Ceria, bulk

Fig. La shows the TPR-MS trace for water (m/e 18) corresponding to the ceria C-HS sample. It is in good agreement with those reported elsewhere [14,15,17,18]. The water released fi-om 773 up to 973K is interpreted as due to the surface reduction process, whereas the second peak, the one featuring at HOOK being related to the ceria bulk reduction. Fig l.b accounts for the behaviour of ceria after successive (up to 4) reduction (1223 K)/reoxidation (standard O2 pretreatment)...

The preceding results suggested that during the reduction of ceria, bulk reduction is very much slower than surface reduction, leading to a possible "selective measurement" of reducible species at the ceria surface. 

The modelling results at 548 and 573 K, not shown, indicate that the conversion of all components increases with temperature. Less N2O is produced as it decomposes faster (step 17). Faster NO desorption leads to less NO storage on ceria. The capacity of the sub-layer (table 2) increases rapidly in this temperature range, clearly indicating the contribution of the ceria bulk. 

Although the dopant dissolves in the ceria lattice, we cannot rule out the presence of an amorphous dopant-rich phase at the surface of the catalyst (even after severe calcining). XPS + XRD measurements show a dopant-lean bulk and a dopant-rich surface. The structural similarity of the different catalysts is supported by the surface area-pore volume relationship (Figure 3). 

Imamura, Kaito, and coworkers—metal-support effects observed after calcination. Imamura et al 9X reported a strong metal-support interaction between Rh and Ce02, whereby high surface area ceria calcined at low temperature (550 °C) was able to transport Rh particles to the bulk, as measured by XPS. They suggested that despite the low degree of exposure of the Rh particle at the surface, the exposed Rh was highly active for the methanol decomposition reaction. 

The Rietveld refinements show that the crystalline structure contains microstrain that is mainly caused by the crystal distortion related to zirconium replacement. It is also found that cationic occupancy number in the crystalline structure is smaller than their normal value 0.02083 present in an ideal crystal, indicating that the crystalline structure is of cationic deficient. As far as the local environment of the cationic defect is concerned, the lattice oxygen ions around it are not fully bonded, which are mobile and more active under the reaction condition compared to the normal ones. Therefore, the creation of cationic defects in the structure is a possible origin of the unusual reducibility and high mobility of oxygen species from bulk to surface exhibited on the ceria-zircnia solids, that are reported by other groups [5, 6]. 

The nanosciences and nanotechniques bestow new perspectives on ceria-based materials in various ways. Compared with the correspondent bulk materials, nanoceria exhibits impressive novel or enhanced... 

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