Formation of CeNbO 4.08 Mixed-Ion Conductor Structure in CuO x /CeNbO x Catalyst to Improve N 2 Selectivity of NH 3 –SCO Reaction

The rising interest of using NH3 as a zero-carbon fuel has triggered the need to develop a high-performance NH3 oxidation catalyst to control its slip. Although CuOx/CeO2 catalysts exhibit promising activity for NH3 selective catalytic oxidation, their practical application is hindered by suboptimal N2 selectivity due to excessive NH3 oxidation. Here, we report a rationally designed CuOx/CeNbOx catalyst with dual-functional active sites, where the introduction of Nb5+ establishes a Ce–Nb cooperative interaction that enables a substantial increase in N2 selectivity with only minimal sacrifice in NH3 conversion activity. Through a combination of characterization techniques (XPS, H2-TPR) and kinetic studies, we show that across a very broad temperature range (275–400 °C) at a high w8 hly space velocity (WHSV) of 150,000 mL·g–1·h–1, the optimized CuOx/CeNbOx (Ce/Nb = 1:1) achieves >90% NH3 conversion. Furthermore, it maintains >80% N2 selectivity over a wide temperature window of 200–350 °C. Mechanistic studies reveal that Nb incorporation increases surface Ce3+ content and oxygen vacancies, modulates Cu redox properties to favor Cu2+ stabilization, and creates balanced acid sites for optimal NH3 adsorption. Critically, in situ spectroscopic evidence confirms the dominance of an internal selective catalytic reduction (i-SCR) pathway, where −NH2 intermediates react with NOx species rather than undergoing direct oxidation.