Catalytic oxidation of lignin to valuable biomass-based platform chemicals: A review

Lignin is the only sustainable aromatic resource in nature, its utilization has attracted much attention worldwide. Oxidation is one of the promising strategies that can convert lignin to a range of value-added platform chemicals. Lignin oxidation is generally carried out in a liquid phase with employed catalytic systems and oxidants, and this process is largely influenced by operation conditions, catalyst types, presence of oxidant, and solvent species. The inter-unit linkages in lignin can be selectively oxidized with the assistance of designed catalytic systems, facilitating the formation of aromatics (phenolic aldehydes, ketones, and acids), benzoquinones, and aliphatic (di)carboxylic acids. This work aims to provide a comprehensive review on traditional and advanced lignin oxidation concerning various catalytic systems for different terminal products. Deficiency in current lignin oxidation is also mentioned which indicates the direction of further lignin oxidative valorization.