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.