High Gravity And Ion-exchange Synthesis Of Ultrafine CeO₂Material

Due to its unique catalytic performance in oxygen storage capacity (OSC) and strong interaction of active species with support, ceria (CeO2) is widely used as an oxygen ion conductor in three-way catalysts, amperometric oxygen monitors and anode electrolyte of solid oxide fuel cells (SOFCs). Synthesis of nano and ultrafine CeO2with high purity and definite size is significant for fundamental and application research.In this thesis, ultrafine CeO2powders with high purity and controllable size are synthesized via a high gravity (Higee) and ion-exchange combination process. Traditional inactive filling is substituted by high active ion-exchange fiber in a Higee reactor. Several important factors, such as radial ion distribution, crystal facial formation, further growth mechanism and size control, are studied by analysis of ion dispersion states and components on fiber surface in the system.As we known, Higee field will produce dramatic hydrodynamic shear force on the surface of ion-exchange fiber as on traditional padding. It is the competition between this hydrodynamic shear force and the strength of surface adsorption that controls particle size of product. Under Higee reaction conditions, the speed of crystal nucleus’ formation is related to rotation rate of main axis. And the former is also associated with surface dispersion, adsorption, and transition ability of adsorbed particles on fiber. All these factors mentioned above interact one another and control the particle size distribution of final product.XRD and TG results show that the powder produced by Higee ion-exchange method before calcinations procedure is mainly CeO2phase (≥84%, weight percent) with cubic crystal structure and high purity.It is concluded that dispersion of adsorbed particles on ion-exchange fiber and products desorbed shows that several synthesis conditions, such as rotation rate, concentration of cerium precursors, and reaction time, have great influence on the particle size and distribution. On this point, we successfully synthesis a series of supported cerium oxide and cerium oxide particles with different particle size distribution. A basic ion-exchange and Higee model is established firstly for ultrafine materials synthesis under special conditions.