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Synthesis of highly ordered and hydrothermally stable mesoporous materials using sodium silicate as a precursor
Materials Letters 64 (2010) 1543–1545
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis of highly ordered and hydrothermally stable mesoporous materials using sodium silicate as a precursor Dahai Pan a, Lei Tan b, Kun Qian b, Liang Zhou b, Yu Fan a, Chengzhong Yu b,⁎, Xiaojun Bao a,⁎ a b
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, 18 Fuxue Road, Changping, Beijing 102249, PR China Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, 220 Handan Road, Shanghai 200433, PR China
a r t i c l e
i n f o
Article history: Received 9 November 2009 Accepted 31 March 2010 Available online 23 April 2010 Keywords: Mesoporous materials Hydrothermal stability Sodium silicate Block copolymer
a b s t r a c t Highly ordered mesoporous silica and aluminosilicate materials with extremely high hydrothermal stability have been synthesized successfully at a high hydrothermal treatment temperature of 200 °C by using inexpensive sodium silicate and sodium aluminate as the silica source and alumina source, respectively. The resultant mesoporous materials possess a hexagonal mesostructure and extraordinary stability towards the steam treatment at 800 °C for 2 h. In addition, the direct incorporation of Al into the mesoporous framework can further enhance the hydrothermal stability of ordered mesoporous materials. Our contribution provides a commercially important approach to synthesize ordered mesoporous materials with highly hydrothermal stability, which may find potential applications for the catalytic cracking in the petroleum industry. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Ordered mesoporous materials with tunable structures, high surface areas and large pore volumes have potential applications as catalysts or catalyst supports [1,2]. A series of ordered mesoporous silica materials have been successfully synthesized via the surfactanttemplated self-assembly of inorganic precursors. A well-known example is mesoporous silica SBA-15 synthesized by using a commercial triblock copolymer and tetraethyl orthosilicate (TEOS) in acidic conditions [3,4]. Despite of its large pore diameter and thick pore walls, the hydrothermal stability of SBA-15 in steam at 800 °C is still far from satisfactory, which poses a serious constraint for the catalytic cracking applications in the petroleum industry. In addition, the cost for producing SBA-15 is another concern because of the use of expensive TEOS. Efforts have been devoted to reduce the cost of SBA15 synthesis in the last decade by using inexpensive sodium silicate as the silica source to replace TEOS [5,6]. However, to the best of our knowledge, the hydrothermal performance of ordered mesoporous materials synthesized from inorganic sources has received little attention. A cheap approach to synthesize highly ordered and hydrothermally stable mesoporous materials is still a challenge. Recently, we have reported a novel pH-adjusting approach via the high temperature hydrothermal treatment process (200 °C) to synthesize ordered and highly hydrothermally stable SBA-15 wherein TEOS was used as the silica precursor [7]. Here, we report the synthesis
⁎ Corresponding authors. Fax: + 86 21 65641740. E-mail addresses: [email protected] (C. Yu), [email protected] (X. Bao). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.03.072
