Ru 3 @Mo 2 CO 2 MXene single-cluster catalyst for highly efficient N 2 -to-NH 3 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 Ru ₃ @Mo ₂ CO ₂ MXene for N ₂ -to-NH ₃ thermal conversion. Our results show that Ru ₃ @Mo ₂ CO ₂ can effectively activate N ₂ and promotes its conversion to NH ₃ through an association mechanism, in which the rate-determining step of NH ₂ * + H* → NH ₃ * has a low energy barrier of 1.29 eV. Notably, with the assistance of Mo ₂ CO ₂ support, the positively charged Ru ₃ cluster active site can effectively adsorb and activate N ₂ , leading to 0.74 |e| charge transfer from Ru ₃ @Mo ₂ CO ₂ to the adsorbed N ₂ . The supported Ru ₃ 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 N ₂ -to-NH ₃ conversion on Ru ₃ @Mo ₂ CO ₂ 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 Fe ₃ /θ-Al ₂ O ₃ (010) reported before. Our work provides a theoretical understanding of the high stability and catalytic mechanism of Ru ₃ @Mo ₂ CO ₂ and guidance for further designing and fabricating MXene-based metal SCCs for ammonia synthesis under mild conditions.
(© The Author(s) 2024. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.)