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

Triruthenium dodecacarbonyl (Ru(CO)) 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(CO) 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 g, which is 1.1, 1.6, and 2 times higher than those of 2Cs-Ru@N-C(450) (14 925.4 µmol h g), 2K-Ru@N-C(450) (10 736.7 µmol h g), and Ru@N-C(450) (8604.2 µmol h g), respectively. A series of characterizations were carried out to explore the 2Ba-Ru@N-C(450) catalysts, such as H-TPR, XPS, and NH-TPD. These results suggest that the Ba promoter played the role of an electronic and structural promoter; moreover, it can promote the NH desorption from the Ru nanoparticles.