Ultimate dispersion of metallic and ionic platinum on ceria

Ceria represents a technologically indispensable reducible catalyst support. Besides the general impact on the surface chemistry, the oxygen content of the ceria surface directly influences the dispersion of ceriasupported metal nanoparticles, and the properties of ceria-supported metal catalysts. We investigate the role of oxygen atoms on a CeO2(111) surface in supporting Pt as smallest metallic Pt clusters or, concurrently, as monodispersed Pt2+ ions. We demonstrate that the necessary condition for the formation of Pt2+ ions is the availability of lattice O or excess O atoms at surface step edges. Although Pt2+ ions can exist on partially reduced surfaces, excess O atoms are required to maximize the capacity of the surface to accommodate Pt2+ and to trigger the redispersion of metallic Pt clusters. Our study provides atomic-level understanding and control of the highest dispersions of Pt on the ceria surface for advancing the state-of-the-art Pt/ceria catalysts that are presently identified at the verge of single-atom Pt dispersion.