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 N2 dissociation, leading to significant energy consumption and carbon emissions. In this work, we systematically studied the catalytic ammonia synthesis from N2 and H2 over C60-supported RhnCo4-n (n = 0-4) clusters through density functional theory calculations. Our findings reveal that the reactions follow a distal association mechanism, with NH2* hydrogenation being identified as the highest energy barrier step and almost barrierless N2 dissociation. All four metal atoms are the active sites in NH3 synthesis. The C60-support effectively promotes nitrogen reduction and lowers the N-H formation barriers. The synergistic effect of Rhn, Co4-n, and the C60-support significantly improves the efficiency of the ammonia synthesis reaction. Higher Rh/Co ratios reduce the NH2* hydrogenation barrier. The C60Rh4 exhibits superior catalytic performance with the lowest NH2* hydrogenation barrier and highest turnover frequency (TOF) values; however, C60Co4 emerges as a more promising catalyst candidate for large-scale applications due to its low cost, unique ability to achieve thermal N2-to-NH3 conversion (unattainable by Rh-doped clusters), and TOF values exceeding all Rh-doped clusters except for Rh4. Our findings provide fundamental insights into catalytically active sites, optimal Rh/Co ratios, and C60's synergistic role, guiding improved catalyst design for efficient NH3 synthesis.
Li et al. (Wed,) studied this question.