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A high surface area nanocrystalline alumina with tailoring texture by mixed template
Materials Letters 153 (2015) 165–167
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A high surface area nanocrystalline alumina with tailoring texture by mixed template Yongfeng Li, Jiaojiao Su, Jinghong Ma, Feng Yu, Ruifeng Li n College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
art ic l e i nf o
a b s t r a c t
Article history: Received 10 November 2014 Accepted 4 April 2015 Available online 17 April 2015
We report a facile synthesis of porous alumina (PA) which enables control of pore structure using a mixture of fatty alcohol polyoxyethylene ether (AEO-7) and poly (alkylene oxide) triblock copolymers (P123) as the template via an evaporation-induced self-assembly (EISA) pathway associated with thermal treatment. N2 adsorption–desorption results show that using over 80 wt% AEO-7, the obtained materials are super-microporous (pore size in the range of 1–2 nm), then if further decrease in the AEO-7 content will transform to mesopore (pore size 42 nm). When the mass fraction of P123 is less than 20 wt%, the material has a large surface area (more than 650 m2/g) and nanocrystalline phase is obtained at 400 1C. Even after calcination at 750 1C for 1 h, the sample of mass fraction 20 wt% P123 still exhibits a high specific area of 450 m2/g with large microporosity. & 2015 Elsevier B.V. All rights reserved.
Keywords: Porous materials Texture Nanocrystalline alumina Evaporation-induced self-assembly Super-microporous Large surface area
1. Introduction High surface area aluminas have enormous commercial importance as adsorbents and catalyst components in many chemical processes, including the petroleum refinement, the automobile emission control, and others [1–3]. The use of alumina can be ascribed to both high thermal stability and suitable surface acidic– basic properties as well as to the fact it is a rather inexpensive material. The catalytic properties of alumina largely depend on their crystalline structures and textural characteristics. Therefore, it is of great importance to obtain alumina with controllable pore structures. A series of mesoporous alumina materials have been successfully synthesized through the sol–gel process [1,2] or by utilizing the nano-casting method [4,5]. Considerable efforts have been invested in the synthesis of mesoporous alumina with surfactants as templates. When surfactants with small molecular weight are used as templates, smaller pore sizes (normally below 4 nm) of mesoporous metal oxides can be obtained. Alternatively, large molecular block copolymers are used to synthesize mesoporous materials with large pore size [2]. Supermicropores, first introduced by Dubinin [6], is defined as nanopores with pore sizes ranging from 1 nm to 2 nm. The materials in this pore size range are greatly important, since they bridge the gap between microporous zeolites and mesoporous materials and have potential applications such as in the size and shape selectivity catalysis for
n
Corresponding author. Tel./fax: þ 86 351 6010121. E-mail address: rfl[email protected] (R. Li).
http://dx.doi.org/10.1016/j.matlet.2015.04.018 0167-577X/& 2015 Elsevier B.V. All rights reserved.
special required molecules. But there are few reports about supermicroporous alumina, especially from super-micropores to mesopores. In the early work, the synthesis of super-microporous zirconia–alumina material was accomplished using low molecular weight nonionic surfactant AEO-7 as the template via the evaporation-induced self-assembly (EISA) pathway [7]. It seems to be the simplest and the fastest to get nanostructured supermicroporous metal oxide. Considering these facts, porous nanocrystalline structurecontrolled aluminas were prepared via the EISA method using mixed templating agents. More importantly, pore structures of these synthesized alumina range from super-micropore to mesopore and exhibit a high thermal stability, which is an excellent advantage in high-temperature catalytic reactions.
2. Experimental procedure In a typical synthesis, a mixture of X g of Pluronic P123 and (1.0 X) g of nonionic surfactant fatty alcohol polyoxyethylene ether (AEO-7) was dissolved in 20 mL of ethanol under magnetic stirring at 30 1C. Then 1.4 mL of 67 wt% nitric acid plus 0.7 g citric acid and 2.04 g (10 mmol) of aluminum iso-propoxide were added into the above solution with vigorous stirring. The resultant mixture was covered with PE film, stirred at 30 1C for about 6 h, and then put into a 60 1C drying oven to undergo the solvent evaporation process. Under these conditions, ethanol was gradually evaporated, and the final product was calcined at 400 1C (1 1C min 1 ramping rate) for 5 h in flowing air to remove the
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Y. Li et al. / Materials Letters 153 (2015) 165–167
Fig. 1. N2 adsorption–desorption isotherms (A) with corresponding pore size distribution curves (B) of the PA-X samples calcined at 400 1C.
