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The influence of alkali cation on the synthesis of zeolite beta from fluoride containing gels
J. Weitkamp, H.G. Karge, H. Pfeifer and W. H6lderich (Eds.) Zeolites and Related Microporous Materials: Stale of the Art 1994 Studies in Surface Science and Catalysis, Vol. 84 0 1994 Elsevier Science B.V. A11 rights reserved.
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The influence of alkali cation on the synthesis of zeolite beta from fluoride containing gels R. Mostowicza, F. Testab, F. Creab, A. Nastrob, R. Aiellob, A. Fonsecac and J. B.Na@. BIndustrial Chemistry Research Institute, 01793 Warszawa, Poland bDepartment of Chemistry, University of Calabria, 87030 Rende, Italy CLaboratoire de Catalyse, Facultes Universitaires Notre Dame de la Paix, Namur, 5000 Namur, Belgium
Zeolite Beta is synthesized from fluoride containing gels in presence of alkali cations using DABCO and methylamine as organics from the gels of the general molar composition: 12.5DABCO-12.6MA-xHF-yMF-zAl~O~-25SiO~ 500H20 with x+y=25 and M=NH4, Li, Na, K and Cs. The influence of SUAl ratio in the reaction mixture, alkali cations used and its amount was investigated. Beta crystals were obtained with 12.5 moles of: NH4-, Li- and CsF. In order to synthesize zeolite Beta in the presence of Na and K fluorides, their amount in the reaction mixture had to be decreased as compared t o the amount of the former cations. The samples were characterized by 27Al-, 29Si- and 13C-NMR spectroscopy and SEM.
1. INTRODUCTION Zeolite Beta is a wide-pore crystalline aluminosilicate, synthesized by Wadlinger et al. [ll. The first synthesis used Na+ and tetraethylammonium (TEA) ions in alkaline media [l] with silica gel or sol, as silica sources. PerezPariente et a1 12-53 reported detailed mechanistic studies on the nucleation and crystal growth of zeolite Beta. It was found that zeolite Beta nuclei were formed via a liquid phase synthesis mechanism and that Al is an essential element for its formation [2]. Both crystallization rate and crystals size of zeolite Beta depend on the alkali content and the molar fraction of each cation in Na- and K-containing gels [4]. No zeolite can be obtained in absence of alkali cations and an optimum value of (Na+K)/SiOzratio seems to exist. Quite recently fluoride ions were used as mineralizing agents in presence of diaza-1,4 bicyclo [2,2,2] octane (DABCO) and methylamine [6-81. The synthesis medium was free from alkaline cations. HF was used as a source of fluoride ions. In order to obtain fully crystalline product, seed crystals were added to the reaction mixture. With the use of this method, zeolite Beta could be prepared in
172
a rather quite narrow range of Si to A1 molar ratio in the framework, i.e., between 9 and 22. The crystals obtained from the system: DABCOmethylamine-HF are typically around 2-3 pm and they are about 10 times larger than Beta crystals obtained in the alkaline medium, in the presence of TEA cation 12-51. In our previous publications, emphasis was put on the role of alkali cations in the synthesis of silicalite-1 in presence of fluoride ions [9, 101. The present work is devoted to the study of the influence of alkali cations on the synthesis of zeolite Beta from fluoride containing gels. 2.EXPElUMENTAL
For the optimization of the SUAl ratio, the following gels have been prepared: I. ~ ~ . ~ D A B C O - ~ ~ . ~ M A - ~ ~ H F - X A ~ ~ O ~ - ~ ~ S ~ O ~ - ~ with ~=1.0,1.25,2.5,3.33 and 5.0. The influence of the alkali cations has been examined on two series of gels having Si/Al ratio: 12.5 and 5 and various cation content. I I. 12.5DABCO-12.5MA-xHF-yMF-zAl~0~-25Si0~-5OOH~O with x+y=25, M=NH4, Li, Na, K and Cs, z=1.0 and 2.5. The ratio (DABCO+MA)/F, recommended in ref. 8 was maintained at a constant value of 1throughout all the syntheses. The gels were prepared as follows: MA (40% aqueous solution, Aldrich) was neutralized with equimolar amount of HF (48% aqueous solution, Merck). The neutralization of an amine was carried out in the narrow-neck polypropylene flask with intensive stirring while cooling down the solution in an ice bath. To a so-obtained MA-HF solution, the aqueous solution of DABCO (Aldrich) was added and the remaining source of fluorides: HF (if necessary) and one of the following: LiF (ICPH), NH4F, NaF, KF (all Carlo Erba) and CsF (Aldrich). Finally, Al(OHI3 (Pfaltz & Bauer) was dissolved and this solution was mixed with fumed silica (Serva). The gel was vigorously stirred and during homogenization 2.5 wt% of Beta-OH seeds in water suspension were added. The so obtained gels were introduced into 20 cm3 PTFE-lined Morey type autoclaves without stirring and heated at 170"C, usually for 15 and 20 days. The Beta-OH crystals used for seeding were obtained from the gels of the following molar composition, according to the procedure given in ref. 4: 1.56Na20-1.38K20-12.5(TEA)20-Al203-50Si02-750H20. The reagents were: NaOH (Fluka), KOH (Baker Reagents), sodium aluminate (Carlo Erba), TEAOH (40%, Fluka), Si02 (Serva). The gels were crystallized in 200 cm3 PTFE lined Morey type autoclaves at 125°C for one week. During crystallization the autoclaves were rotated. After crystallization, the products were centrifuged and washed with distilled water for several times, dried at 105°C overnight and analyzed. The crystalline phases were identified by XRD (Philips PW 1730/10 automated system using CuKa radiation). For the calculation of the crystallinity, the intensity of the peak at d=3.98A was compared with the
173
intensity of a reference sample. As a reference sample, the best sample in series of runs of the same composition was assumed. The A1 and M contents were obtained by atomic absorption, Si by wet chemical method. The NMR spectra of the samples were recorded on either a BRUKER CXP 200 or a BRUKER MSL 400 spectrometer. For crystal morphology studies, a scanning electron microscopy (SEM) Jeol JSM T330 A was used.
