## 2 Results and Discussion
### Catalysts' Characterization
#### 2.1.2 Spectroscopy Studies (FTIR, UV-Vis, Raman, and \({}^{29}\)Si MAS-NMR)
The data obtained by N\({}_{2}\) physisorption experiments (Table 4) showed a reduction of \(S_{total}\), mesoporous surface area (\(S_{meso}\)), and mesopore volume (\(V_{meso}\)) for the cerium-incorporated samples, which could be attributed to the loss of long-range order. The sharp increase observed in all isotherms at the relative pressure range of P/P\({}_{0}\) = 0.9 to 1.0 is related to the presence of interparticle porosity [32] and its effect can be observed in a higher value of the total pore volume (\(V_{total}\)) than \(V_{meso}\). For that reason, the average pore diameter (\(PD\)) was calculated using the penultimate point from the adsorption isotherm (see Materials and Methods) to avoid contributions from interparticle porosities, since the materials showed different particle sizes. The values obtained for \(PD\) were almost identical, which is in agreement with the narrow and uniform pore size distribution expected for the type H1 hysteresis loop observed for all materials and discussed above. However, the sample of Ce-MCM-NO\({}_{3}\) showed a small increase that could be attributed to its different mechanism of pore formation, possibly due to the coating effect of non-framework CeO\({}_{2}\). Additionally, \(PD\) values were used to determine the wall thickness (\(WT\)) of MCM-41 materials, evidencing that cerium incorporation affects this parameter due to framework cerium and non-framework CeO\({}_{2}\). In the case of Ce-MCM-Cl, the increase in \(WT\) was consistent with the incorporation of Ce in the inorganic framework, causing an expansion of the unit cell (\(a\)) and, ultimately, of the pore walls. However, in the case of Ce-MCM-NO\({}_{3}\), not only isomorphic substitution could cause such an increase, but also the existence of non-framework CeO\({}_{2}\) and the higher value of \(WT\) corroborates the possible coating effect mentioned previously, which can make the pore walls appear thicker. These results are in accordance with the higher value of \(a\) found for Ce-MCM-NO\({}_{3}\) (4.97 nm) when compared to Ce-MCM-Cl (4.61 nm), explaining the cell expansion observed by XRD. Finally, the higher \(S_{ext}\) value obtained for cerium-incorporated materials are linked to their smaller particle size when compared to Si-MCM-41, as observed by TEM. Figure 10: Thickness or t-plot curve for Si-MCM-41 (**a**) where the blue line slope corresponds to \(S_{total}\), the red line slope corresponds to \(S_{ext}\), and the dashed black line intercept with the \(y\)-axis corresponds to \(V_{meso}\); N\({}_{2}\) adsorption/desorption isotherm for Si-MCM-41, Ce-MCM-Cl, and Ce-MCM-NO\({}_{3}\) (**b**) where filled circles correspond to adsorption and hollow circles corresponds to desorption. Thermal analyses were performed for the as-synthesized and calcined MCM-41 materials to further analyze the consequences of texture changes towards microstructural aspects. The thermogravimetry (TG), differential thermogravimetry (DTG), and differential scanning calorimetry (DSC) curves for the as-synthesized materials are displayed in Figures 11-13. The values of mass loss, temperature range, and DTG maximum were collected in Table S2 (see Supplementary Material). \begin{table}
\begin{tabular}{c c c c} \hline
**Properties** & **Si-MCM-41** & **Ce-MCM-Cl** & **Ce-MCM-NO3** \\ \hline \(S_{total}\) (m\({}^{2}\) g\({}^{-1}\)) \({}^{1}\) & 1032.1 & 909.7 & 907.0 \\ \(S_{ext}\) (m\({}^{2}\) g\({}^{-1}\)) \({}^{2}\) & 158.1 & 267.6 & 252.4 \\ \(S_{mseq}\) (m\({}^{2}\) g\({}^{-1}\)) \({}^{3}\) & 874.0 & 642.1 & 654.6 \\ \(V_{total}\) (cm\({}^{3}\) g\({}^{-1}\)) \({}^{4}\) & 0.92 & 0.87 & 0.90 \\ \(V_{mmes}\) (cm\({}^{3}\) g\({}^{-1}\)) \({}^{5}\) & 0.80 & 0.68 & 0.71 \\ _PD_ (nm) \({}^{6}\) & 3.40 & 3.43 & 3.64 \\ _WT_ (nm) \({}^{7}\) & 1.08 & 1.18 & 1.33 \\ \hline \end{tabular} \({}^{1}\) Total specific surface area. \({}^{2}\) External specific surface area. \({}^{3}\) Mesoporous surface area. \({}^{4}\) Total pore volume. \({}^{5}\) Mesopore volume. \({}^{6}\) Average pore diameter. \({}^{7}\) Wall thickness.  
\end{table}