Impact of the synthesis parameters on the solid state properties and the CO oxidation performance of ceria nanoparticles

Abstract

Ceria-based materials have received considerable attention in catalysis field due to their unique physicochemical characteristics. Compared to bulk ceria, nanosized ceria received particular interest, due to its high surface to volume ratio, improved reducibility and optimal morphological features. Hence, the fine-tuning of ceria properties by means of advanced synthesis routes is of particular importance. In this regard, the present work aims at investigating the impact of synthesis parameters on the solid state properties of CeO₂ materials. Four different time- and cost-effective preparation methods were followed, i.e. thermal decomposition, co-precipitation and hydrothermal method of low and high NaOH concentration, employing in all cases Ce(NO₃)₃·6H₂O as cerium precursor. A complementary characterization study, involving N₂ adsorption at −196 °C (BET method), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR) and scanning/transmission electron microscopy (SEM/TEM), was carried out to gain insight into the impact of synthesis route on the textural, structural, morphological and redox properties. The results revealed the superiority of the hydrothermal method towards the development of ceria nanoparticles of high specific surface area (>90 m² g⁻¹), well-defined geometry (nanorods) and improved redox properties. CO oxidation was employed as a probe reaction to gain insight into the structure–activity correlation. Ceria nanorods prepared by hydrothermal method of high NaOH concentration demonstrated the optimum CO oxidation performance. A direct quantitative correlation between the catalytic activity and the abundance of easily reduced, loosely bound oxygen species, was revealed. Hence, this particular reactivity descriptor can potentially be used for the rational design of ceria-based materials.