3.RESULTSAND DISCUSSION In order to evaluate the influence of alkali cations on the zeolite Beta crystallization the results of the series runs carried out in system I (chosen after Caullet et al. [81 in the absence of alkali fluorides were compared with the results of the runs in system I1 in which part of the HF was replaced by Li, Na, K, Cs and NH4 fluorides. In series I, with SUAk2.5 in the reaction mixture, no crystalline product was obtained; with SUAk3.75 the product contained only traces of crystalline phase. Beta zeolite of good crystallinity was synthesized in this system at 170°C after 20 days of hydrothermal treatment. After diminution of Al in the reaction gel (Si/Al=lO and 12.5) cocrystallization of a completely silicious MTN-type zeolite (ZSM-39) occurred together with zeolite Beta formation. The higher the Si content in the gel and the longer the crystallization time, the less Beta phase and simoultaneously more MTN phase was formed in the systems with Si/Al 10 and 12.5. These results indicate, that the Si/AI range of the gel composition which produces pure Beta phase is narrower than it was described earlier [81. The difference is probably due to the difference in silica and alumina sources used. The optimal molar ratio Si/Al=5 in the gel has been defined for pure Beta formation. In system I this ratio and the ratio SUAk12.5 were used for the crystallization with NH4 and alkaline metal fluorides. The results of series I1 are presented in Tables 1 and 2. Table 1 comprises the results obtained with the gels of Si/A1=12.5 and containing 12.5 moles of alkali fluorides. With the gels of SUAk12.5 pure zeolite Beta was obtained in the presence of Cs only. Thus, its presence in the reaction mixture suppressed MTN phase formation as compared to the system with HF in the gel. In the system investigated Beta did not crystallize neither with 12.5 NaF nor with 12.5 KF. Interestingly, when both Na and K were present in the gel in equal quantities, MTN phase crystallized. With only one cation present in the reaction mixture, no crystallization occurred. Table 2 presents the results of synthesis runs with the gels containing alkaline cations and Si/A1=5. Similarly to the previous system with SUAk12.5, no crystalline product was obtained with 12.5 NaF, even after 30 days of crystallization. The decreasing of NaF amount in the gel to 6 and 3 moles resulted in pure Beta phase formation.
