# Mo(VI) Complexes Immobilized on SBA-15 as an Efficient Catalyst for 1-Octene Epoxidation
## 2 Results and Discussion
### Characterization of Functionalized SBA-15 Materials and Mo(VI) Supported Catalyst
The main differences between samples S1 & S2 are related to a different proportion of silanol functionalities--higher in the pure silica sample-which are reacted with the organosilane functionality during the grafting process to create T groups, evidencing the efficiency of the first functionalization stage. Figure 1b displays the \({}^{13}\)C MAS-CP NMR spectrum recorded for samples S2 & S3, where the different resonances attributed to the distinct carbon environments are detected, as well as their assignation. Thus, NMR spectrum recorded for sample S2 displays the characteristic signals attributable to the presence of glycidoxy-propyl functionalities. This result confirm the preservation of the oxirane ring during the grafting process, which is the key functionality to build the Schiff base to anchor molybdenum sites. The reaction of these functionalities with 2-picoline (2-aminomethyl-pyridine) leads to some additional resonances in the \({}^{13}\)C CP-MAS-NMR spectrum, which is a consequence of the attachment of the pyridine moiety to the oxirane by reaction through the primary amine group. These results confirm the right organic functionalization of the SBA-15 silica-based support to effectively build the surface-tethered Schiff base, according to Scheme 1, to serve as linkers for molybdenum redox sites. Figure 2 shows FTIR spectra of samples S1-S4 enlarged in three different regions to evaluate the most remarkable vibration signals on each sample spectrum. Thus, in the region from 4000 to 2600 cm\({}^{-1}\) a clear reduction of the signal located at 3440 cm\({}^{-1}\) is observed when grafting (3-glycidyloxypropyl) trimethoxysilane onto the surface of SBA-15 support (S2 vs. S1), indicating an important decrease of the hydroxyl groups population. Bands located between 3000 and 2800 cm\({}^{-1}\) that can be observed for the S2, S3 and S4 samples correspond to the stretching vibration (symmetric and asymmetric) of the  
Figure 1: Solid state NMR analysis of (**a**) \({}^{29}\)Si MAS NMR and (**b**) \({}^{13}\)C CP MAS NMR. C-H bonds existing in the organic functionalities incorporated on silica surface [22]. The signal found around 2980 cm\({}^{-1}\) for samples S3 and S4 (but not for S2), is related to the C-H stretching of aromatic carbons that commonly appear at higher wavenumber than methylene ones [22]. So, this result seems to confirm the incorporation of the aminomethyl pyridine moiety by opening epoxy groups of S2 sample. The region from 1800 to 1400 cm\({}^{-1}\) mainly shows signals corresponding to the C-H bending mode of the different carbons (mostly methylene and aromatic types). Likewise, bending vibration of amine groups (-NH\({}_{2}\) and -NH-) can also be detected here, specifically, the signal at 1575 cm\({}^{-1}\) (observed for samples S3 and S4) could be attributed to these species. Water retained by siliceous materials also presents a characteristic band in this infrared zone (1630 cm\({}^{-1}\)). As observed, the intensity of this band significantly decreases in S2 sample with regards to S1 because of the intensive drying process carried out before SBA-15 functionalization. Finally, a weak intense signal can be seen at 905 cm\({}^{-1}\) for sample S2, a signal typically attributed to the vibration of the C-O bond of epoxy groups [15], confirming the incorporation of glycidyl species by SBA-15 functionalization. As expected, this band disappears in sample S3 where the epoxy rings have been opened by reaction with AMP. Figure 3 displays UV-Vis spectra of samples S2-S4. The three samples show two absorption bands located at 210 and 260 nm corresponding to silica and supported aromatic species, respectively. The presence of the band associated with aromatic species in the spectrum of the sample S2 indicates that some traces of toluene (the solvent used for GPTMS grafting) might remain on this material after the first functionalization step. For samples S3 and S4, the signal located at 260 nm is related to the presence of the aromatic ring existing in the AMP structure.