Ru₃@Mo₂CO₂ MXene single-cluster catalyst for highly efficient N₂-to-NH₃ conversion

Single-cluster catalysts (SCCs) representing structurally well-defined metal clusters anchored on support tend to exhibit tunable catalytic performance for complex redox reactions in heterogeneous catalysis. Here we report a theoretical study on an SCC of Ru₃@Mo₂CO₂ MXene for N₂-to-NH₃ thermal conversion. Our results show that Ru₃@Mo₂CO₂ can effectively activate N₂ and promotes its conversion to NH₃ through an association mechanism, in which the rate-determining step of NH₂* + H* → NH₃* has a low energy barrier of 1.29 eV. Notably, with the assistance of Mo₂CO₂ support, the positively charged Ru₃ cluster active site can effectively adsorb and activate N₂, leading to 0.74 |e| charge transfer from Ru₃@Mo₂CO₂ to the adsorbed N₂. The supported Ru₃ also acts as an electron reservoir to regulate the charge transfer for various intermediate steps of ammonia synthesis. Microkinetic analysis shows that the turnover frequency of the N₂-to-NH₃ conversion on Ru₃@Mo₂CO₂ is as high as 1.45 × 10^-2 s^-1 site^-1 at a selected thermodynamic condition of 48 bar and 700 K, the performance of which even surpasses that of the Ru B5 site and Fe₃/θ-Al₂O₃(010) reported before. Our work provides a theoretical understanding of the high stability and catalytic mechanism of Ru₃@Mo₂CO₂ and guidance for further designing and fabricating MXene-based metal SCCs for ammonia synthesis under mild conditions.