Dimension-Manipulated Ceria Nanostructures (0D Uniform Nanocrystals, 2D Polycrystalline Assembly, and 3D Mesoporous Framework) from Cerium Octylate Precursor in Solution Phases and Their CO Oxidation Activities

Dimension-tunable ceria nanostructures including 0D uniform nanocrystals, 2D polycrystalline assembly, and 3D mesoporous framework were selectively synthesized from the same cerium precursor of Ce(OC 8 H 17 ) 4 with the designed solution methods. The thermolysis of Ce(OC 8 H 17 ) 4 in tri- n -octylphosphine oxide and dioctyl ether at 250 °C yielded uniform ceria nanopolyhedra and elongated nanocrystals (around 2.2 nm in size). Through the polyol alcoholysis in ethylene glycol at 195 °C, polycrystalline assembled nanostructures (PANs) composed of small ceria crystallites (around 3−4 nm) were achieved, showing adjustable cross-linkages in the 2D dendritic structure. The raise of Ce(OC 8 H 17 ) 4 concentration and reaction time would increase the cross-linkages of the PANs. By a conventional sol−gel route, mesoporous ceria gels in an ordered 2D hexagonal mesostructure were synthesized at 40 °C through controlling the hydrolysis rate, and the condensation and aggregation of the metal precursor, as well as the critical micelle concentration (cmc) of the block-copolymer surfactants as used (e.g., EO 20 -PO 70 -EO 20, P123). Catalytic measurements indicated that three CeO 2 catalysts prepared from the above different nanostructures were active for CO oxidation at temperatures beyond 250 °C and showed T 50 (50% conversion of CO) at 310 °C for the PAN catalysts, 340 °C for the nanopolyhedra catalyst, and 390 °C for the mesoporous catalyst.