template. High-temperature treatment was carried out in air for 1 h with a temperature ramp of 10 1C/min. The as-synthesized materials were abbreviated as PA-X-T, where X and T represent the P123 mass and the final calcinated temperature, respectively. Powder X-ray diffraction patterns were recorded on a Shimadzu XRD-6000 diffractometer using Ni-filtered CuKα (0.154 nm) radiation. Transmission electron microscopy (TEM) experiments were performed on a JEOL 2011 microscope operated at 200 kV. The surface area was determined with a Quantachrome measuring instrument using the nitrogen gas adsorption–desorption technique at 196 1C. The surface areas were calculated by Brunauer– Emmett–Teller (BET) formula. Pore diameters were calculated by the density functional theory (DFT) method.
Table 1 BET and micropore surface areas for the PA-X samples calcined at different temperatures. Sample
SBET (m2/g)
t-Method micropore surface area (m2/g)
Pore volume (cm3/g)
PA-0-400 PA-0.1-400 PA-0.2-400 PA-0.3-400 PA-0.5-400 PA-0.7-400 PA-0.8-400 PA-0.2-750 PA-0.2-900 PA-0-750 PA-0-900
672 659 664 407 396 350 281 450 187 186 101
646 521 625 – – – – 351 57 – –
0.23 0.34 0.36 0.30 0.41 0.40 0.32 0.26 0.13 0.18 0.07
3. Results and discussion Fig. 1 shows the nitrogen adsorption–desorption isotherms of the samples of PA-X calcinated at 400 1C for 5 h in air. The isotherms of PA-X (X ¼0, 0.1, 0.2) are type I isotherms and do not show hysteresis in the desorption branch, indicating that the micropores are formed. Pore diameters were calculated by the DFT method, which produced values centered around 1.7 nm. Whereas the isotherms of the samples synthesized with higher content of P123 exhibit a large hysteresis loop, which are the typical characteristic of mesoporous materials, namely a type IV isotherm with H2-shaped hysteresis loop assigned to mesoporous structure. This suggests that the super-micropores transform to the mesopores with increasing P123 contents. It can be seen in Table 1 that, using a single agent AEO-7 (PA-0), the physisorption measurements reveal the largest BET surface area (672 m2/g) and a narrow pore size distribution centered at 1.7 nm pore diameter. The isotherm obtained using PA-0.2, yielded a surface area of 664 m2/g of which 625 m2/g in the form of micropores. The micropore distribution curve indicates that micropores are mostly between 1 and 2 nm in diameter. For samples PA-X calcined at the same temperature, the surface area has little influence with increasing P123 contents from 0 to 20 wt% but a decreased value was obtained for above 20 wt%. Therefore, PA-0 and PA-0.2 were selected to examine the physicochemical properties. The PA-0 and PA-0.2 samples were calcined at higher temperature to test its thermal stability. N2 adsorption isotherms (Fig. 2) of these calcined samples were recorded to reveal framework properties of the materials. After being calcined at 750 1C, type IV isotherms, which are typical for samples with mesopores, were
observed for the sample PA-0, whereas type I isotherms characteristic of adsorption in micropores were observed for the sample PA0.2. For sample PA-0.2, even if treated at 750 1C, the SBET of the sample had the high area of 450 m2/g, indicating a high thermal stability of the microporous structure, although their BET specific surface area, microporous surface areas and pore volume decrease gradually with the increases of temperature (Table 1). When transformed to γ-alumina after calcination at 900 1C, the surface area of the sample is still 188 m2/g, which is much higher than the sample synthesized with the only agent AEO-7 due to the presence of microporous structure. This further indicates that the mixed template method can remarkably increase the thermal stability. The large surface areas and appropriate pore volume associated with excellent thermal stability may improve the potential applications of these nanocrystalline porous alumina in many fields. Fig. 3 shows the wide-angle XRD patterns of PA-0.2 calcined at different temperatures. For the PA-0.2 calcined at 900 1C, several relatively weak diffraction peaks are observed, which can be indexed as the 220, 311, 222, 400, 511, 440 reflections of γ-alumina (JCPDS, 100425). In fact, PA-0 and PA-0.2 with crystalline structure is obtained at 400 1C, which can be further confirmed by the TEM analysis (Fig. S1). The electron diffraction patterns of the disordered wormholelike structure sample confirmed that the walls are polycrystalline, which are reflected by characteristic diffuse electron diffraction rings. Since such particles would be present as small crystallites of no more than 4 nm diameter, which are undetectable by XRD. It was reported that choosing longer alkyl chain surfactants, increasing the temperature of the hydrothermal treatment, using
Y. Li et al. / Materials Letters 153 (2015) 165–167
167
Fig. 2. N2 adsorption–desorption isotherms of the PA-0 (A) and PA-0.2 (B) samples calcined at different temperatures.
