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 O-2)-induced disintegration, while much less is known about the influences of support defects like hydroxyl (OH) and oxygen vacancy (V-O) on the stabilization of metal-reactant complexes. In this article, by using H-2 as a reducing agent, the roles of OH groups and V-O 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-O-x complexes and producing atomically dispersed Ru species, while the surface V-O 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 H-2 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.