Selective Hydrodeoxygenation of Lignin via Aryl Ether C-O Bond Cleavage: Cs-Mediated Cu Surface Engineering

Lignin is a pivotal building block of lignocellulose biomass and the most abundant aromatic polymer in nature. Selective hydrodeoxygenation (HDO) via the target cleavage of aryl ether C-O bonds is of great importance for lignin biorefinery. However, preserving aromaticity during HDO for efficient production of arenes remains a challenge. Herein, the low electronegativity of Cs was utilized to customize the chemical environment and geometric construction of highly dispersed Cu sites on mesoporous SiO2 nanospheres. The electron density around Cu sites evidently increased while the coordination environment of Cu was precisely tailored. The hydrogenation and deoxygenation activities were effectively balanced. Owing to the synergy between electron-rich Cu delta- sites and the Cs center, the saturated hydrogenation of aromatic rings was efficiently inhibited, and preferential selectivity toward aryl ether C-O bond cleavage was obtained. The selectivity of arenes from anisole reached 83% on 2Cs/Cu@NS-SiO2, while the intrinsic production activity of arenes based on active Cu sites significantly increased to 0.34 mmol<middle dot>mCu -2<middle dot>h-1, more than doubled that of Cu@NS-SiO2 without Cs modification. Besides, a remarkable arene selectivity of 76.3% was achieved among the depolymerized monomers from the HDO of organic solvent-extracted lignin. This study offers a promising approach for valorizing lignin into high-value arenes.