A Hydrogen‐Free Ni/MgO Catalyst System for Aqueous‐Phase Hydrodeoxygenation of 4‐Propylguaiacol

ABSTRACT This study focuses on the catalytic transformation of a lignin model compound, 4‐propylguaiacol, without external hydrogen. The reaction using a Ni/MgO catalyst and water as the solvent, conducted at 220°C under 5 bar N 2 for 2 h, achieved 97.8% conversion and 94.8% selectivity toward phenolic products. During the reaction, the methoxy group in 4‐propylguaiacol is cleaved from the aromatic ring at Ni active sites and subsequently reacts with hydrogen radicals generated from water dissociation to form methanol. The methanol then undergoes aqueous‐phase reforming, providing additional in‐situ hydrogen to drive the hydrodeoxygenation process. The Ni/MgO catalyst showed good recyclability over three consecutive cycles, with only a slight decline in activity. Furthermore, this catalyst was applied to the depolymerization of real lignin, and the effects of reaction parameters on product yield were investigated. Among the tested conditions, a maximum monomer yield of 76.7 wt% was obtained at 280°C under 5 bar N 2 for 6 h.