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.