Selective N-monomethylation of amines using CO2/H2 catalyzed by high-activity Cu–ZrOx interface on SBA-15

Abstract

N-methylation of amines using CO2 and H2 addresses the problems of expensive raw materials and harsh reaction conditions. However, designing a high-active and stable interface for the efficient preparation of monomethyl amine compounds in this tandem reaction remains a challenge to be overcome. Here, Cu–ZrOx composites are dispersed on SBA-15, silicalite-1, and ZSM-5 through the oxalic acid precipitation method for the N-methylation of amines using CO2 and H2. Results show that the dispersion of Cu–ZrOx on the surface of SBA-15 is superior to the other two molecular sieves and effectively prevents the sintering of active metals. A 20 wt% Cu–ZrOx/SBA-15 catalyst proves to be optimal for the N-methylation of aniline (AN) using CO2 and H2 to methylaniline (MA) and the catalyst performance remains stable after 5 cycle runs. The optimal catalyst exhibits an AN conversion of 97.6% and a selectivity of 96.5% for MA under the conditions of 180 °C, 4.0 MPa (H2/CO2/N2 = 72/24/4, molar ratio), and 8 h. Spectroscopic investigation and controlled experiments indicated that the preferential adsorbed AN on the catalyst surface reacts with CO2 to generate C–N bond, thereby avoiding the self-coupling side reaction of AN and achieving a high yield of 94.2% for MA.