Platinum-based heterogeneous catalysts are critical to energy production, pollution control, and many other important chemical processes. It is estimated that up to 50% of annual platinum supply has been consumed by catalytic converter production for use in vehicles, without inclusion of many other catalytic applications. The scarcity and unique chemistry of platinum drive the efforts searching for cutting the loading of platinum in a catalyst without compromising its performance. Dispersing the platinum as isolated single atoms on a high-surface-area support seems to be the ultimate goal towards this direction. However, this presents grand challenges in both fundamental science and practice. In fundamental science, it remains an open question whether single atoms can be catalytically active or have better performance than the (sub)nanometer-sized clusters or particles although the size effect is a well-known phenomenon in heterogeneous catalysis. In practice, single atoms are rather mobile and easy to aggregate under realistic reaction conditions. Now, by finely tuning the co-precipitation conditions meanwhile controlling the concentration of Pt, the team synthesized successfully a practical single-atom catalyst consisting of only isolated single Pt atoms anchored onto the surfaces of iron oxide (FeO_x) nanocrystallites. The physico-chemical nature of single atoms is well addressed by a combination of experimental and theoretical studies, in particular by using Sub-Ångström-resolution aberration-corrected scanning transmission electron microscopy (STEM). This single-atom catalyst, in spite of its rather low Pt loading, has extremely high atom efficiency and excellent stability for both CO oxidation and preferential oxidation of CO in H₂ both of which are important in pollution control and hydrogen supply for fuel cells. DFT calculations show that the remarkable catalytic activity and stability of single Pt atoms is correlated with the partially vacant 5d-orbitals of positively charged, high-valent Pt atoms.

This work is the first prove that single atoms can do catalysis better than clusters or particles, which may open a new way to cutting greatly the cost of precious metal catalysts in industry.