174
Table 1. The influence of alkali cation on zeolite Beta crystallization from the gel: 12.5DABCO-12.5MA-12.5HF-12.5MF-Al~O~-25SiO~-5OOH~O at 170°C. Sample
MF
Reaction time, days
Solid products (Crystallinity, %)
BF-10 BF-21 BF-11 BF-12
NH4F NH4F1 NaF KF
BF-14 BF-15
NaF+KF2 CsF
15 15 25 20 25 15 15
Beta, MTN (10) Beta, MTN (10) Amorphous Amorphous MTN (traces) MTN Beta
lOHF-25",
26.25NaF-6.25KF'
Table 2. The influence of NH4-, Li-, Na-, K-, and CsF on Beta zeolite crystallization from the gel: ~ ~ . ~ D A B C O - ~ ~ . ~ M A - X H F - ~ M F - ~ 500H20 where x+y=25 at 170°C. MF, moles x+y=25
12.5
6.0
3.0
Amo=Amorphous
Sample
MF
Solid products
Reaction time, days
BF-23 BF-24 BF-29 BF-28 BF-25
NH4F LiF NaF KF C sF
15 26 30
BF-32
NH4F
BF-30 BF-33
LiF NaF
BF-34
m
BF-31
C sF
BF-35
NaF
BF-36
KF
Beta Beta + Am0 Amo MTN Beta + Am0 Beta Beta Beta Beta Beta + A m 0 Beta Beta (traces) Beta Beta + Am0 Beta Beta + Am0 Beta Beta Beta
22
15 27 14 20 16 14
20 14 20 15 20 15 20 15 20
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With 12.5 KF in the gel crystallization led t o MTN phase. With 6 and 3 moles of KF in the gel Beta phase was obtained. The results with 12.5 NaF and 12.5 KF' in the system indicate, that such amounts of Na- and K-fluorides make Beta crystallization impossible. These results represent a rather rare case in zeolite synthesis, paying regard to the fact, that Na- and K- cations participate in the crystallization of majority of aluminosilicate zeolites. Note, that as it was found by Camblor and Perez-Pariente [5] in the alkaline medium, with TEA as template, zeolite Beta does not crystallize in the absence of these cations. Zeolite Beta has been obtained in the presence of NH4-, Li- and CsF in the system with SilAl=5. However, it was observed, that with NH4F, after prolonged crystallization time zeolite Beta content decreased and MTN amount increased in the product. It is difficult, a t present, to find explanation for the unusual behaviour of Na and K fluorides. The molar solubility of fluorides increases in the series: LiF
H H H H NH4
cs
NH4 NH4 Li
cs
NH4 Li
K K
Na
0.4
5.8 5.4 4.7 4.1 3.8 4.2
10.1 10.9 12.7 14.5 15.7 14.4
0.90 0.93 0.84 0.76 0.86 1.0
0.34 0.43 0.65 0.64 0.68 0.88
18.6
5.1 8.7
11.6 6.3
0.72
0.57
9.7 8.6 4.7 3.2
5.6 8.1 8.3 7.6 6.0
10.4 6.9 6.7 7.4 9.7
0.93 0.89 0.99
0.45 0.54 0.73
3.75 5
10 12.5 12.5 12.5 12.5
5 5 5 5 5 5 5 5
-
-
-
4.25 4.1
14.1 14.7
3.5 2.9 3.4 2.3 3.9
17.3 20.8 17.6 26.8 15.4 12.3
-
4.8
-
M=alkali cation; Si, Aktotal Si and A1 in the product; Si,, Al,=Si and A1 content in the gel; AlT=tetrahedrally coordinated Al.
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The role of the alkali cation in the DABCO polymerization is also being investigated. The results of chemical analysis are included in Table 3. The Si/Al molar ratio of the product was always higher than that of the initial reaction mixture. It means, that only part of the aluminum being present in the gel was introduced into the framework. The products obtained from NH4 and Cs containing gels have similar composition (Si-, Al-content) to that of the products obtained with HF of the same Si/Al ratio. The Li-, Na- and K-containing crystals have Si/Al ratio slightly lower than the one of the respective products obtained in the absence of alkali cations. The yield of incorporation of Si and A1 into the crystals was calculated for some selected samples. The data for each element are given in Table 3 as the ratio between the amount of the element in the product and the amount in the gel (Sig, Alg). For the gels without alkali cations, the degree of aluminum incorporation increases with the increase of Si/Al ratio. The lower the aluminum content in the reaction gel, the higher its percentage of incorporation into the framework. For gels with Si/A1=3.75 and 5.0 the degree of A1 incorporation is below 50%. The low yield of aluminum is the result of easy complexation of this element by fluorine. After such a complex of Al with F is formed, aluminum is not available for incorporation in the zeolite. With NH4 and Li cations present in the gel, the A1 yield is the same as with HF only. Oppositely to Li and NH4, the Al yield increases when Cs and K are present in the gel. The yield of silicon depends also on the Si/Al ratio. For the series with HF as the only source of fluorides, it decreases with the increase of SVAl ratio. With various alkali fluorides in the system, silicon yield is in the range 0.72 - 1.0. Some selected samples from Tables 1 and 2 were analyzed by 27Al-, 29Si- and W-NMR. By means of 27Al-NMR the amount of tetrahedral and octahedral aluminum was calculated. The samples prepared from the gels of Si/Al = 12.5 contained all A1 in T-sites. Quite unexpectedly, the product prepared from the gel with 25 NH4 contained also 100% tetrahedrally coordinated Al. Among the analyzed samples which were crystallized from the gel of Si/Al=5, only the one obtained in the presence of CsF contained 100% A ~ T The . samples with NH4and Li-cations contained 35 and 27% of tetrahedral Al, respectively. Taking into , content per unit cell and s i / A l ~was also consideration the amounts of A ~ Tits calculated (Table 3). The purity of the samples was also checked by 29Si-NMR. The chemical shifts of the different NMR lines denote clearly the presence of a Beta phase (-106, -110 and -115 ppm) and/or an additional MTN phase (-119 ppm) (Figure la). The 13C-NMR spectra provide additional evidences on the nature of the polymer occluded in the zeolitic channels. When the relative intensity of the 55.7 ppm line (high intensity) is correct with respect to the 46 ppm line (low intensity), it is accepted as due t o a good Beta sample (see ref. 8) (Figure lb). The cation content in the crystals was also analyzed (see Table 3). The amount of Cs in the sample BF-15 was 0.4 Cs/u. c. indicating, that this cation practically did not enter the structure. The Li content in the samples BF-24 and
177
-100
-110
-120
ppm
70
60
50
40
PPm
Figurel. Proton enhanced MAS spectra of pure Beta zeolite synthesized from the gel 12.5DABCO-12.5MA-12.5HF-12.5CsF-Al~0~-25Si0~-500H~0 at 170OC: a) 29Si-NMR spectrum; b) 13C-NMR spectrum.
