Engineering at surface-interface triggered by single sites to regulate selectivity of CO₂ reduction

Rational catalyst design and reaction mechanism investigation guided by clarification of relationship between the active sites and elementary reaction steps at molecular level are challenging but essential in heterogeneous catalysis. Here we demonstrate the alteration of active sites on surface-interface by doping Ag-single atoms to Cu-crystal lattice of Cu/Al₂O₃, tuning the selectivity of CO₂ reductive amination from N-methylation to N,N-dimethylation. Characterizations and DFT calculations reveal that active sites for Cu/Al₂O₃ are interface site of [Cu(I)-O/Cu(0)]_inter and surface sites of [Cu]_surf while that change to [Ag(I)-O/Cu(0)]_inter and [Ag₁Cu]_surf after doping Ag-single atoms. Three different elementary reaction steps including N-H activation of amines, CO₂ hydrogenation and C-N coupling are involved and interface sites are beneficial for N-H activation and surface sites are conducive to CO₂ hydrogenation and C-N coupling. Importantly, N-H activation and C-N coupling for N,N-dimethylation are more favorable over [Ag(I)-O/Cu(0)]_inter and [Ag₁Cu]_surf regulating the selectivity, due to the orbitals matching and lower energy barrier.