Synergistic effect of coordinating interface and promoter for enhancing ammonia synthesis activity of Ru@N–C catalyst

Triruthenium dodecacarbonyl (Ru(3)(CO)(12)) was applied to prepare the Ru-based ammonia synthesis catalysts. The catalyst obtained from this precursor exhibited higher activity than the other Ru salts owing to its unique atomic reorganization under mild temperatures. Herein, Ru(3)(CO)(12) as a guest metal source incorporated into the pore of ZIF-8 formed the Ru@N–C catalysts. The results indicated that the Ru nanoparticle (1.7 nm) was dispersed in the confined N coordination environment, which can increase the electron density of the Ru nanoparticles to promote N[triple bond, length as m-dash]N bond cleavage. The promoters donate the basic sites for transferring the electrons to Ru nanoparticles, further enhancing ammonia synthesis activity. Ammonia synthesis investigations revealed that the obtained Ru@N–C catalysts exhibited obvious catalytic activity compared with the Ru/AC catalyst. After introducing the Ba promoter, the 2Ba–Ru@N–C(450) catalyst exhibited the highest ammonia synthesis activity among the catalysts. At 360 °C and 1 MPa, the activity of the 2Ba–Ru@N–C(450) is 16 817.3 µmol h(−1) g(Ru)(−1), which is 1.1, 1.6, and 2 times higher than those of 2Cs–Ru@N–C(450) (14 925.4 µmol h(−1) g(Ru)(−1)), 2K–Ru@N–C(450) (10 736.7 µmol h(−1) g(Ru)(−1)), and Ru@N–C(450) (8604.2 µmol h(−1) g(Ru)(−1)), respectively. A series of characterizations were carried out to explore the 2Ba–Ru@N–C(450) catalysts, such as H(2)-TPR, XPS, and NH(3)-TPD. These results suggest that the Ba promoter played the role of an electronic and structural promoter; moreover, it can promote the NH(3) desorption from the Ru nanoparticles.