A comprehensive molecular-level characterization of the surface chemistry of Ru/CeO2 was performed using FTIR spectroscopy of two complementary probe molecules: CO, the most commonly used IR probe for cationic and metal sites, and 15N2, an inert molecule that selectively detects only the strongest adsorption centers. Blank experiments with bare ceria octahedra were also performed. The effects of oxidative and reductive pretreatments on CO and 15N2 adsorption were systematically examined for both Ru/CeO2 and CeO2. The results show that the oxidized catalyst contains an oxidized Ru-oxide/hydroxide phase covering the metal particles and part of the support surface, thus completely blocking metallic ruthenium sites and markedly reducing the number of available CO adsorption sites on ceria and completely suppressing 15N2 adsorption. This blocking effect is much more pronounced on the highly reactive 110 and 100 facets than on the more stable 111 surface. After reduction, metallic Ru becomes exposed, and some previously inaccessible ceria sites are restored. Structural and electronic characterization using XRD, STEM, H2-TPR, and NAP-XPS provides key complementary information on the morphology, composition, reducibility, and chemical state of the catalysts, enabling consistent interpretation of the IR spectroscopic results.
Bezkrovnyi et al. (Thu,) studied this question.