Efficient hydrogenolysis of lignocellulose into phenolic monomers over a CuO/m-ZrO2 catalyst.

The catalytic reduction of lignin into bio-chemicals is desirable yet remains a challenge due to its heterogeneity and complexes. Herein, a copper oxide supported monoclinic ZrO2 (CuO/m-ZrO2) catalyst is fabricated for efficient reductive catalytic fractionation (RCF) of softwood lignin, affording a yield of monophenols up to 18.7 wt% with a high selectivity (82.3%) for 4-n-propanol guaiacol. Some key parameters, such as β-O-4' models, solvent, mass ratio, reaction temperature and time, are systematically investigated to reveal their effects on the yields of monomers. Notably, mechanistic studies indicate the interactions between metal and acid sites enhance catalytic activity toward the effective scission of C-O bonds. Furthermore, a successful isolation of 68.3% monophenols is achieved in the gram scale amplification reaction. The monophenol formation pathway is deduced by the expansion of β-O-4' model compounds and other substrates. The insights from this work pave a new way for the rational design of non-precious catalysts for the transformation of lignin into fine chemicals.