Selective N-methylation of amines, nitro compounds and nitriles with CO2/H2 by Cu-ZnO/TiO2 catalyst
N -methylation of amines, nitro compounds and nitriles with CO 2 and H 2 offers a promising strategy for CO 2 utilization. However, developing highly efficient and stable Cu-based catalysts for selective mono- N -methylation of aniline remains challenging. Herein, we report the successful synthesis of a Cu-ZnO/TiO 2 catalyst, with the optimized 5 %Cu-7.5 %ZnO/TiO 2 catalyst achieving a 96.7 % yield of N -methylaniline (MA) and an initial turnover frequency (TOF) of 7.4 h −1 after 6 h under 453 K, 2 MPa CO 2 and 4 MPa H 2 . This performance surpasses all reported Cu-based catalysts and rivals noble metal-based systems. The catalyst demonstrated reusability at least four cycles and versatility in the N -methylation of various amines, nitro compounds, and nitriles. Kinetic studies revealed reaction orders of 0 with respect to aniline concentration and CO 2 pressure, and 1 with respect to H 2 pressure. Based on kinetics and extensive characterization, we propose a reaction mechanism over 5 %Cu-7.5 %ZnO/TiO 2 , identifying Cu nanoparticles as the active sites. The process proceeds via N -phenylcarbamic acid and N -phenylformamide intermediates, with the hydrogenation of N -phenylcarbamic acid as the rate-determining step.
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