Barium chromium nitride-hydride for ammonia synthesis catalysis Jianping Guo 1 , Guan, Yeqin 1 , Claudia Weidenthaler 2 , Ping Chen 1 1 Dalian Institute of Chemical Physics, China, 2 Max-Planck-Institut für Kohlenforschung, Germany The development of high-efficiency catalysts for ammonia synthesis typically under mild condition remains a very challenging task. 1 Most prior efforts have been focused on iron and ruthenium-based catalysts. 2 Early transition metals, however, have been received far less attention. Early 3d transition metals such as chromium (Cr) can easily dissociate N 2 to nitrogen atoms, but the subsequent hydrogenation of nitrogen atoms to ammonia is very difficult because they bind nitrogen too strongly. 3 Hence, investigation of Cr-based catalysts for ammonia synthesis is very rare. Here we show that when Cr compounds with Ba, N, and H forming a nitride-hydride structure, effective ammonia synthesis catalysis can be achieved under mild conditions. 4 Specifically, under 573 K and 10 bar, this catalyst has an ammonia synthesis rate (6.8 mmol-NH3 g cat -1 h -1 ) that is about four times that of the Cs-Ru/MgO catalyst. With low apparent activation energy (50.1 kJ mol -1 ) and positive reaction orders of H 2 and N 2 , it can produce observable ammonia at 373 K and 1 bar. The active phase has a Ba 5 CrN 4 H-like structure containing reactive hydrogen (H‾) and nitrogen, which are involved in the ammonia formation. This work discloses a strategy to ‘‘activate’’ the inactive early transition metals for effective ammonia catalysis. References 1. Chen, J.G. et al., Science, 2018, 360, eaar6611. 2. Marakatti, V.S., and Gaigneaux, E.M., ChemCatChem, 2021, 12, 5838–5857.
3. Dowben, P.A. et al., Surface Science, 1988, 193, 336–352. 4. Guan, Y.Q. et al., Chem Catalysis, 2021, 1, 1042–1054
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