Essential role of hydride ion in ruthenium-based ammonia synthesis catalysts

Masaaki Kitano, Yasunori Inoue, Hiroki Ishikawa, Kyosuke Yamagata, Takuya Nakao, Tomofumi Tada, Satoru Matsuishi, Toshiharu Yokoyama, Michikazu Hara, Hideo Hosono

Research output: Contribution to journalArticlepeer-review

195 Citations (Scopus)


The efficient reduction of atmospheric nitrogen to ammonia under low pressure and temperature conditions has been a challenge in meeting the rapidly increasing demand for fertilizers and hydrogen storage. Here, we report that Ca2N:e-, a two-dimensional electride, combined with ruthenium nanoparticles (Ru/Ca2N:e-) exhibits efficient and stable catalytic activity down to 200 °C. This catalytic performance is due to [Ca2N]+·e1-x-Hx- formed by a reversible reaction of an anionic electron with hydrogen (Ca2N:e- + xH ↔ [Ca2N]+·e1-x-Hx-) during ammonia synthesis. The simplest hydride, CaH2, with Ru also exhibits catalytic performance comparable to Ru/Ca2N:e-. The resultant electrons in these hydrides have a low work function of 2.3 eV, which facilitates the cleavage of N2 molecules. The smooth reversible exchangeability between anionic electrons and H- ions in hydrides at low temperatures suppresses hydrogen poisoning of the Ru surfaces. The present work demonstrates the high potential of metal hydrides as efficient promoters for low-temperature ammonia synthesis.

Original languageEnglish
Pages (from-to)4036-4043
Number of pages8
JournalChemical Science
Issue number7
Publication statusPublished - 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Chemistry


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