synthesized by the mixed template method in ethanol solvent. Tunable pore structures make the shape-selective catalysis become possible. For the sample PA-0.2, the sample exhibited a high specific area of 450 m2/g calcinated at 750 1C. Even after thermal treatment at 900 1C, the SBET of the sample had the high area of 188 m2/g, which is essential for further application. Our achievements provide new contributions to synthesize nanocrystalline alumina with tunable pore structures and high thermal stability, which may extend the applications in industry.
Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51172154) and the Shanxi Province Science Foundation for Youths (2013021008-3). Fig. 3. XRD patterns of PA-0.2 calcined at different temperatures.
Appendix A. Supporting information large molecular weight block copolymers as templates, or adding swelling agents can yield mesoporous silica materials with larger pore sizes [8]. Some of these strategies are suitable for the synthesis of mesoporous metal oxides. The commercially available PEO–PPO–PEO triblock copolymers were the first ones used for the synthesis of mesoporous metal oxides with stable mesostructures and large pore sizes [9]. In the case of this system, porous nanocrystalline alumina with tailorable pore structure has been synthesized successfully using a mixture of low molecular weight fatty alcohol polyoxyethylene ether (AEO-7) and poly (alkylene oxide) triblock copolymers P123 as the template. The pore sizes of mesoporous metal oxides templated by block copolymers are larger than those obtained with low molecular weight surfactants. Here, the P123 have the interaction with AEO-7 through the PEO part to form the compact micelles, which is the reason of change of pore structure [7,10]. The pore structure of the synthesized alumina could be turned from super-microporous to mesoporous range by increasing P123 contents. Our experimental results can be further confirmed by the nitrogen adsorption–desorption isotherms. 4. Conclusions Nanocrystalline aluminas with controlled pore properties by tailoring the amount of template AEO-7 used have been successfully
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.04.018. References [1] Cai WQ, Yu JG, Anand C, Vinu A, Jaroniec M. Facile synthesis of ordered mesoporous alumina and alumina-supported metal oxides with tailored adsorption and framework properties. Chem Mater 2011;23:1147–57. [2] Yuan Q, Yin AX, Luo C, Sun LD, Zhang YW, Duan WT, et al. Facile synthesis for ordered mesoporous γ-aluminas with high thermal stability. J Am Chem Soc 2008;130:3465–72. [3] Akarmazyan SS, Panagiotopoulou P, Kambolis A, Papadopoulou C, Kondarides DI. Methanol dehydration to dimethylether over Al2O3 catalysts. Appl Catal B: Environ 2014;145:136–48. [4] Liu Q, Wang A, Wang X, Zhang T. Ordered crystalline alumina molecular sieves synthesized via a nanocasting route. Chem Mater 2006;18:5153–5. [5] Wu ZX, Li QA, Feng D, Webley PA, Zhao DY. Ordered mesoporous crystalline γ-Al2O3 with variable architecture and porosity from a single hard template. J Am Chem Soc 2010;132:12042–50. [6] Dubinin MM. On physical feasibility of Bruauer's micropore analysis method. J Colloid Interface Sci 1974;46:351–6. [7] Li YF, Su JJ, Ma JH, Yu F, Pan DH, Li RF. A super-microporous zirconia–alumina nanomaterial with high thermal stability. Mater Lett 2014;136:183–6. [8] Wan Y, Zhao DY. On the controllable soft-templating approach to mesoporous silicates. Chem Rev 2007;107:2821–60. [9] Yang PD, Zhao DY, Margolese DI, Chmelka BF, Stucky BF. Generalized syntheses of large-poremesoporous metal oxides with semicrystalline frameworks. Nature 1998;396:152–5. [10] Liang CD, Li ZJ, Dai S. Mesoporous carbon materials: synthesis and modification. Angew Chem Int Ed 2008;47:3696–717.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A high surface area nanocrystalline alumina with tailoring texture by mixed template Yongfeng Li, Jiaojiao Su, Jinghong Ma, Feng Yu, Ruifeng Li n College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
art ic l e i nf o
a b s t r a c t
Article history: Received 10 November 2014 Accepted 4 April 2015 Available online 17 April 2015
We report a facile synthesis of porous alumina (PA) which enables control of pore structure using a mixture of fatty alcohol polyoxyethylene ether (AEO-7) and poly (alkylene oxide) triblock copolymers (P123) as the template via an evaporation-induced self-assembly (EISA) pathway associated with thermal treatment. N2 adsorption–desorption results show that using over 80 wt% AEO-7, the obtained materials are super-microporous (pore size in the range of 1–2 nm), then if further decrease in the AEO-7 content will transform to mesopore (pore size 42 nm). When the mass fraction of P123 is less than 20 wt%, the material has a large surface area (more than 650 m2/g) and nanocrystalline phase is obtained at 400 1C. Even after calcination at 750 1C for 1 h, the sample of mass fraction 20 wt% P123 still exhibits a high specific area of 450 m2/g with large microporosity. & 2015 Elsevier B.V. All rights reserved.
