A novel and efficient In2O3@RhPt catalyst for solvent-free transfer hydrogenation of TDC to HTDC: Catalytic performance and mechanism

Abstract

Selective hydrogenation of dimethyl toluene-2,4-dicarbamate (TDC) to methylcyclohexyl-2,4-dicarbamate (HTDC) is an essential intermediate step in the new green route for synthesizing methylcyclohexyl-2,4-diisocyanate (HTDI). Herein, we investigated the synthesis of HTDC from TDC by a solvent-free, mild and safe catalytic transfer hydrogenation (CTH) process using isopropanol as H-donor. Firstly, a bimetallic catalyst In₂O₃@RhPt with a high metal dispersion was prepared by one-pot method. The characterization results demonstrated that Rh and Pt atoms formed alloy structure and their interaction led to an electron-rich Pt and an electron-deficient Rh. What’s more, Pt could also stabilize the surface of In₂O₃. Then the Rh/Pt ratio was optimized and In₂O₃@Rh₄₉Pt₅₁ catalyst was found to show the best catalytic performance: about 99% of TDC conversion and 100% of HTDC selectivity at 80 ℃ and ambient pressure. It was proved by the designed experiments that isopropanol dehydrogenation was the dominant step and the active hydrogen species existed in the form of radicals in the CTH process of TDC to HTDC. Additionally, the synergistic effect in the RhPt alloy boosted the catalytic performance. Finally, the CTH reaction pathway and mechanism was elucidated based on the experimental and DFT calculation results.