Alumination and Ion Exchange of Mesoporous SBA-15 Molecular Sieves

Abstract

Mesoporous silica SBA-15 molecular sieve has been synthesized and incorporated with aluminum via three different postsynthesis procedures by reacting SBA-15 with AlCl 3 in dry ethanol (route 1), with aluminum isopropoxide in dry hexane (route 2) and with an aqueous solution of sodium aluminate (route 3) followed by calcination. Characterization by transmission electron microscopy, N 2 adsorption, electron probe microanalysis, powder X-ray diffraction, 27 Al magic-angle-spinning NMR, and electron spin resonance spectroscopies has been carried out to evaluate the efficiency of these alumination methods and their effect on the pore structure and ion exchange capacity of SBA-15. The Si/Al ratios in the resulting materials are in close agreement with the composition in the postsynthesis mixtures over a range of 40-10, indicating that the aluminum is mostly incorporated into silica SBA-15. The silanol groups on the internal wall surfaces of SBA-15 are suggested to be the sites for aluminum incorporation. The incorporation procedure has a strong effect on the aluminum coordination, pore structure and ion exchange capacity of the resulting materials. At comparable Si/Al ratios around 20, the percentage of aluminum with tetrahedral symmetry in the synthesized materials is about 100% (route 3) > 76% (route 1) > 71% (route 2), indicating that alumination by aqueous sodium aluminate is most effective. This is probably due to the presence of Na + ions which balance the negative charges associated with tetrahedral aluminums. The BET specific surface areas are 85% (route 1) > 60% (route 2) > 42%(route 3), showing that alumination by AlCl 3 in ethanol best maintains the mesoporous structure of SBA-15. Electron-spin resonance reveals a linear dependence of the Cu(II) ion exchange capacity on the tetrahedral aluminum content of the aluminum-containing SBA-15 materials. This suggests that the incorporated aluminums in the tetrahedral framework do serve as ion exchange sites.

Single Site Supported Cationic Rhodium(I) Complexes for the Selective Redox Isomerization of Allylic Alcohols

“…Different mesoporousm aterials, silica MCM-41, [31] MCM-48, [31] and SBA-15, [32] aluminosilica AlSBA-15, [33] Information). When the sulfonated phosphine (MeO-TPPMS, 1b)i su sed, the immobilization can take place through hydrogen bonding between the silanol groups on the silica support and the sulfonate group in the ligand (Figure 2a).…”

“…[33] Am ixture of silica SBA-15 (2.0 g, approx. 32 mmol) and AlCl 3 (0.134 g, 1.10 mmol) was heated to reflux in anhydrous ethanol at 80 8Cf or 10 h. The resulting solid was filtered, washed repeatedly with anhydrous ethanol, and dried in air at room temperature.…”

Nanometric palladium confined in mesoporous silica as efficient catalysts for toluene oxidation at low temperature

“…The short column SBA-15 type supports used in this work were prepared by dissolving 4 g of Pluronic P123 (EO 20 PO 70 EO 20 ) in 160 g of 2 M HCl solution at 35 • C, followed by adding 9.1 ml of tetraethyl orthosilicate (TEOS), 0.66 g of ZrOCl 2 and different amounts of Al 2 (SO 4 ) 3 . The mixture was stirred at 35 • C for 20 h, and then aged at 85 • C for 48 h. After the procedures described above, the pH of the mixture was adjusted to 7.5 by adding NH 4 OH dropwise at room temperature and the obtained mixture was hydrothermally heated again at 85 • C for 48 h. The recovered soil was extensively washed with deionized water and dried at 60 • C for 24 h. Template removal was performed by calcinations in air using two successive procedures, i.e., heating at 350 • C for 3 h and then at 550 • C for 4 h, to prevent the silica matrix from shrinking, and hence maintained the original size and volume of micro-and mesopores.…”

“…The procedure of direct-synthesis is relatively simple, however, only a small amount of heteroatoms can be introduced into the mesoporous silica. Compared with directsynthesis, post-grafting can introduce more heteroatoms into the framework of mesoporous silica, however, the post-grafting routes are very complicated and the uniform mesostructure of products are sometimes severely destroyed [20]. Recently, Wu et al [21] reported a simple and efficient "pH-adjusting" approach which can introduce large amount of heteroatoms into mesoporous silica without destroying its original mesostructure.…”

A Continuous-Flow System for Asymmetric Hydrogenation Using Supported Chiral Catalysts

“…In order to prove that the reaction was heterogeneously catalyzed, and to exclude the possibility of homogeneous catalysis, filtration test was carried out [9]. After addition of the substrate to the supernatant of the fifth cycle, the hydrogenation was continued for 2 h. No further reaction was observed, whereas the original catalyst in the sixth cycle completely hydrogenated the substrate.…”