# Effects of Different Variables on the Formation of Mesopores in Y Zeolite by the Action of CTA+
## 3 Results
### Influence of Base Concentration
The observed main influence on the modification of the textural properties of the zeolites by the concentration of the alkaline medium was further investigated via chemical analyses of the materials. The different chemical environments of the aluminum in the zeolites were investigated by \({}^{27}\)Al NMR (Figure 11). The signal corresponding to octahedral aluminum (Al\({}^{\text{VI}}\)) was observed at 0 ppm, whereas tetracoordinated aluminum (Al\({}^{\text{IV}}\)) was identified both within and outside the zeolitic structure, as shown by signals located at 60 and 53 ppm, respectively. The spectra indicated that the use of a higher NaOH concentration led to a decrease in the tetracoordinated aluminum in the zeolite structure, accompanied by an increase in non-structural or distorted tetracoordinated aluminum, as reported previously [17]. Figure 11: \({}^{27}\)Al nuclear magnetic resonance (NMR) spectra of the calcined modified zeolites produced using different alkaline medium concentrations. Figure 10: Pore size distributions obtained using the BJH method applied to the isotherms (desorption branch) for the original zeolite and the modified zeolites produced using different base concentrations. This change in the chemical environment of the aluminum led to a decrease in Bronsted acid sites, since these sites are generated due to the presence of tetrahedral aluminum in the zeolite structure. The presence of distorted or external (outside the structure) tetracoordinated aluminum generates Lewis acid sites [17; 18]. The TPD-NH\({}_{3}\) profiles (Figure 12) showed two peaks: the first around 208-217 \({}^{\circ}\)C and the second around 325-360 \({}^{\circ}\)C. The peak at the lower temperature could be attributed to the release of weakly adsorbed NH\({}_{3}\), whereas the peak at the higher temperature could be explained by the release of NH\({}_{3}\) from NH\({}_{4}\)\({}^{+}\) bound at stronger acid sites [19; 20]. Considering the total amounts of ammonia desorbed at higher temperatures (Table 4), the original USY zeolite contained a greater quantity of acid sites compared to the modified zeolites, demonstrating that the process used to create mesoporous resulted in fewer acid sites [2; 10]. A yield of 97.6% was obtained for the modification performed under the most severe conditions (x = 0.08, y = 0.1). ICP analysis showed that the amount of silicon present in the filtrate was insignificant and corresponded to only 0.07% of the silicon present in the original zeolite. This was supported by the constancy of the global Si/Al ratio (Table 4), confirming that the modification led to no significant \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **T (\({}^{\circ}\)C)** & **NH\({}_{3}\) (\(\frac{\text{{num}}}{\text{g}}\))** & **NH\({}_{3}\)total** (\(\frac{\text{{num}}}{\text{g}}\)) & **Si/Al** \\ \hline \multirow{2}{*}{USY} & 209 & 101 & \multirow{2}{*}{547} & \multirow{2}{*}{14} \\  & 358 & 446 & & \\ \hline \multirow{2}{*}{YB0.02-S0.1} & 208 & 144 & \multirow{2}{*}{535} & \multirow{2}{*}{15} \\  & 358 & 391 & & \\ \hline \multirow{2}{*}{YB0.04-S0.1} & 216 & 115 & \multirow{2}{*}{462} & \multirow{2}{*}{14} \\  & 350 & 347 & & \\ \hline \multirow{2}{*}{YB0.08-S0.1} & 216 & 99 & \multirow{2}{*}{344} & \multirow{2}{*}{14} \\  & 325 & 245 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Quantification of the total acidity of the zeolites. Figure 12: TPD-NH\({}_{3}\) profiles of the calcined original zeolite and the zeolites produced using different base concentrations. loss of silicon contained in the material. The Si removed from the structure by the alkaline treatment was subsequently associated with the surfactant micelles and was recrystallized.