## 2 Results and Discussion
### Catalytic Oxidation of Ethylbenzene
#### 2.1.3 Oxidant Effect  
When H\({}_{2}\)O\({}_{2}\) (30% aq.) is used as oxidant instead of _t_-BuOOH, no PhEt reaction is observed in the presence of CeNR during 150 h, at 70 \({}^{\circ}\)C. It was previously reported for a ceria possessing a cubic crystal structure of the fluorite type (67 m\({}^{2}\) g-1, 12 nm crystallite size), used as catalyst in the oxidation of PhEt with H\({}_{2}\)O\({}_{2}\) and acetonitrile as solvent, that the reaction is sluggish giving _ca._ 4% conversion after 6 h, at 60 \({}^{\circ}\)C, and benzaldehyde and acetophenone were the only products [20]. The decomposition of H\({}_{2}\)O\({}_{2}\) has been used as a test reaction for investigating the redox properties of ceria materials [1]. In the case of the CeNR/H\({}_{2}\)O\({}_{2}\) system, the poor catalytic results may be due to the  
Figure 4: **(A)** - Ethylbenzene oxidation with _t_-BuOOH, in the presence of CeNR, at 55 \({}^{\circ}\)C (\(\bigdiamond\)), 70 \({}^{\circ}\)C (run 1 - **(O)**; run 2 - **(\(\bigcirc\))), 90 \({}^{\circ}\)C (\(\bigtriangleup\)), 105 \({}^{\circ}\)C (\(\square\)), using acetonitrile as solvent. **(B)** - Dependence of selectivity to PhEtOOT (solid lines) and acetophenone (dashed lines) on conversion for the reactions conditions indicated in (A) - the same symbols were used for each reaction. relatively fast 'non-productive' decomposition of H\({}_{2}\)O\({}_{2}\) by CeNR. In order to investigate this hypothesis, iodometric titrations were performed for the reactions of CeNR with H\({}_{2}\)O\({}_{2}\) or _t_-BuOOH (without PhEt) after 4 h, at 70 \({}^{\circ}\)C. These results revealed that H\({}_{2}\)O\({}_{2}\) was totally consumed, whereas _t_-BuOOH conversion after 4 h was negligible, supporting the above hypothesis. It is worth mentioning that acetamide, which may be formed from the reaction of CH\({}_{3}\)CN with H\({}_{2}\)O\({}_{2}\)_via_ the intermediate formation of the correspondent peroxynimidic acid was not detected in the reaction mixtures [21]. According to the literature, CeNR may undergo morphological changes in the presence of H\({}_{2}\)O\({}_{2}\)[8]. A similar destructive effect of H\({}_{2}\)O\({}_{2}\) has also been reported for cerium-containing SBA-15, in that cerium was removed from the silica framework, forming fine CeO\({}_{2}\) crystallites on the surface [22]. To the best of our knowledge, the influence of _t_-BuOOH on the physico-chemical properties of CeNR has not been reported. In order to get some insight into the effect of the oxidant on the catalytic activity, the solids used in the reactions of PhEt with _t_-BuOOH or H\({}_{2}\)O\({}_{2}\), at 70 \({}^{\circ}\)C, were recovered after 120 h in a similar fashion to that described above for the catalyst recycling experiments, and subsequently characterized: the resulting solids are denoted CeNR-PhEt-BuOOH and CeNR-PhEt-H\({}_{2}\)O\({}_{2}\), respectively. On the other hand, for comparative studies, CeNR was treated with H\({}_{2}\)O\({}_{2}\) or _t_-BuOOH, in the absence of PhEt, in an ultrasonic bath, as described in the experimental part, giving CeNR-H\({}_{2}\)O\({}_{2}\) and CeNR-BuOOH, respectively. The TEM images of CeNR-BuOOH and CeNR-PhEt-BuOOH show some fragmentation of the nanorods and the formation of 6-8 nm spherical particles, and this effect is major for CeNR-H\({}_{2}\)O\({}_{2}\) and CeNR-PhEt-H\({}_{2}\)O\({}_{2}\) (Figure 2). The ATR-FTIR spectra of CeNR-BuOOH and CeNR-H\({}_{2}\)O\({}_{2}\) are similar to that of CeNR in the region 1300-1600 cm\({}^{-1}\), with the main difference being that the band at ca. 1640 cm-1 assigned to H-O-H bending vibration is very weak in the case of CeNR-BuOOH (not shown).The powder XRD patterns of CeNR-H\({}_{2}\)O\({}_{2}\) and CeNR-BuOOH are similar to that of CeNR (see introduction of the section 2), albeit the peaks are slightly broader, especially in the case of CeNR-H\({}_{2}\)O\({}_{2}\) (Figure 1).