Catalytic oxidative depolymerization of lignin dimers over NiMn-MOF-derived catalysts in the presence of oxygen†

Abstract

The catalytic oxidative depolymerization of lignin and its dimers is key for the effective utilization of biomass. In this work, a metal–organic framework (MOF) was chosen as the precursor, and a series of nickel–manganese bimetallic catalysts with different metal ratios were prepared via a hydrothermal method using 1,3,5-tricarboxylic acid as the ligand. The effects of metal ratio and calcination temperature on the activity of the catalyst were considered, and the oxidative depolymerization of the lignin dimer (2-phenoxy-1-acetophenone) was investigated in detail. The selective conversion of 2-phenoxy-1-acetophenone was achieved over the Ni₂Mn₁-MOF catalyst in an oxygen atmosphere with methanol as the solvent. Through the optimization of different reaction parameters, including reaction temperature, oxygen pressure, reaction time and solvent, it was found that under optimal reaction conditions (140 °C, 4 h, 0.5 MPa O₂), the Ni₂Mn₁-MOF catalyst exhibited a good catalytic performance for the efficient conversion of 2-phenoxy-1-acetophenone to phenol and methyl benzoate. Furthermore, its specific reaction mechanism was discussed based on the distribution of products in the lignin dimer oxidation process, which was useful for understanding the further oxidative depolymerization of lignin.