Thermal, photonic, and electrocatalysis in lignin depolymerization research.

In order to realize a sustainable bio-based future, it is essential to fully harness the potential of biomass, including lignin - a readily available biopolymer that ranks second in abundance and serves as a renewable source of aromatics. While lignin has traditionally been used for lower-value applications like fuel and power generation, unlocking its higher-value potential through diverse conversion and upgrading techniques is of paramount importance. This review focuses on the catalytic conversion of lignin, with a specific emphasis on selective depolymerization, a process that not only supports economically and environmentally sustainable biorefineries but also aligns with Green Chemistry principles, mitigating adverse environmental impacts. Furthermore, we provide a comprehensive discussion of reaction pathways and mechanisms, including C-O and C-C bond cleavage, among different catalysts. Lastly, we analyze and briefly discuss the prospects of rational catalyst design in biomass valorization.