- Email: [email protected]
One-step synthesis of hierarchical Zn-ZSM-11 via a facile ZnO route
Materials Letters 124 (2014) 204–207
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
One-step synthesis of hierarchical Zn-ZSM-11 via a facile ZnO route Qingjun Yu a, Yang Li a, Xiaojing Meng a, Qiukai Cui b, Chunyi Li a,n a b
State Key Laboratory of Heavy Oil Processing, Department of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, China Dagang Petrochemical Company, PetroChina Corporation, Tianjin 300280, China
art ic l e i nf o
a b s t r a c t
Article history: Received 31 October 2013 Accepted 15 March 2014 Available online 20 March 2014
Zn containing ZSM-11 is of great importance for producing aromatics. Herein we report a facile route for synthesizing hierarchical Zn-ZSM-11 with olive-shaped intergrowth morphology by using ZnO as zinc source. This material exhibits excellent mesoporous properties and remarkably enhanced Lewis acid amount. More importantly, this sample shows good catalytic activity for methanol conversion. & 2014 Elsevier B.V. All rights reserved.
Keywords: Zn-ZSM-11 ZnO Hierarchical Olive-shape Porous materials Crystal structure
Zn containing ZSM-11 zeolites have been viewed as efficient catalysts for dehydrogenation-aromatization of alkane [1] and decomposition of low-density polyethylene [2]. Generally, Zn species can be incorporated into the zeolite phase by post-treatment methods of ionexchange and impregnation [1,2]. However, obvious disadvantages exist like the poor dispersion of Zn species on the outer surface of crystals and complex preparation procedure. By contrast, the direct synthesis method of incorporating metal ions into the zeolite phase during the crystallization process seems to be more ideal for its simplification to obtain well-dispersed and stable metal species in the zeolite framework. In most cases, ammonia was used to react with zinc nitrate to obtain the soluble [Zn(NH3)4]2þ to participate in the formation of zeolite framework. For instance, the Zn containing ZSM-5 zeolites have been successfully synthesized by introducing [Zn(NH3)4]2þ aqueous solution into the ZSM-5 gel precursors [3,4]. Here, we developed a very facile and convenient route to synthesize Zn-ZSM-11 with hierarchical structure by adding ZnO into a TBA þ –Si– Al gel precursor. To the best of our knowledge, this is the first report on the synthesis of Zn containing zeolite by using ZnO as Zn source.
of silica sol, tetrabutyl ammonium bromide and deionized water. Then a bit of calcinated ZSM-11 seeds (5%) prepared in the literature [5] were introduced to accelerate the crystallization process, followed by addition of ZnO powder. After vigorous stirring for 2 h, the seeded mixture with molar composition of 12.0Na2O:1.0Al2O3:4.0ZnO:65SiO2:1.5(TBA)2O:1300 H2O was transferred into autoclaves for hydrothermal treatment at 170 1C. The obtained solid (designated as ZnZ11) was washed, filtered, dried and calcinated in air at 550 1C for 3 h. For comparison, pure ZSM-11 (Z11) was synthesized from the system without ZnO, while Zn/Z11 was prepared by impregnating Z11 with zinc nitrate solution followed by calcination at 550 1C for 2 h. The samples were characterized by X-ray diffraction patterns on the X’Pert PRO MPD (DANalytical Co.) diffractometer, thermogravimetry (TG) and differential thermal analysis (DTA) (NETZSCH Proteus STA449C), scanning electron microscopy (S-4800), transmission electron microscopy (JEM-2100UHR), X-ray fluorescence spectroscopy (Axios Advanced X-ray Spectrometer), 27Al and 29Si nuclear magnetic resonance (Bruker AV-400), nitrogen adsorption-desorption (Quantachrome) and infrared spectra for pyridine adsorption (Nicolet Co., USA).