Figure 2. SEM pictures of zeolite Beta crystals obtained from the system: 12.5DABCO-12.5 MAxHF-yMF-2.5Al203-25SiO2-500H~O: BF-17) 25HF; BF-31) 19HF-GCsF; BF-32) 19HF6NH4F; BF-36)22HF-3KF
30 was higher than the amount of Al. The reason of this excess is the presence of an amorphous material in the product. The examples of crystal morphology of zeolite Beta obtained in the present work are shown in Figure 2. Their crystal size is about 1.5-3.0 pm. The crystals appear to be round and some of them show truncated square bypiramidal morphology, described previously by Caullet et al. 181. Crystals obtained in the presence of potassium and sodium cations are smaller than those synthesized in the presence of HF, NH4, Li and Cs.Their crystal size is in the range 1-1.8 Clm.
178
4. CONCLUSIONS The formation of zeolite Beta in the presence of HF or in the presence of NH4 and alkali cations (Li, Na, K, Cs) has been examined and compared with the synthesis in the presence of HF as a sole source of fluorides. 1,4-diazabicyclo [2, 2, 21 octane (DABCO) together with methylamine were used as organic templates. With HF, as the only source of fluorides, the optimal value of Si/A1=5 has been determined for pure Beta phase formation. The syntheses of zeolite Beta were carried out from the gels of composition: 12.5DABCO-12.5MA-12.5HF12.5MF-xA1203-25Si02-50OH~O with x=l and 2.5 and M=NH4, Li, Na, K and Cs. The alkali cations fall into two groups: the activating ones, which form Beta phase (Li, Cs and NH4) and the deactivating cations (Na, K), which suppress zeolite Beta crystallization. With 12.5Na and 12.5K in the system, zeolite Beta did not crystallize. In order to obtain the Beta phase in the presence of these deactivating cations, their content in the gel had to be diminished. 5. ACKNOWIXDGEMENT
R. Mostowicz is grateful to the Commission of the European Communities (COST program) for research grant. A. Fonseca acknowledges the Regional Government of Wallonie for financial support. This work was in part funded by the Belgian National Program of Inter-University Research Projects initiated by the State Prime Minister Office (Science Policy Programming) and by the Italian National Research Council (CNR-Progetto Finalizzato Chimica Fine). The Authors would like t o thank Mr Guy Daelen from the University of Namur for his skillful help in taking the NMR spectra.
1.R.L. Wadlinger, G.T. Kerr and E.J. Rosinski, U. S. Pat. No.3 308 069 (1967). 2. J. Perez-Pariente, J.A. Martens and P.A. Jacobs, Appl. Catal., 31 (1987) 35. 3. J. Perez-Pariente, J.A. Martens and P.A. Jacobs, Zeolites, 8 (1988) 46. 4. M.A. Camblor and J. Perez-Pariente, Zeolites, 11(1991) 202. 5. M.A. Camblor, A. Misfud and J. Perez-Pariente, Zeolites, 11(1991) 792. 6. P. Caullet, J.L. Guth, A.C. Faust, F. Raatz, J.F. Joly and J.M. Deves, Fr. Pat. 89/12556 (1989). 7. A. Ajot, J.F. Joly, J. Lynch, F. Raatz and P. Caullet, Stud. Surf. Sci. Catal., 62 (1991)583. 8. P. Caullet, J. Hazm, J.L. Guth, J.F. Joly, J. Lynch and F. Raatz, Zeolites, 12 (1992)240. 9. F. Crea, R. Mostowicz, R. Aiello, A. Nastro and J. B.Nagy in Proc. 9th Intern. Zeolite Conf., Montreal 1992, J.B. Higgins, R. Von Balmoos, M.M.J. Treacy (eds.), Butterworth-Heineman 1993, Vol. I, p. 147. 10. R. Mostowicz, F. Crea and J. B.Nagy, Zeolites, 13 (1993) 678. 11. R. Mostowicz, F. Testa, F. Crea, R. Aiello and J. B.Nagy, in preparation.
