First-Principles Study of Stability and N₂ Activation on the Octahedron RuRh Clusters

The geometric and electronic structures of different octahedron RuRh clusters are studied using density functional theory calculations. The binding energy, electronic structure, and energy gap of the clusters have been obtained to determine the possible stable structures. The results show that the Ru4Rh2 cluster is the most stable structure which has D4h symmetry with the largest ionization potential, smallest affinity energy and larger energy gap. Furthermore, the information on adsorption and dissociation of multiple nitrogen molecules and the density of state for the octahedral Ru4Rh2 cluster is analyzed. The dissociation barrier of three nitrogen molecules further decreases to 1.18 eV with an increase in the number of N2 molecules. The co-adsorption of multiple N2 molecules facilitates the dissociation of N2 on the Ru4Rh2 cluster. The strong interaction between the antibonding orbital of N2 and the d orbital of the Ru4Rh2 cluster is illustrated by calculating and analyzing the results of PDOS, which stretches the N−N bond length and reduces the activation energy to dissociation. The antibonding orbital of the nitrogen molecule shows distinct and unique catalytic activity for the dissociation of the adsorbed nitrogen molecule on the octahedral Ru4Rh2 cluster.