Keywords: Porous materials Texture Nanocrystalline alumina Evaporation-induced self-assembly Super-microporous Large surface area
1. Introduction High surface area aluminas have enormous commercial importance as adsorbents and catalyst components in many chemical processes, including the petroleum refinement, the automobile emission control, and others [1–3]. The use of alumina can be ascribed to both high thermal stability and suitable surface acidic– basic properties as well as to the fact it is a rather inexpensive material. The catalytic properties of alumina largely depend on their crystalline structures and textural characteristics. Therefore, it is of great importance to obtain alumina with controllable pore structures. A series of mesoporous alumina materials have been successfully synthesized through the sol–gel process [1,2] or by utilizing the nano-casting method [4,5]. Considerable efforts have been invested in the synthesis of mesoporous alumina with surfactants as templates. When surfactants with small molecular weight are used as templates, smaller pore sizes (normally below 4 nm) of mesoporous metal oxides can be obtained. Alternatively, large molecular block copolymers are used to synthesize mesoporous materials with large pore size [2]. Supermicropores, first introduced by Dubinin [6], is defined as nanopores with pore sizes ranging from 1 nm to 2 nm. The materials in this pore size range are greatly important, since they bridge the gap between microporous zeolites and mesoporous materials and have potential applications such as in the size and shape selectivity catalysis for
n
Corresponding author. Tel./fax: þ 86 351 6010121. E-mail address: rfl[email protected] (R. Li).
http://dx.doi.org/10.1016/j.matlet.2015.04.018 0167-577X/& 2015 Elsevier B.V. All rights reserved.
special required molecules. But there are few reports about supermicroporous alumina, especially from super-micropores to mesopores. In the early work, the synthesis of super-microporous zirconia–alumina material was accomplished using low molecular weight nonionic surfactant AEO-7 as the template via the evaporation-induced self-assembly (EISA) pathway [7]. It seems to be the simplest and the fastest to get nanostructured supermicroporous metal oxide. Considering these facts, porous nanocrystalline structurecontrolled aluminas were prepared via the EISA method using mixed templating agents. More importantly, pore structures of these synthesized alumina range from super-micropore to mesopore and exhibit a high thermal stability, which is an excellent advantage in high-temperature catalytic reactions.
2. Experimental procedure In a typical synthesis, a mixture of X g of Pluronic P123 and (1.0 X) g of nonionic surfactant fatty alcohol polyoxyethylene ether (AEO-7) was dissolved in 20 mL of ethanol under magnetic stirring at 30 1C. Then 1.4 mL of 67 wt% nitric acid plus 0.7 g citric acid and 2.04 g (10 mmol) of aluminum iso-propoxide were added into the above solution with vigorous stirring. The resultant mixture was covered with PE film, stirred at 30 1C for about 6 h, and then put into a 60 1C drying oven to undergo the solvent evaporation process. Under these conditions, ethanol was gradually evaporated, and the final product was calcined at 400 1C (1 1C min 1 ramping rate) for 5 h in flowing air to remove the
166
Y. Li et al. / Materials Letters 153 (2015) 165–167
Fig. 1. N2 adsorption–desorption isotherms (A) with corresponding pore size distribution curves (B) of the PA-X samples calcined at 400 1C.
