Breaking the limit of lignin monomer production via cleavage of interunit carbon-carbon linkages

Conversion of lignin into monocyclic hydrocarbons as commodity chemicals and drop-in fuels is a highly desirable target for biorefineries. However, this is severely hindered by the presence of stable interunit carbon-carbon linkages in native lignin and those formed during lignin extraction. Herein, we report a new multifunctional catalyst Ru/NbOPO4 that achieves the first example of catalytic cleavage of both interunit C-C and C-O bonds in one-pot lignin conversions, yielding 124-153% of monocyclic hydrocarbons; that is 1.2-1.5 times those yields obtained from the established nitrobenzene oxidation method. This catalyst also exhibits high stability and selectivity (up to 68%) to monocyclic arenes over repeated cycles. The mechanism of the activation and cleavage of 5-5 C-C bonds in biphenyl, as a lignin model adopting the most robust C-C linkages, has been revealed via in situ inelastic neutron scattering, coupled with modelling. This study breaks the conventional theoretical limit on lignin monomer production.