Cascade catalysis on dual-atom iridium-tungsten catalysts for enhanced ammonia selective oxidation

Abstract

Overcoming the trade-off between activity and selectivity has long been a challenge in catalytic reactions. Dual-atom catalysts (DACs) exhibit exceptional catalytic performance in cascade catalysis, owing to the synergistic effects of distinct active sites, which make them particularly promising for enhancing catalytic selectivity. Here, we present dual-atom Ir-Wx/CeO2 catalysts that integrate both oxidation (Ir) and reduction (W) sites for the selective catalytic oxidation of ammonia, a major precursor of air pollutants. Comprehensive characterizations revealed that Ir atoms were embedded on the CeO2 planes in single-atom form, while W sites were anchored on the CeO2 surface, forming Ir-W dimer structures. Operando studies and theoretical calculations demonstrated that NH3 was oxidized on Ir sites, producing NO, which then reacted with NH3 on W sites via selective catalytic reduction (SCR) to generate N2 and H2O. The synergistic effect of the Ir-W dual-atom dimer significantly enhanced low-temperature activity (≥ 92% at 200 °C) and high-temperature selectivity (≥ 92% at 300 °C) on the Ir-W7/CeO2 catalyst. Furthermore, this dual-atom strategy extends to Ir-Mo/CeO2 and Ir-Nb/CeO2 catalysts, demonstrating broad applicability. These findings highlight the potential of DACs for the rational design and application in various cascade catalytic reactions.