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Synthesis of zeolite omega by magadiite conversion method and an insight into the changes of medium-range structure during the crystallization Tianming Lv, Shoulei Zhang, Zhe Feng, Fushi Wang, Shaoqing Zhang, Jiqi Zheng, Xin Liu, Changgong Meng, and Yu Wang Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 02 Jun 2017 Downloaded from http://pubs.acs.org on June 6, 2017
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Synthesis of zeolite omega by magadiite conversion method and an insight into the changes of medium-range structure during the crystallization Tianming Lv, Shoulei Zhang, Zhe Feng, Fushi Wang, Shaoqing Zhang, Jiqi Zheng, Xin Liu, Changgong Meng, Yu Wang* School of Chemistry, Dalian University of Technology, Dalian 116024, China. Abstract Zeolite omega has been synthesized directly in the presence of tetramethylammonium ions (TMA+) by magadiite conversion method. Using the reactive gel composition: 20 SiO2: Al2O3: 3.6 Na2O: 180 H2O: 0.96 TMABr, pure and high crystalline zeolite omega could be obtained at 100 oC for 72 h. It is found that most of long-range order structure of magadiite was retained, despite that part of it was collapsed, as its primary structure during the crystallization process. Meanwhile, the crystallization behaviour and changes of medium-range structure in the synthesis were characterized. The growth of zeolite omega occurs on the surface of magadiite and 4-membered rings probably from the connection by 5-membered rings are formed after 10 h. The Al atoms prefer to occupy the position in 6-membered rings of gmelinite in zeolite omega. The influence of reaction time, temperature and composition in starting gel was examined.
Fig. 1 X-ray powder diffraction patterns of samples
Fig. 6 Raman spectra of the samples
Fig. 5 IR spectra of the samples
Fig. 8 27Al MAS NMR spectrum of the samples
Yu Wang, E-mail:
[email protected] Address: P.O.Box288, No.2 Linggong Road, Ganjingzi District, Dalian City, Liaoning Province, P.R.C., 1160024. Tel: +86-411-84708545
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Synthesis of zeolite omega by magadiite conversion method and an insight into the changes of medium-range structure during the crystallization Tianming Lv, Shoulei Zhang, Zhe Feng, Shaoqing Zhang, Jiqi Zheng, Xiaoyu Liu, Xin Liu, Changgong Meng, Yu Wang*
School of Chemistry, Dalian University of Technology, Dalian 116024, China.
E-mail:
[email protected]
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Abstract Zeolite omega has been synthesized directly in the presence of tetramethylammonium ions (TMA+) by magadiite conversion method. Using the reactive gel composition: 20 SiO2: Al2O3: 3.6 Na2O: 180 H2O: 0.96 TMABr, pure and high crystalline zeolite omega could be obtained at 100 oC for 72 h. It is found that most of long-range order structure of magadiite was retained, despite that part of it was collapsed, as its primary structure during the crystallization process. Meanwhile, the crystallization behaviour and changes of medium-range structure in the synthesis were characterized. The growth of zeolite omega occurs on the surface of magadiite and 4-membered rings probably from the connection by 5-membered rings are formed after 10 h. The Al atoms prefer to occupy the position in 6-membered rings of gmelinite in zeolite omega. The influence of reaction time, temperature and composition in starting gel was examined.
1. Introduction Zeolite omega, the synthetic counterpart of the natural mineral mazzite, was firstly prepared by Union Carbide at the end of the sixties 1-3. Its framework is composed of columns of gmelinite cages bridged by oxygen atoms arranged to give a 12-membered cylindrical main channel and a small pore, consisting of 8-membered rings, along the crystallographic c axis 4-6. After this disclosure above, zeolite omega has attracted a lot of
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research interests used as a catalyst in aromatic alkylation 3, 7, hydrocracking 8, gas-oil cracking 9 and paraffin isomerization 10.
In general, zeolite omega is synthesized in hydrothermal system containing tetramethylammonium cations (TMA+), which appears to be powerful structure-directing agents (SDAs), at temperature around 80-150 oC by transformation of aluminosilicate hydrogel 11. Fajula’s group 12 obtained pure zeolite omega in Na2O-SiO2-Al2O3-TMA2O-H2O system at 100 oC for 15 d or 135 oC for 1 d. According to the research reported by Shiralkar’s group, the Ga-substituted zeolite omega was also successfully prepared in the presence of TMA+ 13. Meanwhile, zeolite omega can also be synthesized in the presence of p-dioxane 14, glycerol 15, 16, piperazine 17 or choline 18. In addition, Honda et al. 19 reported the interzeolite conversion of FAU and BEA-type zeolites into MAZ-type zeolites driving by seed crystals. At the same year, zeolite omega was also obtained using seed-directed method by Okubo’s group 20.
