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Submicron ZSM-5 synthesized by green and fast route
Materials Letters 196 (2017) 245–247
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Submicron ZSM-5 synthesized by green and fast route Feng Pan a, Xuchen Lu a,b,⇑, Tizhuang Wang a, Yan Yan a a b
State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences (CAS), Beijing 100190, PR China United Research Center for Resource and Materials, Wuhai 016000, PR China
a r t i c l e
i n f o
Article history: Received 29 June 2016 Received in revised form 7 February 2017 Accepted 11 March 2017 Available online 14 March 2017 Keywords: Porous materials Particles Natural clay Submicron ZSM-5 Crystal seeds Template free
a b s t r a c t Submicron ZSM-5 was fast synthesized from coal series kaolin without organic templates with the assistance of crystal seeds. The crystallization conditions (seeds amount and SiO2/Al2O3 molar ratio), the crystallization processes and the mechanism were investigated. The results clearly indicated that the crystallization time could be shortened to 6 h by adding crystal seeds, and the crystal size was effectively reduced to submicron grade. Crystallization process demonstrated that hexa-coordinated Al of leached metakaolin was totally converted to tetra-coordinated Al, involved in the formation of ZSM-5 skeleton with Si species in the form of Si (1Al) and Si (2Al). The crystallization process of sub-micron ZSM-5 synthesized from coal series kaolin also abode by the solution-mediated transport mechanism. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction As one of the most important zeolites, ZSM-5 has been broadly applied in many important catalytic reactions because of its unique pore structure and properties [1]. To realize the green synthesis and reduce the cost, some researchers have devoted to synthesizing highly crystalline ZSM-5 zeolite without any organic templates [2–4] or adopting the cheap raw materials [5–8]. However, the final products crystal size was usually over 5 lm. Moreover, to obtain highly crystalline ZSM-5, at least 24 h should be required at 190 °C. It is unfavorable for the large-scale industrial production. These disadvantages can be overcome by adding a small amount of seed crystals (ZSM-5, silicalite-1) in the TPA+free reaction mixture [9,10]. Nevertheless, the addition of crystal seed is usually adopted in the synthesis of nano ZSM-5. Generally, the synthesis of crystal seed requires organic template and a long time pretreatment at low temperature. Submicron-sized ZSM-5 crystals with uniform size are not only a potential industrial catalyst for important catalytic processes but also be regarded as the ideal model for the deep study of the sizedepended catalytic properties of zeolite [11]. However, only few documents were concerned on the synthesis of sub-micron ZSM5 [11,12].
Herein, this paper adopted the coal-series kaolin as raw materials, preparation of ZSM-5 as crystal seed, environmentally friendly and rapidly synthesized sub-micron ZSM-5. 2. Experimental section 2.1. Synthesis of submicron ZSM-5 Coal series kaolin was pretreated (named as precursor) and the crystal seeds were synthesized according to our previous work [5]. Then, the precursor was mechanically mixed with NaOH, water and 0–5.0 wt% crystal seeds by ball milling for 4.0 h (400 r/min). After that, the dispersion was left stand for 0–9 h in 50 ml stainless steel autoclave at 190 °C. At last, the samples were filtered, washed with deionized water, and dried. 2.2. Characterization Powder XRD patterns of the samples were recorded by a PANalytical X’pert diffractometer with CuKa radiation. The relative crystallinity could be calculated as follows [13]:
Relative ⇑ Corresponding author at: No. 1 Bei-er-tiao, Zhong-guan-cun, Haidian District, Beijing 100190, China. E-mail addresses: [email protected] (F. Pan), [email protected] (X. Lu). http://dx.doi.org/10.1016/j.matlet.2017.03.060 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Crystallinity ð%Þ ¼
peak areas of product peak areas of reference sample ð1Þ
Morphology was characterized by field-emission scanning electron microscopy (SEM) (JEM-7001F, JEOL, Japan).