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The influence of alkali cation on the synthesis of zeolite beta from fluoride containing gels R. Mostowicza, F. Testab, F. Creab, A. Nastrob, R. Aiellob, A. Fonsecac and J. B.Na@. BIndustrial Chemistry Research Institute, 01793 Warszawa, Poland bDepartment of Chemistry, University of Calabria, 87030 Rende, Italy CLaboratoire de Catalyse, Facultes Universitaires Notre Dame de la Paix, Namur, 5000 Namur, Belgium
Zeolite Beta is synthesized from fluoride containing gels in presence of alkali cations using DABCO and methylamine as organics from the gels of the general molar composition: 12.5DABCO-12.6MA-xHF-yMF-zAl~O~-25SiO~ 500H20 with x+y=25 and M=NH4, Li, Na, K and Cs. The influence of SUAl ratio in the reaction mixture, alkali cations used and its amount was investigated. Beta crystals were obtained with 12.5 moles of: NH4-, Li- and CsF. In order to synthesize zeolite Beta in the presence of Na and K fluorides, their amount in the reaction mixture had to be decreased as compared t o the amount of the former cations. The samples were characterized by 27Al-, 29Si- and 13C-NMR spectroscopy and SEM.
1. INTRODUCTION Zeolite Beta is a wide-pore crystalline aluminosilicate, synthesized by Wadlinger et al. [ll. The first synthesis used Na+ and tetraethylammonium (TEA) ions in alkaline media [l] with silica gel or sol, as silica sources. PerezPariente et a1 12-53 reported detailed mechanistic studies on the nucleation and crystal growth of zeolite Beta. It was found that zeolite Beta nuclei were formed via a liquid phase synthesis mechanism and that Al is an essential element for its formation [2]. Both crystallization rate and crystals size of zeolite Beta depend on the alkali content and the molar fraction of each cation in Na- and K-containing gels [4]. No zeolite can be obtained in absence of alkali cations and an optimum value of (Na+K)/SiOzratio seems to exist. Quite recently fluoride ions were used as mineralizing agents in presence of diaza-1,4 bicyclo [2,2,2] octane (DABCO) and methylamine [6-81. The synthesis medium was free from alkaline cations. HF was used as a source of fluoride ions. In order to obtain fully crystalline product, seed crystals were added to the reaction mixture. With the use of this method, zeolite Beta could be prepared in
172
a rather quite narrow range of Si to A1 molar ratio in the framework, i.e., between 9 and 22. The crystals obtained from the system: DABCOmethylamine-HF are typically around 2-3 pm and they are about 10 times larger than Beta crystals obtained in the alkaline medium, in the presence of TEA cation 12-51. In our previous publications, emphasis was put on the role of alkali cations in the synthesis of silicalite-1 in presence of fluoride ions [9, 101. The present work is devoted to the study of the influence of alkali cations on the synthesis of zeolite Beta from fluoride containing gels. 2.EXPElUMENTAL
For the optimization of the SUAl ratio, the following gels have been prepared: I. ~ ~ . ~ D A B C O - ~ ~ . ~ M A - ~ ~ H F - X A ~ ~ O ~ - ~ ~ S ~ O ~ - ~ with ~=1.0,1.25,2.5,3.33 and 5.0. The influence of the alkali cations has been examined on two series of gels having Si/Al ratio: 12.5 and 5 and various cation content. I I. 12.5DABCO-12.5MA-xHF-yMF-zAl~0~-25Si0~-5OOH~O with x+y=25, M=NH4, Li, Na, K and Cs, z=1.0 and 2.5. The ratio (DABCO+MA)/F, recommended in ref. 8 was maintained at a constant value of 1throughout all the syntheses. The gels were prepared as follows: MA (40% aqueous solution, Aldrich) was neutralized with equimolar amount of HF (48% aqueous solution, Merck). The neutralization of an amine was carried out in the narrow-neck polypropylene flask with intensive stirring while cooling down the solution in an ice bath. To a so-obtained MA-HF solution, the aqueous solution of DABCO (Aldrich) was added and the remaining source of fluorides: HF (if necessary) and one of the following: LiF (ICPH), NH4F, NaF, KF (all Carlo Erba) and CsF (Aldrich). Finally, Al(OHI3 (Pfaltz & Bauer) was dissolved and this solution was mixed with fumed silica (Serva). The gel was vigorously stirred and during homogenization 2.5 wt% of Beta-OH seeds in water suspension were added. The so obtained gels were introduced into 20 cm3 PTFE-lined Morey type autoclaves without stirring and heated at 170"C, usually for 15 and 20 days. The Beta-OH crystals used for seeding were obtained from the gels of the following molar composition, according to the procedure given in ref. 4: 1.56Na20-1.38K20-12.5(TEA)20-Al203-50Si02-750H20. The reagents were: NaOH (Fluka), KOH (Baker Reagents), sodium aluminate (Carlo Erba), TEAOH (40%, Fluka), Si02 (Serva). The gels were crystallized in 200 cm3 PTFE lined Morey type autoclaves at 125°C for one week. During crystallization the autoclaves were rotated. After crystallization, the products were centrifuged and washed with distilled water for several times, dried at 105°C overnight and analyzed. The crystalline phases were identified by XRD (Philips PW 1730/10 automated system using CuKa radiation). For the calculation of the crystallinity, the intensity of the peak at d=3.98A was compared with the
173
intensity of a reference sample. As a reference sample, the best sample in series of runs of the same composition was assumed. The A1 and M contents were obtained by atomic absorption, Si by wet chemical method. The NMR spectra of the samples were recorded on either a BRUKER CXP 200 or a BRUKER MSL 400 spectrometer. For crystal morphology studies, a scanning electron microscopy (SEM) Jeol JSM T330 A was used.