2. Experimental
3. Results and discussion
In a typical run, aluminum sulfate and sodium hydroxide were dissolved in deionized water, followed by addition of the mixture
Fig. 1a shows XRD patterns evolution of ZnO containing system with time. Evidently, ZnO is gradually dissolved under severe alkaline hydrothermal environment and well crystallized ZSM-11 structure is obtained after 12 h. These results indicate that Zn species have been well incorporated into the zeolite crystals during the crystallization
1. Introduction
n
Corresponding author. Tel.: þ 86 532 86981862. E-mail address: [email protected] (C. Li).
http://dx.doi.org/10.1016/j.matlet.2014.03.075 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Q. Yu et al. / Materials Letters 124 (2014) 204–207
205
Fig. 1. XRD peaks evolution of ZnO containing system with crystallization time (a) and TG-DTA curves (b) of Z11 and ZnZ11. Table 1 Physicochemical properties and catalytic activity of ZSM-11 and Zn-ZSM-11 samples. Sample R.C. (%) XRD IR(I550/I450) Pore characterization Smicro (m2/g) Sext (m2/g) Vmicro (cm3/g) Vmeso (cm3/g) Acidity (mmol/g) B acid L acid Conv. (wt%) Selectivity (C-mol%) C01–4 C2H4 C3H6 C4H8 C5þ Selectivity of BTX in gasoline (wt%)
Z11
ZnZ11
Zn/Z11
100 0.87
62.6 0.84
91.0 0.86
340.7 72.3 0.14 0.10
250.0 60.3 0.10 0.12
304.0 47.4 0.13 0.08
0.147 0.134 99.90
0.088 0.294 99.40
0.094 0.393 98.21
12.34 10.58 24.30 14.42 8.51 36.83
9.39 11.39 28.60 15.83 7.79 50.62
9.14 9.95 26.58 15.38 7.56 45.18
process, either in the form of dispersing on the crystal outer surface or being incorporated into the zeolitic framework. The crystallinity, as assessed by both XRD and FTIR techniques, is listed in Table 1. The IR bands 550/450 cm 1 (I550/I450) ratio, which can be used to estimate the crystallinity of pentasil zeolite structure, is larger than 0.7, suggesting that ZSM-11 framework is well crystallized [2]. However, the XRD-R.C. of ZnZ11 is only 62.5%. Generally, XRD peak intensity reflects the relative content of a certain phase in the whole sample. Therefore, as Zn is introduced, the intensity of ZSM-11 peaks decreases as a result of dilution effect, resulting in a lower XRD-R.C. value. For instance, the Zn/Z11 sample containing 7.3% Zn has the XRD-R.C. value of 91.0%, in accordance with the dilution of ZSM-11 phase by Zn species. By contrast, the sample ZnZ11 with the similar Zn content (XRF) shows a much lower XRD-R.C. value. These results demonstrate that Zn species might have been incorporated into zeolitic framework, and therefore generate some defects, leading to the decreased XRD peak intensity. Fig. 2(a,c) shows the SEM images of Zn-ZSM-11 prepared by different methods. Evidently, no ZnO clusters are observed in Zn/Z11, indicating that Zn species are well dispersed on the ZSM-11 particles. Different from spherical morphology of Z11, ZnZ11 exhibits an olive-shaped intergrowth morphology. Taking into account the significant role of TBA þ in determining the morphology of product zeolite [6], it can be deduced that the Zn species existing in the gel
might have interaction with the template and finally affect the morphology of ZnZ11. This postulation can be confirmed by the TG-DTA curves in Fig. 1b. For Z11, main weight loss assigned to the combustion of template appears at 400–500 1C. However, additional weight loss and exothermic peak are observed at 300– 400 1C in ZnZ11, which might be attributed to the combustion of carbonaceous organic species formed by Zn species interacting with template. TEM images are used to illustrate the fine structure of Zn-ZSM-11 samples. As shown in Fig. 2d, obvious nanoparticles are observed in Zn/Z11, which are ascribed to ZnO clusters formed after the calcination of Zn(NO3)2 impregnated Z11. By contrast, ZnZ11 reveals clear lattice fringes with no nanoparticles (Fig. 2b), further indicating that Zn species are incorporated into the ZSM-11 framework rather than disperse on the external surface. In order to confirm the influence of Zn species on the textural properties of zeolite, the calcinated ZnZ11 is tested by nitrogen adsorption–desorption experiment. Table 1 gives the detailed surface area and pore volume of ZSM-11 with and without Zn species. After Zn is introduced by impregnation method, the sample Zn/Z11 shows a slight decrease in both micropore surface area (Smicro) and volume (Vmicro) due to the dilution effect. By contrast, the external