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F. Pan et al. / Materials Letters 196 (2017) 245–247
FT-IR spectra were recorded on an ALPHA FT-IR spectrometer (Bruker, Germany) using dried KBr disk technique, in the range of 400–4000 cm1. 29 Si and 27Al MAS-NMR spectroscopy was performed at room temperature using a Bruker Advance III 400 spectrometer operated at 104.0 MHz for 27Al and 79.3 MHz for 29Si. The recycle delay was 1.0 s for 27Al and 2.0 s for 29Si. The pulse duration (or pulse width) was 1.0 ms for 27Al and the contact time was 5.0 ms for 29Si. 3. Results and discussions 3.1. Effect of crystal seeds content To investigate the influence of the crystal seeds amount on the crystallization kinetics, 0–5.0 wt% ZSM-5 crystal seeds that synthesized from coal series kaolin without organic template were added into the dispersion. In the present study, the chemical composition of the initial system was 1SiO2–0.223NaOH–0.026Al2O3–35.5H2O. As illustrated in the crystallization curves (Fig. 1), the content of crystal seeds dramatically influenced the growth kinetics. For instance, highly crystalline ZSM-5 obtained only within 6 h when 5.0 wt% seed was used, while the amount of seed decreased to 0.5 wt% resulted in a longer crystallization time (12 h). In an obvious contrast, it needed as long as 24 h to obtain highly crystalline samples without adding seeds. Thus, the addition of seeds was deemed necessary to reduce the crystallization time by serving as nuclei and/or promoting nucleation through dissolving into the gel [14]. 3.2. Relationship between SiO2/Al2O3 and the morphology The tendency towards changing the morphology with the change of SiO2/Al2O3 could be seen from the SEM photographs (Fig. 2). Sample (a) with SiO2/Al2O3 25.68 exhibited spindle type with crystal size ca.1 um. In contrast, sample (b) with SiO2/Al2O3 31.39 showed brick type with coarse surface. It was interesting to note that the crystals exhibited hexagonal sheet structure with smooth surface when SiO2/Al2O3 ratio was 37.74–41.96. As reported by Wang [15,16], in order to obtain the primary building units for nucleation and crystal growth, the Al–O and Si–O layers of kaolin should dissolve into the gel firstly. However, the Al–O layers were much easier to dissolve than the Si–O layers [16]. In addition, it was difficult for kaolin to form homogeneous phase due to its insolubility, this situation caused the concentration of active alu-
Fig. 1. Crystal growth curves of ZSM-5 synthesized with different content of crystal seeds.
Fig. 2. SEM of the obtained samples with (a) SiO2/Al2O3 = 25.68; (b) SiO2/ Al2O3 = 31.39; (c) SiO2/Al2O3 = 37.74; (d) SiO2/Al2O3 = 41.96.
minosilicate species were relatively low. So, the nucleation rates were different among the precursors with different SiO2/Al2O3 ratio. The SiO2/Al2O3 ratio affected the process of crystallization as well as influenced the properties of the composition [17,18]. Thus, different morphology could be formed as the SiO2/Al2O3 ratio changed. From the foregoing experimental details, it could be concluded that different SiO2/Al2O3 ratios influenced the rate of dissolution and nucleation, and the orientation of crystal growth. Consequently, ZSM-5 with different morphology could be obtained. 3.3. Crystallization process and mechanism According to the XRD patterns (Fig. 3 a), only a broad and flat diffraction band at 2h = 15–38° could be observed for the initial
Fig. 3. (a) XRD patterns, (b) IR spectra and morphology evolution of the synthesized samples (c) 1 h, (d) 3 h, (e) 6 h, (f) 9 h.
F. Pan et al. / Materials Letters 196 (2017) 245–247
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seeds dissolved and provided nucleus; (3) the raw material gradually dissolved into the system, grew into ZSM-5 crystals round the nucleus and hydrous Na+. Therefore, the crystallization process of submicron ZSM-5 form coal series kaolin also abode by the solution-mediated transformation mechanism. 4. Conclusions
Fig. 4.
