Visible-light-driven selective cleavage of C-C bonds in lignin model substrates using carbon nitride-supported ruthenium single-atom catalyst

The selective cleavage of the C-C bonds in lignin is highly pursued to obtain aromatic monomers from renewable resources but remains challenging due to their high dissociation energies and steric hindrance be-tween bulky aromatic groups. Herein, a mesoporous carbon nitride-supported ruthenium single-atom photo-catalyst (Ru1/MCN) is reported for efficient oxidative C alpha-C beta bonds scissoring towards lignin beta-O-4 model compounds with high activity and selectivity under visible-light irradiation and room temperature. With this strategy, a nearly total conversion of > 99% and > 98% selectivity of C-C bond cleavage can be achieved upon 2-phenoxy-1-phenylethanol. In-depth investigations verify that the C beta-H extraction by photogenerated holes is the critical step of the transformation, which directly generates the C beta radical intermediates and thus promotes the selective C alpha-C beta bonds breaking by coupling with superoxide radicals induced by photogenerated electrons. This work explores the potential of single-atom catalysts for photocatalytic production of aromatics from renewable biomass feedstocks.