The highly selective conversion of lignin models and organosolv lignin to amines over a Ru/C catalyst

Abstract

The efficient conversion of lignin into high-value chemicals is a significant and challenging process for sustainable development. In this study, we successfully achieved the direct conversion of lignin model compounds and realistic lignin into amines using H₂ and NH₃ over a Ru/C catalyst. We specifically investigated diphenyl ether (DPE) as a model molecule due to the high dissociation energy of its C–O bond, aiming to gain insights into the reaction mechanism. The results revealed that the C–O bond is initially broken, resulting in the production of benzene and phenol. Subsequently, cyclohexanone is obtained through the hydrogenation of phenol. Furthermore, cyclohexanone, acting as the key intermediate, reacts with NH₃ to yield amines. Notably, the kinetics of phenol hydrogenation to cyclohexanone is more favorable than the C–O bond cleavage of DPE. Therefore, the C–O bond rupture in lignin plays a crucial role in the depolymerization of lignin and its conversion into amines in this study. This developed strategy for lignin conversion to amines opens up new possibilities for the highly efficient utilization of lignin.