Selective Production of Anilines by Reductive Amination of Lignin and Its Derivatives

Abstract

Anilines are fundamental building blocks for pharmaceuticals, agrochemicals, and advanced materials, yet their traditional synthesis is heavily dependent on fossil-based petrochemical feedstocks. In this study, we present a two-step catalytic strategy for converting lignin and its derived phenols into high-value anilines using a Pd/C catalyst. A comparative evaluation of Pd/C with different supports (e.g., ZrO₂, TiO₂, CeO₂, and ZnO) demonstrates that Pd/C exhibits high activity and selectivity toward anilines, achieving a maximum 70.6% yield of 4-propylaniline in the reductive amination of 4-propylphenol under optimized conditions. Mechanistic insights reveal that the catalytic performance of Pd/C stems from its combination of high specific surface area and porous architecture, which enhances Pd nanoparticle dispersion, improves substrate adsorption, and facilitates the uptake of hydrogen and ammonia, collectively accelerating the reaction. Furthermore, the Pd/C catalyst exhibits favorable stability and broad applicability, delivering aniline mass yields of 12.9 wt % from camphor lignin and 10.1 wt % from camphor lignin oil. This work establishes a robust pathway for the selective conversion of renewable lignin into anilines, promoting lignin valorization and offering a critical step toward reducing reliance on nonrenewable resources.