27
Al (a) and
29
Si (b) MAS NMR spectra of the representative samples.
sample, indicating the sample was amorphous phase. After hydrothermal treated for 2 h, the characteristic diffraction peaks of ZSM-5 at 2h = 7–9°, 22–25° began to appear (JCPDS Card no. 00-037-0361), and a band at 550 cm1 that belongs to the fivemembered ring emerged in the IR spectra (Fig. 3 b). When prolonged the crystallization time to 6 h, the amorphous aluminosilicates completely converted to highly crystalline ZSM-5, it was proved by the intensively characteristic diffraction peaks and uniform morphology in the SEM images (Fig. 3 c). Two resonance peaks at 50 ppm and 0 ppm could be observed in 27Al NMR spectra for the initial sample (Fig. 4 a), which were assigned to tetrahedrally coordinated aluminium in framework and octahedral non-framework aluminium, respectively [19]. The resonance peak of 27Al NMR at around 0 ppm disappeared gradually as the extension of hydrothermal treatment, demonstrating that octahedral non-framework Al translateded into tetracoordinated Al of ZSM-5. To obtain specific anuminosilicate zeolites with high crystallinity, Si species should coordinate with Al according to a certain way. For ZSM-5, Si species can combine with Al species in the manner of (Si(OAl)4-n(OSi)n, n = 0–4). A major peak at 100 ppm with a shoulder centered at 110 ppm could be seen in the spectrum of initial material, corresponding to Si atoms in Si (1Al) and Si (0Al) configurations [20,21], respectively. A new shoulder centered at 98 ppm was assigned to Si(2Al) peak appeared after hydrothermal treated 6 h [22]. Furthermore, the peak at 110 ppm gradually shifted to 105 ppm which belonged to Si (OSi)3(OAl) [23], demonstrating that monosilicates (Si0) coordinated with tetra-coordinated Al after hydrothermal treatment. Therefore, 29Si NMR spectrum indicated that almost all the Si species were incorporated into the framework in the form of Si (1Al) and Si (2Al) groups after crystallization for 6 h at 190 °C. Based on above characterized results and our previous researches [6,15], the crystallization process of submicron ZSM-5 synthesized from coal series kaolin can be summarized as follows: (1) activation of coal series kaolin by calcination; (2) the crystal
In summary, a facile, rapid and low-cost approach was proposed for the synthesis of submicron ZSM-5 without organic template from natural clay. The current study showed that submicron ZSM-5 with highly crystalline could be obtained within 6 h by introducing crystal seeds. 29Si- and 27Al-MAS NMR results indicated that Al could be successively incorporated into the framework and coordinated with Si in the form of Si (1Al) and Si (2Al) groups. The crystallization process of sub-micron ZSM-5 synthesized from coal series kaolin included dissolution, nucleation, crystallization stages. The crystallization mechanism abode by the solution-mediated transport mechanism. Acknowledgement The authors would like to thank Wuhai Tian-yu Chemical Hightech Co. Ltd. (China) for the financial and raw materials assistance. References [1] Y. Adewuyi, D. Klocke, J. Buchanan, Appl. Catal. A 131 (1995) 121–133. [2] H. Pan, Q. Pan, Y. Zhao, Y. Luo, X. Shu, M. He, Ind. Eng. Chem. Res. 49 (2010) 7294–7302. [3] N. Ren, J. Bronic, B. Subotic, X.C. Lv, Z.J. Yang, Y. Tang, Microporous Mesoporous Mater. 139 (2011) 197–206. [4] X. Huang, R. Zhang, Z. Wang, Chin. J. Catal. 33 (2012) 1290–1298. [5] F. Pan, X. Lu, Y. Wang, S. Chen, T. Wang, Y. Yan, Microporous Mesoporous Mater. 184 (2014) 134–140. [6] F. Pan, X. Lu, Y. Wang, S. Chen, T. Wang, Y. Yan, Mater. Lett. 115 (2014) 5–8. [7] S.M. Holmes, S.H. Khoo, A.S. Kovo, Green Chem. 13 (2011) 1152–1154. [8] H. Feng, C. Li, H. Shan, Catal. Lett. 129 (2009) 71–78. [9] G. Majano, A. Darwiche, S. Mintova, V. Valtchev, Ind. Eng. Chem. Res. 48 (2009) 7084–7091. [10] N. Ren, J. Bronic´, T.A. Jelic´, A. Palcˇic´, B. Subotic´, Cryst. Growth Des. 12 (2012) 1736–1745. [11] N. Ren, Z.J. Yang, X.C. Lv, J. Shi, Y.H. Zhang, Y. Tang, Microporous Mesoporous Mater. 