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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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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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.
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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Experimental procedures; products characterization; X-ray crystallographic analysis; kinetic, electrochemical and DFT studies.
Crystallographic Information File for compounds 6a, CCDC 1860066
Crystallographic Information File for compounds 6b, CCDC 1860067
Crystallographic Information File for compounds 7, CCDC 1860068
Crystallographic Information File for compounds 8, CCDC 1860069
Crystallographic Information File for compounds 9, CCDC 1860070
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Nakajima, K., Toda, H., Sakata, K. et al. Ruthenium-catalysed oxidative conversion of ammonia into dinitrogen. Nat. Chem. 11, 702–709 (2019). https://doi.org/10.1038/s41557-019-0293-y
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