Oxidative Redispersion-Derived Single-Site Ru/CeO2 Catalysts with Mobile Ru Complexes Trapped by Surface Hydroxyls Instead of Oxygen Vacancies

Controlling the oxidative redispersion behavior of supported metal nanoparticles is of central importance in producing high-performance catalysts applied under industry-related oxidation conditions. So far, considerable efforts have been paid to understanding reactant (including O2)-induced disintegration, while much less is known about the influences of support defects like hydroxyl (OH) and oxygen vacancy (VO) on the stabilization of metal–reactant complexes. In this article, by using H2 as a reducing agent, the roles of OH groups and VO in oxidative redispersion of Ru over CeO2 nanorods were distinguished and further disentangled by comparison with the cases of CO-pretreated Ru/CeO2. Supported by electron microscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, in situ X-ray photoelectron spectroscopy, Raman, and other characterizations, we showed that the doubly bridging OH (II) groups on CeO2(111) steps (type II or III) played major roles in stabilizing Ru–Ox complexes and producing atomically dispersed Ru species, while the surface VO sites assisted dehydrogenation and prevented OH overcapping on the reactive Ru sites. The propylene combustion activity of the thus-obtained single-site Ru/CeO2 was far superior to that of a benchmark Pt/Al2O3 catalyst. The results suggested that well-designed H2 treatments could be used to maximize the effectiveness of (reactant-induced) metal redispersion over CeO2, and attention should be paid on possible metal redispersion when dealing with catalysis over systems accessible to reactants (e.g., hydrogen, water, and/or hydrocarbons) that give rise to CeO2 surface hydroxyls in working conditions.