## 3 Results and Discussion
### Structural Characterization of Silicalite-1 Zeolites by MAS NMR Spectroscopy
#### 3.2.1 Characterization of the Framework and Guest Species
The signals that appear at \(\delta^{1}\)H \(\approx\) 5-6 ppm decrease in intensity when evacuating the TPA-MFI zeolite in the rotor under mild conditions (100 \({}^{\circ}\)C, 10 h, see TPA-MFI in Figure 6b) and are assigned to physisorbed or occluded water in the material. The signal at \(\delta^{1}\)H = 10.5 ppm due to connectivity defects [67] (SiO\({}^{\circ}\)... HOSi) increases its intensity as the amount of TPP in the zeolite increases. This phenomena is totally in agreement with the evolution of the F/OSDA ratio, which decreases as the P content increases, as shown in Table 2, as previously reported for the TEA/TEP system [64]. The fluorine distribution in the zeolites was analyzed by \({}^{19}\)F MAS NMR spectroscopy. The spectra are shown in Figure 7a and consist of two signals which appear at \(\delta^{19}\)F = \(-\)64.4 ppm and \(\delta^{19}\)F = \(-\)80.0 ppm. The deconvolution of the spectra, using DMFFit software [68], requires two components for the signal which appear at higher chemical shifts and a unique component for the signal at lower chemical shifts as shown for the zeolite TPP-MFI in Figure 7a. The first one is asymmetric, and is attributed to fluorine in a dynamic situation (forming and breaking bond) between two Si atoms in the T9 position of the _t-mel_ subunit of MFI structure [62; 63]. Another signal appears at \(\delta^{19}\)F = \(-\)80.0 ppm with a relative intensity that depends on the amount of TPP incorporated, being more pronounced at higher TPP loadings; the total amount of fluorine decreases in the same direction. The \({}^{19}\)F MAS NMR spectra (Figure 7a) were simulated using two components for the signal at \(\delta^{19}\)F = \(-\)64.4 ppm and a single component for the signal appearing at \(\delta^{19}\)F = \(-\)80.0 ppm. The results show that the relative proportion of the signal at \(-\)80.0 ppm is 6.9% (TPA-MFI), 9.7% (TPX-MFI\({}_{25}\)), 12.3% (TPX-MFI\({}_{45}\)), and 18.8% (TPP-MFI) of the total fluorine; that is, it increases as the TPP content in the zeolites increases. Previously, this signal (\(\delta^{19}\)F = \(-\)80.0 ppm) has been associated with the different interaction of fluorine atoms with dicationic OSDAs or the presence of defects [69; 70; 71]. The results obtained in this work support the last interpretation and seem to be related with the increment of the structural defects with the increase of the TPP content in the samples. This is in agreement with the TEA/TEP system in which the amount of total fluorine also decreases when using P-based OSDAs (see Table 2) and confirms the increase of the proportion of framework connectivity defects as the P incorporated in the zeolite increases [64]. Figure 6: \({}^{31}\)P and \({}^{1}\)H MAS NMR spectra of silicalite-1 samples synthesized using different OSDAs: (**a**) \({}^{31}\)P MAS NMR spectra of the zeolites prepared using TPP and TPP/TPA mixtures; (**b**) \({}^{1}\)H MAS NMR spectra of the zeolites prepared using TPP, TPA, and mixtures of them. Amplification corresponds to the evacuation of the TPA-MFI sample in the NMR rotor under mild conditions (100 \({}^{\circ}\)C, 10 h). The characterization of the zeolite framework was done by measuring the \({}^{29}\)Si MAS NMR spectra, which can be seen in Figure 7b. The spectra are all similar exhibiting four main bands in the Q\({}^{4}\) range (\(-108\) to \(-120\) ppm) that become broader when the TPP content in the zeolites increases due to the presence of a higher proportion of defects, as confirmed by the band at \(\delta^{29}\)Si \(\approx-104\) ppm attributed to zeolitic connectivity defects. The \({}^{29}\)Si MAS NMR spectra of the zeolites synthesized do not show the typical doublet attributed to pentacoordinated silicon due to the dynamic nature of the fluorine jumping between two crystallographic positions as previously described in the literature [62,63].