Recrystallization of layered silicate, like magadiite, into zeolite has drawn a lot of attention because of the scientific research and industrial application. In 1987, ZSM-5 and ZSM-11 were synthesized by Jacobs and Martens 21. Since then, FER, FU-1 and some other types of zeolites were obtained by using magadiite conversion method in the presence of piperidine, hexametonium or other organic SDAs 22-24. Adopting this method, Mn-silicate-1 was obtained from Mn2+ ion-exchanged magadiite 25. In our previous 3
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studies, several types of zeolites such as MOR 26, MFI 27, FER 27, 28, OFF 29 and MAZ 30 were prepared from magadiite using various SDAs such as cyclohexylamine, 1, 6hexamethylenediamine, ethylenediamine, tetramethylammon bromine and glycerol. In addition, zeolite L was synthesized successfully without using organic SDAs and the changes of medium-range structure in the course of crystallization of zeolite L were discussed 19. The details of the influence of short-chain tetraalkylammonium cations on the crystallization of zeolite using magadiite as the starting material were also proposed by our group 31.
The efficient synthesis of zeolites can be realized by understanding the crystallization mechanisms. Many groups devote to exploit the mechanisms of synthesizing of zeolites 32, 33
. But so far, there are some problems which have not been fully understood during
crystallization process. In the past decades, several papers described the changes of medium-range structure during zeolite crystallization using vibrational and NMR technologies which are powerful tools to explore the development of crystallization 34-38. Using Raman spectroscopy, Xiong et al. have proposed that the formation of zeolite X may experience these steps: 4-membered rings (4Rs) connect with each other via 6-membered rings (6Rs) to form SOD cages and then SOD cages interconnect via double 6-membered rings (D6Rs) to form the framework of zeolite X 39. Similarly, the formation mechanisms of zeolite Y 35, 40, ZSM-5 35, zeolite A 34 are also be proposed. Using magadiite as starting materials could give rise to a fast crystallization rate and a high 4
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selectivity to a particular zeolite in the conversion process. So studying the changes of medium-range structure of conversion of magadiite would help to exploit the mechanisms of zeolites.
It is the aim of the present work to elaborate the conversion of magadiite into zeolite omega in a TMA+ system in details. Particularly effort was devoted to the characterization of the products obtained at different reaction time in order to gain more insight into the changes of medium-range structure of the conversion process, the crystallization behaviour and the location of the SDA during the crystallization of the zeolite omega. Additionally, the influences of reaction time, substrate composition and reaction temperature sequence upon the crystallization of zeolite omega were also discussed.
2. Experimental 2.1 Synthesis of magadiite According to the method described in literature 41, magadiite was prepared from colloidal silica (30 wt % SiO2). From a suspension containing SiO2, H2O and NaOH with molar ratios of H2O/SiO2 = 18.5 and NaOH/SiO2 = 0.23, magadiite could be obtained after a reaction time of 48 h at 150 oC in a Teflon-lined autoclave. After cooling at room temperature, magadiite was collected by filtration, washing with deionized water until neutrality and drying at 100 oC overnight. 5
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2.2 Conversion of magadiite into zeolite omega
The synthesis of zeolite omega was achieved in alkaline media, using tetramethylammonium bromide (TMABr) as SDA, sodium aluminate as Al source and magadiite as starting materials. The specific procedures are described as follows: Firstly, sodium aluminate and sodium hydroxide were mixed with deionized water to obtain a clear solution, and then TMABr was added into the prepared solution. Finally, magadiite was slowly added to the clear solution under vigorous stirring to form a gel. The molar composition of the reaction mixture was x SiO2: Al2O3: y Na2O: 180 H2O: z TMABr. The homogenous solution was transferred to a stainless-steel autoclave and subjected to crystallization treatment for different reaction time in a convection oven under autogenous pressure and static conditions. After crystallization, the product was collected by filtration, washing with deionized water till pH = 7-8 and drying at 70 oC overnight. For comparison, the starting gel using colloidal silica (30% SiO2) as Si source was also prepared.
2.3 Characterization The power X-ray diffraction (XRD) patterns of the solid product were determined by a Panalytical X’Pert powder diffractometer with CuKα radiation from 2θ = 3-50° at a scanning speed of 8o min-1. The relative fraction of zeolite omega (X %) was evaluated from the areas ratios of selected peaks of the XRD diffractograms. 6
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X % = Ao/(Ao + Am)×100 % Where, Ao is the area of peaks of XRD diffractogram of zeolite omega, Am is the area of peaks of XRD diffractogram of magadiite.
The crystal sizes and morphologies were studied using a QUANTA450 scanning electron microscopy (SEM) at a 30 kV accelerating voltage. Fourier transform infrared (FTIR) analysis of the solid product was achieved on a Nicolet 6700 FTIR spectrometer over the spectral region from 400-1200 cm-1 with a resolution of 4 cm-1 using the KBr disc technique. Raman spectra were collected using a Thermo Scientific Spectrometry with a 532 nm excitation line. Thermoanalytical analyses (TG and DTA) were performed using a Mettler-Toledo SDTA 851 from 50 to 800 oC at a heating rate of 10 oC min-1 in air. The SiO2/Al2O3 of the solid product was determined by Inductively Coupled Plasma mass spectrometer (ICP, Optima2000DV, Perkin Elmer). 27Al MAS NMR spectra were recorded at 156.4 MHz, a pluse length of 0.5 µs and a recycle delay of 1 s and 1000 scans on a Bruker AVANCE III 600 spectrometer. Al(NO3)3 was used as an external reference for the measure of the chemical shifts.
