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

Abstract

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(OC8H17)4 with the designed solution methods. The thermolysis of Ce(OC8H17)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(OC8H17)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., EO20-PO70-EO20, P123). Catalytic measurements indicated that three CeO2 catalysts prepared from the above different nanostructures were active for CO oxidation at temperatures beyond 250 °C and showed T50 (50% conversion of CO) at 310 °C for the PAN catalysts, 340 °C for the nanopolyhedra catalyst, and 390 °C for the mesoporous catalyst.