template. High-temperature treatment was carried out in air for 1 h with a temperature ramp of 10 1C/min. The as-synthesized materials were abbreviated as PA-X-T, where X and T represent the P123 mass and the final calcinated temperature, respectively. Powder X-ray diffraction patterns were recorded on a Shimadzu XRD-6000 diffractometer using Ni-filtered CuKα (0.154 nm) radiation. Transmission electron microscopy (TEM) experiments were performed on a JEOL 2011 microscope operated at 200 kV. The surface area was determined with a Quantachrome measuring instrument using the nitrogen gas adsorption–desorption technique at 196 1C. The surface areas were calculated by Brunauer– Emmett–Teller (BET) formula. Pore diameters were calculated by the density functional theory (DFT) method.
Table 1 BET and micropore surface areas for the PA-X samples calcined at different temperatures. Sample
SBET (m2/g)
t-Method micropore surface area (m2/g)
Pore volume (cm3/g)
PA-0-400 PA-0.1-400 PA-0.2-400 PA-0.3-400 PA-0.5-400 PA-0.7-400 PA-0.8-400 PA-0.2-750 PA-0.2-900 PA-0-750 PA-0-900
672 659 664 407 396 350 281 450 187 186 101
646 521 625 – – – – 351 57 – –
0.23 0.34 0.36 0.30 0.41 0.40 0.32 0.26 0.13 0.18 0.07
3. Results and discussion Fig. 1 shows the nitrogen adsorption–desorption isotherms of the samples of PA-X calcinated at 400 1C for 5 h in air. The isotherms of PA-X (X ¼0, 0.1, 0.2) are type I isotherms and do not show hysteresis in the desorption branch, indicating that the micropores are formed. Pore diameters were calculated by the DFT method, which produced values centered around 1.7 nm. Whereas the isotherms of the samples synthesized with higher content of P123 exhibit a large hysteresis loop, which are the typical characteristic of mesoporous materials, namely a type IV isotherm with H2-shaped hysteresis loop assigned to mesoporous structure. This suggests that the super-micropores transform to the mesopores with increasing P123 contents. It can be seen in Table 1 that, using a single agent AEO-7 (PA-0), the physisorption measurements reveal the largest BET surface area (672 m2/g) and a narrow pore size distribution centered at 1.7 nm pore diameter. The isotherm obtained using PA-0.2, yielded a surface area of 664 m2/g of which 625 m2/g in the form of micropores. The micropore distribution curve indicates that micropores are mostly between 1 and 2 nm in diameter. For samples PA-X calcined at the same temperature, the surface area has little influence with increasing P123 contents from 0 to 20 wt% but a decreased value was obtained for above 20 wt%. Therefore, PA-0 and PA-0.2 were selected to examine the physicochemical properties. The PA-0 and PA-0.2 samples were calcined at higher temperature to test its thermal stability. N2 adsorption isotherms (Fig. 2) of these calcined samples were recorded to reveal framework properties of the materials. After being calcined at 750 1C, type IV isotherms, which are typical for samples with mesopores, were
observed for the sample PA-0, whereas type I isotherms characteristic of adsorption in micropores were observed for the sample PA0.2. For sample PA-0.2, even if treated at 750 1C, the SBET of the sample had the high area of 450 m2/g, indicating a high thermal stability of the microporous structure, although their BET specific surface area, microporous surface areas and pore volume decrease gradually with the increases of temperature (Table 1). When transformed to γ-alumina after calcination at 900 1C, the surface area of the sample is still 188 m2/g, which is much higher than the sample synthesized with the only agent AEO-7 due to the presence of microporous structure. This further indicates that the mixed template method can remarkably increase the thermal stability. The large surface areas and appropriate pore volume associated with excellent thermal stability may improve the potential applications of these nanocrystalline porous alumina in many fields. Fig. 3 shows the wide-angle XRD patterns of PA-0.2 calcined at different temperatures. For the PA-0.2 calcined at 900 1C, several relatively weak diffraction peaks are observed, which can be indexed as the 220, 311, 222, 400, 511, 440 reflections of γ-alumina (JCPDS, 100425). In fact, PA-0 and PA-0.2 with crystalline structure is obtained at 400 1C, which can be further confirmed by the TEM analysis (Fig. S1). The electron diffraction patterns of the disordered wormholelike structure sample confirmed that the walls are polycrystalline, which are reflected by characteristic diffuse electron diffraction rings. Since such particles would be present as small crystallites of no more than 4 nm diameter, which are undetectable by XRD. It was reported that choosing longer alkyl chain surfactants, increasing the temperature of the hydrothermal treatment, using
Y. Li et al. / Materials Letters 153 (2015) 165–167
167
Fig. 2. N2 adsorption–desorption isotherms of the PA-0 (A) and PA-0.2 (B) samples calcined at different temperatures.
