Catalytic Ammonia Synthesis from N 2 and H 2 over Fullerene-Supported Rh n Co 4– n ( n = 0–4) Clusters: A Theoretical Study

The development of new, efficient, and environmentally friendly ammonia synthesis catalysts is crucial, as the widely utilized Haber–Bosch process requires high temperature and high pressure for N 2 dissociation, leading to significant energy consumption and carbon emissions. In this work, we systematically studied the catalytic ammonia synthesis from N 2 and H 2 over C 60 -supported Rh n Co 4– n ( n = 0–4) clusters through density functional theory calculations. Our findings reveal that the reactions follow a distal association mechanism, with NH 2 * hydrogenation being identified as the highest energy barrier step and almost barrierless N 2 dissociation. All four metal atoms are the active sites in NH 3 synthesis. The C 60 -support effectively promotes nitrogen reduction and lowers the N–H formation barriers. The synergistic effect of Rh n, Co 4– n, and the C 60 -support significantly improves the efficiency of the ammonia synthesis reaction. Higher Rh/Co ratios reduce the NH 2 * hydrogenation barrier. The C 60 Rh 4 exhibits superior catalytic performance with the lowest NH 2 * hydrogenation barrier and highest turnover frequency (TOF) values; however, C 60 Co 4 emerges as a more promising catalyst candidate for large-scale applications due to its low cost, unique ability to achieve thermal N 2 -to-NH 3 conversion (unattainable by Rh-doped clusters), and TOF values exceeding all Rh-doped clusters except for Rh 4 . Our findings provide fundamental insights into catalytically active sites, optimal Rh/Co ratios, and C 60 ’s synergistic role, guiding improved catalyst design for efficient NH 3 synthesis.