N-Methylation of N-Methylaniline with Carbon Dioxide and Molecular Hydrogen over a Heterogeneous Non-Noble Metal Cu/TiO2 Catalyst

Graphical Another drop of copper : A non-noble metal catalyst of Cu/TiO 2 is effective for the heterogeneous N -methylation of N -methylaniline with CO 2 and H 2 , in which CHO* is formed as methyl reagent, and it reacts with N -methylaniline to produce intermediate N -methylformanilide followed by its hydrogenation to N,N -dimethylaniline. A non-noble heterogeneous catalyst of Cu/TiO 2 was prepared for N -methylation of N -methylaniline (MA) with CO 2 and H 2 . 5 wt.–% Cu loaded TiO 2 (P25) catalyst exhibited a high performance, with 82 % MA conversion and 98 % N,N -dimethylaniline (DMA) selectivity under the reaction conditions used (4 MPa H 2 , 2 MPa CO 2 , 180 °C, 36 h). The Cu/TiO 2 catalyst was more effective with respective to the total conversion and the DMA selectivity as compared to 5 wt.–% Cu loaded catalysts on CeO 2 , ZnO and activated carbon materials. The possible active species of Cu/TiO 2 catalyst should be both Cu + and Cu 0 which contributed to the high activity as the reaction conversion increased linearly with them exposed on the surface of catalyst. Moreover, the reaction pathways involved were studied; it was likely that the reaction took place via an intermediate of formaldehyde that was formed from CO 2 and H 2 , as confirmed by in situ diffuse reflectance Fourier-transform infrared spectroscopy, then it reacted with MA to give N -methylformanilide (MFA), and finally MFA was hydrogenated to DMA.