Selective Catalytic Depolymerization of Lignin to Targeted Phenolic Monomers Using Noble Metals Supported on MgAl<sub>2</sub>O<sub>4</sub> without External Hydrogen
Shukun Qiu, Zhiping Wu, Xudong Liu, Pengyun Liu, Zhicheng Jiang, Mingyu Xie, Chao Yan, Rukuan Liu, Changzhu Li, Zhihong Xiao, Zicheng Zhao
Abstract
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, MgAl 2 O 4 -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/MgAl 2 O 4 was comparable to that obtained under a H 2 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 MgAl 2 O 4 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.