Photocatalytic conversion of lignin into aromatic monomers with adsorbents of radical species from water dissociation

Photocatalytic conversion of lignin into aromatic monomers by cleaving interunit C–O bonds is a promising approach to reduce reliance on fossil fuel resource. However, industrial implementation is hindered by insufficient reaction efficiency and selectivity for target monomers. This study addresses these challenges by applying adsorbent-mediated catalysis and developing a quaternary Cd _xZn _1–xIn ₂S ₄ photocatalyst. This catalyst utilizes radical species from photocatalytic water dissociation to promote the cleavage of aryl ether C–O bonds in lignin model compounds, achieving nearly complete conversion with over 90% selectivity for target aromatic monomers. This is a significant improvement over the 50% or less conversion and selectivity performed by water-free photocatalytic system. The study shows that H∗ and ∗OH from water dissociation can modify the catalytic microenvironment and reaction kinetics, increasing the energy barrier for side reactions and enhancing hydrogen transfer efficiency. Therefore, the target C–O cleavages can be remarkably promoted while the oxy-dehydrogenation side reactions can be impeded.