## 2 Results and Discussion
### Catalysts' Characterization
#### 2.1.2 Spectroscopy Studies (FTIR, UV-Vis, Raman, and \({}^{29}\)Si MAS-NMR)
Higher values for the mentioned ratio and lower ones for Si molar% indicates more condensed Si-O-Si bonds in the inorganic framework. These quantitative data were compiled in Table 3.  
Figure 7: \({}^{29}\)Si MAS-NMR spectra for the calcined MCM-41 materials, highlighting the position of each chemical environment detected by deconvolution. From the values displayed in Table 3, it was possible to infer that: (i) For Ce-MCM-Cl, even though the content of terminal silanols (Q\({}^{3}\)) decreases, the siloxane group (Q\({}^{4}\)) does not increase significantly when compared to geminal silanols (Q\({}^{2}\)), suggesting that even if the condensation of Si-O-Si bonds slightly increases, the percentage of silanol groups (Si molar%) remains relatively constant if Q\({}^{2}\) increases; and (ii) for Ce-MCM-NO\({}_{3}\), the modification decreases drastically the content of silanol groups, indicating that the non-framework cerium species might be located in the mesopores' wall or external surface, but Raman data suggests the former. Once again, there is little contribution from the literature to explain effectively the reason for differences in \({}^{29}\)Si MAS NMR arising solely with varying the counterion in cerium precursor. Even though this is a scarce topic, it is well known that such effects in silaceous molecular sieves are dependent more in the synthetic procedure than in any other aspect and the fact that cerium incorporation can lead to a more or less condensed degree of chemical bonds has already been reported [32; 51]. Thus, the MAS-NMR data is in good agreement with the observations made earlier due to the crystallization mechanism proposed: (i) The smaller aggregation effect of chloride anions on CTA\({}^{+}\) assemblies and the formation of framework Ce-O-Si bonds led to the emergence of silanol defects (Q\({}^{2}\)); and (ii) the precipitation of Ce(OH)\({}_{3}\) and conversion to non-framework CeO\({}_{2}\) resulted in a coating effect in the MCM-41 surface, leading to the decrease of Q\({}^{2}\). 1.3 Morphological (TEM and HRTEM), Textural (Surface Area and Pore Volume), and Thermal Analyses (TG/DTG/DSC)  
The morphology of the calcined MCM-41 materials was accessed through low-resolution transmission electron microscopy (TEM). Representative images are selected and displayed in Figure 8.  
For Si-MCM-41, perfectly spherical nanoparticles were obtained (mean size of \(61.8\pm 15.9\) nm). There is little aggregation between the particles, possibly a synthetic consequence of the rapid formation of ethanol as a side product during TEOS hydrolysis [83]. On the other hand, the modified materials present smaller and spherical nanoparticles, with a mean size of around \(34.2\pm 14.5\) nm and \(38.7\pm 9.1\) nm for Ce-MCM-Cl and Ce-MCM-NO\({}_{3}\), respectively. Also, the nanoparticles have a more aggregated aspect when compared with Si-MCM-41, exhibiting more irregular shapes. These  
Figure 8: TEM images for the calcined MCM-41 materials: Si-MCM-41 (**A**); Ce-MCM-Cl (**B**); and Ce-MCM-NO\({}_{3}\) (**C**). \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **Q\({}^{2}\) (\%) 1** & **Q\({}^{3}\) (\%) 1** & **Q\({}^{4}\) (\%) 1** & **Q\({}^{4}\)/(Q\({}^{2}\) + Q\({}^{3}\))** & **Silanol (Si molar\%) 2** \\ \hline Si-MCM-41 & 12.4 & 33.1 & 54.5 & 1.20 & 57.9 \\ Ce-MCM-Cl & 19.3 & 21.2 & 59.5 & 1.47 & 59.7 \\ Ce-MCM-NO\({}_{3}\) & 0.4 & 25.6 & 74.0 & 2.85 & 26.4 \\ \hline \end{tabular}  
* Calculated from normalization of the area of each peak. 2 Calculated from Equation (4).  
\end{table} 
Table 3: Content of Q\({}^{n}\)-groups and related parameters obtained from \({}^{29}\)Si MAS-NMR spectra of the calcined MCM-41 materials. observations are possibly an evidence of a faster nucleation process, a consequence of the presence of cerium precursors in the synthetic medium. This supports the loss of long-range ordering observed previously by XRD, as well as the disordering effect of the supramolecular assembly of CTA\({}^{+}\) cations evidenced by Raman spectroscopy.