## 2 Results and Discussion
### Catalysts' Characterization
#### 2.1.2 Spectroscopy Studies (FTIR, UV-Vis, Raman, and \({}^{29}\)Si MAS-NMR)
The asymmetric methylene C-H mode around 2885 cm\({}^{-1}\) is less intense than in the solid CTAB and the signals assigned to methyl C-H modes were considerably displaced, both evidence of higher statistical chances for attaining the gauche configuration, i.e., a more disordered state [57; 61; 62]. This was even more noticeable for the broad band around 2920 to 2928 cm\({}^{-1}\) for CTA\({}^{+}\) occluded and in solution. This band is a composite of two overlapping modes, one from the polymethylene chain (usually around 2920 cm\({}^{-1}\)) and the other from the methyl group (at 2941 cm\({}^{-1}\) for solid CTAB), making it sensitive to conformational disorder of the long methylene chain, since the former contributes more than the latter [61; 62]. As mentioned before, changes in the intensity of C-H and C-C stretching modes can reveal effects towards disordering since liquid-like states permit an increase in the number of molecules that can attain the gauche conformation. In the literature, it was demonstrated that the ratio between the intensities of certain long alkyl chain Raman bands can reflect their conformational state [61; 62; 63]. Therefore, we employed such parameters to understand the influence of different cerium precursors in the assembly of the template molecules. Two of the most employed ratios are those between the C-C gauche stretching around 1080 cm\({}^{-1}\) and the C-C asymmetric stretching around 1120 cm\({}^{-1}\)[57; 62]; and the C-H stretchings around 2920 and 2850 cm\({}^{-1}\)[61; 63]. Higher values for these parameters are related to an increase of feasibility to attain the gauche conformation and, consequently, disordered the template assembly more in the synthetic medium that was retained in MCM-41 pores. Both ratios for the as-synthesized materials were calculated and are compiled in Table 2.  
The I\({}_{2920}\)/I\({}_{2850}\) ratio demonstrates small changes in its value when compared to the I\({}_{1080}\)/I\({}_{1120}\) ratio, which indicates that the latter is a more sensible parameter towards conformational disordering than the former [62]. Nonetheless, the values presented for both ratios allowed the materials to be organized in increasing disorder of template assemblies: A-Si-MCM-41 \(<\) A-Ce-MCM-NO\({}_{3}\)\(<\) A-Ce-MCM-Cl Thus, it was possible to perceive that: (i) The presence of cerium species altered the supramolecular arrangement of CTA\({}^{+}\) cations; (ii) the disordering was more prominent when utilizing cerium(III) chloride as the precursor; and (iii) the degree of disordering obtained for A-Ce-MCM-NO\({}_{3}\) was close to A-Si-MCM-41. To explain these observations, it is worth recalling the chemistry of cerium species in high pH aqueous mediums [64; 65; 66] and the synthetic procedure used in this work to prepare Ce-MCM-41 materials (see Materials and Methods). Under basic conditions, the hydrolysis of Ce(III) generates [Ce(OH)\({}_{y}\)]\({}^{(3-y)}\) species, where \(y\) goes from 0 to 3. During our synthesis, the dropwise \begin{table}
\begin{tabular}{c c c} \hline \hline
**As-Synthesized Sample** & **I\({}_{1080}\)/I\({}_{1120}\)**1 & **I\({}_{2920}\)/I\({}_{2850}\)**2 \\ \hline A-Si-MCM-41 & 1.994 & 0.731 \\ A-Ce-MCM-Cl & 2.310 & 0.760 \\ A-Ce-MCM-NO\({}_{3}\) & 2.024 & 0.747 \\ \hline \hline \end{tabular} \({}^{1}\) Ratio between the intensities of bands around 1080 and 1120 cm\({}^{-1}\). \({}^{2}\) Ratio between intensities of bands around 2920 and 2850 cm\({}^{-1}\).  
\end{table} 
Table 2: Template assembly disorder for the as-synthesized MCM-41 materials. addition of cerium(III) precursor turned the clear solution into a dark slurry before it became a light brown/purple solid. This could be addressed by assuming that [Ce(OH)]\({}^{2+}\), [Ce(OH)\({}_{2}\)]\({}^{+}\), and [Ce(OH)\({}_{3}\)] formation occurred progressively and continuously [65].