surface area (Sext) and mesopore volume (Vmeso) are smaller than the theoretical calculated data (Table S1), which can be resulted from the dispersion of ZnO nanoparticles on the outer surface of ZSM-11 crystals. Compared with Zn/Z11, sample ZnZ11 directly synthesized from the ZnO–gel presents much smaller Smicro and Vmicro, which might be ascribed to the occupation of Zn species in the framework. The micropore size distribution gives a powerful proof for this inference. As shown in Fig. 3A, both Z11 and Zn/Z11 exhibit a mode pore diameter of about 0.54 nm, while ZnZ11 presents a smaller micropore size of about 0.48 nm. In spite of the weaker micropore properties, ZnZ11 presents evidently enhanced mesoporous properties than Zn/Z11, especially a largest mesopore volume of 0.12 cm3/g and this can be attributed to the special morphology caused by Zn incorporation. 29 Si MAS NMR spectra are taken to clarify the influence of Zn incorporation on the coordination of Si species in zeolite frameworks. As shown in Fig. 3B, both Z11 and Zn/Z11 show the similar four peaks in the range of 116 to 103 ppm, which are assigned to the nonequivalent framework T sites corresponding to Si(0Al) groupings ( 112 and 116 ppm) and Si(1Al) groupings ( 107 and 103 ppm), respectively. However, two additional signals centered at 99 and 96 ppm are also observed in ZnZ11, which can be attributed to Si(2Al) and Si(3Al) sites [7]. It has been reported that Zn is incorporated as a counter ion, so two Al are required in a nearly geometrical neighborhood to interact with one Zn [1]. Consequently, more Si(2Al) and Si(3Al) sites will be formed as Zn
206
Q. Yu et al. / Materials Letters 124 (2014) 204–207
Fig. 2. SEM and TEM images of ZSM-11 and Zn-ZSM-11 zeolites: (a,b) ZnZ11; (c,d) Zn/Z11.
Fig. 3. Micropore size distribution (A), (c) Zn/Z11.
29
Si MAS NMR spectra (B) and Py-IR (C) of ZSM-11 and ZnZSM-11 samples prepared by different methods: (a) Z11; (b) ZnZ11;
species are incorporated into the framework of ZSM-11. Besides, the interaction between Zn and Al species also causes the decrease in Brønsted acid site amount (Fig. 3C) [3]. Conversely, the Lewis acid amount shows a significant increase as a result of new Lewis acid sites generated by zinc incorporation, which can be observed in the new signal at 1616 cm 1 and double bands at 1450 cm 1 [2]. Compared with ZnZ11, the sample Zn/Z11 prepared by impregnation method also exhibits decreased Brønsted acid amount and increased Lewis acid amount. However, both types of acid amount are smaller than that of ZnZ11. Encouraged by the superior mesopore properties and acidity of ZnZ11 prepared from the ZnO containing gel precursor, the catalytic behavior of ZnZ11 is evaluated in the conversion of methanol (450 1C, 5.53 h 1, Table 1). Notably, as Zn is introduced into zeolite phase, both ZnZ11 and Zn/Z11 showed remarkably
enhanced light olefin and BTX selectivity compared with Z11, which can be ascribed to the decreased Brønsted acid amount [8] and Zn species, respectively. Furthermore, ZnZ11 presents evident higher conversion and better selectivity to light olefins and BTX than Zn/Z11. This phenomenon could be explained in that ZnZ11 possesses superior mesopore properties than Zn/Z11, which does a favor to the diffusion of products and inhibit their further transform into vice products [3].
4. Conclusion In conclusion, a novel and very facile ZnO route has been firstly applied to prepare Zn containing ZSM-11 materials with good mesoporous properties. This material possesses olive-shaped
Q. Yu et al. / Materials Letters 124 (2014) 204–207
intergrowth morphology and much enhanced Lewis acid amount than pure ZSM-11. The characterizations on this sample demonstrate that the Zn species can be well incorporated into the ZSM-11 framework during the crystallization process. What's more, this material exhibited good catalytic activity for methanol conversion. Acknowledgments This work is supported by both the National 973 Program of China (No. 2012CB215006) and the Fundamental Research Funds for the Central Universities (No. 2472012039A). Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2014.03.075. References [1] Anunziata OA, Cussa J, Beltramone AR. Simultaneous optimization of methane conversion and aromatic yields by catalytic activation with ethane over ZnZSM-11 zeolite: the influence of the Zn-loading factor. Catal Today 2011;171: 36–42.