of ordered SBA-15 with extremely high hydrothermal stability from a commercial silica source (sodium silicate) by using a similar approach [7]. It is also demonstrated that the introduction of Al by using sodium aluminate can further increase the mesostructural ordering and hydrothermal stability of SBA-15. 2. Experimental section 2.1. Synthesis procedure In a typical synthesis, 1 g of a triblock copolymer EO20PO70EO20 (denoted as P123, where EO is poly(ethylene oxide) and PO is poly (propylene oxide)) was dissolved in 24 mL of a 2 M HCl solution containing 1.55 g of HAc to obtain solution A. Then, 2.4 g of a sodium silicate solution (Na2Si3O7 with 25% SiO2 and 14% NaOH) and a required amount of sodium aluminate (0 or 0.12 g) were added into 6 mL of deionized water to yield solution B. Solution B was stirred at room temperature for 10 min, then added to solution A under stirring. White precipitates appeared ∼ 1 min later and the resultant mixture was stirred at 38 °C for 24 h. The precipitates were filtrated and washed for three times. The product was mixed with 20 g of deionized water and the pH value of the solution was adjusted to 1.65 using 2 M HCl. The mixture was transferred into an autoclave for hydrothermal treatment at 200 °C for 24 h to increase the cross-linking of mesoporous walls [8]. The final products (denoted as S-1.65 or AlS1.65 according to the amount of Al incorporated) were collected by filtering, washing, drying in air, and calcined at 650 °C for 5 h. For comparison purposes, following the original synthesis method of SBA15 without adding HAc and adjusting the hydrothermal pH [3,4], the sample named as S-2M was synthesized using sodium silicate as the
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D. Pan et al. / Materials Letters 64 (2010) 1543–1545
silica source, the other synthesis procedures were the same as described above. 2.2. Hydrothermal stability evaluation The high temperature hydrothermal stability of calcined samples was tested by treating samples at 800 °C for 2 h under 15% steam in nitrogen atmosphere, and the flow rate of nitrogen was 45 mL/min. 2.3. Characterization Small-angle X-ray powder diffraction (XRD) patterns were recorded on a Bruker D8 diffractometer using Ni-filtered Cu Kα (0.154 nm) radiation. Transmission electron microscopy (TEM) experiments were performed on a JEOL 2011 microscope operated at 200 kV. N2 physisorption was conducted on a Quantachrome analyzer. 3. Results and discussion Fig. 1 presents the XRD patterns of calcined mesoporous materials prepared with sodium silicate as the silica source and hydrothermally treated at 200 °C before and after the steaming treatment at 800 °C for 2 h. It shows that both calcined samples S-1.65 and AlS-1.65 prepared with the hydrothermal treatment pH of 1.65 and the addition of HAc during the synthesis exhibit three well-resolved peaks, which can be indexed as (100), (110), and (200) diffractions of a p6mm hexagonal symmetry (Fig. 1A). From the intense (100) peak the unit cell parameters of 11.7 and 11.3 nm can be calculated for S-1.65 and AlS1.65, respectively (Table 1). For comparison, for calcined S-2M prepared via the original synthesis method [3,4], only one peak is observed even before the steam test (Fig. 1A), showing that adjusting hydrothermal treatment pH and adding HAc during the synthesis are important to synthesize highly ordered mesostructure through the high temperature hydrothermal treatment process [7]. The N2 sorption–desorption isotherms and corresponding pore size distribution curves of calcined and steamed samples are shown in Fig. 2. Calcined S-1.65 and AlS-1.65 both exhibit a typical type IV isotherm and a very steep capillary condensation step occurred at a relative pressure (P/P0) ranging from 0.65 to 0.85. The surface areas, pore volumes and pore sizes are 332 and 341 m2/g, 0.83 and 0.81 cm3/g, 12.9 and 11.1 nm for calcined S-1.65 and AlS-1.65, respectively (Table 1). For calcined S2M, the isotherm shows a less steep capillary condensation step at higher P/P0 and an indiscernible pore size distribution curve (Fig. 2B),
Table 1 The structure parameters of samples before and after steam treatment at 800 °C for 2 h. Sample
d100 (nm)
p (nm)
S (m2/g)
V (cm3/g)
S-1.65 Steaming AlS-1.65 Steaming S-2M
10.1 10.0 9.8 9.8 10.3
12.9 8.0 11.1 11.2 –
332 247 341 349 195
0.83 0.46 0.81 0.80 0.62
Vloss (%) 44.6 1.2
Note: d100 is the d-spacing calculated from the first peak, p is the pore size calculated from the adsorption branch using the BJH method, S is BET surface area, V is the total pore volume, Vloss is the total pore volume reduction in percentage after hydrothermal treatment.
