Self‐organized Ruthenium–Barium Core–Shell Nanoparticles on a Mesoporous Calcium Amide Matrix for Efficient Low‐Temperature Ammonia Synthesis

• Published in: Angewandte Chemie International Edition 2018-03, Vol.57 (10), p.2648-2652
• Main Authors: Kitano, Masaaki, Inoue, Yasunori, Sasase, Masato, Kishida, Kazuhisa, Kobayashi, Yasukazu, Nishiyama, Kohei, Tada, Tomofumi, Kawamura, Shigeki, Yokoyama, Toshiharu, Hara, Michikazu, Hosono, Hideo
• Format: Article
• Language: English
• Subjects: alkaline-earth-metal amides; Ammonia; Barium; Calcium; Catalysis; Catalysts; Chemical synthesis; Core-shell particles; core–shell structures; Low temperature; low-temperatures; mesoporous; Nanoparticles; Pretreatment; Ruthenium; Temperature; Temperature effects; Temperature requirements; Wustite
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201712398

A low‐temperature ammonia synthesis process is required for on‐site synthesis. Barium‐doped calcium amide (Ba‐Ca(NH2)2) enhances the efficacy of ammonia synthesis mediated by Ru and Co by 2 orders of magnitude more than that of a conventional Ru catalyst at temperatures below 300 °C. Furthermore, the presented catalysts are superior to the wüstite‐based Fe catalyst, which is known as a highly active industrial catalyst at low temperatures and pressures. Nanosized Ru–Ba core–shell structures are self‐organized on the Ba‐Ca(NH2)2 support during H2 pretreatment, and the support material is simultaneously converted into a mesoporous structure with a high surface area (>100 m2 g−1). These self‐organized nanostructures account for the high catalytic performance in low‐temperature ammonia synthesis. Ruthenium–barium core–shell nanoparticles and a mesoporous calcium amide matrix (Ru/Ba‐Ca(NH2)2) self‐organize during treatment with hydrogen gas. The resultant composite material presents much higher catalytic performance in low‐temperature ammonia synthesis than other ruthenium catalysts and an industrial iron catalyst.