Efficient hydrogenolysis of lignin model compounds and lignin by Ni-M /C and NaOH synergistic catalysis

Abstract

Efficient hydrogenolysis of C-O bonds in lignin offers a promising pathway for producing high-value-added biofuels and chemicals. However, designing an easily synthesized, highly active catalyst for this process remains a challenge. In this paper, a series of Ni-M(Pd, Pt, Ru)/C catalysts were prepared and synergized with NaOH to produce aromatic compounds from β-O-4 model compound (MC). Among the catalyst systems, Ni-0.25 % Pd/C-NaOH completely converted β-O-4 MC at mild conditions (150 °C, 2 MPa H2, 3 h) to produce monomers with a yield of 95.6 wt% and excellent selectivity of the bond-breaking products as high as 85.5 %. Recycling tests showed that the Ni-0.25 % Pd/C catalyst remained stable after five cycles, with high activity and without the need for a further reduction before runs. Further, the catalytic system has proven to exhibit high activity for the cleavage of other types of lignin MC, such as 4-O-5, α-O-4, β-O-4 and ether bond (diphenyl ether, benzyl phenyl ether, Guaiacolylglycerol-β-guaiacol ether, benzyl ether) and also effective for lignin from enzymatic cleavage (LEC). Hydrogenolysis of LEC achieved a monomer yield of 34.5 wt%; the molecular weight (555 g/mol) of the hydrogenolysis oligomer was significantly reduced compared to LEC (2872 g/mol). The highly active and stable Ni-0.25 % Pd/C-NaOH catalytic system provides a promising pathway for the efficient hydrogenolysis of lignin and lignin model compounds to produce high-value biofuels and chemicals.