Boosting aromatic monomer yield of lignin hydrogenolysis by using Co/C coupled with NaOH catalyst

An efficient hydrogenolysis for organosolv lignin was proposed by using Co/C coupled with NaOH catalyst in this work. A boosted aromatic monomer yield was achieved, which was superior to the noble metal-based catalysts. The optimal 15%Co/C catalyst coupled with NaOH exhibited the best hydrogenolysis performance, with lignin conversion of 94.5 % and aromatic monomers yield of 43.4 %. Wherein, the product of benzyl alcohols showed the highest yield 23.5 %. The recycling performance of 15%Co/C catalyst was outstanding, with lignin conversion above 92.8 % after three runs and the yield of aromatic monomer slightly dropped to 38 %. The hydrogenolysis reaction pathway was also investigated based on the β-O-4 dimer model compound study. 2-(2-methoxyphenoxy)-1-phenyl ethanol was selected as lignin β-O-4 dimer model compound, and the hydrogenolysis reaction was conducted efficiently at 160 °C under the synergistic catalysis effect of metal sites and base sites. NaOH promoted the initial depolymerization of lignin through protonation, which improved the accessibility of lignin product to Co/C catalyst, and thus enhanced the reactivity of catalytic hydrogenolysis. NaOH also facilitated the etherification of intermediate products with solvents. And the presence of Co metal site stabilized free radicals and inhibited monomer product etherification. This catalytic system provides a potential strategy for the large-scale lignin utilization, with the advantage of high efficiency and handleability.