207
[2] Lerici LC, Renzini MS, Sedran U, Pierella LB. Tertiary recycling of low-density polyethylene by catalytic cracking over ZSM-11 and BETA zeolites modified with Zn2 þ : stability study. Energy Fuels 2013;27:2202–8. [3] Ni Y, Sun A, Wu X, Hai G, Hu J, Li T, et al. The preparation of nano-sized H [Zn, Al] ZSM-5 zeolite and its application in the aromatization of methanol. Micro Meso Mater 2011;143:435–42. [4] Wang L, Sang S, Meng S, Zhang Y, Qi Y, Liu Z. Direct synthesis of Zn-ZSM-5 with novel morphology. Mater Lett 2007;61:1675–8. [5] Yu Q, Cui C, Zhang Q, Chen J, Li Y, Sun J, et al. Hierarchical ZSM-11 with intergrowth structures: synthesis, characterization and catalytic properties. J Energy Chem 2013;22:761–8. [6] Wang J, Groen JC, Yue W, Zhou W, Coppens M-O. Single-template synthesis of zeolite ZSM-5 composites with tunable mesoporosity. Chem Commun 2007:4653–5. [7] Dě deček Ji, Sklenak S, Li C, Wichterlová B, Gábová V, Ji Brus, et al. Effect of Al Si Al and Al Si Si Al pairs in the ZSM-5 zeolite framework on the 27Al NMR spectra. A combined high-resolution 27Al NMR and DFT/MM study. J Phys Chem C 2009;113:1447–58. [8] Mei C, Wen P, Liu Z, Liu H, Wang Y, Yang W, et al. Selective production of propylene from methanol: mesoporosity development in high silica HZSM-5. J Catal 2008;258:243–9.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
One-step synthesis of hierarchical Zn-ZSM-11 via a facile ZnO route Qingjun Yu a, Yang Li a, Xiaojing Meng a, Qiukai Cui b, Chunyi Li a,n a b
State Key Laboratory of Heavy Oil Processing, Department of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, China Dagang Petrochemical Company, PetroChina Corporation, Tianjin 300280, China
art ic l e i nf o
a b s t r a c t
Article history: Received 31 October 2013 Accepted 15 March 2014 Available online 20 March 2014
Zn containing ZSM-11 is of great importance for producing aromatics. Herein we report a facile route for synthesizing hierarchical Zn-ZSM-11 with olive-shaped intergrowth morphology by using ZnO as zinc source. This material exhibits excellent mesoporous properties and remarkably enhanced Lewis acid amount. More importantly, this sample shows good catalytic activity for methanol conversion. & 2014 Elsevier B.V. All rights reserved.
Keywords: Zn-ZSM-11 ZnO Hierarchical Olive-shape Porous materials Crystal structure
Zn containing ZSM-11 zeolites have been viewed as efficient catalysts for dehydrogenation-aromatization of alkane [1] and decomposition of low-density polyethylene [2]. Generally, Zn species can be incorporated into the zeolite phase by post-treatment methods of ionexchange and impregnation [1,2]. However, obvious disadvantages exist like the poor dispersion of Zn species on the outer surface of crystals and complex preparation procedure. By contrast, the direct synthesis method of incorporating metal ions into the zeolite phase during the crystallization process seems to be more ideal for its simplification to obtain well-dispersed and stable metal species in the zeolite framework. In most cases, ammonia was used to react with zinc nitrate to obtain the soluble [Zn(NH3)4]2þ to participate in the formation of zeolite framework. For instance, the Zn containing ZSM-5 zeolites have been successfully synthesized by introducing [Zn(NH3)4]2þ aqueous solution into the ZSM-5 gel precursors [3,4]. Here, we developed a very facile and convenient route to synthesize Zn-ZSM-11 with hierarchical structure by adding ZnO into a TBA þ –Si– Al gel precursor. To the best of our knowledge, this is the first report on the synthesis of Zn containing zeolite by using ZnO as Zn source.