3. Results and discussion 3.1 Influence of time and the changes of medium-range structure during the crystallization
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Table 1 lists the initial gel composition and characteristics of the products. Fig. 1 shows XRD patterns of starting materials magadiite and the product samples withdrawn at various time of synthesis zeolite omega from magadiite at 100 oC with the molar composition: 20 SiO2: Al2O3: 3.6 Na2O: 180 H2O: 0.96 TMABr. Fig. 1(a) represents the XRD pattern of magadiite (Run no. 1, Table 1). All the reflections are typical of magadiite and reveal that the product is free from impurities. When reaction time is prolonged to 9 h as shown in Fig. 1(b), the product is still magadiite (Run no. 2, Table 1), but the degree of crystallinity decreases compared to the initial reactant, implied parts of structure of magadiite was collapsed. The evolution of the relative fraction of zeolite omega (X %), which presents the conversion ratio of magadiite into zeolite omega, is represented in Fig. 2. It can be found that X % increases progressively with time goes by and the curve exhibits a sigmoidal nature, indicating different rates of conversion of magadiite at different synthesis time. Combining Fig. 1 and Fig. 2, we propose that the first 9 h with low reaction rate is corresponding to nucleation of zeolite omega. This is followed by the rapid formation of the crystalline structure found in Fig. 2, which is consistent to the results shown in Fig. 1. The characteristic peaks corresponding to zeolite omega initially appear at the heating time of 10 h with the X % only 8.54 (Fig. 1(c), Run no. 3, Table 1). In general, the long-range order of magadiite is destroyed and it would decompose into amorphous phase during the conversion of magadiite 30, 38. But in this work, it is worth mentioning that most of the long-range order of magadiite was still 8
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retained and transformed into zeolite omega little by little. As the reaction time was increased to 17 h (Fig. 1(d), Run no. 4, Table 1), the percentage of the amount of zeolite omega increased rapidly reaching to 41.35 %. We can see that most of the diffraction peaks of the product belong to zeolite omega. By calculating, X % is 62.38 after 24 h (Run no. 5, Table 1). Lastly, it can be found that the rate of the conversion decreases as the process approaches completion in Fig. 2. The proportion of amount of zeolite omega in product obtained at 48 h is 86.15 % (Run no. 6, Table 1). When the reaction time was prolonged to 70 h (Fig. 1(e), Run no. 9, Table 1), only little magadiite existed in the solid product. At the heating time of 72 h, the high crystallization and pure zeolite omega (X % = 100) could be obtained (Fig. 1(f), Run no. 7, Table 1). Upon heating 360 h, no alteration was observed from the XRD patterns (Fig. 1(g), Run no. 10, Table 1). To clarify the advantage of the synthesis of zeolite omega using magadiite conversion method, we also attempted to synthesize zeolite omega from colloidal silica (Run no. 11, Table 1). But the amorphous only can be obtained, which indicates the advantage and uniqueness of magadiite conversion method for the preparation of pure and highly crystallized zeolite omega.
Fig. 3 presents the SEM images of the starting magadiite and the crystals at different stages of their development, which help us to study the evolution of morphology of the crystallization. As shown in Fig. 3(a), the magadiite as-synthesized is in the form of uniform rosette-like shape with diameter of 10 µm. After 10 h, the layered structure of 9
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magadiite still exists, but the diameter of it only 6µm and some changes happened that amounts of small spherical crystals appear on the surface of magadiite, indicating zeolite omega begins to grow. Upon heating for 17 h, the amount of crystalline zeolite omega with spherical shape increases and the structure of magadiite is destroyed in some degree but the layered structure does not disappear. As the reaction time goes by, the amount of zeolite omega increases in place of magadiite. We can hardly observe the existent of magadiite at 70 h. Up on heating for 72 h, it can be observed that the zeolite omega is micrometer sizes and formed as aggregates in spherical structure which are consistent with the description in previous literatures 14. The morphology of zeolite omega did not change when reaction time prolong to 360 h. These results prove again most of long-range order structure of magadiite was retained, despite that part of it was collapsed, as its primary structure during the crystallization process and indicate that the zeolite omega nucleates on the surface of magadiite and then grows progressively 12. This property that zeolite omega are formed basing on the structure of magadiite helps us to explore the changes of medium-range structure efficiently during the crystallization.
