Dinitrogen Activation by Heteronuclear Metal Carbide Cluster Anions Y_1-3CoC_1,2⁻: An Experimental and DFT Study

Mass spectrometry was used to observe the reactions between Y−Co heteronuclear metal carbide cluster anions Y_1-3CoC_1,2⁻ and N₂ at room temperature. Y₂CoC_1,2⁻ can produce Co ejection products, in which Y₂CoC⁻ also has N₂ association products; YCoC₂⁻ and Y₃CoC⁻ only generate N₂ association products, while YCoC⁻ and Y₃CoC₂⁻ are inert to N₂. Detailed reaction pathways were obtained through density functional theory calculations, which reasonably explain the experimental phenomena. Co is superior to Y as the electrophilic reaction site in the clusters and is the preferential initial adsorption site for N₂. Some crucial steps were identified, including N−N dissociation, CC−N formation, C−CN dissociation, and C−N formation. The energy barriers of these steps are closely related to the coordination mode of N/N₂ and C/C₂ in clusters. Two indicators, the N−N bond length and the Mayer bond order, were utilized to describe the activation degree of the N−N bond. Analyses on the density of states and the frontier molecular orbitals reveal the electronic structures of key intermediates for N−N dissociation. The reaction mechanisms of N₂ activation on Y−Co carbide clusters obtained may lay a preliminary foundation for the further development of catalysts for nitrogen reduction reaction (NRR).