131 (2010) 103–114. [12] N. Ren, J. Bronic´, B. Subotic´, X.-C. Lv, Z.-J. Yang, Y. Tang, Microporous Mesoporous Mater. 139 (2011) 197–206. [13] J. Gu, Y. Jin, Y. Zhou, M. Zhang, Y. Wu, J. Wang, Journal of Materials Chemistry A 1 (2013) 2453–2460. [14] F. Xu, M. Dong, W. Gou, J. Li, Z. Qin, J. Wang, W. Fan, Microporous Mesoporous Mater. 163 (2012) 192–200. [15] T. Wang, X. Lu, Y. Yan, Microporous Mesoporous Mater. 136 (2010) 138–147. [16] T. Wang, X. Lu, Y. Yan, Microporous Mesoporous Mater. 168 (2013) 155–163. [17] S. Bhat, P. Niphadkar, T. Gaydhankar, S. Awate, A. Belhekar, P. Joshi, Microporous Mesoporous Mater. 76 (2004) 81–89. [18] O. Larlus, V.P. Valtchev, Chem. Mater. 16 (2004) 3381–3389. [19] W. Guo, C. Xiong, L. Huang, Q. Li, J. Mater. Chem. 11 (2001) 1886–1890. [20] R. Ryoo, J.M. Kim, Journal of the chemical society, Chem. Commun. (1995) 711–712. [21] A. Steel, S.W. Carr, M.W. Anderson, Chem. Mater. 7 (1995) 1829–1832. [22] W. Chang, C.-H. Lee, M.Y. Kim, B.J. Ahn, J. Ind. Eng. Chem.-Seoul 7 (2001) 121– 125. [23] G. Woolery, G. Kuehl, H. Timken, A. Chester, J. Vartuli, Zeolites 19 (1997) 288– 296.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Submicron ZSM-5 synthesized by green and fast route Feng Pan a, Xuchen Lu a,b,⇑, Tizhuang Wang a, Yan Yan a a b
State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences (CAS), Beijing 100190, PR China United Research Center for Resource and Materials, Wuhai 016000, PR China
a r t i c l e
i n f o
Article history: Received 29 June 2016 Received in revised form 7 February 2017 Accepted 11 March 2017 Available online 14 March 2017 Keywords: Porous materials Particles Natural clay Submicron ZSM-5 Crystal seeds Template free
a b s t r a c t Submicron ZSM-5 was fast synthesized from coal series kaolin without organic templates with the assistance of crystal seeds. The crystallization conditions (seeds amount and SiO2/Al2O3 molar ratio), the crystallization processes and the mechanism were investigated. The results clearly indicated that the crystallization time could be shortened to 6 h by adding crystal seeds, and the crystal size was effectively reduced to submicron grade. Crystallization process demonstrated that hexa-coordinated Al of leached metakaolin was totally converted to tetra-coordinated Al, involved in the formation of ZSM-5 skeleton with Si species in the form of Si (1Al) and Si (2Al). The crystallization process of sub-micron ZSM-5 synthesized from coal series kaolin also abode by the solution-mediated transport mechanism. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction As one of the most important zeolites, ZSM-5 has been broadly applied in many important catalytic reactions because of its unique pore structure and properties [1]. To realize the green synthesis and reduce the cost, some researchers have devoted to synthesizing highly crystalline ZSM-5 zeolite without any organic templates [2–4] or adopting the cheap raw materials [5–8]. However, the final products crystal size was usually over 5 lm. Moreover, to obtain highly crystalline ZSM-5, at least 24 h should be required at 190 °C. It is unfavorable for the large-scale industrial production. These disadvantages can be overcome by adding a small amount of seed crystals (ZSM-5, silicalite-1) in the TPA+free reaction mixture [9,10]. Nevertheless, the addition of crystal seed is usually adopted in the synthesis of nano ZSM-5. Generally, the synthesis of crystal seed requires organic template and a long time pretreatment at low temperature. Submicron-sized ZSM-5 crystals with uniform size are not only a potential industrial catalyst for important catalytic processes but also be regarded as the ideal model for the deep study of the sizedepended catalytic properties of zeolite [11]. However, only few documents were concerned on the synthesis of sub-micron ZSM5 [11,12].
