# Mesoporous Niobium Oxyhydroxide Catalysts for Cyclohexene Epoxidation Reactions
## 3 Results and Discussion  
### Characterization of Catalysts  
The results obtained through thermogravimetric analysis (Figure 1a) show that materials that were not calcined (ClNbS and ClNbS-AC) present three main mass loss events. The first two must be related to external and bulk hydroxylates of the catalysts. The mass loss above 350 \({}^{\circ}\)C is attributed to the decomposition of the surfactant group anchored to the surface of the material [24]. No significant mass loss events were observed for calcined catalysts (ClNbS-600 and ClNbS-AC-600); which means that the calcination temperature was sufficient to remove all surfactant and hydroxyls, leaving only Nb\({}_{2}\)O\({}_{5}\). The X ray diffractograms (Figure 1b) showed higher crystallinity for the calcined catalysts, since those that were not thermally treated presented as totally amorphous. The catalysts ClNbS-600 and ClNbS-AC-600 presented a typical diffraction profile of niobium oxide (Nb\({}_{2}\)O\({}_{5}\)), consistent with the standard JCPDS 27-1003. The N\({}_{2}\) adsorption/desorption analyzes were performed and are presented in Figure 2. The data presented in Table 1 show that the calcination process decreases the specific area in relation to non-calcined catalysts, is attributed to the occurrence of particle agglomeration and crystallization, reducing the likely porous structure of the material. Another relationship observed in the surface area data is in relation to the form of aging: the CINbS catalyst presents a larger surface area than CINbS-AC, which may be associated with larger organization of the CINbS-AC pores, since there was a control pressure and temperature in the synthesis. The isotherms of the catalysts CINbS-AC and CINbS-600 indicate the absence of pores, being type II, according to the classification suggested by IUPAC, typical of non-porous materials. The hysteresis formed by the desorption isotherm of these catalysts can be classified as H3, as it does not reach a \begin{table}
\begin{tabular}{c c c} \hline
**Catalyst** & **BET Surface Area (m\({}^{2}\) g\({}^{-1}\))** & **Pore Volume (cm\({}^{3}\) g\({}^{-1}\))** \\ \hline CINbS & 198 & 0.17 \\ CINbS-600 & 44 & 0.10 \\ CINbS-AC & 153 & 0.15 \\ CINbS-AC-600 & 64 & 0.09 \\ \hline \end{tabular}
\end{table} 
Table 1: BET specific area values and pore volume by the BjH method for the synthesized catalysts. Figure 1: (a) Thermogravimetric curves for the catalysts under air atmosphere and (b) X ray diffraction patterns of CINbS-600 and CINbS-AC-600 catalysts. Figure 2: N\({}_{2}\) adsorption/desorption of the catalysts. saturation level and is reported for aggregate materials, forming pores of the crack type associated with a portion of interparticle pores [25; 26]. In the case of the CINbS and CINbS-AC-600 samples, the profile of the type IV isotherm present in the same proportion of materials suggests the presence of mesopores, confirmed by the pore size distribution (not shown here). When reaching a saturation level in the adsorption of N\({}_{\text{2(g)}}\), during the desorption, the CINbS forms a hysteresis classified as H2, considered as bottle-type pores [26]. For the CINbS-AC-600 the formed hysteresis is classified as H3. Table 1 shows the BET specific area values and pore volume of the materials. The calcined catalysts were subjected to acidity analysis by adsorption of pyridine to qualitatively evaluate the type of acid sites present in these materials. For the non-calcined catalysts the analyzes were not carried out because the surfactant had adsorption bands in the same region where the pyridine adsorbed at the Lewis sites (1447 cm\({}^{-1}\)) and adsorbed at the Bronsted sites (1550 cm\({}^{-1}\)) were observed. The CINbS-600 catalyst exhibits acidity Bronsted, while CINbS-AC-600 catalyst presented Bronsted acid and Lewis acid sites (Figure 3), indicating that the aging process in an autoclave provides a difference in the type of acidic material.