indicating that the mesopores have been essentially destroyed during the high temperature hydrothermal treatment process. Generally, increasing the hydrothermal treatment temperature can improve the hydrothermal stability of mesoporous materials [9]. From the XRD patterns of steamed samples (Fig. 1B), it can be seen that after steam treatment at 800 °C for 2 h, samples S-1.65 and AlS1.65 still display three well-resolved peaks, indicating that the ordered mesostructure is well maintained. For steamed S-1.65, the well-ordered hexagonal arrays along [100] and [110] directions can be easily seen from the TEM images displayed in Fig. 3A and B, respectively, in agreement with the XRD results. The results of N2 adsorption–desorption also validate the extremely high hydrothermal stability of S-1.65 and AlS-1.65 (Fig. 2). For steamed samples S-1.65 and AlS-1.65, the pore size distribution curves are still quite narrow. It is also notable that the surface area and pore volume are hardly affected for the AlS-1.65 after hydrothermal treatment at 800 °C for 2 h, while the total pore volume of steamed S-1.65 decreases by 44.6% (Table 1) after the same treatment, indicating that the hydrothermal stability is further improved by introducing Al during the synthesis. Combined with the results of XRD and N2 adsorption–desorption, it can be seen that the samples prepared with sodium silicate by the novel pH-adjusting approach show the same mesostructural properties and hydrothermal stability as those of samples prepared with TEOS [7]. In our study, because the synthesis of AlS-1.65 was carried out at a strong acidic condition (2 M HCl), there is only a very small amount of Al incorporated into the product. Compared with the initial Si/Al ratio of 20 during the synthesis, the EDX analysis and ICP analysis show that the final Si/Al ratio of the calcined sample are 247 and 210, respectively, indicating that most of the Al species were not incorporated into the framework [7,9].
Fig. 1. XRD patterns of samples calcined at 650 °C for 5 h (A) and steamed at 800 °C for 2 h (B), respectively.
D. Pan et al. / Materials Letters 64 (2010) 1543–1545
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Fig. 2. N2 sorption isotherms (A) and the corresponding pore size distribution curves (B) of calcined and steamed samples. For clarity, in (A), the isotherms of S-1.65, AlS-1.65, S-2M, and steamed S-1.65 are offset along the Y axis by 800, 600, 450 and 200 cm3/g, respectively. In (B), the pore size distributions for S-1.65, AlS-1.65, S-2M, and steamed S-1.65 are offset by 10, 7, 5.5, and 3.5 cm3/g, respectively.
Fig. 3. TEM images (A, B) of S-1.65 steamed at 800 °C for 2 h viewed along [100] and [110] directions, respectively.
4. Conclusion Ordered and highly hydrothermal stable mesoporous materials have been successfully synthesized at a high hydrothermal treatment temperature of 200 °C using low-cost sodium silicate as the silica source through simultaneously adjusting hydrothermal treatment pH and adding HAc. The ordered mesostructure can be well preserved after being steamed at 800 °C for 2 h. In addition, the direct incorporation of Al can further increase the hydrothermal stability of resultant materials. Our achievements provide an economical approach to synthesize ordered and highly hydrothermal stable mesoporous materials, which are crucial for their large-scale applications. Acknowledgments This work was financially supported by the 973 Program of China (2010CB226901), NSFC (20573021 and 20825621), SLADP (B108, B113), the Ministry of Education of China (20060246010), and STC of Shanghai (08DZ2270500).
References [1] Corma A. From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem Rev 1997;97:2373–419. [2] Tao YS, Kanoh H, Abrams L, Kaneko K. Mesopore-modified zeolites: preparation, characterization, and applications. Chem Rev 2006;106:896–910. [3] Zhao DY, Feng JL, Huo QS, Melosh N, Fredrickson GH, Chmelka BF, et al. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 Angstrom pores. Science 1998;279:548–52. [4] Zhao DY, Huo QS, Feng JL, Chmelka BF, Stucky GD. Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures. J Am Chem Soc 1998;120:6024–36. [5] Kim JM, Stucky GD. Synthesis of highly ordered mesoporous silica materials using sodium silicate and amphiphilic block copolymers. Chem Commun 2000:1159–60. [6] Corriu RJP, Mehdi A, Reye C, Thieuleux C. Direct syntheses of functionalized mesostructured silica by using an inexpensive silica source. Chem Commun 2004: 1440–1. [7] Pan DH, Yuan P, Zhao LZ, Liu N, Zhou L, Wei GF, et al. New understanding and simple approach to synthesize highly hydrothermally stable and ordered mesoporous materials. Chem Mater 2009;21:5413–25. [8] Han Y, Li DF, Zhao L, Song JW, Yang XY, Li N, et al. High-temperature generalized synthesis of stable ordered mesoporous silica-based materials by using fluorocarbon-hydrocarbon surfactant mixtures. Angew Chem Int Edit 2003;42:3633–7. [9] Li CL, Wang YQ, Guo YL, Liu XH, Guo Y, Zhang ZG, et al. Synthesis of highly ordered, extremely hydrothermal stable SBA-15/Al-SBA-15 under the assistance of sodium chloride. Chem Mater 2007;19:173–8.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis of highly ordered and hydrothermally stable mesoporous materials using sodium silicate as a precursor Dahai Pan a, Lei Tan b, Kun Qian b, Liang Zhou b, Yu Fan a, Chengzhong Yu b,⁎, Xiaojun Bao a,⁎ a b
