Effect of barium promoter in carbon-supported ruthenium catalyst for nitrogen activation

Ammonia is essential for fertiliser production and is also considered a promising carbon-free energy carrier; however, its large-scale synthesis through the Haber-Bosch process remains highly energy-intensive. Carbon-supported Ru catalysts promoted by Ba have shown high activity for ammonia synthesis under mild conditions, yet the atomic-level role of Ba in N 2 adsorption, activation, and initial N–N cleavage tendency remains incompletely understood. In this study, density-functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations were employed to investigate defective graphene-supported Ru/Ba systems containing either isolated Ru atoms or Ru 11 clusters. Structural and electronic analyses, including Bader charge, charge-density difference, density of states, and Crystal Orbital Hamilton Population (COHP) analyses, show that Ba acts as an auxiliary electronic promoter that pre-modulates the Ru electronic structure, enhances Ru-mediated back-donation to N 2 , and weakly stabilises the Ru-polarised distal N atom at the Ru–Ba–N 2 interface, thereby strengthening Ru–N interactions and weakening the N ≡ N bond.