3.RESULTSAND DISCUSSION In order to evaluate the influence of alkali cations on the zeolite Beta crystallization the results of the series runs carried out in system I (chosen after Caullet et al. [81 in the absence of alkali fluorides were compared with the results of the runs in system I1 in which part of the HF was replaced by Li, Na, K, Cs and NH4 fluorides. In series I, with SUAk2.5 in the reaction mixture, no crystalline product was obtained; with SUAk3.75 the product contained only traces of crystalline phase. Beta zeolite of good crystallinity was synthesized in this system at 170°C after 20 days of hydrothermal treatment. After diminution of Al in the reaction gel (Si/Al=lO and 12.5) cocrystallization of a completely silicious MTN-type zeolite (ZSM-39) occurred together with zeolite Beta formation. The higher the Si content in the gel and the longer the crystallization time, the less Beta phase and simoultaneously more MTN phase was formed in the systems with Si/Al 10 and 12.5. These results indicate, that the Si/AI range of the gel composition which produces pure Beta phase is narrower than it was described earlier [81. The difference is probably due to the difference in silica and alumina sources used. The optimal molar ratio Si/Al=5 in the gel has been defined for pure Beta formation. In system I this ratio and the ratio SUAk12.5 were used for the crystallization with NH4 and alkaline metal fluorides. The results of series I1 are presented in Tables 1 and 2. Table 1 comprises the results obtained with the gels of Si/A1=12.5 and containing 12.5 moles of alkali fluorides. With the gels of SUAk12.5 pure zeolite Beta was obtained in the presence of Cs only. Thus, its presence in the reaction mixture suppressed MTN phase formation as compared to the system with HF in the gel. In the system investigated Beta did not crystallize neither with 12.5 NaF nor with 12.5 KF. Interestingly, when both Na and K were present in the gel in equal quantities, MTN phase crystallized. With only one cation present in the reaction mixture, no crystallization occurred. Table 2 presents the results of synthesis runs with the gels containing alkaline cations and Si/A1=5. Similarly to the previous system with SUAk12.5, no crystalline product was obtained with 12.5 NaF, even after 30 days of crystallization. The decreasing of NaF amount in the gel to 6 and 3 moles resulted in pure Beta phase formation.
