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Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store

Abstract

Industrially, the artificial fixation of atmospheric nitrogen to ammonia is carried out using the Haber–Bosch process, but this process requires high temperatures and pressures, and consumes more than 1% of the world's power production. Therefore the search is on for a more environmentally benign process that occurs under milder conditions. Here, we report that a Ru-loaded electride [Ca24Al28O64]4+(e)4 (Ru/C12A7:e), which has high electron-donating power and chemical stability, works as an efficient catalyst for ammonia synthesis. Highly efficient ammonia synthesis is achieved with a catalytic activity that is an order of magnitude greater than those of other previously reported Ru-loaded catalysts and with almost half the reaction activation energy. Kinetic analysis with infrared spectroscopy reveals that C12A7:e markedly enhances N2 dissociation on Ru by the back donation of electrons and that the poisoning of ruthenium surfaces by hydrogen adatoms can be suppressed effectively because of the ability of C12A7:e to store hydrogen reversibly.

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Figure 1: Ru-loaded C12A7 electride catalyst for ammonia synthesis.
Figure 2: Catalytic performance of Ru/C12A7:e at atmospheric pressure.
Figure 3: Catalytic performance of Ru/C12A7:e under high-pressure conditions.
Figure 4: FT-IR and kinetic analyses.
Figure 5: Possible pathway for the ammonia synthesis reaction over Ru/C12A7:e.

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Acknowledgements

We deeply appreciate K. Aika for his suggestions. Discussions with K. Nakajima and Y. Toda are acknowledged. We thank T. Yoshizumi, S. Nakamura and D. Lu for their technical assistance. This work was supported by a Funding Program for World-Leading Innovative R&D on Science and Technology from the Japan Society for the Promotion of Science. A part of this work was supported by a fund from the Element Strategy Initiative Project of the Ministry of Education, Culture, Sports and Science for Technology in Japan.

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H.H. proposed the idea behind this research and M.H. and H.H. directed the entire project. M.K., Y.I., Y.Y., F.H., S.M., S.K., T.Y. and S-W.K. performed the synthesis, characterization and catalytic testing of Ru/C12A7:e. All the authors discussed the results and commented on the study. M.K., M.H. and H.H. co-wrote the manuscript.

Corresponding authors

Correspondence to Michikazu Hara or Hideo Hosono.

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The authors declare no competing financial interests.

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Kitano, M., Inoue, Y., Yamazaki, Y. et al. Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store. Nature Chem 4, 934–940 (2012). https://doi.org/10.1038/nchem.1476

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