Ru@MoCO MXene single-cluster catalyst for highly efficient N-to-NH 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@MoCO MXene for N-to-NH thermal conversion. Our results show that Ru@MoCO can effectively activate N and promotes its conversion to NH through an association mechanism, in which the rate-determining step of NH* + H* → NH* has a low energy barrier of 1.29 eV. Notably, with the assistance of MoCO support, the positively charged Ru cluster active site can effectively adsorb and activate N, leading to 0.74 |e| charge transfer from Ru@MoCO to the adsorbed N. The supported Ru 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-to-NH conversion on Ru@MoCO is as high as 1.45 × 10 s site 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/θ-AlO(010) reported before. Our work provides a theoretical understanding of the high stability and catalytic mechanism of Ru@MoCO and guidance for further designing and fabricating MXene-based metal SCCs for ammonia synthesis under mild conditions.