Size of cerium dioxide support nanocrystals dictates reactivity of highly dispersed palladium catalysts.

The catalytic performance of heterogeneous catalysts can be tuned by modulation of the size and structure of supported transition metals, which are typically regarded as the active sites. In single-atom metal catalysts, the support itself can strongly affect the catalytic properties. Here, we demonstrate that the size of cerium dioxide (CeO 2 ) support governs the reactivity of atomically dispersed palladium (Pd) in carbon monoxide (CO) oxidation. Catalysts with small CeO 2 nanocrystals (~4 nanometers) exhibit unusually high activity in a CO-rich reaction feed, whereas catalysts with medium-size CeO 2 (~8 nanometers) are preferred for lean conditions. Detailed spectroscopic investigations reveal support size-dependent redox properties of the Pd-CeO 2 interface.