Lignin depolymerization for aromatic compounds over Ni-Ce/biochar catalyst under aqueous-phase glycerol

Developing an advanced catalytic system for the purposeful depolymerization of lignin into aromatic compounds has presented a significant prospect for green manufacturing. In this paper, the catalytic process of microporous biochar (BC) derived from lignin supported Ni-Ce catalysts (xNi-Ce/BC) coupling with the aqueous-phase glycerol medium was reported for the depolymerization of Kraft lignin to guaiacol and 4-alkyl guaiacols. Under the optimal conditions, 3Ni-Ce/BC yielded 59.02 % of lignin oil and simultaneously realized the highest yields of guaiacol (243.94 mg/g lignin) and 4-alkyl guaiacols (265.65 mg/g lignin). The characterization results revealed BC promoted the formation of metallic Ni sites and the interaction of Ni with CeO2 drove the generation of Ni-CeO2-x interfaces and oxygen vacancies (OV). These could adsorb and activate the C-C and C-O bonds of lignin and its depolymerized fragments to form reactive intermediates. Then, the Ni sites activated the aqueous -phase glycerol to form adsorbed H atoms, which then spilled over to the adjacent OV to stabilize reactive in-termediates. Subsequently, the optimal distribution between Bronsted acid sites (BAS) and Lewis acid sites (LAS) in 3Ni-Ce/BC enhanced the yields of guaiacol and 4-alkyl guaiacols. The kinetic analysis adopting 2-phenoxy-1-phenylethanol as the beta-O-4 bond model demonstrated that 3Ni-Ce/BC significantly reduced both the bond dissociation energy of beta-O-4 bond and the apparent activation energy. Finally, the possible reaction mechanism