of silica sol, tetrabutyl ammonium bromide and deionized water. Then a bit of calcinated ZSM-11 seeds (5%) prepared in the literature [5] were introduced to accelerate the crystallization process, followed by addition of ZnO powder. After vigorous stirring for 2 h, the seeded mixture with molar composition of 12.0Na2O:1.0Al2O3:4.0ZnO:65SiO2:1.5(TBA)2O:1300 H2O was transferred into autoclaves for hydrothermal treatment at 170 1C. The obtained solid (designated as ZnZ11) was washed, filtered, dried and calcinated in air at 550 1C for 3 h. For comparison, pure ZSM-11 (Z11) was synthesized from the system without ZnO, while Zn/Z11 was prepared by impregnating Z11 with zinc nitrate solution followed by calcination at 550 1C for 2 h. The samples were characterized by X-ray diffraction patterns on the X’Pert PRO MPD (DANalytical Co.) diffractometer, thermogravimetry (TG) and differential thermal analysis (DTA) (NETZSCH Proteus STA449C), scanning electron microscopy (S-4800), transmission electron microscopy (JEM-2100UHR), X-ray fluorescence spectroscopy (Axios Advanced X-ray Spectrometer), 27Al and 29Si nuclear magnetic resonance (Bruker AV-400), nitrogen adsorption-desorption (Quantachrome) and infrared spectra for pyridine adsorption (Nicolet Co., USA).
2. Experimental
3. Results and discussion
In a typical run, aluminum sulfate and sodium hydroxide were dissolved in deionized water, followed by addition of the mixture
Fig. 1a shows XRD patterns evolution of ZnO containing system with time. Evidently, ZnO is gradually dissolved under severe alkaline hydrothermal environment and well crystallized ZSM-11 structure is obtained after 12 h. These results indicate that Zn species have been well incorporated into the zeolite crystals during the crystallization
1. Introduction
n
Corresponding author. Tel.: þ 86 532 86981862. E-mail address: [email protected] (C. Li).
http://dx.doi.org/10.1016/j.matlet.2014.03.075 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Q. Yu et al. / Materials Letters 124 (2014) 204–207
205
Fig. 1. XRD peaks evolution of ZnO containing system with crystallization time (a) and TG-DTA curves (b) of Z11 and ZnZ11. Table 1 Physicochemical properties and catalytic activity of ZSM-11 and Zn-ZSM-11 samples. Sample R.C. (%) XRD IR(I550/I450) Pore characterization Smicro (m2/g) Sext (m2/g) Vmicro (cm3/g) Vmeso (cm3/g) Acidity (mmol/g) B acid L acid Conv. (wt%) Selectivity (C-mol%) C01–4 C2H4 C3H6 C4H8 C5þ Selectivity of BTX in gasoline (wt%)
Z11
ZnZ11
Zn/Z11
100 0.87
62.6 0.84
91.0 0.86
340.7 72.3 0.14 0.10
250.0 60.3 0.10 0.12
304.0 47.4 0.13 0.08
0.147 0.134 99.90
0.088 0.294 99.40
0.094 0.393 98.21
12.34 10.58 24.30 14.42 8.51 36.83
9.39 11.39 28.60 15.83 7.79 50.62
9.14 9.95 26.58 15.38 7.56 45.18
process, either in the form of dispersing on the crystal outer surface or being incorporated into the zeolitic framework. The crystallinity, as assessed by both XRD and FTIR techniques, is listed in Table 1. The IR bands 550/450 cm 1 (I550/I450) ratio, which can be used to estimate the crystallinity of pentasil zeolite structure, is larger than 0.7, suggesting that ZSM-11 framework is well crystallized [2]. However, the XRD-R.C. of ZnZ11 is only 62.5%. Generally, XRD peak intensity reflects the relative content of a certain phase in the whole sample. Therefore, as Zn is introduced, the intensity of ZSM-11 peaks decreases as a result of dilution effect, resulting in a lower XRD-R.C. value. For instance, the Zn/Z11 sample containing 7.3% Zn has the XRD-R.C. value of 91.0%, in accordance with the dilution of ZSM-11 phase by Zn species. By contrast, the sample ZnZ11 with the similar Zn content (XRF) shows a much lower XRD-R.C. value. These results demonstrate that Zn species might have been