A First-Principles Microkinetic Investigation of NO Reduction Reaction by CO on a Multifaceted Cu Catalyst

Understanding how surface structure and temperature govern catalytic activity is essential for designing efficient exhaust-gas purification catalysts, particularly under cold-start conditions. Copper (Cu) is a promising non-precious metal catalyst for low-temperature NO + CO conversion. However, the nature of its active sites remains unclear. Here, we employ first-principles microkinetic modeling to investigate NO + CO reactions on a multifaceted Cu catalyst, including Cu(100), Cu(111), Cu(110), Cu(211), and Cu(221), under lean, stoichiometric, and rich three-way-catalysis conditions. We uncover a pronounced facet- and temperature-dependent reaction mechanism. At cold-start temperatures (T < 600 K), NO is efficiently converted to N2 via dimer-mediated NO dissociation mainly on Cu(211). While N2O can form on multiple Cu facets, its re-adsorption and decomposition to N2 occur predominantly on Cu(211), facilitated by the low barrier for CO oxidation, which enables rapid oxygen removal and promotes N2O re-adsorption and decomposition. As temperature increases, the dominant pathway shifts to NO monomer dissociation on Cu(110). The predicted NO and CO conversions reproduce experimental trends across all gas compositions. Comparison with Rh catalysts further highlights the distinctive low-temperature behavior of Cu: whereas literature reports show measurable N2O release on Rh below ∼900 K due to surface poisoning by accumulated O and N, our microkinetic analysis predicts that Cu shows essentially no N2O release in the active temperature window because the active Cu facets remain sufficiently accessible for N2O re-adsorption and rapid conversion to N2. It is noted, however, that Cu reactivity relies on Cu(211) and Cu(110); because these facets make up only a small fraction of Cu nanoparticles, the overall activity is constrained by surface morphology. These results provide atomic-level insight into Cu reactivity and establish mechanistic design principles for efficient and robust non-PGM exhaust catalysts.