Herein, this paper adopted the coal-series kaolin as raw materials, preparation of ZSM-5 as crystal seed, environmentally friendly and rapidly synthesized sub-micron ZSM-5. 2. Experimental section 2.1. Synthesis of submicron ZSM-5 Coal series kaolin was pretreated (named as precursor) and the crystal seeds were synthesized according to our previous work [5]. Then, the precursor was mechanically mixed with NaOH, water and 0–5.0 wt% crystal seeds by ball milling for 4.0 h (400 r/min). After that, the dispersion was left stand for 0–9 h in 50 ml stainless steel autoclave at 190 °C. At last, the samples were filtered, washed with deionized water, and dried. 2.2. Characterization Powder XRD patterns of the samples were recorded by a PANalytical X’pert diffractometer with CuKa radiation. The relative crystallinity could be calculated as follows [13]:
Relative ⇑ Corresponding author at: No. 1 Bei-er-tiao, Zhong-guan-cun, Haidian District, Beijing 100190, China. E-mail addresses: [email protected] (F. Pan), [email protected] (X. Lu). http://dx.doi.org/10.1016/j.matlet.2017.03.060 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Crystallinity ð%Þ ¼
peak areas of product peak areas of reference sample ð1Þ
Morphology was characterized by field-emission scanning electron microscopy (SEM) (JEM-7001F, JEOL, Japan).
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F. Pan et al. / Materials Letters 196 (2017) 245–247
FT-IR spectra were recorded on an ALPHA FT-IR spectrometer (Bruker, Germany) using dried KBr disk technique, in the range of 400–4000 cm1. 29 Si and 27Al MAS-NMR spectroscopy was performed at room temperature using a Bruker Advance III 400 spectrometer operated at 104.0 MHz for 27Al and 79.3 MHz for 29Si. The recycle delay was 1.0 s for 27Al and 2.0 s for 29Si. The pulse duration (or pulse width) was 1.0 ms for 27Al and the contact time was 5.0 ms for 29Si. 3. Results and discussions 3.1. Effect of crystal seeds content To investigate the influence of the crystal seeds amount on the crystallization kinetics, 0–5.0 wt% ZSM-5 crystal seeds that synthesized from coal series kaolin without organic template were added into the dispersion. In the present study, the chemical composition of the initial system was 1SiO2–0.223NaOH–0.026Al2O3–35.5H2O. As illustrated in the crystallization curves (Fig. 1), the content of crystal seeds dramatically influenced the growth kinetics. For instance, highly crystalline ZSM-5 obtained only within 6 h when 5.0 wt% seed was used, while the amount of seed decreased to 0.5 wt% resulted in a longer crystallization time (12 h). In an obvious contrast, it needed as long as 24 h to obtain highly crystalline samples without adding seeds. Thus, the addition of seeds was deemed necessary to reduce the crystallization time by serving as nuclei and/or promoting nucleation through dissolving into the gel [14]. 3.2. Relationship between SiO2/Al2O3 and the morphology The tendency towards changing the morphology with the change of SiO2/Al2O3 could be seen from the SEM photographs (Fig. 2). Sample (a) with SiO2/Al2O3 25.68 exhibited spindle type with crystal size ca.1 um. In contrast, sample (b) with SiO2/Al2O3 31.39 showed brick type with coarse surface. It was interesting to note that the crystals exhibited hexagonal sheet structure with smooth surface when SiO2/Al2O3 ratio was 37.74–41.96. As reported by Wang [15,16], in order to obtain the primary building units for nucleation and crystal growth, the Al–O and Si–O layers of kaolin should dissolve into the gel firstly. However, the Al–O layers were much easier to dissolve than the Si–O layers [16]. In addition, it was difficult for kaolin to form homogeneous phase due to its insolubility, this situation caused the concentration of active alu-
Fig. 1. Crystal growth curves of ZSM-5 synthesized with different content of crystal seeds.
