## 3 Results and Discussion  
During each step of the gel preparation and after the specific times of the hydrothermal synthesis, the pH of the mixture was carefully measured. The obtained values and behavior of the pH are viewed in Figure 2.  
During the first step of the gel preparation, the pH for the mixture of pseudoboehmite with water increased slowly from 6.90 to 7.15 in approximately 60 min due to the low reactivity of pseudoboehmite. After addition of phosphoric acid solution for the mixture, the pH decreased to 1.00, and a formation of a viscous gel was observed. The pH of the system increased slowly as the reaction mixture was aged with vigorous agitation until pH 1.90 after 200 min. This evolution of pH is due to the difficulty of phosphoric in reacting with the bulk after the surface has reacted, Equation (1). When the DIPA was added to the mixture, the gel became very viscous, and the pH value skipped to 5.70 and immediately stabilized in 3.20, Equation (2). \[\mathrm{H_{3}PO_{4}+AlOCH=AlPO_{4}+2H_{2}O} \tag{1}\]  
\[\mathrm{AlPO_{4}+(C_{3}H_{7})_{2}NH=AlPO_{4}\ (C_{3}H_{7})_{2}NH} \tag{2}\]  
The sample obtained in 2 h of heating presented a pH of 5.10. The XRD analysis of this sample did not indicate a crystalline phase of the material, as shown in Figure 3. It was assumed that this pH increasing was due to the reaction of phosphoric acid with pseudoboehmite to form amorphous aluminum phosphate. The samples S4h, S6h, S10h and S15h exhibited crescent values of pH evidencing that the reaction of formation of amorphous aluminum phosphate is still occurring, however, the XRD profiles show characteristic peaks of AlPO\({}_{4}\)-11. The pH in the sample S48h presented the greater value among all the samples, ca. 8.10, evidencing that all phosphoric acid was consumed at the reaction with the pseudoboehmite and a basic pH is due to the excess of amine in solution. The pH decreasing for S74h sample probably was occasioned by the dissolution of the material already crystallized in the mother liquor, which released species in solution that lowered the pH. This phenomenon was also observed for synthesis of VPI-5 with di-n-propylamine [21]. In addition, a decrease in the crystallinity of the S74h sample was observed, as measured by XRD and FT-IR techniques. XRD patterns were performed with the calcined samples to verify the stability of the AlPO\({}_{4}\)-11. The results showed the presence of well-defined crystalline phase identified as AEL structure (AEL = Aluminophosphate Eleven) AlPO\({}_{4}\)-11, as shown in Figure 3.  
Infrared spectra of the solid phase obtained during the crystallization are shown in Figure 4. These spectra were obtained for the as-synthesized samples. The attribution for the main absorption bands were done in the 1400-400 cm\({}^{-1}\) structural region of the spectra [22]. From FT-IR data, two kinds of absorption bands are observed, as summarized in Table 1: one due to internal vibrations of the TO\({}_{4}\) tetrahedral, with T = Al or P, which are structure insensitive, and other due to external vibrations of the tetrahedral that are structure sensitive. This last type of vibration was used as an indicative property of the degree of crystallinity of the material. Figure 2: Curves of pH during the gel preparation and after remotion of each sample during the crystallization process. Figure 3: XRD pattern of the samples obtained during the crystallization process of AlPO\({}_{4}\)-11, monitored at different times. The peaks labeled with (*) were used for determination of the crystallinity. The thermogravimetry (TG) was used to determine the thermal stability, range of temperature to remove the organic template, and pore volume of the samples. Figure 5 illustrates the TG curves and its respective derivatives (DTG). The TG curves of the samples S2h and S4h showed different behavior from the others, because they presented a large amount of amorphous material, as determined by XRD analyses.