Asymmetric Dual-Atom Ruthenium–Tungsten on CeO2 Enabled Highly Active and Selective NH3 Oxidation

Abstract Ru single-atom catalysts are promising for NH3 oxidation but still suffer from poor activity and N2 selectivity, mainly owing to the poisoning of the isolated Ru active sites by the over-strong NH3 adsorption. Herein, we fabricated an asymmetric Ru-W atomic pair anchored on CeO2 (Ru1–W1/Ce) exhibiting considerable low-temperature activity (∼90% at 200 °C), high N2 selectivity (∼85% at 350 °C), and notable stability (∼500 h at 200 °C), surpassing most of the previously reported catalysts for NH3 oxidation. Systematic experimental and theoretical investigations demonstrated that a strong d-f orbital interaction between Ru and W atoms was revealed, inducing the smooth electron transfer from W to Ru atoms. The electron-rich Ru single atom not only weakened NH3 adsorption strength to alleviate NH3 poisoning but also reduced the energy barrier of the rate-determining step of NH3 activation. Besides, isolated W atoms coordinated with active Ru species, leading to a decrease in Ru–O–Ce coordination number. This could suppress the activation of O2 and thereby the deep oxidation of NH3. Accordingly, the reaction mechanism over this asymmetric Ru–W catalyst changed from the initial i-SCR to an imide-like pathway, accounting for its considerable catalytic performance. This work provided a paradigm for advanced Ru-based catalysts enabling both high activity and high N2 selectivity in NH3 oxidation.