Fig. 2. SEM of the obtained samples with (a) SiO2/Al2O3 = 25.68; (b) SiO2/ Al2O3 = 31.39; (c) SiO2/Al2O3 = 37.74; (d) SiO2/Al2O3 = 41.96.
minosilicate species were relatively low. So, the nucleation rates were different among the precursors with different SiO2/Al2O3 ratio. The SiO2/Al2O3 ratio affected the process of crystallization as well as influenced the properties of the composition [17,18]. Thus, different morphology could be formed as the SiO2/Al2O3 ratio changed. From the foregoing experimental details, it could be concluded that different SiO2/Al2O3 ratios influenced the rate of dissolution and nucleation, and the orientation of crystal growth. Consequently, ZSM-5 with different morphology could be obtained. 3.3. Crystallization process and mechanism According to the XRD patterns (Fig. 3 a), only a broad and flat diffraction band at 2h = 15–38° could be observed for the initial
Fig. 3. (a) XRD patterns, (b) IR spectra and morphology evolution of the synthesized samples (c) 1 h, (d) 3 h, (e) 6 h, (f) 9 h.
F. Pan et al. / Materials Letters 196 (2017) 245–247
247
seeds dissolved and provided nucleus; (3) the raw material gradually dissolved into the system, grew into ZSM-5 crystals round the nucleus and hydrous Na+. Therefore, the crystallization process of submicron ZSM-5 form coal series kaolin also abode by the solution-mediated transformation mechanism. 4. Conclusions
Fig. 4.
27
Al (a) and
29
Si (b) MAS NMR spectra of the representative samples.
sample, indicating the sample was amorphous phase. After hydrothermal treated for 2 h, the characteristic diffraction peaks of ZSM-5 at 2h = 7–9°, 22–25° began to appear (JCPDS Card no. 00-037-0361), and a band at 550 cm1 that belongs to the fivemembered ring emerged in the IR spectra (Fig. 3 b). When prolonged the crystallization time to 6 h, the amorphous aluminosilicates completely converted to highly crystalline ZSM-5, it was proved by the intensively characteristic diffraction peaks and uniform morphology in the SEM images (Fig. 3 c). Two resonance peaks at 50 ppm and 0 ppm could be observed in 27Al NMR spectra for the initial sample (Fig. 4 a), which were assigned to tetrahedrally coordinated aluminium in framework and octahedral non-framework aluminium, respectively [19]. The resonance peak of 27Al NMR at around 0 ppm disappeared gradually as the extension of hydrothermal treatment, demonstrating that octahedral non-framework Al translateded into tetracoordinated Al of ZSM-5. To obtain specific anuminosilicate zeolites with high crystallinity, Si species should coordinate with Al according to a certain way. For ZSM-5, Si species can combine with Al species in the manner of (Si(OAl)4-n(OSi)n, n = 0–4). A major peak at 100 ppm with a shoulder centered at 110 ppm could be seen in the spectrum of initial material, corresponding to Si atoms in Si (1Al) and Si (0Al) configurations [20,21], respectively. A new shoulder centered at 98 ppm was assigned to Si(2Al) peak appeared after hydrothermal treated 6 h [22]. Furthermore, the peak at 110 ppm gradually shifted to 105 ppm which belonged to Si (OSi)3(OAl) [23], demonstrating that monosilicates (Si0) coordinated with tetra-coordinated Al after hydrothermal treatment. Therefore, 29Si NMR spectrum indicated that almost all the Si species were incorporated into the framework in the form of Si (1Al) and Si (2Al) groups after crystallization for 6 h at 190 °C. Based on above characterized results and our previous researches [6,15], the crystallization process of submicron ZSM-5 synthesized from coal series kaolin can be summarized as follows: (1) activation of coal series kaolin by calcination; (2) the crystal
