Fabrication of Cobalt-Doped Ceria Nanorods for p-Xylene Deep Oxidation: Effects of Cobalt Precursor and Loading

Abstract

In this work, a series of cobalt-doped ceria nanorods have been synthesized coming from two cobalt precursors by the impregnation method, based on ceria nanorods pre-formed by the hydrothermal method. The properties of obtained catalysts were investigated by various techniques, including Brunauer-Emmett-Teller nitrogen physisorption measurements (BET), X-ray powder diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The catalytic activities of as-prepared samples were studied in the deep oxidation of p-xylene at low temperatures (225–300°C). The catalyst characterizations evidenced the crystalline phase formations of CeO₂ and Co₃O₄ with the average crystallite sizes of 17.5–45.8 nm and 11.1–23.4 nm, respectively. The cobalt addition by cobalt nitrate into CeO₂ decreased the surface area of CeO₂ nanorods (67.9 m².g⁻¹), in contrast to the increase using cobalt acetate (76.0–82.5 m².g⁻¹). Co₃O₄/CeO₂ catalysts showed reduction peaks at much lower temperatures than that of pure nanorod ceria. 7.5 mass% Co₃O₄ supported on nanorod CeO₂ catalyst synthesized from cobalt acetate as a type of cobalt precursor with the smallest nanoparticle size and high BET surface area was the most efficient for p-xylene deep oxidation, achieving more than 95% of p-xylene conversion to CO₂ at 275°C, and its performance was stabilized for more than 100 hours tested.

Fig. 7 Effects of cobalt precursor (a) and Co₃O₄ loading (b) on the activity in p-xylene oxidation of catalysts.