Environment of Metal–O–Fe Bonds Enabling High Activity in CO2 Reduction on Single Metal Atoms and on Supported Nanoparticles

Single-atom catalysts are often reported to have catalytic properties that surpass those of nanoparticles, while a direct comparison of sites common and different for both is lacking. Here we show that single atoms of Pt-group metals embedded into the surface of Fe3O4 have a greatly enhanced interaction strength with CO2 compared with the Fe3O4 surface. The strong CO2 adsorption on single Rh atoms and corresponding low activation energies lead to 2 orders of magnitude higher conversion rates of CO2 compared to Rh nanoparticles. This high activity of single atoms stems from the partially oxidic state imposed by their coordination to the support. Fe3O4-supported Rh nanoparticles follow the behavior of single atoms for CO2 interaction and reduction, which is attributed to the dominating role of partially oxidic sites at the Fe3O4–Rh interface. Thus, we show a likely common catalytic chemistry for two kinds of materials thought to be different, and we show that single atoms of Pt-group metals on Fe3O4 are especially successful materials for catalyzed reactions that depend primarily upon sites with the metal–O–Fe environment.