Selective oxidative cleavage of lignin through tailored reactive oxygen species

Transforming lignin into valuable aromatic compounds is a critical objective for sustainable biorefining. While oxidative depolymerization has been proven effective in breaks down lignin's macromolecule, its practical application has been limited by low selectivity. This review presents a paradigm shift in the field, moving from broad, non-selective oxidative degradation methods to highly targeted catalytic processes driven by controlled reactive oxygen species (ROS). It offers a comprehensive analysis of how various catalytic systems—utilizing O2, H2O2, metals oxides, electricity, light, and organic oxidants—generate distinct ROS profiles, ranging from non-specific hydroxyl radicals to more selective superoxide anions or high-valent metal-oxo complexes. These ROS serve as ''molecular scissors'', directly influencing the efficiency of C–O and C–C bond cleavage, thereby determining the yields of key products such as aldehydes, ketones, and acids. This review also explores emerging strategies, including single-atom catalysis and external field activation, which provide unparalleled precision in managing these reactive intermediates. Finally, it addresses ongoing challenges related to catalyst stability and the heterogeneity of lignin, while outlining promising future research directions focused on tandem processes and real-time mechanistic studies, to further unlock lignin's potential as a renewable source of aromatic feedstocks.