Rapid microwave-assisted hydrothermal synthesis of CeO2 octahedra with mixed valence states and their catalytic activity for thermal decomposition of ammonium perchlorate

Abstract

Cerium dioxide (CeO₂) octahedra were synthesized by a facile microwave-assisted hydrothermal method. The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that octahedra were enclosed by eight (111) facets with an edge length of 180 nm. The possible growth mechanism of CeO₂ octahedra was proposed by adjusting the reaction temperature, solvent, molar ratios of polyvinyl pyrrolidone (PVP)/Ce³⁺ and reaction time. The formation of the octahedra was attributed to the oxygen terminated structure of (111) facets and the steric hindrance effect of PVP. Furthermore, the catalytic activity of CeO₂ octahedra on the thermal decomposition of ammonium perchlorate (AP) was investigated by thermogravimetry and differential scanning calorimetry (TG-DSC). Compared with cubes, the CeO₂ octahedra exhibited enhanced activity on the decomposition of AP. Upon addition of 4 wt% CeO₂ octahedra, the ending mass loss temperature of AP decreased by 52.1 °C. The higher catalytic activity was attributed to the synergistic effect between the exposed (111) facets and high concentration of oxygen vacancies that arised from the mixed valence state of Ce ions.