Vibrational spectroscopy, such as infrared (IR) and Raman spectra, can provide valuable structural information including the framework connectivity, T-O-T band angles and the size of the ring systems formed by TO4 tetrahedra in zeolite 42. What’s more, the internal vibrational of the framework TO4 tetrahedron is insensitive to variations in framework structure. But the vibrations related to external linkages between tetrahedra 10
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are sensitive to the framework structure and some secondary building units (SBUs) 43. The combination of the two kinds of spectroscopies is particularly appropriate since the two techniques are often complementary and have different selection rules, which have been utilized to deduce the zeolite dynamics and structure 44, 45. Fig. 4 shows the IR and Raman spectra of magadiite as-synthesized. According to the previous literatures 46, 47, the peaks at 1237 cm-1 and 618 cm-1 in the IR spectrum (Fig. 4(a)) are characteristic of the five-membered rings (5Rs) and 6Rs in the structure, respectively. The appearance of strong band at 465 cm-1 in Raman spectrum (Fig. 4(b)) is assigned to the T-O-T bands 44. The IR and Raman spectra of the samples crystallized for 10 h, 17 h, 70 h and 72 h are presented in Fig. 5 and Fig. 6, respectively. Fig. 5(A)(a) shows the IR spectrum of sample crystallized for 10 h, in which the peaks of zeolite omega initially appear, with bands at 460, 618, 783, 818, 1098 and 1487 cm-1. According to the previous reports, the band at 460 cm-1 is assigned to the T-O bending mode 43. And the band at 818 cm-1 is attributed to the internal tetrahedral oxygen bridges Si-O-Al (Fig. 5(A)(a)) 38, implying that Al atoms have taken part in the framework of zeolite omega, which will be proved again in more details in following contents. The weak band at 1487 cm-1 could be ascribed to CH2 deformation vibration (Fig. 5(A)(a)) 48, indicating that TMA+ interacts with the framework of zeolite omega after 10 h, which also revealed the formation of zeolite omega consistence with the result shown in Fig. 1(c). Some significant changes in the Raman spectra are observed after 10 h, compared to the spectrum of magadiite, as shown 11
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in Fig. 6(a). The sample spectrum exhibits bands at 496, 465 and 370 cm-1, which are characteristic for 4Rs, T-O-T bands and 5Rs, respectively 45. The appearance of 4Rs proves once more that zeolite omega begins to grow. With prolonged crystallization time from 17 h to 70 h (Fig. 5(A)(b) - (c)), the intensity of the double band at 818 cm-1 associated with Si-O-Al increases but the other at 783 cm-1 corresponding to the internal tetrahedral oxygen bridges Si-O-Si decreases, indicating that more and more Al atoms take part in the framework of zeolite omega, which also can be demonstrated by the results of ICP shown in Table 2. But there are some differences that the intensity of the double bands at 818 cm-1 and 783 cm-1 all decrease when continue to prolong reaction time to 72 h, the relative content of Al decrease which was proved by ICP result shown in Table 2. Fig. 5(B) shows the height strength ratios of the bands at 818 cm-1 and 783 cm-1 as a function of time. It is clear that the band at 818 cm-1 increases obviously than that of the band at 783 cm-1 during the crystallization process, indicating that the number of Si-O-Al is on the increase. So it can be seen that the Si/Al ratio of products decreases gradually with the development of the reaction time from the ICP results shown in Table 2. Flanigen reported the concentration of Al changed in zeolite will cause the shift of peak corresponding to T-O band 49. So the changes of the number of Al atoms per unit cell for zeolite omega result in the peak at 1098 cm-1 (Fig. 5(A)(a)), attributed to the asymmetric stretching mode of T-O band, becoming broaden and shifting towards lower wavenumber (1056 cm-1) (Fig. 5(A)(c)) and then shifting to 1082 cm-1 (Fig. 5(A)(d)). In 12
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addition, the peak at 618 cm-1, attributed to 6Rs in magadiite, still exist in the spectra (Fig. 5(A)). According to the work being done by Xiao 45, during the crystallization of zeolite X, the band at 520 cm-1 associated with 4Rs basically remains unchanged, but the band at 390 cm-1 associated with 6Rs increases extensively in Raman spectra. Then they suggest that the growth of zeolite X is accompanied by the formation of 6Rs, possibly from the connection of 4Rs. The similar results appear in this work, in Raman spectra as shown in Fig. 6, the peak at 496 cm-1 increases progressively with the reaction time goes by, and finally 496 cm-1 becomes the major peak in pure zeolite omega which possesses major 4Rs. Another peak at 370 cm-1 in Fig. 6 assigned to 5Rs has few changes, and only becomes narrower and sharper. So we proposed that crystallization of zeolite omega is accompanied by the formation of 4Rs, which could be from the connection of 5Rs.
In the framework of zeolite omega as shown in Fig.7, there are two crystallographically non-equivalent sites denoted as T1 and T2 which are located in 4Rs and 6Rs, respectively 50. Considering that site T1 outnumbers site T2 by a factor of 2, a random distribution of Al atoms between the two types of sites corresponds to an AlT1/AlT2 ratio of 2. And the area under each of the peaks gives the quantitative measure of the number of these sites. The chemical state of Al atoms in zeolite omega was investigated by 27Al MAS NMR 11. As shown in Fig. 8, all spectra consist of two peaks centered at 61 ppm and 55 ppm attributed to the framework Al in T1 and T2, respectively 51
. But there are some differences in Fig. 8(a), the spectrum presents only a major peak at 13
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61 ppm along with very weak shoulder, indicating the formation of 4Rs which is consistent with the results obtained from Raman spectra. After heating the mixture for 17 h, the peak at 55 ppm increases obviously thus Al in site T2 increases and the intensity of band at 618 cm-1 in Fig. 5(A) increases with development of reaction time. All the results revealed that more and more Al atoms took part in the formation of 6Rs during the crystallization. The AlT1/AlT2 ratio was deduced by deconvolution each 27Al MAS NMR spectrum in two Lorentzian curves as usually done 51, 52. By calculating, the ratio of AlT1/AlT2 is around 1.34 (Fig. 8(b)) thus showing a preferential incorporation of Al in the 6Rs. It can be observed that the ratio of AlT1/AlT2 is almost consistent with the reaction proceeding (Fig. 8(c) - (d)), suggesting that the solids get more organized and the formation of zeolite omega was transformed from magadiite in order. In addition, extra-framework Al species at 0 ppm was hardly observed in all samples, indicating all the Al atoms were incorporated in the lattice 52.