incorporated into zeolitic framework, and therefore generate some defects, leading to the decreased XRD peak intensity. Fig. 2(a,c) shows the SEM images of Zn-ZSM-11 prepared by different methods. Evidently, no ZnO clusters are observed in Zn/Z11, indicating that Zn species are well dispersed on the ZSM-11 particles. Different from spherical morphology of Z11, ZnZ11 exhibits an olive-shaped intergrowth morphology. Taking into account the significant role of TBA þ in determining the morphology of product zeolite [6], it can be deduced that the Zn species existing in the gel
might have interaction with the template and finally affect the morphology of ZnZ11. This postulation can be confirmed by the TG-DTA curves in Fig. 1b. For Z11, main weight loss assigned to the combustion of template appears at 400–500 1C. However, additional weight loss and exothermic peak are observed at 300– 400 1C in ZnZ11, which might be attributed to the combustion of carbonaceous organic species formed by Zn species interacting with template. TEM images are used to illustrate the fine structure of Zn-ZSM-11 samples. As shown in Fig. 2d, obvious nanoparticles are observed in Zn/Z11, which are ascribed to ZnO clusters formed after the calcination of Zn(NO3)2 impregnated Z11. By contrast, ZnZ11 reveals clear lattice fringes with no nanoparticles (Fig. 2b), further indicating that Zn species are incorporated into the ZSM-11 framework rather than disperse on the external surface. In order to confirm the influence of Zn species on the textural properties of zeolite, the calcinated ZnZ11 is tested by nitrogen adsorption–desorption experiment. Table 1 gives the detailed surface area and pore volume of ZSM-11 with and without Zn species. After Zn is introduced by impregnation method, the sample Zn/Z11 shows a slight decrease in both micropore surface area (Smicro) and volume (Vmicro) due to the dilution effect. By contrast, the external surface area (Sext) and mesopore volume (Vmeso) are smaller than the theoretical calculated data (Table S1), which can be resulted from the dispersion of ZnO nanoparticles on the outer surface of ZSM-11 crystals. Compared with Zn/Z11, sample ZnZ11 directly synthesized from the ZnO–gel presents much smaller Smicro and Vmicro, which might be ascribed to the occupation of Zn species in the framework. The micropore size distribution gives a powerful proof for this inference. As shown in Fig. 3A, both Z11 and Zn/Z11 exhibit a mode pore diameter of about 0.54 nm, while ZnZ11 presents a smaller micropore size of about 0.48 nm. In spite of the weaker micropore properties, ZnZ11 presents evidently enhanced mesoporous properties than Zn/Z11, especially a largest mesopore volume of 0.12 cm3/g and this can be attributed to the special morphology caused by Zn incorporation. 29 Si MAS NMR spectra are taken to clarify the influence of Zn incorporation on the coordination of Si species in zeolite frameworks. As shown in Fig. 3B, both Z11 and Zn/Z11 show the similar four peaks in the range of 116 to 103 ppm, which are assigned to the nonequivalent framework T sites corresponding to Si(0Al) groupings ( 112 and 116 ppm) and Si(1Al) groupings ( 107 and 103 ppm), respectively. However, two additional signals centered at 99 and 96 ppm are also observed in ZnZ11, which can be attributed to Si(2Al) and Si(3Al) sites [7]. It has been reported that Zn is incorporated as a counter ion, so two Al are required in a nearly geometrical neighborhood to interact with one Zn [1]. Consequently, more Si(2Al) and Si(3Al) sites will be formed as Zn
206
Q. Yu et al. / Materials Letters 124 (2014) 204–207
Fig. 2. SEM and TEM images of ZSM-11 and Zn-ZSM-11 zeolites: (a,b) ZnZ11; (c,d) Zn/Z11.
Fig. 3. Micropore size distribution (A), (c) Zn/Z11.