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, 18 Fuxue Road, Changping, Beijing 102249, PR China Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, 220 Handan Road, Shanghai 200433, PR China
a r t i c l e
i n f o
Article history: Received 9 November 2009 Accepted 31 March 2010 Available online 23 April 2010 Keywords: Mesoporous materials Hydrothermal stability Sodium silicate Block copolymer
a b s t r a c t Highly ordered mesoporous silica and aluminosilicate materials with extremely high hydrothermal stability have been synthesized successfully at a high hydrothermal treatment temperature of 200 °C by using inexpensive sodium silicate and sodium aluminate as the silica source and alumina source, respectively. The resultant mesoporous materials possess a hexagonal mesostructure and extraordinary stability towards the steam treatment at 800 °C for 2 h. In addition, the direct incorporation of Al into the mesoporous framework can further enhance the hydrothermal stability of ordered mesoporous materials. Our contribution provides a commercially important approach to synthesize ordered mesoporous materials with highly hydrothermal stability, which may find potential applications for the catalytic cracking in the petroleum industry. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Ordered mesoporous materials with tunable structures, high surface areas and large pore volumes have potential applications as catalysts or catalyst supports [1,2]. A series of ordered mesoporous silica materials have been successfully synthesized via the surfactanttemplated self-assembly of inorganic precursors. A well-known example is mesoporous silica SBA-15 synthesized by using a commercial triblock copolymer and tetraethyl orthosilicate (TEOS) in acidic conditions [3,4]. Despite of its large pore diameter and thick pore walls, the hydrothermal stability of SBA-15 in steam at 800 °C is still far from satisfactory, which poses a serious constraint for the catalytic cracking applications in the petroleum industry. In addition, the cost for producing SBA-15 is another concern because of the use of expensive TEOS. Efforts have been devoted to reduce the cost of SBA15 synthesis in the last decade by using inexpensive sodium silicate as the silica source to replace TEOS [5,6]. However, to the best of our knowledge, the hydrothermal performance of ordered mesoporous materials synthesized from inorganic sources has received little attention. A cheap approach to synthesize highly ordered and hydrothermally stable mesoporous materials is still a challenge. Recently, we have reported a novel pH-adjusting approach via the high temperature hydrothermal treatment process (200 °C) to synthesize ordered and highly hydrothermally stable SBA-15 wherein TEOS was used as the silica precursor [7]. Here, we report the synthesis
⁎ Corresponding authors. Fax: + 86 21 65641740. E-mail addresses: [email protected] (C. Yu), [email protected] (X. Bao). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.03.072
of ordered SBA-15 with extremely high hydrothermal stability from a commercial silica source (sodium silicate) by using a similar approach [7]. It is also demonstrated that the introduction of Al by using sodium aluminate can further increase the mesostructural ordering and hydrothermal stability of SBA-15. 2. Experimental section 2.1. Synthesis procedure In a typical synthesis, 1 g of a triblock copolymer EO20PO70EO20 (denoted as P123, where EO is poly(ethylene oxide) and PO is poly (propylene oxide)) was dissolved in 24 mL of a 2 M HCl solution containing 1.55 g of HAc to obtain solution A. Then, 2.4 g of a sodium silicate solution (Na2Si3O7 with 25% SiO2 and 14% NaOH) and a required amount of sodium aluminate (0 or 0.12 g) were added into 6 mL of deionized water to yield solution B. Solution B was stirred at room temperature for 10 min, then added to solution A under stirring. White precipitates appeared ∼ 1 min later and the resultant mixture was stirred at 38 °C for 24 h. The precipitates were filtrated and washed for three times. The product was mixed with 20 g of deionized water and the pH value of the solution was adjusted to 1.65 using 2 M HCl. The mixture was transferred into an autoclave for hydrothermal treatment at 200 °C for 24 h to increase the cross-linking of mesoporous walls [8]. The final products (denoted as S-1.65 or AlS1.65 according to the amount of Al incorporated) were collected by filtering, washing, drying in air, and calcined at 650 °C for 5 h. For comparison purposes, following the original synthesis method of SBA15 without adding HAc and adjusting the hydrothermal pH [3,4], the sample named as S-2M was synthesized using sodium silicate as the
