## 2 Results and Discussion
### Catalytic Oxidation of Ethylbenzene  
#### 2.1.1 General  
CeNR promotes the liquid-phase oxidation of ethylbenzene (PhEt), using _tert_-butyl hydroperoxide (_t_-BuOOH) as the oxidant and acetonitrile (CH\({}_{3}\)CN) as the solvent, at 55-105 \({}^{\circ}\)C. At 55 \({}^{\circ}\)C, 1-phenyl-ethyl-_tert_-butyl-peroxide (PhEtOOT) is the only reaction product until 51% conversion (reached after 120 h) (Figure 4): no reaction takes place without a catalyst. To the best of our knowledge, the formation of PhEtOOT in the catalytic oxidation of PhEt with _t_-BuOOH has not yet been reported. Syntheses procedures for PhEtOOT are based on the reaction of \(\alpha\)-phenyl-ethyl bromide with potassium salt of _t_-butyl hydroperoxide [14]. In the range 70-105 \({}^{\circ}\)C, PhEtOOT selectivity decreases with PhEt conversion, while that to acetophenone increases (Figure 4B). These results suggest that acetophenone is formed from PhEtOOT. On the other hand, the PhEtOOT selectivity tends to decrease with the reaction temperature whereas that of acetophenone increases reaching 70% at 89% conversion, at 105 \({}^{\circ}\)C (Figure 4B, Table 2). Aromatic ring oxidation products were never detected revealing excellent regioselectivity of this catalytic system towards the side-aliphatic chain oxidation. Increasing the temperature from 55 \({}^{\circ}\)C to 90 \({}^{\circ}\)C enhances the reaction rate: conversion at 6 h/120 h increases from 6%/51%, at 55 \({}^{\circ}\)C, to 31%/96%, at 90 \({}^{\circ}\)C (Figure 4A, Table 2). Increasing the temperature above 90 \({}^{\circ}\)C does not further increase the PhEt conversion. For the reaction carried out at 105 \({}^{\circ}\)C, the conversion of PhEt at 6 h/120 h is 22/88% and after 120 h remains nearly constant (89% at 175 h). Probably, the thermal decomposition (disproportionation) of _t_-BuOOH becomes a major competitive reaction for PhEt oxidation at high temperatures (see section 2.1.3) [15]. When a radical scavenger (2,6-di-_tert_-butyl-4-methyl-phenol) is added initially to the reaction of PhEt with _t_-BuOOH in the presence of CeNT, at 70 \({}^{\circ}\)C, no reaction takes place, in contrast to that observed without the radical scavenger. These results indicate that a radical-chain process is involved. The initial induction periods of at least 120 min and 10 min observed for the reactions carried out at 55 \({}^{\circ}\)C and 70 \({}^{\circ}\)C, respectively (at higher temperatures no induction periods were detected), may be due to mechanistic factors. Possibly, the CeNR material acts as an initiator in the homolysis of _t_-BuOOH into free alkoxy (_t_-BuO**') and alkylperoxy radicals (_t_-BuO**') _via_ the net redox reaction represented in Equation 1: Ce\({}^{4+}\) is a relatively strong one-electron oxidant, and the resulting Ce\({}^{3+}\) species may be re-oxidized by _t_-BuOOH [16]. The _t_-BuO**' radical can abstract a proton from the substrate to give the corresponding radical (PhEt'), Equation 2[17], which reacts with _t_-BuO**' radicals to give PhEtOOT (Equation 3). It has been reported for the liquid-phase oxidation of arylbenzene compounds in homogeneous phase, in the presence of cerium ammonium nitrate/KBrO\({}_{3}\) that radicals of the substrates may reduce Ce\({}^{4+}\) into Ce\({}^{3+}\) species, forming intermediate carbocations, which are subsequently oxidized [18]. Accordingly, cerium ions may promote the introduction of the alkylperoxy group of _t_-BuOOH into PhEt**' _via_ the net redox reaction represented in Equation 4. The reactions represented by Equations 5-6 are typically involved in radical chain processes of oxidation of hydrocarbons, using _t_-BuOOH as oxidant oxidant [16]. A control experiment showed that the oxidation of PhEt in the  
Figure 3: CeNR nitrogen adsorption-desorption isotherm (77 K) and (inset) pore-size distribution curve calculated for the desorption branch, using the Barrett-Joiner- Halenda method. presence of CeNT and in the absence of _t_-BuOOH does not take place.