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

Abstract

Single-cluster catalysts (SCCs) representing structurally well-defined metal clusters anchored on support tend to exhibit tuneable 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. Especially, 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 (TOF) 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 those of the Ru B5 site and Fe3/θ-Al2O3(010) reported before. Our work provides a theoretical understanding on 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.