Research progress on vanillin synthesis by catalytic oxidation of lignin: A review

Biomass resources are abundant in nature. Reasonable utilization of these resources can yield high-value-added products. Lignin is the second-largest biomass resource in the plant world, only after cellulose, is currently underutilized, resulting in significant waste. By processing lignin from pulping waste liquor and agroforestry solid waste, it can be converted into vanillin, a high-value-added product, making resource utilization more efficient. Herein, the research progress of synthesizing vanillin from lignin by catalytic oxidation throughout the world in recent years is summarized, including thermal catalytic oxidation, photocatalytic oxidation, electrochemical catalytic oxidation, and combination of various technologies. The reaction conditions for the preparation of vanillin through various catalytic oxidation methods are summarized, the existing problems and possible solutions are put forward, and the development direction of vanillin preparation from lignin in the future is prospected.