Single atom catalysts (SACs) were the frontier in catalyst research, because they combine the advantages both in homogeneous and heterogeneous catalysts: nearly 100% atomic utilization (similar to homogeneous catalysts), high stability and easy separation from reaction media (features of heterogenous catalysts), and it shows excellent performance for many important chemical transforms. However, the synthesis of metal single atom catalysts remains somewhat ad hoc, with no universal strategy yet reported that allows their generic synthesis. Recently, the synthesis of transition metal single atom catalysts containing Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Pt or combinations thereof was reported by a group in Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, and their research results were published in Nature Communications at October 8th, 2019.

This group developed a universal synthesis method for transition metal (M)-SACs, and nine M-SACs were synthesized successfully. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy confirmed that all M-SACs contained metals atomically dispersed in porphyrin-like MN4 sites over the carbon support. Moreover, this method can sythesis high metal loading M-SACs in large scale. And the as-synthesized Ni-SAC showed excellent performance for electrochemical CO₂ reduction.

The EXAFS R space plots of nine SACs obtained from BSRF. All the M-SACs had no obvious peak at relevant metal-metal bond, indicated that there has no metal-metal bonds in all M-SACs. And all the M-SACs showed only a single peak at 1-2 ？, correponding to M-N bonds, indicated metal atom were coordinated with nitrogen forming single atom sites in all M-SACs.

After this work published, a highlight paper writed by Pro. Buxing Han was published in Chem. Res. Chinese Universities titled with ‘Large scale synthesis of transition metal single atom catalysts by a universal ligand mediated method’. He regarded that: "This work offers a simple and versatile route toward synthesizing transition metal SACs in large scale and the as-synthesized Ni-SAC exhibits excellent activity for CO₂ electroreduction. It is believed that this work will encourage the research interest in the area of SACs, and the as-synthesized SACs are expected to be used for diverse important chemical transformations." (Chem. Res. Chinese Universities 2019, 35 (6), 951)

This work provided method for synthesizing M-SACs in large scale which can be used for CO₂ reduction, oxygen reduction and other important reactions. In this work, 1W1B-XAFS station of BSRF helped this group confirm the metal atoms are atomically dispersed in M-SACs and further confirm the coordination structure of metal atoms. "In furture, the active sites structure in SACs may be adjusted more complicated and exquisitely. In actual catalytic conditions, there have challanges to research the tiny changes of structure around the metal atoms. Therefore, a deeper analysis of the fine structure of single-atom catalysts and a deeper understanding of the catalytic mechanism will be of great significance. More advanced synchrotron beams will help to more accurately analyze the structure of SACs and deeply understand the reaction mechanism." explained by Tierui Zhang, the team leader and the professor of Technical Institute of Physics and Chemistry, Chinese Academy of Sciences.

Article:

Hongzhou Yang, Lu Shang, Qinghua Zhang, Run Shi, Geoffrey I.N. Waterhouse, Lin Gu & Tierui Zhang*, A universal ligand mediated method for large scale synthesis of transition metal single atom catalysts. Nature Communications, 10, 4585 (2019).