174
Table 1. The influence of alkali cation on zeolite Beta crystallization from the gel: 12.5DABCO-12.5MA-12.5HF-12.5MF-Al~O~-25SiO~-5OOH~O at 170°C. Sample
MF
Reaction time, days
Solid products (Crystallinity, %)
BF-10 BF-21 BF-11 BF-12
NH4F NH4F1 NaF KF
BF-14 BF-15
NaF+KF2 CsF
15 15 25 20 25 15 15
Beta, MTN (10) Beta, MTN (10) Amorphous Amorphous MTN (traces) MTN Beta
lOHF-25",
26.25NaF-6.25KF'
Table 2. The influence of NH4-, Li-, Na-, K-, and CsF on Beta zeolite crystallization from the gel: ~ ~ . ~ D A B C O - ~ ~ . ~ M A - X H F - ~ M F - ~ 500H20 where x+y=25 at 170°C. MF, moles x+y=25
12.5
6.0
3.0
Amo=Amorphous
Sample
MF
Solid products
Reaction time, days
BF-23 BF-24 BF-29 BF-28 BF-25
NH4F LiF NaF KF C sF
15 26 30
BF-32
NH4F
BF-30 BF-33
LiF NaF
BF-34
m
BF-31
C sF
BF-35
NaF
BF-36
KF
Beta Beta + Am0 Amo MTN Beta + Am0 Beta Beta Beta Beta Beta + A m 0 Beta Beta (traces) Beta Beta + Am0 Beta Beta + Am0 Beta Beta Beta
22
15 27 14 20 16 14
20 14 20 15 20 15 20 15 20
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With 12.5 KF in the gel crystallization led t o MTN phase. With 6 and 3 moles of KF in the gel Beta phase was obtained. The results with 12.5 NaF and 12.5 KF' in the system indicate, that such amounts of Na- and K-fluorides make Beta crystallization impossible. These results represent a rather rare case in zeolite synthesis, paying regard to the fact, that Na- and K- cations participate in the crystallization of majority of aluminosilicate zeolites. Note, that as it was found by Camblor and Perez-Pariente [5] in the alkaline medium, with TEA as template, zeolite Beta does not crystallize in the absence of these cations. Zeolite Beta has been obtained in the presence of NH4-, Li- and CsF in the system with SilAl=5. However, it was observed, that with NH4F, after prolonged crystallization time zeolite Beta content decreased and MTN amount increased in the product. It is difficult, a t present, to find explanation for the unusual behaviour of Na and K fluorides. The molar solubility of fluorides increases in the series: LiF
H H H H NH4
cs
NH4 NH4 Li
cs
NH4 Li
K K
Na
0.4
5.8 5.4 4.7 4.1 3.8 4.2
10.1 10.9 12.7 14.5 15.7 14.4
0.90 0.93 0.84 0.76 0.86 1.0
0.34 0.43 0.65 0.64 0.68 0.88
18.6
5.1 8.7
11.6 6.3
0.72
0.57
9.7 8.6 4.7 3.2
5.6 8.1 8.3 7.6 6.0
10.4 6.9 6.7 7.4 9.7
0.93 0.89 0.99
0.45 0.54 0.73
3.75 5
10 12.5 12.5 12.5 12.5
5 5 5 5 5 5 5 5
-
-
-
4.25 4.1
14.1 14.7
3.5 2.9 3.4 2.3 3.9
17.3 20.8 17.6 26.8 15.4 12.3
-
4.8
-
M=alkali cation; Si, Aktotal Si and A1 in the product; Si,, Al,=Si and A1 content in the gel; AlT=tetrahedrally coordinated Al.
176
The role of the alkali cation in the DABCO polymerization is also being investigated. The results of chemical analysis are included in Table 3. The Si/Al molar ratio of the product was always higher than that of the initial reaction mixture. It means, that only part of the aluminum being present in the gel was introduced into the framework. The products obtained from NH4 and Cs containing gels have similar composition (Si-, Al-content) to that of the products obtained with HF of the same Si/Al ratio. The Li-, Na- and K-containing crystals have Si/Al ratio slightly lower than the one of the respective products obtained in the absence of alkali cations. The yield of incorporation of Si and A1 into the crystals was calculated for some selected samples. The data for each element are given in Table 3 as the ratio between the amount of the element in the product and the amount in the gel (Sig, Alg). For the gels without alkali cations, the degree of aluminum incorporation increases with the increase of Si/Al ratio. The lower the aluminum content in the reaction gel, the higher its percentage of incorporation into the framework. For gels with Si/A1=3.75 and 5.0 the degree of A1 incorporation is below 50%. The low yield of aluminum is the result of easy complexation of this element by fluorine. After such a complex of Al with F is formed, aluminum is not available for incorporation in the zeolite. With NH4 and Li cations present in the gel, the A1 yield is the same as with HF only. Oppositely to Li and NH4, the Al yield increases when Cs and K are present in the gel. The yield of silicon depends also on the Si/Al ratio. For the series with HF as the only source of fluorides, it decreases with the increase of SVAl ratio. With various alkali fluorides in the system, silicon yield is in the range 0.72 - 1.0. Some selected samples from Tables 1 and 2 were analyzed by 27Al-, 29Si- and W-NMR. By means of 27Al-NMR the amount of tetrahedral and octahedral aluminum was calculated. The samples prepared from the gels of Si/Al = 12.5 contained all A1 in T-sites. Quite unexpectedly, the product prepared from the gel with 25 NH4 contained also 100% tetrahedrally coordinated Al. Among the analyzed samples which were crystallized from the gel of Si/Al=5, only the one obtained in the presence of CsF contained 100% A ~ T The . samples with NH4and Li-cations contained 35 and 27% of tetrahedral Al, respectively. Taking into , content per unit cell and s i / A l ~was also consideration the amounts of A ~ Tits calculated (Table 3). The purity of the samples was also checked by 29Si-NMR. The chemical shifts of the different NMR lines denote clearly the presence of a Beta phase (-106, -110 and -115 ppm) and/or an additional MTN phase (-119 ppm) (Figure la). The 13C-NMR spectra provide additional evidences on the nature of the polymer occluded in the zeolitic channels. When the relative intensity of the 55.7 ppm line (high intensity) is correct with respect to the 46 ppm line (low intensity), it is accepted as due t o a good Beta sample (see ref. 8) (Figure lb). The cation content in the crystals was also analyzed (see Table 3). The amount of Cs in the sample BF-15 was 0.4 Cs/u. c. indicating, that this cation practically did not enter the structure. The Li content in the samples BF-24 and
177
-100
-110
-120
ppm
70
60
50
40
PPm
Figurel. Proton enhanced MAS spectra of pure Beta zeolite synthesized from the gel 12.5DABCO-12.5MA-12.5HF-12.5CsF-Al~0~-25Si0~-500H~0 at 170OC: a) 29Si-NMR spectrum; b) 13C-NMR spectrum.
