Sustainable and Facile Route to Nearly Monodisperse Spherical Aggregates of CeO₂ Nanocrystals with Ionic Liquids and Their Catalytic Activities for CO Oxidation

This article reports a novel preparation of nearly monodisperse spherical aggregates of CeO₂ nanocrystals by using ionic liquid (1-hexadecyl-3-methylimidazolium bromide, C₁₆MimBr) as both template and solvent. The products were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV−vis spectroscopy, FT-IR spectroscopy, and N₂ adsorption−desorption methods. The spherical aggregates, with average diameter of 100 − 150 nm, are composed of ca. 3.5 nm CeO₂ nanocrystals as building units, giving rise to three-dimensional (3D) open porous structures with high Brunauer−Emmett−Teller surface area of 119 m²·g⁻¹. Mesoporous CeO₂ with surface area up to 227 m²·g⁻¹ was prepared by simply tuning the amount of the ionic liquids. Loaded with 5 wt% CuO, both the spherical aggregates and the mesoporous CeO₂ exhibit high catalytic activities for CO conversion with 100% conversion rates at low temperature of 150 °C, suggesting potential applications in preferential oxidation (PROX) and water-gas shift reaction (WGSR). This sustainable and facile method may be extended to the preparation of other metal oxide nanoarchitectures and provides guidance for structure-controlled synthesis.