Effect of Barium Promoter in Carbon-Supported Ruthenium Catalyst for Nitrogen Activation

Abstract

Ammonia is essential for fertilisers and a promising carbon-free fuel, yet its industrial synthesis through the Haber-Bosch process remains highly energy-intensive and CO2-emitting. In response, carbon-supported ruthenium (Ru) catalysts with promoters such as barium (Ba) have gained significant attention, as they exhibit high intrinsic activity under milder conditions. However, the atomic-scale mechanism of Ba’s promotional effect on nitrogen activation and Ru’s electronic structure is still not well understood, limiting rational catalyst design. Here, we employ first-principles calculations to investigate the catalytic behaviour of the Ba–Ru/C system. Adsorption geometries and energies of N2 were evaluated at different surface sites, and the electronic structure was analysed through charge density distribution, density of states, and crystal orbital Hamilton population (COHP) analysis to elucidate bonding interactions. The results, obtained from both structural optimisations and ab initio molecular dynamics simulations, reveal that Ru clusters preferentially occupy defect sites, displacing Ba atoms initially located there. Ru clusters act as active centres that attract and bind N2, while Ba functions as an electronic promoter by donating electrons to the Ru-N system. This strengthens orbital interactions between Ru-d and N-p states, thereby enhancing the donation-backdonation process and promoting more efficient N≡N bond cleavage under mild conditions. Overall, the study reveals the cooperative roles of Ru and Ba in nitrogen activation and provides mechanistic insights to guide the design of next-generation carbon-supported Ru catalysts for sustainable ammonia synthesis.