Fragmented Ultrathin Carbon Buffed Copper Clusters for Selective Hydrogenation of <i>N</i>-Heteroarenes under Ambient Pressure

Selective hydrogenation of quinolines to 1,2,3,4-tetrahydroquinolines (py-THQ) realized by cost-effective catalysts holds great importance in the pharmaceutical and agrochemical industries but is challenging due to the high requirement of antipoisoning ability and selectivity. Herein, we propose a universal strategy for the preparation of ultrathin carbon-coated Cu nanoclusters inside the channels of MCM-41 by etching the carbonized template with oxygen-containing gas. The optimized catalyst (Cu/C@MCM-A) exhibits 100% quinoline conversion and 100% py-THQ selectivity at 80 °C and atmospheric pressure. This catalyst also maintained a nearly 100% py-THQ yield at 0.3 MPa for 100 h. In situ characterizations reveal that adjusting the oxygen content in the etching gas enables precise control of the carbon layer thickness and Cu particle size. Experimental results and DFT calculations confirm that the introduction of fragmented ultrathin carbon generates numerous Cu-C interfaces, which can prevent catalyst deactivation by poisoning and reduce the H₂ dissociation barrier by increasing local charge density. The synergy between Cu⁰ and Cu⁺ species ensures efficient and specific transformation. Moreover, Cu/C@MCM-A demonstrates highly selective hydrogenation activities toward other quinoline derivatives, as well as indole, naphthalene, and indene. This work unlocks a unique route for constructing carbon-confined metal clusters to achieve continuous production in selective hydrogenation.