Safe and direct conversion of 2,4-Dinitrotoluene into 1-Methyl-2,4-Cyclohexane-Diamine: A One-Pot hydrogenation reaction route catalyzed by Lithium-Modified γ-Al₂O₃-Supported ruthenium nanoclusters

The hydrogenation of 2,4-dinitrotoluene (2,4-DNT) into 1-methyl-2,4-cyclohexanediamine (2,4-MCHD), a significant yet underutilized raw material for the synthesis of methylcyclohexane diisocyanate (HTDI) with exceptional properties, represents one of the most promising reactions for the development of diisocyanate chemical processes. In this study, we developed a highly efficient and stable heterogeneous catalytic system for the direct hydrogenation of 2,4-DNT to 2,4-MCHD using Li-modified γ-Al₂O₃ supported Ru nanoclusters (Li-modified-Ru/γ-Al₂O₃). Under mild reaction conditions, we successfully inhibited side reactions, such as deamination, achieving a selectivity exceeding 95% for 2,4-MCHD, while the conversion of 2,4-DNT surpassed 99%. Kinetic studies revealed that the hydrogenation of 2,4-DNT in this system occurs as a tandem reaction, with the hydrogenation of the benzene ring identified as the rate-determining step. Investigations into the structure–activity relationship indicated that the valence state of the Ru nanocluster, the acid-base properties of the catalyst, the modification by Li, and the synergistic effects of various elements within the catalyst are critical factors contributing to the high activity and stability of the Li-modified-Ru/γ-Al₂O₃ catalyst for the hydrogenation of 2,4-DNT to produce 2,4-MCHD. This work represents the first example of the direct hydrogenation of dinitroaromatic compounds to yield diamino aliphatic compounds and provides a solid foundation for understanding such reaction systems.