Figure 2. SEM pictures of zeolite Beta crystals obtained from the system: 12.5DABCO-12.5 MAxHF-yMF-2.5Al203-25SiO2-500H~O: BF-17) 25HF; BF-31) 19HF-GCsF; BF-32) 19HF6NH4F; BF-36)22HF-3KF
30 was higher than the amount of Al. The reason of this excess is the presence of an amorphous material in the product. The examples of crystal morphology of zeolite Beta obtained in the present work are shown in Figure 2. Their crystal size is about 1.5-3.0 pm. The crystals appear to be round and some of them show truncated square bypiramidal morphology, described previously by Caullet et al. 181. Crystals obtained in the presence of potassium and sodium cations are smaller than those synthesized in the presence of HF, NH4, Li and Cs.Their crystal size is in the range 1-1.8 Clm.
178
4. CONCLUSIONS The formation of zeolite Beta in the presence of HF or in the presence of NH4 and alkali cations (Li, Na, K, Cs) has been examined and compared with the synthesis in the presence of HF as a sole source of fluorides. 1,4-diazabicyclo [2, 2, 21 octane (DABCO) together with methylamine were used as organic templates. With HF, as the only source of fluorides, the optimal value of Si/A1=5 has been determined for pure Beta phase formation. The syntheses of zeolite Beta were carried out from the gels of composition: 12.5DABCO-12.5MA-12.5HF12.5MF-xA1203-25Si02-50OH~O with x=l and 2.5 and M=NH4, Li, Na, K and Cs. The alkali cations fall into two groups: the activating ones, which form Beta phase (Li, Cs and NH4) and the deactivating cations (Na, K), which suppress zeolite Beta crystallization. With 12.5Na and 12.5K in the system, zeolite Beta did not crystallize. In order to obtain the Beta phase in the presence of these deactivating cations, their content in the gel had to be diminished. 5. ACKNOWIXDGEMENT
R. Mostowicz is grateful to the Commission of the European Communities (COST program) for research grant. A. Fonseca acknowledges the Regional Government of Wallonie for financial support. This work was in part funded by the Belgian National Program of Inter-University Research Projects initiated by the State Prime Minister Office (Science Policy Programming) and by the Italian National Research Council (CNR-Progetto Finalizzato Chimica Fine). The Authors would like t o thank Mr Guy Daelen from the University of Namur for his skillful help in taking the NMR spectra.
1.R.L. Wadlinger, G.T. Kerr and E.J. Rosinski, U. S. Pat. No.3 308 069 (1967). 2. J. Perez-Pariente, J.A. Martens and P.A. Jacobs, Appl. Catal., 31 (1987) 35. 3. J. Perez-Pariente, J.A. Martens and P.A. Jacobs, Zeolites, 8 (1988) 46. 4. M.A. Camblor and J. Perez-Pariente, Zeolites, 11(1991) 202. 5. M.A. Camblor, A. Misfud and J. Perez-Pariente, Zeolites, 11(1991) 792. 6. P. Caullet, J.L. Guth, A.C. Faust, F. Raatz, J.F. Joly and J.M. Deves, Fr. Pat. 89/12556 (1989). 7. A. Ajot, J.F. Joly, J. Lynch, F. Raatz and P. Caullet, Stud. Surf. Sci. Catal., 62 (1991)583. 8. P. Caullet, J. Hazm, J.L. Guth, J.F. Joly, J. Lynch and F. Raatz, Zeolites, 12 (1992)240. 9. F. Crea, R. Mostowicz, R. Aiello, A. Nastro and J. B.Nagy in Proc. 9th Intern. Zeolite Conf., Montreal 1992, J.B. Higgins, R. Von Balmoos, M.M.J. Treacy (eds.), Butterworth-Heineman 1993, Vol. I, p. 147. 10. R. Mostowicz, F. Crea and J. B.Nagy, Zeolites, 13 (1993) 678. 11. R. Mostowicz, F. Testa, F. Crea, R. Aiello and J. B.Nagy, in preparation.