Encapsulating Cu nanoparticles within MIL-101 for efficient and selective N-methylation of amines using CO2/H2

The use of CO 2 /H 2 for amine N-methylation provides a green and sustainable pathway for CO 2 utilization and the production of N-methylamines. However, the research on advanced catalysts still poses a challenge. Herein, we confined ultrasmall Cu nanoparticles within MIL-101 for catalyzing the N-methylation of amines using CO 2 /H 2 . When the molar ratio of NaBH 4 /Cu was 2:1, the 5 %Cu@MIL-101(Cr) catalyst exhibited excellent catalytic performance and cycling stability. Using cyclohexane as the solvent, under conditions of 4 MPa (P H2 /P CO2 = 3), and 200 °C for 8 h, the conversion of aniline (AN) reached 94.8 %, with a selectivity of 93.1 % for methylaniline (MA). Benefiting from the confinement effect of the MOF cages, no significant agglomeration of Cu particles was observed in the catalyst after the reaction. The coexistence of Cu 0 -Cu + -Cu 2+ and their synergistic interaction with the Cr–oxo clusters facilitated the high activity of Cu@MIL-101(Cr). Control experiments indicated that CO 2 activated on the Cu + and O 2− of the Cr–oxo clusters preferentially reacts with the AN adsorbed on adjacent Cu 2+ and unsaturated Cr 3+ sites, forming a phenylcarbamic acid intermediate. This intermediate is subsequently stepwise hydrogenated to MA by spillover H* atoms dissociated on neighboring Cu 0 sites. • Ultrasmall Cu nanoparticles (NPs) were confined within MIL-101 via the double-solvent method for catalyzing the selective N-methylation of amines using CO 2 /H 2 . • The 5 wt%Cu@MIL-101(Cr) catalyst possesses an optimal Cu 0 -Cu + -Cu 2+ ratio, and an aniline (AN) conversion of 94.8 % and an methylaniline (MA) selectivity of 93.1 % were achieved. • Benefiting from the confinement effect of the MOF cages, no significant agglomeration of Cu particles was observed in the catalyst after the reaction. • The coexistence of Cu 0 -Cu + -Cu 2+ and their synergistic interaction with the Cr–oxo clusters facilitated the high activity of the catalyst.