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

Article https://doi.org/10.1038/s41467-025-66144-6 Cascade catalysis on dual-atom iridiumtungsten catalysts for enhanced ammonia selective oxidation Received: 17 April 2025 Check for updates 1234567890():,; 1234567890():,; Accepted: 30 October 2025 Tingxu Chen1,2,4, Diru Liu2,3,4, Mengyuan Zhang2,3, Yueqing He1,2, Lin Zhao1,2, Yiying Wang1,2, Qiang Wang1 , Guangyan Xu 2,3 & Hong He 2,3 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 dualatom 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. Single-atom catalysts (SACs), which consist of atomically dispersed metal atoms as active centers, have garnered significant attention due to their high atomic utilization efficiency, exceptional catalytic activity, and improved stability1–5. As a result, SACs have been widely applied in a range of catalytic processes, including thermochemical, electrochemical, and photochemical conversions6–9. However, their performance in complex reactions remains constrained by the linear relationship between the adsorption energies of reaction intermediates10–13, a limitation inherent to the isolated single-site nature, which struggles to stabilize multiple reactants simultaneously14,15. While increasing metal loading to create dense SACs could be a potential solution16–18, excessive metal density may lead to metal aggregation, ultimately causing significant catalyst deactivation19,20. In contrast, dual-atom catalysts (DACs), consisting of paired homonuclear or heteronuclear metal sites21,22, offer spatially proximate yet isolated active centers capable of cooperative interactions23, enabling regulate reactant activation and intermediates formation/ desorption as needed24,25. The synergistic interactions between the two metal atoms in DACs, facilitated by their sub-nanometer proximity, has been shown to significantly enhance catalytic performance, even in the absence of direct bonding26. By coupling two distinct active sites, DACs overcome the limitations of SACs, thus rendering them highly suitable for cascade catalysis, where they not only efficiently facilitate 1 College of Environmental Science and Engineering, Beijing Forestry University, Beijing, China. 2State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China. 3University of Chinese Academy of e-mail: ; ; Sciences, Beijing, China. 4These authors contributed equally: Tingxu Chen, Diru Liu. Nature Communications | (2025)16:11179 1 Article sequential intermediate steps but also simplify reaction processes26. This approach has enhanced activity and selectivity in various cascade reactions, including methane dry reforming27, selective hydrogenation28, simultaneous purification of hydrocarbon and nitrogen oxides (NOx)29, and three-way catalysis30. Selective catalytic oxidation of ammonia (NH3-SCO) into N2 and H2O represents a promising approach for NH3 abatement in exhaust purification31,32. However, ammonia oxidation catalysts (AOCs) usually exhibit a ‘seesaw relationship’ between activity and selectivity, in which the enhancement of low-temperature activity often comes at the expense of high-temperature selectivity33,34. For example, noble metal catalysts excel in low-temperature activity but suffer from limited N2 selectivity due to over-oxidation35,36, while transition metal catalysts tend to achieve high N2 selectivity but lack sufficient activity at lower temperatures37,38. Researchers have explored numerous approaches to address this trade-off, including optimizing the metal-support interaction38, constructing dual-layer catalyst structures39, and synthesizing bimetallic catalysts containing both noble and transition metals40. Our recent work demonstrated the efficacy of a bifunctional Pt/Cu-SSZ-13 catalyst for ammonia catalytic oxidation, achieving high selectivity by integrating both an NH3 oxidation component and a selective catalytic reduction (SCR) component41. Therefore, coupling NH3 oxidation and NO reduction reactions represents an important and effective strategy to improve both the activity and selectivity of SCO catalysts. Our previous studies have demonstrated that the single-atom Ir/ CeO2 catalyst exhibits superior low-temperature activity in ammonia oxidation; however, it also produces significant amounts of NOx, which unfortunately, leads to reduced N2 selectivity34. In the present study, we designed and synthesized a dual-atom Ir–W/CeO2 catalyst, consisting of oxidation site (Ir–O–Ce) and reduction site (W–O–Ce), using a wet chemical method for efficient ammonia catalytic oxidation. On the Ir–Wx/CeO2 catalysts, Ir and W atoms formed highly dispersed dimer structures, which, through their synergistic interaction, facilitated the NH3–SCO process via a cascade mechanism. Specifically, NH3 was adsorbed and deeply oxidized on the single-atom Ir–O–Ce sites, resulting in the formation of N2 and NOx. The NOx then further reacted with adsorbed NH3 on the adjacent single-atom W–O–Ce sites, leading to the production of N2 and H2O via the SCR reaction, thereby achieving high activity and enhanced N2 selectivity. Additionally, the dual-atom strategy demonstrated broad applicability, as comparable performance improvements were achieved when other acidic metals, such as Nb and Mo, were employed as co-catalysts. This work highlights the significant potential of dual-atom catalysts in cascade catalysis, providing valuable insights that advance the design of highperformance DACs capable of overcoming the long-standing trade-off between activity and selectivity in conventional thermal catalysis, thereby contributing to the development of more efficient and sustainable catalytic processes. R (...truncated)