Catalytic hydrogenolysis of lignin in ethanol/isopropanol over an activated carbon supported nickel-copper catalyst

Abstract

Lignin is the renewable and abundant source of aromatics on earth, and the depolymerization of lignin provides significant potential for producing valuable monophenols. In this work, catalytic hydrogenolysis of organosolv poplar lignin (OPL) in ethanol/isopropanol solvent over monometallic and bimetallic nonprecious catalysts was investigated. Ni/C and a series of NiCu/C catalyst with different Cu loadings were prepared and applied for depolymerization of OPL. The highest yield of phenolic monomers was 63.4 wt% achieved over the Ni₁₀Cu₅/C catalyst at 270 °C without external H₂. The introduction of Cu in catalysts further promoted the hydrogen donor process of ethanol/isopropanol solvent and facilitated the cleavage of lignin linkages, resulting in the decreased molecular weight of bio-oil. The possible lignin dimer type structures, such as diphenylethane (β-1) type, phenylcoumaran (β-5) type, and pinoresinol (β-β) type structures, were proposed and identified by MALDI-TOF MS, giving a better understanding of the NiCu/C catalyzed lignin depolymerization.

Keywords: Catalysis; Hydrogenolysis; Lignin; MALDI-TOF MS; Mixed solvent.