Comparative Study of CeO2 and Doped CeO2 with Tailored Oxygen Vacancies for CO Oxidation

We report on the preparation and characterization of CeO2 nanofibers (CeO2-NFs) and nanocubes (CeO2-NCs), as well as Sm-and Gd-doped CeO2 nanocubes (Sm-CeO2-NCs and Gd-CeO2-NCs), synthesized by a simple hydrothermal process for CO catalytic oxidation. The samples were characterized by Xray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence spectroscopy. Their oxygen-storing capacity (OSC) was examined by means of hydrogen temperature-programmed reduction (H-2-TPR) and oxygen pulse techniques. Their catalytic properties for CO catalytic oxidation were comparatively investigated. The results showed that the CeO2-NFs possessed a higher catalytic activity compared to the CeO2-NCs because of their smaller size and the greater number of oxygen vacancies. The activity of the Sm-CeO2-NCs was higher than that of the CeO2-NCs due to an increase in the number of oxygen vacancies, which results from the substitution of Ce4+ species with Sm3+ ions. In contrast, Gd doping had a negative effect on the CO catalytic oxidation due to the special electron configuration of Gd3+ (4f(7)). Our work demonstrates that the oxygen vacancies in pure CeO2 and the electron configuration of the dopants in doped CeO2 play an important role in CO oxidation.