29
Si MAS NMR spectra (B) and Py-IR (C) of ZSM-11 and ZnZSM-11 samples prepared by different methods: (a) Z11; (b) ZnZ11;
species are incorporated into the framework of ZSM-11. Besides, the interaction between Zn and Al species also causes the decrease in Brønsted acid site amount (Fig. 3C) [3]. Conversely, the Lewis acid amount shows a significant increase as a result of new Lewis acid sites generated by zinc incorporation, which can be observed in the new signal at 1616 cm 1 and double bands at 1450 cm 1 [2]. Compared with ZnZ11, the sample Zn/Z11 prepared by impregnation method also exhibits decreased Brønsted acid amount and increased Lewis acid amount. However, both types of acid amount are smaller than that of ZnZ11. Encouraged by the superior mesopore properties and acidity of ZnZ11 prepared from the ZnO containing gel precursor, the catalytic behavior of ZnZ11 is evaluated in the conversion of methanol (450 1C, 5.53 h 1, Table 1). Notably, as Zn is introduced into zeolite phase, both ZnZ11 and Zn/Z11 showed remarkably
enhanced light olefin and BTX selectivity compared with Z11, which can be ascribed to the decreased Brønsted acid amount [8] and Zn species, respectively. Furthermore, ZnZ11 presents evident higher conversion and better selectivity to light olefins and BTX than Zn/Z11. This phenomenon could be explained in that ZnZ11 possesses superior mesopore properties than Zn/Z11, which does a favor to the diffusion of products and inhibit their further transform into vice products [3].
4. Conclusion In conclusion, a novel and very facile ZnO route has been firstly applied to prepare Zn containing ZSM-11 materials with good mesoporous properties. This material possesses olive-shaped
Q. Yu et al. / Materials Letters 124 (2014) 204–207
intergrowth morphology and much enhanced Lewis acid amount than pure ZSM-11. The characterizations on this sample demonstrate that the Zn species can be well incorporated into the ZSM-11 framework during the crystallization process. What's more, this material exhibited good catalytic activity for methanol conversion. Acknowledgments This work is supported by both the National 973 Program of China (No. 2012CB215006) and the Fundamental Research Funds for the Central Universities (No. 2472012039A). Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2014.03.075. References [1] Anunziata OA, Cussa J, Beltramone AR. Simultaneous optimization of methane conversion and aromatic yields by catalytic activation with ethane over ZnZSM-11 zeolite: the influence of the Zn-loading factor. Catal Today 2011;171: 36–42.
207
[2] Lerici LC, Renzini MS, Sedran U, Pierella LB. Tertiary recycling of low-density polyethylene by catalytic cracking over ZSM-11 and BETA zeolites modified with Zn2 þ : stability study. Energy Fuels 2013;27:2202–8. [3] Ni Y, Sun A, Wu X, Hai G, Hu J, Li T, et al. The preparation of nano-sized H [Zn, Al] ZSM-5 zeolite and its application in the aromatization of methanol. Micro Meso Mater 2011;143:435–42. [4] Wang L, Sang S, Meng S, Zhang Y, Qi Y, Liu Z. Direct synthesis of Zn-ZSM-5 with novel morphology. Mater Lett 2007;61:1675–8. [5] Yu Q, Cui C, Zhang Q, Chen J, Li Y, Sun J, et al. Hierarchical ZSM-11 with intergrowth structures: synthesis, characterization and catalytic properties. J Energy Chem 2013;22:761–8. [6] Wang J, Groen JC, Yue W, Zhou W, Coppens M-O. Single-template synthesis of zeolite ZSM-5 composites with tunable mesoporosity. Chem Commun 2007:4653–5. [7] Dě deček Ji, Sklenak S, Li C, Wichterlová B, Gábová V, Ji Brus, et al. Effect of Al Si Al and Al Si Si Al pairs in the ZSM-5 zeolite framework on the 27Al NMR spectra. A combined high-resolution 27Al NMR and DFT/MM study. J Phys Chem C 2009;113:1447–58. [8] Mei C, Wen P, Liu Z, Liu H, Wang Y, Yang W, et al. Selective production of propylene from methanol: mesoporosity development in high silica HZSM-5. J Catal 2008;258:243–9.