Selective Catalytic Depolymerization of Lignin to Targeted Phenolic Monomers Using Noble Metals Supported on MgAl₂O₄ without External Hydrogen

Reductive catalytic depolymerization of lignin to obtain value-added phenolic monomers has great potential. However, achieving the efficient depolymerization of lignin under hydrogen-free conditions while selectively obtaining specific monomers remains a significant challenge. In this study, MgAl₂O₄-based catalysts with well-developed pore structures and abundant oxygen vacancies were fabricated, exhibiting excellent catalytic performance in the depolymerization of various kinds of biomass. Importantly, a 39.0 wt % yield of phenolic monomers under hydrogen-free conditions over 5 wt % Pd/MgAl₂O₄ was comparable to that obtained under a H₂ atmosphere from poplar. Furthermore, a high selectivity of 91.3% toward propanol-substituted monomers was obtained from pine. The efficient catalytic hydrogenolysis ability of the catalyst could be attributed to the highly dispersed small-sized metal nanoparticles, strong interaction between noble metal and MgAl₂O₄ support, and abundant medium-to-strong acidic sites. This study provides a green and efficient catalytic strategy for the valorization of lignin, contributing to the fabrication of phenolic monomers with high selectivity.