(9d) Ceria-Zirconia-Yttria Mesostructures Synthesized Via Classical Sol-Gel and EISA Methods: In-Depth Study of Factors Affecting the Formation of Ordered Structures

Mesoporous ceria-zirconia-yttria (CZY) catalyst supports were synthesized via classical sol-gel and evaporation induced self-assembly (EISA) methods using inorganic salts and Pluronic triblock copolymer F127 as the structure directing agent (SDA). The mesostructures obtained exhibited excellent properties but difficulties towards forming an ordered framework. A detailed analysis of the factors and mechanisms that promote the creation of an ordered structure is presented. Classical sol-gel methods are reaction-limited syntheses in which, for the case of CZY materials, the formation of polyoxides occurs rapidly as a result of the availability of water and hydrolyzing agents in the initial solution yielding disordered oxide mesostructures. Alternatively, EISA is a diffusion-limited process where the rate of oxide forming reactions is limited by the slow diffusion of water into the initial ethanolic-metal salts solution. The slow loss of ethanol by evaporation enables the polymer template to self-organize and permits a controlled influx of water into the system. Simultaneously, metal oxides condense and polymerize to generate a robust oxide network around the periphery of the ordered polymer templates. This study gives insight into these processes explaining the reasons behind this behavior.