非表示:
キーワード:
ammonia synthesis; nitride-hydride; hydride; chromium; barium; nitrogen fixation; heterogeneous catalysis; early transition metal
要旨:
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 mmolNH3gcat−1h−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-) 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.
