Ruthenium-catalysed oxidative conversion of ammonia into dinitrogen

Abstract

Conversion of ammonia into dinitrogen has attracted broad scientific interest in relation to molecular models of the heterogeneous nitrogen fixation process, environmental treatment for denitrification and utilization of ammonia as an energy carrier. Here we show that some ruthenium complexes bearing 2,2′-bipyridyl-6,6′-dicarboxylate ligands work as catalysts for the ammonia oxidation reaction. Production of dinitrogen is observed when ammonium salts are treated with a triarylaminium radical as an oxidant and 2,4,6-collidine as a base in the presence of the ruthenium catalysts. Based on the characterization of some intermediates, we propose a reaction pathway via a bimetallic nitride–nitride coupling process. The proposed reaction pathway is supported by density functional theory calculations. Further investigation of the ammonia oxidation reaction under the electrochemical conditions revealed that the ruthenium complex works as a new anode catalyst for ammonia oxidation.

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Fig. 1: Catalytic reactions to convert ammonia into N2.
Fig. 2: Transformations of ruthenium complexes 1a and 1b.
Fig. 3: DFT calculations.
Fig. 4: Electrochemical analysis.

Data availability

Crystallographic data for the structure reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition nos. CCDC 1860066 (6a), 1860067 (6b), 1860068 (7), 1860069 (8) and 1860070 (9) (Supplementary Table 5). All other data supporting the findings of this study are available within the Article and its Supplementary Information, or from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by CREST, JST (JPMJCR1541). The authors acknowledge support from JSPS KAKENHI grants nos. JP15H05798, JP17H01201, JP18K19093 and JP19K15556 from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT). We also thank J. C. Peters and S. Schneider for helpful discussions.

Author information

K.S. and Y.N. directed and conceived this project. K.N. and H.T. conducted the experimental work. K.S. conducted the computational work. All authors discussed the results and wrote the manuscript.

Correspondence to Ken Sakata or Yoshiaki Nishibayashi.

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Competing interests

K.N., H.T. and Y.N. have filed a patent based on the work described here (Japanese patent application no. 2018-036966).

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Supplementary information

Supplementary Information

Experimental procedures; products characterization; X-ray crystallographic analysis; kinetic, electrochemical and DFT studies.

6a-CH4O.cif

Crystallographic Information File for compounds 6a, CCDC 1860066

6b-2CH4O.cif

Crystallographic Information File for compounds 6b, CCDC 1860067

7-H2O.cif

Crystallographic Information File for compounds 7, CCDC 1860068

8.cif

Crystallographic Information File for compounds 8, CCDC 1860069

9.cif

Crystallographic Information File for compounds 9, CCDC 1860070

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