Journal
CHEM CATALYSIS
Volume 1, Issue 5, Pages 1042-1054Publisher
CELL PRESS
DOI: 10.1016/j.checat.2021.08.006
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Funding
- National Natural Science Foundation of China [21922205, 21872137, 21633011, 21988101]
- Youth Innovation Promotion Association CAS [2018213]
- DICP [DICP DCLS201701]
- K.C. Wong Education Foundation [GJTD-2018-06]
- Liaoning Revitalization Talents Program [XLYC2007173]
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This study reveals a strategy to activate early transition metals for effective ammonia catalysis by forming nitride-hydride compounds. The catalyst shows high ammonia synthesis rate and low apparent activation energy under mild conditions. The active phase contains reactive hydrogen and nitrogen that are involved in ammonia formation.
Early 3d metals such as chromium can easily dissociate N2, but the subsequent hydrogenation to ammonia is difficult because they bind nitrogen too strongly. 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, effective ammonia synthesis catalysis can be achieved under mild conditions. Under 573 K and 10 bar, this catalyst has an ammonia synthesis rate (6.8 mmolNH3 gcat(-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 H2 and N2, it can produce observable ammonia at 373 K and 1 bar. The active phase has a Ba5CrN4H-like structure containing reactive hydrogen ( H-1) 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.
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