Microwave-assisted depolymerization of lignin with synergic alkali catalysts and a transition metal catalyst in the aqueous system

In this study, synergic alkali catalysts (NaOH + NaAlO 2 ) and Ni/ZrO 2 were used for microwave-assisted lignin depolymerization. The effect of temperature, alkali dosage, Ni/ZrO 2 dosage, and solid-to-liquid mass ratio was studied to improve the catalytic degradation efficiency and the yield of phenolic compounds. The results showed that more than 87.7% of lignin was converted and more than 0.582 mmol g −1 total phenolic hydroxyl concentration was obtained at 180 °C. Furthermore, the characterization results of FT-IR, UV-VIS, TG-DSC, GPC and 1 H-NMR clearly demonstrated that the synergistic system of an alkali and Ni/ZrO 2 effectively improved the degradation efficiency and inhibited the formation of char, and resulted in a series of compounds with low molecular weight (