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

Abstract 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 mmolNH3·gcat−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.