reaction remains one of the major reasons for the underutilization of lignin to produce valuable chemicals. Monometallic catalysts have many limitations such as limited catalytic sites for interacting with different lignin linkages, poor catalytic activity, low lignin conversion, and low product selectivity. It is due to lack of synergy with other metallic catalysts that can enhance the catalytic activity, stability, selectivity, and overall catalytic performance. To overcome these limitations, works on the application of bimetallic catalysts that can offer higher activity, selectivity, and stability have been initiated. In this review, cutting-edge insights into the catalytic hydrogenolysis of lignin, focusing on the production of phenolic and aromatic monomers using bimetallic catalysts within an internal hydrogen donor solvent are discussed. The contribution of this work lies in a critical discussion of recent reported findings, in-depth analyses of reaction mechanisms, optimal conditions, and emerging trends in lignin catalytic hydrogenolysis. The specific effects of catalytic active components on the reaction outcomes are also explored. Additionally, this review extends beyond current knowledge, offering forward-looking suggestions for utilizing lignin as a raw material in the production of valuable products across various industrial processes. This work not only consolidates existing knowledge but also introduces novel perspectives, paving the way for future advancements in lignin utilization and catalytic processes.