Minimizing the use of precious metal catalysts is crucial for many applications. Single-atom catalysts (SACs) have gained attention because all metal atoms can be used for surface reactions. However, SACs cannot catalyze some important reactions requiring ensemble sites.
Researchers prepared Rh catalysts by hydrothermally treating 2 wt % Rh/CeO2 at 750°C for 25 hours. This treatment achieved nearly 100% dispersion of Rh atoms, but they were not isolated, creating ensemble sites (ENS).
These ENS catalysts effectively oxidized C3H6 and C3H8 at low temperatures, unlike the Rh SAC. When simultaneously oxidizing CO, C3H6, and C3H8, the T20 (temperature at 20% conversion) for CO oxidation increased significantly on SAC due to competitive adsorption of hydrocarbons but increased much less on ENS. ENS showed superior low-temperature oxidation activity. During the 25-hour treatment, Rh size initially increased then decreased, and surface hydroxyl groups helped detach Rh atoms from clusters and prevent reaggregation, leading to a fully dispersed catalyst with maximum atom efficiency.
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