## 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 organic material incorporated in the zeolites was characterized by measuring the corresponding NMR spectra of the different nuclei (\({}^{1}\)H/\({}^{13}\)C CP, \({}^{31}\)P and \({}^{1}\)H) of the samples synthesized with TPP and/or TPA. The \({}^{1}\)H/\({}^{13}\)C CP MAS NMR spectra of the zeolites prepared are shown in Figure 5.  
Figure 4: TGA-DTG analyses of silicalite-1 samples synthesized using TPA, TPP, and mixtures of them as OSDAs. Solid lines stand for TGA curves and dashed ones for DTG. The \({}^{1}\)H/\({}^{13}\)C CP MAS NMR spectrum of the TPA-MFI zeolite contains three groups of signals at: (1) \(\delta^{13}\)C = 10.0 ppm and \(\delta^{13}\)C = 11.3 ppm due to the -CH\({}_{3}\) groups that are attributed to the orientation of the alkyl chains towards the sinusoidal and straight channels, respectively; (2) a group of signals at around \(\delta^{13}\)C = 16.0 ppm corresponding to the -CH\({}_{2}\)-groups, indicating that there are slight differences regarding their local environment, probably due to the orientation of the alkyl chain to one channel or another; and (3) two signals around \(\delta^{13}\)C = 64.0 ppm with a 1:3 ratio corresponding to the N-CH\({}_{2}\)- group, which have been previously attributed to the angular deformation (NCC or NCCC) of the alkyl chains of the OSDA [65; 66]. The \({}^{1}\)H/\({}^{13}\)C CP MAS NMR spectrum of the TPP-MFI zeolite shows three groups of signals at \(\delta^{13}\)C \(\approx\) 15.5 ppm, \(\delta^{13}\)C \(\approx\) 17.0 ppm, and \(\delta^{13}\)C \(\approx\) 21.0 ppm, corresponding to the -CH\({}_{3}\), -CH\({}_{2}\)-, and -CH\({}_{2}\)-P groups of the TPP cation, respectively. The asymmetric shape of the -CH\({}_{3}\) group signals, which contains two components, can be attributed to the different orientation of the alkyl chains in the sinusoidal and straight channels of the material analogously to that observed in TPA-MFI. Finally, a group of four signals appears at \(\delta^{13}\)C \(\approx\) 21.0 resulting from the overlapping of two doublets of the P-CH\({}_{2}\)- group, due to the scalar J coupling between \({}^{31}\)P and \({}^{13}\)C atoms of the two chains oriented to each channel. The \({}^{1}\)H/\({}^{13}\)C CP MAS NMR spectra of the TPX-MFI\({}_{\rm XX}\) samples contain the signals coming from the TPA and TPP described above. However, the splitting of the signal of the -CH\({}_{3}\) groups of TPA is remarkable and depends on the amount of TPP incorporated in the zeolite. This result indicates that the presence of TPP directly influences the chemical shift of the -CH\({}_{3}\) groups of TPA by modifying their environment and strongly supports the coexistence of both cations in the MFI crystals. The zeolites synthesized in the presence of the P-containing OSDA were also studied by measuring the \({}^{31}\)P MAS NMR spectra, which are shown in Figure 6a. They consist of slightly asymmetric signals at \(\delta^{31}\)P \(\approx\) 30.0 ppm indicating the existence of more than one \({}^{31}\)P environment, in agreement with the splitting of the -CH\({}_{2}\)-P signals in the \({}^{1}\)H/\({}^{13}\)C CP MAS NMR shown in Figure 5. The \({}^{31}\)P signal of TPP is shifted in the zeolites containing also TPA supporting the coexistence of both cations in the zeolite crystals and that one affects the other. Figure 5: \({}^{1}\)H/\({}^{13}\)C CP MAS NMR spectra of silicalite-1 samples synthesized using TPA, TPP, and mixtures of them as OSDAs. The \({}^{1}\)H MAS NMR spectra displayed in Figure 6b contain a broad signal between \(\delta^{1}\)H = 0-4 ppm with the maximum at \(\delta^{1}\)H \(\approx\) 1.4 ppm attributed to protons of the organic molecules, it not being possible to identify the signals of the three non-equivalent \({}^{1}\)H groups.