In summary, a facile, rapid and low-cost approach was proposed for the synthesis of submicron ZSM-5 without organic template from natural clay. The current study showed that submicron ZSM-5 with highly crystalline could be obtained within 6 h by introducing crystal seeds. 29Si- and 27Al-MAS NMR results indicated that Al could be successively incorporated into the framework and coordinated with Si in the form of Si (1Al) and Si (2Al) groups. The crystallization process of sub-micron ZSM-5 synthesized from coal series kaolin included dissolution, nucleation, crystallization stages. The crystallization mechanism abode by the solution-mediated transport mechanism. Acknowledgement The authors would like to thank Wuhai Tian-yu Chemical Hightech Co. Ltd. (China) for the financial and raw materials assistance. References [1] Y. Adewuyi, D. Klocke, J. Buchanan, Appl. Catal. A 131 (1995) 121–133. [2] H. Pan, Q. Pan, Y. Zhao, Y. Luo, X. Shu, M. He, Ind. Eng. Chem. Res. 49 (2010) 7294–7302. [3] N. Ren, J. Bronic, B. Subotic, X.C. Lv, Z.J. Yang, Y. Tang, Microporous Mesoporous Mater. 139 (2011) 197–206. [4] X. Huang, R. Zhang, Z. Wang, Chin. J. Catal. 33 (2012) 1290–1298. [5] F. Pan, X. Lu, Y. Wang, S. Chen, T. Wang, Y. Yan, Microporous Mesoporous Mater. 184 (2014) 134–140. [6] F. Pan, X. Lu, Y. Wang, S. Chen, T. Wang, Y. Yan, Mater. Lett. 115 (2014) 5–8. [7] S.M. Holmes, S.H. Khoo, A.S. Kovo, Green Chem. 13 (2011) 1152–1154. [8] H. Feng, C. Li, H. Shan, Catal. Lett. 129 (2009) 71–78. [9] G. Majano, A. Darwiche, S. Mintova, V. Valtchev, Ind. Eng. Chem. Res. 48 (2009) 7084–7091. [10] N. Ren, J. Bronic´, T.A. Jelic´, A. Palcˇic´, B. Subotic´, Cryst. Growth Des. 12 (2012) 1736–1745. [11] N. Ren, Z.J. Yang, X.C. Lv, J. Shi, Y.H. Zhang, Y. Tang, Microporous Mesoporous Mater. 131 (2010) 103–114. [12] N. Ren, J. Bronic´, B. Subotic´, X.-C. Lv, Z.-J. Yang, Y. Tang, Microporous Mesoporous Mater. 139 (2011) 197–206. [13] J. Gu, Y. Jin, Y. Zhou, M. Zhang, Y. Wu, J. Wang, Journal of Materials Chemistry A 1 (2013) 2453–2460. [14] F. Xu, M. Dong, W. Gou, J. Li, Z. Qin, J. Wang, W. Fan, Microporous Mesoporous Mater. 163 (2012) 192–200. [15] T. Wang, X. Lu, Y. Yan, Microporous Mesoporous Mater. 136 (2010) 138–147. [16] T. Wang, X. Lu, Y. Yan, Microporous Mesoporous Mater. 168 (2013) 155–163. [17] S. Bhat, P. Niphadkar, T. Gaydhankar, S. Awate, A. Belhekar, P. Joshi, Microporous Mesoporous Mater. 76 (2004) 81–89. [18] O. Larlus, V.P. Valtchev, Chem. Mater. 16 (2004) 3381–3389. [19] W. Guo, C. Xiong, L. Huang, Q. Li, J. Mater. Chem. 11 (2001) 1886–1890. [20] R. Ryoo, J.M. Kim, Journal of the chemical society, Chem. Commun. (1995) 711–712. [21] A. Steel, S.W. Carr, M.W. Anderson, Chem. Mater. 7 (1995) 1829–1832. [22] W. Chang, C.-H. Lee, M.Y. Kim, B.J. Ahn, J. Ind. Eng. Chem.-Seoul 7 (2001) 121– 125. [23] G. Woolery, G. Kuehl, H. Timken, A. Chester, J. Vartuli, Zeolites 19 (1997) 288– 296.