synthesized by the mixed template method in ethanol solvent. Tunable pore structures make the shape-selective catalysis become possible. For the sample PA-0.2, the sample exhibited a high specific area of 450 m2/g calcinated at 750 1C. Even after thermal treatment at 900 1C, the SBET of the sample had the high area of 188 m2/g, which is essential for further application. Our achievements provide new contributions to synthesize nanocrystalline alumina with tunable pore structures and high thermal stability, which may extend the applications in industry.
Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51172154) and the Shanxi Province Science Foundation for Youths (2013021008-3). Fig. 3. XRD patterns of PA-0.2 calcined at different temperatures.
Appendix A. Supporting information large molecular weight block copolymers as templates, or adding swelling agents can yield mesoporous silica materials with larger pore sizes [8]. Some of these strategies are suitable for the synthesis of mesoporous metal oxides. The commercially available PEO–PPO–PEO triblock copolymers were the first ones used for the synthesis of mesoporous metal oxides with stable mesostructures and large pore sizes [9]. In the case of this system, porous nanocrystalline alumina with tailorable pore structure has been synthesized successfully using a mixture of low molecular weight fatty alcohol polyoxyethylene ether (AEO-7) and poly (alkylene oxide) triblock copolymers P123 as the template. The pore sizes of mesoporous metal oxides templated by block copolymers are larger than those obtained with low molecular weight surfactants. Here, the P123 have the interaction with AEO-7 through the PEO part to form the compact micelles, which is the reason of change of pore structure [7,10]. The pore structure of the synthesized alumina could be turned from super-microporous to mesoporous range by increasing P123 contents. Our experimental results can be further confirmed by the nitrogen adsorption–desorption isotherms. 4. Conclusions Nanocrystalline aluminas with controlled pore properties by tailoring the amount of template AEO-7 used have been successfully
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.04.018. References [1] Cai WQ, Yu JG, Anand C, Vinu A, Jaroniec M. Facile synthesis of ordered mesoporous alumina and alumina-supported metal oxides with tailored adsorption and framework properties. Chem Mater 2011;23:1147–57. [2] Yuan Q, Yin AX, Luo C, Sun LD, Zhang YW, Duan WT, et al. Facile synthesis for ordered mesoporous γ-aluminas with high thermal stability. J Am Chem Soc 2008;130:3465–72. [3] Akarmazyan SS, Panagiotopoulou P, Kambolis A, Papadopoulou C, Kondarides DI. Methanol dehydration to dimethylether over Al2O3 catalysts. Appl Catal B: Environ 2014;145:136–48. [4] Liu Q, Wang A, Wang X, Zhang T. Ordered crystalline alumina molecular sieves synthesized via a nanocasting route. Chem Mater 2006;18:5153–5. [5] Wu ZX, Li QA, Feng D, Webley PA, Zhao DY. Ordered mesoporous crystalline γ-Al2O3 with variable architecture and porosity from a single hard template. J Am Chem Soc 2010;132:12042–50. [6] Dubinin MM. On physical feasibility of Bruauer's micropore analysis method. J Colloid Interface Sci 1974;46:351–6. [7] Li YF, Su JJ, Ma JH, Yu F, Pan DH, Li RF. A super-microporous zirconia–alumina nanomaterial with high thermal stability. Mater Lett 2014;136:183–6. [8] Wan Y, Zhao DY. On the controllable soft-templating approach to mesoporous silicates. Chem Rev 2007;107:2821–60. [9] Yang PD, Zhao DY, Margolese DI, Chmelka BF, Stucky BF. Generalized syntheses of large-poremesoporous metal oxides with semicrystalline frameworks. Nature 1998;396:152–5. [10] Liang CD, Li ZJ, Dai S. Mesoporous carbon materials: synthesis and modification. Angew Chem Int Ed 2008;47:3696–717.