Strontium carbonate: A bifunctional support to enhance Ru catalysts for ammonia synthesis under mild conditions

Toward enhancing the NH₃ synthesis activity of Ru-based catalysts under mild conditions, various electron donors have been intensively investigated. The electron donation typically originates from either the support itself or the external promoter that transforms into a near-metallic state during the reaction, yet single materials combining both pathways remain rarely reported. This work developed such a bifunctional support, strontium carbonate (SrCO₃). Over the Ru-SrCO₃/carbon nanotubes (CNTs) catalyst, surface SrCO₃ was partially reduced in-situ to form near-metallic Sr⁰ species, which, together with the unreduced basic Sr²⁺ in the bulk SrCO₃, donate electrons to Ru sites, achieving highly efficient N₂ activation. Moreover, the SrCO₃ support can also boost NH₃ desorption and mitigate hydrogen poisoning. The potassium-promoted catalyst K-Ru-SrCO₃/CNTs even delivers an outstanding NH₃-synthesis rate of 61.6 ${\text{mmol}}_{{\text{NH}}_3}$·g_cat⁻¹·h⁻¹ at 400 °C and 0.9 MPa, outperforming most state-of-the-art Ru-based catalysts with Ru mass-loading ≤ 5 wt.% reported to date.