According to the studies, we can conclude the following points: 1) Nucleation of zeolite omega occurs on the surface of magadiite and then grows gradually by transforming from magadiite; 2) Most of long-range order structure of magadiite was retained, despite that part of it was collapsed, as its primary structure during the crystallization process.; 3) 4Rs are formed after 10 h possibly by connecting of 5Rs; 4) The Al atoms are incorporated progressively in the lattice of zeolite omega and preferentially occupy site T2 (6Rs). 14
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3.2 Thermal analysis.
The relative thermal stabilities of the as-synthesized zeolite omega is evaluated by calcining of the samples at 700, 800 and 900 oC for 1 h in flowing air. The results are given in Fig. 9. It can be observed that the structure of zeolite omega is preserved after calcined at 700 oC, but the crystallinity decreases a little after heating at 800 oC. The framework was collapsed completely at 900 oC. All the results indicated that zeolite omega is stable up to about 800 oC.
The result of TG/DTA of as-synthesized zeolite omega is shown in Fig. 10. The sample led to three distinct stages of weight loss as evidenced. The first stage up to 280 o
C (around 9.78 wt %) is due to dehydrating of physically sorbed water with an
endothermic process. It is then followed by a very slow loss up to 570 oC (around 3.82wt %) probably due to the decomposition of physically occluded template molecules. Finally, a sharp loss in weight occurs from 570 to 650 oC (around 4.43 wt %) due to the oxidative decomposition of templating species 13. So last two stages are caused by the decomposition of TMA+, which also produce two exothermic peaks in DTA curve. Their difference is that the peak between 280 oC and 570 oC is due to the decomposition of the more accessible TMA+ in main channel and the peak between 570 oC and 650 oC is attributed to TMA+ in gmelinite cages 12. This result revealed that a small part of TMA+ is in 12Rs channels and most of TMA+ is encaged in gemlinite units. Furthermore, it can 15
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be found that the band at 1487 cm-1 improves with the reaction time goes by (Fig. 5(A)), which implies that more and more TMA+ was encaged in the framework of zeolite omega. Similarly, the samples obtained at various time during the crystallization have some differences in weight loss shown in Table 2. When reaction time is 10 h, the amount of TMA+ in the product is only 2.17 wt %, and it increases obviously with the reaction time development that the amount of TMA+ is 3.39 wt % at 17 h, 4.81 wt % at 70 h and 8.25 wt % in pure zeolite omega. This result implies that more and more TMA+ has the interaction with zeolite framework which is consistent with the results obtained from IR.
3.3 Factors affecting the crystallization The effect of temperature, SiO2/Al2O3 ratio, TMA+/Al2O3 ratio and alkalinity in the starting mixture on the conversion of magadiite into zeolite omega is studied. In general, higher temperature favors the formation of denser phase like NaP and SOD, but at lower temperature the rate of synthesis will decrease 53. The pure zeolite omega is obtained at 100 oC for 72 h with composition molar 20 SiO2: Al2O3: 3.6 Na2O: 180 H2O: 0.96 TMABr. Fig. 11 shows the XRD patterns of products obtained at different temperature for 72 h. As expected, when the crystalline temperature decreases to 90 oC, unconverted magadiite is observed (Fig. 11(a), Run no. 12, Table 1). On the contrary, high crystalline temperature (110 oC) would give rise to impure phase NaP and SOD (Fig. 11(b), Run no.
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13, Table 1). So 100 oC is used as the optimized reaction temperature in the following studies.
The ratio of SiO2/Al2O3 in the initial gel has a great influence on the synthesis of zeolite omega. Fixing other conditions, when SiO2/Al2O3 ratio in the starting mixture is 15 (Fig. 12(a), Run no. 14, Table 1), NaP and SOD are observed with zeolite omega simultaneously. If SiO2/Al2O3 ratio increases to 25, magadiite could not transform to zeolite omega completely (Fig. 12(b), Run no. 15, Table 1). As reported earlier, with high alkalinity in the system, selectively toward zeolite omega is lost and denser products are obtained, while the synthesis at lower alkalinity presented a significant induction time and prolonged the reactant time 14, 54. The similar results appear in our studies. Fig. 13 presents the XRD patterns of the samples collected from the molar ratio of Na2O/ Al2O3 =2.4 or 4.8. It was found that when Na2O/ Al2O3 ratio is 2.4, a trace amount of magadiite still exists with zeolite omega (Fig. 13(a), Run no. 16, Table 1). While an increase of the Na2O/ Al2O3 ratio led to the crystallization of NaP and SOD as well as zeolite omega (Fig. 13(b), Run no. 17, Table 1). TMA+ is a powerful SDA in the synthesis of zeolite omega. But the range of the amount of TMABr added is narrow. The influence of TMA+ is determined by changing its content and keeping the other component of the reaction mixture constant. While the TMA+/Al2O3 ratio is 0.48 or 1.44, zeolite omega with unreacted magadiite is observed (Fig.14, Run nos. 18 and 19, Table 1 ). Importantly, the
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denser products can be prevented by decreasing alkalinity, reducing temperature or increasing the ratio of SiO2/Al2O3. 4. Conclusion In summary, zeolite omega was successfully prepared by recrystallization of magadiite in the presence of TMA+. The nucleation and growth of zeolite omega occur on the surface of magadiite. It has been proposed that most of long-range order structure of magadiite was still retained, despite that part of it was collapsed, as its primary structure during the crystallization process, and transformed into zeolite omega little by little. In this system, 4Rs are formed after 10 h possibly from the connection of 5Rs. A preferential location of Al atoms in the 6Rs of the gmelinite in zeolite omega was observed. TG/DTA implies that most of TMA+ is encaged in gmelinite and a small part of TMA+ is in main channels of zeolite omega. Decreasing alkalinity, reducing temperature or increasing SiO2/Al2O3 ratio could effectively prevent the appearance of denser phase like NaP and SOD. The finding of this study is expect to be design for preparing zeolite using magadiite through regulating the quantity and category of different templates, which provides a new idea for the high selectivity and variety in zeolites synthesis. Furthermore, the result of the changes of medium-range structure will promote to establish the research methods and theories on crystallization of zeolites from silicates and explore the mechanism of synthesis of zeolites.
