Scission of C–O and C–C linkages in lignin over RuRe alloy catalyst

The performance of lignin depolymerization is basically determined by the interunit C–O and C–C bonds. Numerous C–O bond cleavage strategies have been developed, while the cleavage of C–C bond between the primary aromatic units remains a challenging task due to the high dissociation energy of C–C bond. Herein, a multifunctional RuRe alloy catalyst was designed, which exhibited exceptional catalytic activity for the cleavage of both C–O and C–C linkages in a broad range of lignin model compounds (β-1, α-5, 5–5, β-O-4, 4-O-5) and two stubborn lignins (kraft lignin and alkaline lignin), affording 97.5% overall yield of monocyclic compounds from model compounds and up to 129% of the maximum theoretical yield of monocyclic products based on C–O bonds cleavage from realistic lignin. Scanning transmission electron microscopy (STEM) characterization showed that RuRe (1:1) alloy particles with hexagonal close-packed structure were homogeneously dispersed on the support. Quasi-in situ X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) indicate that Ru species were predominantly metallic state, whereas Re species were partially oxidized; meanwhile, there was a strong interaction between Ru and Re, where the electron transfer from Re to Ru was occurred, resulting in great improvement on the capability of C–O and C–C bonds cleavage in lignin conversion.