## 2 Results and Discussion
### Catalytic Tests  
The liquid-phase oxidation of benzyl alcohol (BzOH) was used to further analyze the consequences of cerium precursors in the generation of catalytic active species. In all reaction analyses, the only products detected were benzaldehyde (BzD) and benzoic acid (HBz), both oxidation products. The other possible product, benzyl benzoate, was not observed. The reaction parameters were varied to achieve an optimal condition (see Materials and Methods for reaction details), where the maximum BzD yield was used as a reference. The results of all catalytic essays were compiled in Tables 5 and 6 for Ce-MCM-Cl and Ce-MCM-NO\({}_{3}\), respectively. The first parameter studied was the type of oxidant: Hydrogen peroxide (H\({}_{2}\)O\({}_{2}\), 30 wt.%); _tert_-butyl hydroperoxide (TBHP, 70 wt.%); and di-_tert_-butyl peroxide (DTBP), runs 1 to 3. As can be perceived in Tables 5 and 6, the only peroxide that produced significant values of BzOH conversion (\(C\), %) and BzD yield (\(Y\), %) was TBHP. Other studies involving the use of cerium-modified molecular sieves in different oxidation reactions suggest the use of H\({}_{2}\)O\({}_{2}\) as a milder oxidant [91; 92]. However, the catalysts' behavior in this work were consistent with the reactive conditions reported by [PERSON] and co-workers [32], which performed liquid-phase BzOH oxidation with cerium-modified mesoporous materials. The values of \(Y\) and \(TON\) with TBHP as the oxidant were different for both cerium materials: 22.0% and 74.0 mol mol\({}_{\text{cat}}\)\({}^{-1}\) for Ce-MCM-Cl; 17.5% and 49.5 mol mol\({}_{\text{cat}}\)\({}^{-1}\) for Ce-MCM-NO\({}_{3}\), respectively. Thus, in these conditions, Ce-MCM-Cl presented better \(Y\) and was more active than Ce-MCM-NO\({}_{3}\). This result was consistent with previous literature indicating that non-framework CeO\({}_{2}\) species (observed mostly in Ce-MCM-NO\({}_{3}\)) are less active and selective as catalytic sites [48; 51]. Figure 14: TG curves for the calcined MCM-41 materials. To further optimize the system, the use of solvents was tested to observe if the changes in hydrophobicity/hydrophilicity of the medium can affect positively the reaction towards better BzD yields. Acetonitrile (CH3 CN) and isopropanol (_i_-ProH) were selected to observe this influence (runs 4 and 5, respectively). For both cerium materials, the use of CH3 CN and _i_-ProH resulted in less efficient conditions towards BzD yield and catalyst activity, even though BzD selectivity improved significantly (up to 99%). The lowering of \(C\) was the main issue, and this parameter was more affected using _i_-ProH, possibly due to adsorptive competition of the protic solvent molecules [93]. The next parameter studied was the BzOH:TBHP molar ratio, since reactions so far were done in stoichiometric quantities. Changes in the chemical equilibrium can possibly affect the catalytic output and two conditions were tested: Excess of alcohol (2:1, run 6) and excess of TBHP (1:2, run 7). For Ce-MCM-Cl and Ce-MCM-NO3, excess of alcohol decreased \(C\), 25.8% and 19.7%, and _TON_, 56.8 and 48.8 mol molcat\({}^{-1}\), respectively. Even though there was a better peroxide efficiency in the molar ratio of 2:1, lower \(Y\) values were obtained (19.4% and 15.9% for Ce-MCM-Cl and Ce-MCM-NO3). With the excess of peroxide, the main improvement was in the catalytic efficiency (_TON_), exhibiting 76.1 mol molcat\({}^{-1}\) for Ce-MCM-Cl and 68.4 mol molcat\({}^{-1}\) for Ce-MCM-NO3. However, the little improvements observed in \(Y\) for both materials do not justify such an increase in the oxidant amount. Thus, the following essays were done in stoichiometric proportions of alcohol:oxidant.