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References
(1) E.M. Flanigen, E. R. K., US. Pat. Appl. 1966, 569805. (2) E.M. Flanigen, E. R. K. Dutch Pat. 1967, 6710729. (3) E.M. Flanigen, E. R. K. US. Pat. 1980, 4241036. (4) Barrer, R. M.; Villiger, H., Zeitschrift fur Kristallographie, Bd. 1969, 128, (3-6), 352-370. (5) Galli, E., Cryst. Struct. Commun. 1974, 3, 339-344. (6) Rinaldi, R.; Pluth, J. J.; Smith, J. V., Acta Crystallogr. B, 1975, 31, 1603-1608. (7) E. Bowes, J. J. W. US. Pat. 1971, 3578728. (8) J.F. Cole, H. W. K., Molecular Sieves. ed.; ACS Symposium. American Chemical Society: Washington DC, 1973; Vol. 121, p 583. (9) Perrotta, A. J.; Kibby, C.; Mitchell, B. R.; Tucci, E. R., J. Catal. 1978, 55, (2), 240-249. (10) F. Raatz, C. T., C. Marcilly, US. Pat. 1991, 5157198. (11) Martucci, A.; Alberti, A.; Guzman-Castillo, M. D.; Di Renzo, F.; Fajula, F., Micropor. Mesopor. Mat. 2003, 63, (1-3), 33-42. (12) Fajula, F.; Verapacheco, M.; Figueras, F., Zeolites 1987, 7, (3), 203-208. (13) Mirajkar, S. P.; Eapen, M. J.; Tamhankar, S. S.; Rao, B. S.; Shiralkar, V. P., J.Incl. Phenom. Macro. 1993, 16, (2), 139-153. (14) DeWitte, B.; Patarin, J.; Guth, J. L.; Cholley, T., Micropor. Mat. 1997, 10, (4-6), 247-257. (15) Edmunds, M. P. W.; Hill, S. J.; Latham, K.; Williams, C. D., Zeolites 1994, 14, (7), 529-532. (16) Yang, S. Y.; Vlessidis, A. G.; Evmiridis, N. P., Micropor. Mat. 1997, 9, (5-6), 273-286. 19
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(17) Xu, H.; Dong, P.; Liu, L.; Wang, J. G.; Deng, F.; Dong, J. X., J. Porous. Mat. 2007, 14, (1), 97-101. (18) M.K. Rubin, C. J. P., E.J. Rosinski . US. Pat. 1977, 4021447. (19) Honda, K.; Yashiki, A.; Sadakane, M.; Sano, T., Micropor. Mesopor. Mat. 2014, 196, 254-260. (20) Ogawa, A.; Iyoki, K.; Kamimura, Y.; Elangovan, S. P.; Itabashi, K.; Okubo, T., Micropor. Mesopor. Mat. 2014, 186, 21-28. (21) P.A. Jacobs, J. A. M., stud. Surf. Sci. Catal. 1987, 33, 17-20. (22) Zones, S. I. S. Francisco, U.S. Pat. 1987, 4676958. (23) Pal-Borbely, G.; Beyer, H. K.; Kiyozumi, Y.; Mizukami, F., Micropor. Mesopor. Mat. 1998, 22, (1-3), 57-68. (24) Selvam, T.; Schwieger, W., In Impact Of Zeolites And Other Porous Materials on the New Technologies at the Beginning Of the New Millennium, Pts a And B, Aiello, R.; Giordano, G.; Testa, F., Eds. 2002; Vol. 142, pp 407-414. (25) Ko, Y. H.; Kim, S. J.; Kim, M. H.; Park, J. H.; Parise, J. B.; Uh, Y. S., Micropor. Mesopor. Mat. 1999, 30, (2-3), 213-218. (26) Shi, Z. F.; Wang, Y.; Meng, C. G.; Liu, X. Y., Micropor. Mesopor. Mat. 2013, 176, 155-161. (27)Wang, Y.; Lv, T. M.; Wang, H. L.; Zhao, Y. L.; Meng, C. G.; Liu, H., Micropor. Mesopor. Mat. 2015, 208, 66-71. (28) Wang, Y.; Yang, Y.; Cui, M.; Sun, J. B.; Qi, L.; Ji, S. H.; Meng, C. G., Solid State Sci. 2011, 20
