Relationships between structural/morphological modifications and oxygen storage-redox behavior of silica-doped ceria

The reduction/oxidation and oxygen storage behavior of silica-doped ceria is described with particular attention to structural transformation occurring under these conditions. It is shown that the reduction properties of CeO2 are strongly dependent on the amount of silicon. In particular, the use of silicates during the preparation of ceria endows the material with remarkable reduction behavior. TPR studies and thermogravimetric analysis of ceria under H-2 show a promotion of reduction, especially after thermal redox cycles at high temperature. This is correlated to the formation upon reduction of a Ce-9.33(SiO4)(6)O-2 phase, which was detected by XRD and HREM-EDX studies. Reoxidation of this phase in the range of temperatures between 773 K and 1073 K gives a mixture of amorphous silica and small ceria crystallites which are responsible for the enhancement of oxygen storage behavior, measured by alternately pulsing CO and O-2 over the catalysts.