Studies of Ce Redox Behavior in Catalytic Oxide Materials

Studies of Ce Redox Behavior in Catalytic Oxide Materials 

Ce species formed upon reduction of Ce02 are known to be reoxidized quickly by exposure to even small O2 pressures [127] this easy Ce oxidation was observed even for the (highly amorphous) hydroxides which appear in the first stages of preparation via precipitation [128]. It is thus striking that nanocrystalline 

Ce02/Al203 supports were studied in detail by Shyu et al. [108], who examined specimens with different ceria loadings prepared by impregnating AI2O3 with Ce nitrate and calcination at 1073 K. From XPS-measured Ce/Al ratios they concluded that transition from highly dispersed ceria species to bulk phases occurred for loads 

In the case of mixed Ce-Zr oxides, both reducibility and segregation effects have been monitored. Thus, high reducibility of Ce has been reported in powder (Ce,Zr)02 samples displaying no surface enrichment in any of both cations [141] surface enrichment in Ce was however observed in other high surface area samples with Ce Zr ratio=l l, accompanied by significant Ce reduction (ca. 50% decrease in %(u )) [142] a trend towards surface Ce enrichment upon calcination was found also for low-Ce (Ce,Zr)02 aerogels [143]. An important spontaneous reduction 

Mixed oxides of Ce and other lanthanides (La, Nd) were studied by Kubsch et al. [133], who found segregation of these trivalent ions to the surface in samples calcined at 1253 K a high Eb peak in the 01s feature was observed, being ascribed to carbonates formed in the trivalent ion-rich surface. A tendency to formation of such mixed oxides was detected in (Ce,Tb)Ox supported on lanthana-promoted alumina after calcination the La XP spectrum displayed two components, ascribed to La species on the AI2O3 surface and dissolved into the Ce,Tb oxide respectively [146]. A high Eb 01s peak observed there was ascribed to both alumina O ions and carbonate species on La-rich zones while the (Ce,Tb) oxide gave lower Eb values. 

---