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13, (12), 2124-2128. (29) Wang, Y.; Shang, Y.; Wu, J.; Zhu, J.; Yang, Y.; Meng, C., J. Chem. Technol. Biot. 2010, 85, (2), 279-282. (30)Cui, M.; Wang, Y.; Liu, X. Y.; Zhu, J.; Sun, J. B.; Lv, N.; Meng, C. G., J. Chem. Technol. Biot. 2014, 89, (3), 419-424. (31) Wang, Y.; Wu, J. A.; Zhu, J. A.; Yang, Y.; Qi, L.; Ji, S. H.; Meng, C. G., Micropor. Mesopor. Mat. 2010, 135, (1-3), 143-148. (32) Mintova, S.; Olson, N. H.; Valtchev, V.; Bein, T., Science 1999, 283, (5404), 958-960. (33) Choy, J. H.; Lee, S. R.; Han, Y. S.; Park, M.; Park, G. S., Chem. Commun. 2003, (15), 1922-1923. (34) Dutta, P. K.; Shieh, D. C., J. Phys. Chem. 1986, 90, (11), 2331-2334. (35) Dutta, P. K.; Puri, M., J. Phys. Chem. 1987, 91, (16), 4329-4333. (36)Cui, M.; Zhang, Y. F.; Liu, X. Y.; Wang, L.; Meng, C. G., Micropor. Mesopor. Mat. 2014, 200, 86-91. (37) Cui, M.; Wang, L.; Zhang, Y. F.; Wang, Y.; Meng, C. G., Micropor. Mesopor. Mat. 2015, 206, 52-57. (38) Wang, Y.; Lv, T. M.; Ma, Y.; Tian, F. P.; Shi, L.; Liu, X. Y.; Meng, C. G., Micropor. Mesopor. Mat. 2016, 228, 86-93. (39)Xiong, G.; Yu, Y.; Feng, Z. C.; Xin, Q.; Xiao, F. S.; Li, C., Micropor. Mesopor. Mat. 2001, 42, (2-3), 317-323. 21
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(40) Dutta, P. K.; Shieh, D. C.; Puri, M., J. Phys. Chem. 1987, 91, (9), 2332-2336. (41) Kosuge, K.; Yamazaki, A.; Tsunashima, A.; Otsuka, R., J. Ceram. Soc. Jpn. 1992, 100, (3), 326-331. (42) Huang, Y. N.; Jiang, Z. M.; Schwieger, W., Micropor. Mesopor. Mat. 1998, 26, (1-3), 215-219. (43) Edith M. Flanigen, H. K., H.A. Szymanski, Molecular Sieve Zeolite-I. ed.; Adavabces in Chemistry, American Chemical Society: 1971; p 201. (44) Huang, Y. N.; Jiang, Z. M.; Schwieger, W., Chem. Mater. 1999, 11, (5), 1210-1217. (45) Yu, Y.; Xiong, G.; Li, C.; Xiao, F. S., Micropor. Mesopor. Mat. 2001, 46, (1), 23-34. (46) Garces, J. M.; Rocke, S. C.; Crowder, C. E.; Hasha, D. L., Clay. Clay Miner. 1988, 36, (5), 409-418. (47) Mozgawa, W., J. Mol. Struct. 2001, 596, 129-137. (48) Zelent, B.; Nucci, N. V.; Vanderkooi, J. M., J. Phys. Chem. A. 2004, 108, (50), 11141-11150. (49) Flanigen, E., Zeolite Chemistry and Catalysis. ed.; American Chemical Society: Washington DC, 1976; p 80. (50) Goossens, A. M.; Feijen, E. J. P.; Verhoeven, G.; Wouters, B. H.; Grobet, P. J.; Jacobs, P. A.; Martens, J. A., Micropor. Mesopor. Mat. 2000, 35-6, 555-572. (51) Massiani, P.; Fajula, F.; Figueras, F.; Sanz, J., Zeolites 1988, 8, (4), 332-337. (52) Massiani, P.; Fajula, F.; Direnzo, F., J. Chem. Soc.Chem. Commun. 1988, (12), 814-815. (53) Yang, S.; Evmiridis, N. P., In Zeolites And Related Microporous Materials: State Of the Art 22
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1994, Weitkamp, J.; Karge, H. G.; Pfeifer, H.; Holderich, W., Eds. 1994; Vol. 84, pp 155-162. (54) Castillo, M. L. G.; Di Renzo, F.; Fajula, F.; Bousquet, J., Micropor. Mesopor. Mat. 2006, 90, (1-3), 221-228.
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Table 1 Synthesis conditions and characteristics of products prepared from magadiite
Run no.
