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

Abstract

The selective cleavage of the CC 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 between bulky aromatic groups. Herein, a mesoporous carbon nitride-supported ruthenium single-atom photocatalyst (Ru1/MCN) is reported for efficient oxidative Cα-Cβ bonds scissoring towards lignin β-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 CC bond cleavage can be achieved upon 2–phenoxy–1–phenylethanol. In-depth investigations verify that the Cβ-H extraction by photogenerated holes is the critical step of the transformation, which directly generates the Cβ radical intermediates and thus promotes the selective Cα-Cβ 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.