Insights into N-Coordinated Bimetallic Site Synergy during NO Selective Catalytic Reduction by CO

The nature of the synergistic effect in bimetallic catalysts remains a challenging issue, due to the difficulty in understanding the adjacent interaction between dual metals at the atomic level. Herein, a CuFe-N/C catalyst featuring diatomic metal-nitrogen sites was prepared through a sequential ion exchange strategy and applied for NO selective catalytic reduction by CO (CO-SCR). The bimetallic CuFe-N/C catalyst exhibits high N2 selectivity with a NO conversion efficiency of nearly 100% over a wide temperature range from 225 to 400 °C, significantly higher than that of its single-component counterparts. The synergistic effect of bimetallic Cu-Fe sites is well revealed using the combined in situ FTIR technique and DFT calculations. Bifunctional Cu-Fe sites are demonstrated not only to provide two different preferential adsorption centers for the CO molecule and ONNO intermediate but also to achieve a complete electron cycle for efficient interfacial electron transfer upon ONNO uptake. The unique electron transfer mechanism stemmed from 4s-3d-type electron coupling, and different 3d shell fillings of Cu (3d10) and Fe (3d6) atoms are presented. These fundamental insights pave the way for the understanding of N-coordinated bimetallic site synergy and rational design of highly active atomic-scale metal catalysts for SCR applications.