Hydrogen Transfer Hydrogenolysis of Organosolv Chinese Fir Lignin to Monophenols over NiZnAlO_x Catalyst

Abstract

Lignin is the only naturally renewable aromatized polymer consisting of several phenyl propane structures linked by C−O and C−C bonds, so lignin can be depolymerized into value-added chemicals or liquid fuels. In this study, M 5 Zn 5 AlO x (M = Co, Ni and Cu) catalysts were obtained by the co-precipitation method and then were used in organosolv lignin depolymerization. Among these catalysts, the Ni 5 Zn 5 AlO x catalyst possessed the largest surface area and abundant surface oxygen vacancies as well as strong acidic sites on the surface, giving the highest yield of monophenols (about 14.49 wt %). The effect of Ni/Zn ratios on the lignin depolymerization was also investigated, and it was found that the surface area and the proportion of surface oxygen vacancies and strong acidic sites of the NiZnAlO x catalysts increased and then decreased with the Ni/Zn ratios increasing. Similarly, the yield of monomeric compounds increased and then decreased with the Ni/Zn ratios increasing. The highest yield of monophenols was 17.18 wt % obtained over the Ni 3 Zn 7 AlO x catalyst, a remarkable monomer yield from organosolv lignin. The two-dimensional 1 H-13 C heteronuclear single-quantum coherence nuclear magnetic resonance spectroscopy of bio-oil revealed that the linkage bonds in lignin could be effectively broken over the Ni 3 Zn 7 AlO x catalyst. This study provided an effective route to obtain high-value chemicals from organosolv lignin under nickel-based catalysts.