## 2 Results and Discussion
### Catalysts' Characterization
#### 2.1.2 Spectroscopy Studies (FTIR, UV-Vis, Raman, and \({}^{29}\)Si MAS-NMR)
To further study the modified materials, high-resolution transmission electron microscopy (HRTEM) was used to access the formation of CeO\({}_{2}\) species on Ce-MCM-41 materials and representative images are displayed in Figure 9. As one can see, some of the irregular entities observed in TEM for both materials showed dark nanorods on their surface that were not observable on Si-MCM-41. High magnifications of these nanorods (Figure S5 in Supplementary Material) displayed lattices fringes around 0.33 nm, consistent with the interplanar distance characteristic to 110 XRD reflection of CeO\({}_{2}\), thus confirming their identity. For Ce-MCM-Cl, these nanorods displayed lengths between 22.0 and 70.0 nm and widths between 1.75 and 2.50 nm, while for Ce-MCM-NO\({}_{3}\), these entities were bigger and thicker, with lengths between 100 and 250 nm and widths between 5.0 and 6.7 nm. The differences observed in their measures were consistent with the crystallization mechanism proposed for non-framework cerium species, where longer and thicker rods were expected for Ce-MCM-NO\({}_{3}\) due to the aggregation effect of micelles attributed to the nitrate anion. Also, the formation of these nanorods was consistent with the mechanism proposed for non-framework cerium species. The formation of ceria nanorods is widely studied in the literature [84; 85] and includes surfactant-assisted synthetic procedures using CTAB. However, these methodologies are normally performed under hydrothermal conditions with high temperatures (80-160 \({}^{\circ}\)C), longer time periods (8-96 h), and low Ce/CTAB molar ratios (0.33-0.66) [84; 85]. The results observed in this work suggest that nanorods can also form under milder conditions (30-35 \({}^{\circ}\)C and 4 h) and high Ce/CTAB molar ratios (3.8). The textural characterization of the calcined MCM-41 materials was performed by N\({}_{2}\) physisorption using t-plot curves obtained from analytical functions for each portion of the \(P/P_{0}\) domain (see Equations (5)-(8) in Materials and Methods) [86]. The initial part of the curve was used to calculate the total specific surface area (\(S_{total}\)) of the materials using the slope of the linear fit going through the origin (red line in Figure 10a). On the other hand, the final part of the curve was used to calculate the external specific surface area (\(S_{ext}\)), indicated in Figure 10a by the blue line. Figure 10b exhibits the N\({}_{2}\) adsorption/desorption isotherms obtained for Si-MCM-41, Ce-MCM-Cl, and Ce-MCM-NO\({}_{3}\), respectively. According to the IUPAC classification [87], all curves were type IV isotherms, presenting a characteristic hysteresis loop associated with capillary condensation in mesopores. This hysteresis was type H1 according to the IUPAC classification [87] and could be associated with a narrow and uniform pore size distribution. This result implies that the MCM-41 pore system in cerium-incorporated materials was preserved and that the long-range disorder was responsible for the loss of the mesophase observed by XRD. This is not uncommon and even in highly  
Figure 9: HRTEM images for the calcined Ce-MCM-Cl (**a**) and Ce-MCM-NO\({}_{3}\) (**b**) materials. disordered materials, such as titanosilicate ETS-10, short-range ordering could not be affected by long-range disordering [88]. The initial part of the isotherm, before capillary condensation, is associated to monolayer-multilayer adsorption on both mesopores and external surface, and consequently, was used to calculate \(S_{total}\), as described above [86]. Similarly, in the final part of the isotherm, after capillary condensation, adsorption occurs only on the external surface and, for that reason, was used to determine \(S_{ext}\). The capillary condensation is identified by an increase of adsorbed N\({}_{2}\) at the relative pressure range of P/P\({}_{0}\) = 0.30 to 0.45, due to the filling of mesopores.