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

Abstract

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 CeO 2 nanorods were distinguished and further disentangled by comparison with the cases of CO-pretreated Ru/CeO 2 . 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 CeO 2 (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/ CeO 2 was far superior to that of a benchmark Pt/Al 2 O 3 catalyst. The results suggested that well-designed H 2 treatments could be used to maximize the effectiveness of (reactant-induced) metal redispersion over CeO 2 , 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 CeO 2 surface hydroxyls in working conditions.

Strong Metal–Support Interactions in Cu(I)-Dark TiO2 Nanoscale Photocatalysts Prepared by Pulsed Laser Ablation for Hydrogen Evolution Reaction

“…Moreover, Cu 1+ is located near the surface oxygen vacancies and/or near cleaved bridge bonds Ti 3+ ···O δ− –Ti 4+ . This placement is due to the tendency of copper to occupy a region with higher electron density. − The ALT also leads to an increase in the content of surface OH groups (Figures S2 and S3), which are sites for the glycerol adsorption on the catalyst surface (Figure b) . When the system is exposed to light, the high dispersion/isolation of Cu 1+ particles can lead to a SMSI effect, similar to the operation of Pt/dark TiO 2 , where dark TiO 2 was also used as a support.…”

“…The Cu 2 O powder for electrokinetic studies was prepared by PLAL of the Cu metal target in water followed by drying in air at 60 °C. More details about the preparation and properties of copper oxide are presented in refs and (for comparison with low concentrations of introduced copper up to 1 wt %), and CuO was prepared by annealing the Cu 2 O at a temperature of 400 °C (for comparison with the samples containing more than 1 wt % Cu). The structures of the reference copper oxides were confirmed by XRD (Figure S6).…”