Fig. 4. (a) Reaction time profiles for ammonia synthesis from N2 and D2 over Ru/Ca2N:e– at 340 °C (reaction conditions: catalyst, 0.2 g; reaction gas, N2 : D2 = 1 : 3; reaction pressure, 60 kPa). Prior to reaction, Ru/Ca2N:e– was heated under N2 + H2 flow (N2 : H2 = 1 : 3) at 340 °C for 10 h to form Ru/Ca2NH. (b) TPD profiles of Ru/Ca2N:e– after the reaction (a). TPD measurements were performed (10 °C min–1) with Ar flow. (c) Schematic illustration of ammonia synthesis over Ru/Ca2N:e–. During ammonia synthesis over Ru/Ca2N:e–, H2 is incorporated into Ca2N:e– as H– ions to form Ca2NH (reaction 1). The H– ions are released from Ca2NH, which leaves electrons to form a hydrogen vacancy near the Ru-support interface (reaction 2). The cleavage of N2 proceeds effectively on Ru surfaces due to electron injection from [Ca2N]+·e1–x–Hx– and the nitrogen adatoms react with H radicals to form ammonia (reaction 3).
