# 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  
Table 1 summarizes the textural and physicochemical properties of the different samples obtained during each one of the steps followed in the preparation of the molybdenum-containing SBA-15-based epoxidation catalyst. All the samples display type IV N\({}_{2}\)-adsorption-desorption isotherms (not shown) typical from SBA-15 mesostructured materials. Accordingly, the calculated values for the textural properties match fairly well with those usually reported for this type of silica-based material. However, all the evaluated parameters--surface area, mean pore size, and pore volume--experience a slight reduction with each chemical modification accomplished on the material, as a consequence of the occupation of the mesopores by the organic functionalities attached to the silica support. As for the influence of the different steps of the chemical modification of the surface of the materials, the elemental analysis confirms that the functionalization of the parent pure-silica SBA-15 material though the procedure described in Scheme 1 proceeds as it was expected. Thus, grafting of glycidoxpropyl functionalities onto the silica-based material (Sample S2) leads to the incorporation of 4.3 wt % of carbon to the mesoporous materials, whereas the attachment of the 2-aminomethyl pyridine segment (sample S3) provided some nitrogen, to yield a C:N elemental ratio of 7.2. This value corresponds closely to an amino-methyl pyridine group per glycidoxy functionality, so that the formation of the Schiff base seems to be attained almost quantitatively. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & **S\({}_{\text{SET}}\)1** & **D\({}_{\text{P}}\)2** & **V\({}_{\text{P}}\)3** & **C 4** & **H 4** & **N 4** & **Mo 5** \\ \hline S1 (SBA-15 parent material) & 623 & 77 & 0.97 & - & - & - & - \\ S2 (SBA + GLY) & 508 & 69 & 0.73 & 8.3 & - & 0.36 & - \\ S3 (SBA + GLY + AMP) & 463 & 68 & 0.68 & 6.4 & 1.04 & 0.54 & - \\ S4 (SBA + GLY + AMP + Mo) & 429 & 66 & 0.61 & 9.6 & 0.98 & 0.83 & 3.56 \\ \hline \hline \end{tabular}  
* BET surface area (m\({}^{2}\) g\({}^{-1}\)); 2 Mean pore size (Å) calculated by applying the NLDFT method assuming cylindrical pore geometry, 3 Total pore volume recorded at P/P0 = 0.95; 4 Atom composition obtained by elemental analysis (wt %); 5 Determined by ICP-OES.  
\end{table} 
Table 1: Physicochemical and textural properties of the synthesized SBA-15-type materials. Finally, the incorporation of molybdenum species provide a material (sample S4) showing 3.56 wt % of this metal (0.37 mmol/g), which involves a N:Mo elemental ratio of 1.9, almost that matching with that corresponding to a molybdenum site per Schiff base (N:Mo = 2). The analysis of the chemical functionalization of the surface of SBA-15 materials has been assessed by means of solid state \({}^{29}\)Si MAS-NMR and \({}^{13}\)C CP-MAS-NMR spectroscopy. Figure 1a depicts the \({}^{29}\)Si NMR recorded for samples S1 & S2, which show a different resonance envelope in their \({}^{29}\)Si NMR spectra as consequence of the presence of two different types of silicon species in these materials: Q and T silicon species. Thus, Q silicon groups are formed through condensation of the silicon precursor in three forms, depending on the Si-O-Si bridges: 4 (Q\({}_{4}\) species, \(\delta\) = \(\sim\)\(-\)110 ppm), 3 (Q\({}_{3}\) species, \(\delta\) = \(\sim\)\(-\)100 ppm) or 2 (Q\({}_{2}\) species, \(\delta\) = \(\sim\)\(-\)90 ppm), being the rest of the bondings completed with hydroxyl functionalities. T groups are related to silicon species directly bonded to carbon atoms, such as the glycoloxyppropyl silane functionalities. The deconvolution of the \({}^{29}\)Si NMR spectra allows calculating the proportion of each type of silicon species.