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silica source, the other synthesis procedures were the same as described above. 2.2. Hydrothermal stability evaluation The high temperature hydrothermal stability of calcined samples was tested by treating samples at 800 °C for 2 h under 15% steam in nitrogen atmosphere, and the flow rate of nitrogen was 45 mL/min. 2.3. Characterization Small-angle X-ray powder diffraction (XRD) patterns were recorded on a Bruker D8 diffractometer using Ni-filtered Cu Kα (0.154 nm) radiation. Transmission electron microscopy (TEM) experiments were performed on a JEOL 2011 microscope operated at 200 kV. N2 physisorption was conducted on a Quantachrome analyzer. 3. Results and discussion Fig. 1 presents the XRD patterns of calcined mesoporous materials prepared with sodium silicate as the silica source and hydrothermally treated at 200 °C before and after the steaming treatment at 800 °C for 2 h. It shows that both calcined samples S-1.65 and AlS-1.65 prepared with the hydrothermal treatment pH of 1.65 and the addition of HAc during the synthesis exhibit three well-resolved peaks, which can be indexed as (100), (110), and (200) diffractions of a p6mm hexagonal symmetry (Fig. 1A). From the intense (100) peak the unit cell parameters of 11.7 and 11.3 nm can be calculated for S-1.65 and AlS1.65, respectively (Table 1). For comparison, for calcined S-2M prepared via the original synthesis method [3,4], only one peak is observed even before the steam test (Fig. 1A), showing that adjusting hydrothermal treatment pH and adding HAc during the synthesis are important to synthesize highly ordered mesostructure through the high temperature hydrothermal treatment process [7]. The N2 sorption–desorption isotherms and corresponding pore size distribution curves of calcined and steamed samples are shown in Fig. 2. Calcined S-1.65 and AlS-1.65 both exhibit a typical type IV isotherm and a very steep capillary condensation step occurred at a relative pressure (P/P0) ranging from 0.65 to 0.85. The surface areas, pore volumes and pore sizes are 332 and 341 m2/g, 0.83 and 0.81 cm3/g, 12.9 and 11.1 nm for calcined S-1.65 and AlS-1.65, respectively (Table 1). For calcined S2M, the isotherm shows a less steep capillary condensation step at higher P/P0 and an indiscernible pore size distribution curve (Fig. 2B),
Table 1 The structure parameters of samples before and after steam treatment at 800 °C for 2 h. Sample
d100 (nm)
p (nm)
S (m2/g)
V (cm3/g)
S-1.65 Steaming AlS-1.65 Steaming S-2M
10.1 10.0 9.8 9.8 10.3
12.9 8.0 11.1 11.2 –
332 247 341 349 195
0.83 0.46 0.81 0.80 0.62
Vloss (%) 44.6 1.2
Note: d100 is the d-spacing calculated from the first peak, p is the pore size calculated from the adsorption branch using the BJH method, S is BET surface area, V is the total pore volume, Vloss is the total pore volume reduction in percentage after hydrothermal treatment.
indicating that the mesopores have been essentially destroyed during the high temperature hydrothermal treatment process. Generally, increasing the hydrothermal treatment temperature can improve the hydrothermal stability of mesoporous materials [9]. From the XRD patterns of steamed samples (Fig. 1B), it can be seen that after steam treatment at 800 °C for 2 h, samples S-1.65 and AlS1.65 still display three well-resolved peaks, indicating that the ordered mesostructure is well maintained. For steamed S-1.65, the well-ordered hexagonal arrays along [100] and [110] directions can be easily seen from the TEM images displayed in Fig. 3A and B, respectively, in agreement with the XRD results. The results of N2 adsorption–desorption also validate the extremely high hydrothermal stability of S-1.65 and AlS-1.65 (Fig. 2). For steamed samples S-1.65 and AlS-1.65, the pore size distribution curves are still quite narrow. It is also notable that the surface area and pore volume are hardly affected for the AlS-1.65 after hydrothermal treatment at 800 °C for 2 h, while the total pore volume of steamed S-1.65 decreases by 44.6% (Table 1) after the same treatment, indicating that the hydrothermal stability is further improved by introducing Al during the synthesis. Combined with the results of XRD and N2 adsorption–desorption, it can be seen that the samples prepared with sodium silicate by the novel pH-adjusting approach show the same mesostructural properties and hydrothermal stability as those of samples prepared with TEOS [7]. In our study, because the synthesis of AlS-1.65 was carried out at a strong acidic condition (2 M HCl), there is only a very small amount of Al incorporated into the product. Compared with the initial Si/Al ratio of 20 during the synthesis, the EDX analysis and ICP analysis show that the final Si/Al ratio of the calcined sample are 247 and 210, respectively, indicating that most of the Al species were not incorporated into the framework [7,9].
