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

Abstract

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. Controlling catalyst selectivity requires linking atomic sites to each reaction step. Adding isolated silver atoms to copper reshapes surface and interface sites, steering carbon dioxide amination from single to double methylation.