Synthesis conditions (initial gels)
SiO2/Al2O3
H2O/ Al2O3
TMABr/ Al2O3
Na2O/ Al2O3
Product Temp. (oC)
Time (h)
Phase
X%
1
20
180
0.96
3.6
100
0
ma
0
2
20
180
0.96
3.6
100
9
m
0
3
20
180
0.96
3.6
100
10
oa+m
8.54
4
20
180
0.96
3.6
100
17
o+m
41.35
5
20
180
0.96
3.6
100
24
o+m
62.38
6
20
180
0.96
3.6
100
48
o+m
86.15
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7
20
180
0.96
3.6
100
72
o
100
8
20
180
0.96
3.6
100
96
o
100
9
20
180
096
3.6
100
70
o+m
10
20
180
0.96
3.6
100
360
o
11b
20
180
0.96
3.6
100
72
Am,a
-
12
20
180
0.96
3.6
90
72
o+m
-
13
20
180
0.96
3.6
110
72
o+sa+pa
-
14
15
180
0.96
3.6
100
72
o+s+p
-
15
25
180
0.96
3.6
100
72
o+m
-
16
20
180
0.96
2.4
100
72
o+m
-
25
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17
20
180
0.96
4.8
100
72
o+s+p
-
18
20
180
0.48
3.6
90
72
o+m
-
19
20
180
1.44
3.6
110
72
o+m
-
a: m= magadiite, o= zeolite omega, Am=amorphous, s=SOD, p=Na-P
b:silica source is colloidal silica (30 wt % SiO2).
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Table 2 ICP and TG analysis of the samples obtained at different time
Reaction
Content (wt %)
Ration of Si/Al
Weight loss (100 wt%)
time
Si
25-280 oC
Al
280-570 oC
570-650 oC
10 h
32.77
6.442
4.90
12.35
1.72
0.45
17 h
32.08
6.987
4.43
10.47
2.67
0.72
70 h
32.83
8.237
3.84
10.03
3.08
1.73
72 h
19.00
4.88
3.62
9.78
3.82
4.43
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Figures
Fig. 1
Fig. 1 X-ray powder diffraction patterns of (a) magadiite and the samples withdrawn at various intervals of hydrothermal conversion of magadiite into zeolite omega at 100 o C for (b) 9 h, (c) 10 h, (d) 17 h, (e) 70 h, (f) 72 h and (g) 360 h. (No. 1-4, 7 and 9-10, Table 1).
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Fig. 2
Fig. 2 Crystalline fraction of zeolite omega (X %) as a function of synthesis time at 100 oC. Batch composition of 20 SiO2: Al2O3: 3.6 Na2O: 180 H2O: 0.96 TMABr. (No. 1-8, Table 1)
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Fig. 3
Fig. 3 SEM images of (a) magadiite and the samples prepared by heating the reactants for (b) 10 h, (c) 17 h, (d) 70 h, (e) 72 h and (f) 360 h. (No. 1, 3-4, 7 and 9-10, Table 1)
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Fig. 4
Fig. 4 (a) IR and (b) Raman spectra of magadiite.
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Fig. 5
Fig. 5 (A)IR spectra of the samples synthesized by heating the reactants for (a) 10 h, (b) 17 h, (c) 70 h and (d) 72 h (No. 3-4, 7 and 9, Table 1), (B) The height strength ratios of the bands at 818 cm-1 and 783 cm-1 for the samples obtained at various time intervals during the crystallization.
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Fig. 6
Fig. 6 Raman spectra of the samples obtained by heating the reactants for(a) 10 h, (b) 17 h, (c) 70 h and (d) 72 h (No. 3-4, 7 and 9, Table 1).
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Fig. 7
Fig. 7 Structure of zeolite omega: (a) chain of gmelinite cages seen in perspective perpendicular to c-axis; (b) the framework seen in parallel projection along c-axis. The unit cell is indicated by continuous lines.
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Fig. 8
Fig. 8 27Al MAS NMR spectrum of the sample obtained by heating reactants for (a) 10 h, (b) 17 h, (c) 70 h and (d) 72 h (No. 3-4, 7 and 9, Table 1).
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Fig. 9
Fig. 9 XRD Patterns of as-synthesized products (No. 7, Table 1) caclined at (a) 700 oC , (b) 800 oC, and (c) 900 oC for 1 h in flowing air.
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Fig. 10
Fig. 10 TG/DTA curves of as-synthesized zeolite omega (No. 7, Table 1).
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Fig. 11
Fig. 11 XRD patterns of products obtained at various temperature: (a) 90 oC and (b) 110 oC for 72 h. (No. 12-13, Table 1).
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Fig. 12
Fig. 12 XRD patterns of products obtained at various SiO2/Al2O3 ratios: (a) 15 and (b) 25 for 72 h. (No. 14-15, Table 1).
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Fig. 13
Fig. 13 XRD patterns of products obtained at various Na2O/ Al2O3 ratios: (a) 2.4 and (b) 4.8 for 72 h. (No. 16-17, Table 1).
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Fig. 14
Fig. 14 XRD patterns of products obtained at various TMABr/ Al2O3 ratios: (a) 0.48 and (b) 1.44 for 72 h. (No. 18-19, Table 1).
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For Table of Contents Use Only
Synthesis of zeolite omega by magadiite conversion method and an insight into the changes of medium-range structure during the crystallization Tianming Lv, Shoulei Zhang, Zhe Feng, Fushi Wang, Shaoqing Zhang, Jiqi Zheng, Xin Liu, Changgong Meng, Yu Wang*
Table of Contents (TOC) Image
Synopsis ♦
High crystalline and pure zeolite omega could be obtained using recrystallization of magadiite method.
♦
Crystallization behaviours and Changes of medium-range structure during the crystallization process were investigated.
♦
The various parameters as reaction temperature, time and substrate composition all have very important influence on the crystallization of zeolite omega.
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