Fig. 1. XRD patterns of samples calcined at 650 °C for 5 h (A) and steamed at 800 °C for 2 h (B), respectively.
D. Pan et al. / Materials Letters 64 (2010) 1543–1545
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Fig. 2. N2 sorption isotherms (A) and the corresponding pore size distribution curves (B) of calcined and steamed samples. For clarity, in (A), the isotherms of S-1.65, AlS-1.65, S-2M, and steamed S-1.65 are offset along the Y axis by 800, 600, 450 and 200 cm3/g, respectively. In (B), the pore size distributions for S-1.65, AlS-1.65, S-2M, and steamed S-1.65 are offset by 10, 7, 5.5, and 3.5 cm3/g, respectively.
Fig. 3. TEM images (A, B) of S-1.65 steamed at 800 °C for 2 h viewed along [100] and [110] directions, respectively.
4. Conclusion Ordered and highly hydrothermal stable mesoporous materials have been successfully synthesized at a high hydrothermal treatment temperature of 200 °C using low-cost sodium silicate as the silica source through simultaneously adjusting hydrothermal treatment pH and adding HAc. The ordered mesostructure can be well preserved after being steamed at 800 °C for 2 h. In addition, the direct incorporation of Al can further increase the hydrothermal stability of resultant materials. Our achievements provide an economical approach to synthesize ordered and highly hydrothermal stable mesoporous materials, which are crucial for their large-scale applications. Acknowledgments This work was financially supported by the 973 Program of China (2010CB226901), NSFC (20573021 and 20825621), SLADP (B108, B113), the Ministry of Education of China (20060246010), and STC of Shanghai (08DZ2270500).
References [1] Corma A. From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem Rev 1997;97:2373–419. [2] Tao YS, Kanoh H, Abrams L, Kaneko K. Mesopore-modified zeolites: preparation, characterization, and applications. Chem Rev 2006;106:896–910. [3] Zhao DY, Feng JL, Huo QS, Melosh N, Fredrickson GH, Chmelka BF, et al. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 Angstrom pores. Science 1998;279:548–52. [4] Zhao DY, Huo QS, Feng JL, Chmelka BF, Stucky GD. Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures. J Am Chem Soc 1998;120:6024–36. [5] Kim JM, Stucky GD. Synthesis of highly ordered mesoporous silica materials using sodium silicate and amphiphilic block copolymers. Chem Commun 2000:1159–60. [6] Corriu RJP, Mehdi A, Reye C, Thieuleux C. Direct syntheses of functionalized mesostructured silica by using an inexpensive silica source. Chem Commun 2004: 1440–1. [7] Pan DH, Yuan P, Zhao LZ, Liu N, Zhou L, Wei GF, et al. New understanding and simple approach to synthesize highly hydrothermally stable and ordered mesoporous materials. Chem Mater 2009;21:5413–25. [8] Han Y, Li DF, Zhao L, Song JW, Yang XY, Li N, et al. High-temperature generalized synthesis of stable ordered mesoporous silica-based materials by using fluorocarbon-hydrocarbon surfactant mixtures. Angew Chem Int Edit 2003;42:3633–7. [9] Li CL, Wang YQ, Guo YL, Liu XH, Guo Y, Zhang ZG, et al. Synthesis of highly ordered, extremely hydrothermal stable SBA-15/Al-SBA-15 under the assistance of sodium chloride. Chem Mater 2007;19:173–8.