Robust Ru single-atom alloy catalysts coupled with adjacent Fe-site for highly stable ammonia synthesis under mild conditions

In our pursuit of an efficient catalyst for ammonia production, we developed ruthenium (Ru)-based single atom alloy catalysts on a layered double hydroxide-derived support. The extended X-ray absorption fine structure studies provided evidence of single Ru atoms as a Fe-Ru alloy. High-resolution transmission electron microscopy showcased a larger particle size with higher Ru loading, emphasizing the role of Ru site geometry in catalytic activity. The MgFeO_x-0.1Ru catalyst, with optimal Ru dispersion and smaller Fe-Ru particle size (1.6 nm), outperformed other catalysts in NH₃ synthesis and demonstrated exceptional stability. Remarkably, the catalyst with 0.1 wt% Ru exhibited superior performance, achieving an exceptional NH₃ formation rate of 17,897 µmol g⁻¹ h⁻¹ (at 400 °C, 5 MPa, and Weight hourly space velocity (WHSV) of 50,000 mL g⁻¹ h⁻¹) along with maintaining a consistent NH₃ synthesis rate of 7,217 µmol g⁻¹ h⁻¹ (at 400 °C, WHSV of 10,000 mL g⁻¹ h⁻¹, and 5 MPa), for a notable duration of 150 h. Our first-principles calculations show that Ru weakened the binding of both molecular and atomic nitrogen on the catalyst's surface, facilitating the desorption of N-intermediates. The optimized MgFeO_x-0.1Ru catalyst composition with characteristics such as small Fe-Ru alloy particle size and the presence of all active Ru sites on the surface improves lifetime, reducing costs and marking a significant stride towards sustainable and economically viable NH₃ production.