Catalytic depolymerization of alkaline lignin to value-added phenolic-based compounds over Ni/CeO2-ZrO2 catalyst synthesized with a one-step chemical reduction of Ni species using NaBH4 as the reducing agent

Alkaline lignin obtained from paper manufacturing is a potential feedstock for upgrading to produce value-added chemicals. This study demonstrates the efficiencies of synthesized Ni supported CeO2-ZrO2 catalysts to convert this low-cost alkaline lignin into value-added phenolic-based chemicals for further commercial applications. Lignin depolymerization was performed under mild reaction conditions, namely, reaction temperature of 200-300 degrees C, and reaction time of 1-5 h. Three different catalyst preparation methods (simple wet-impregnation, wet-impregnation assisted reduction in H-2 atmosphere and one-step chemical reduction) were investigated and used to evaluate possible correlations between the active Ni phase and catalytic performance in lignin depolymerization. The active Ni phase was successfully formed by one-step chemical reduction method which showed a significant improvement on product yield, especially lignin oil. The best result obtained in lignin depolymerization was by using 10%Ni/CeO2-ZrO2-red catalyst which resulted in producing a high yield of lignin oil (46.8%) from lignin feedstock under mild condition of 250 degrees C. The major phenolic compounds in lignin oil were: guaiacol, methyl-guaiacol, ethyl-guaiacol, vanillin, acetovanillone, and homovanillic acid. Furthermore, the reaction temperature affected the product yield and product distribution resulting in higher diversity of phenolic compounds in lignin oil.