## 2 Results and Discussion
### Catalytic Tests
At higher temperatures, a better activation of oxidants and generation of reactive species were obtained, but it was only beneficial until a certain point, since a loss of selectivity was visible at 90 \({}^{\circ}\)C for both materials when compared to 80 \({}^{\circ}\)C. Therefore, the following essays were performed at 80 \({}^{\circ}\)C.  
The final parameter evaluated was the catalyst amount, 5 and 15 wt.%, runs 10 and 11, respectively. In the case of Ce-MCM-Cl, both changes led to less efficient catalytic situations in terms of \(C\) and \(Y\), where decreases of up to 20.0% for the latter and around 40.0% of the former were perceived when compared to run 8 (10 wt.%). This can be associated to a more exacerbated decomposition of TBHP in the case of 15 wt.% and a less efficient activation of the oxidant at 5 wt.%, achieving the optimal mass and active sites' amount around 10 wt.% for this catalyst. Surprisingly, a different trend was observed for Ce-MCM-NO\({}_{3}\), where the catalyst amount of 5 wt.% showed a negligible decrease of \(C\) and a considerable increase of \(S\) (33.7% and 64.3%, respectively). This combination resulted in the same \(Y\) and better catalytic performance (TON = 160.3 mol molcat\({}^{-1}\)) than from run 8 (10 wt.%), while the use of 15 wt.% catalyst increased \(C\) to 63.7% with concomitant decrease in \(S\) to 31.9%, resulting in a decrease in \(Y\) (20.3%) and catalytic performance (TON = 103.5 mol molcat\({}^{-1}\)). This can be associated to the mass transfer in Ce-MCM-NO\({}_{3}\) mesopores, while 5 wt.% offered an optimal condition of catalytic site usage and diffusion of reactants and products; 10 or 15 wt.% seems to lead to conditions where over-oxidation was favored due to an excess of active sites. These results are consistent with the fact that mainly non-framework CeO\({}_{2}\) (less selective) is present in the material's constitution as mentioned before. Thus, the amount of catalyst plays a significant role in attaining better \(Y\), but also in differentiating the applicability of both active materials in this study. Also, for comparison means, Si-MCM-41 was tested in the optimal conditions found for Ce-MCM-Cl and Ce-MCM-NO\({}_{3}\) (run 12), and negligible values of \(C\) and \(Y\) (less than 1%) were obtained, proving that the activity of MCM-41 materials is due to the presence of cerium species. In order to evaluate the reusability of the catalysts, the solids from the optimized conditions were recovered and studied for further cycles, see Materials and Methods. After each cycle, the cerium content and coordination state were analyzed by XRF and Raman to understand possible changes in the catalytic performance. The recycled results are compiled in Figure 15.  
As can be perceived from Figure 15, BzD \(Y\) of both catalysts maintains a stable state after three catalytic cycles, but the conversion of both materials decreases. For Ce-MCM-Cl, the conversion decreases from 54.3% to 43.9% in the second cycle and 39.3% in the third cycle. Meanwhile,  
Figure 15: Performance of recovered solids after three catalytic cycles: Ce-MCM-Cl (**A**) and Ce-MCM-NO\({}_{3}\) (**B**). the conversion of Ce-MCM-NO\({}_{3}\) decreases from 33.4% to 27.3% in the second cycle and 25.0% in the third cycle. Also, according to XRF analyses of the recovered solids, the amount of cerium in Ce-MCM-Cl diminishes from 5.89% to 5.77% in the last cycle, while for Ce-MCM-NO\({}_{3}\), the diminishment goes from 5.24% to 5.16%. Thus, it is possible to conclude from the previous data that: (i) Ce-MCM-Cl deactivates in a higher rate than Ce-MCM-NO\({}_{3}\); and (ii) the main reason for deactivation can be associated to microstructural changes in the recovered materials, since cerium leaching was negligible. According to [PERSON] and coworkers [92], changes in the Ce coordination environment can occur after oxidation processes due to etching effects of peroxides in the surface of cerium-incorporated silica materials, where framework sites (more active) can turn to non-framework species (less active).