Syntheses of Pentasil Silica-Zeolites From Nonaqueous Systems

P.A. Jacobs and R.A. van Santcn (Editors), Zeohs: Fncts, Figures, Future b 1989 Elscvier Science PublishersB.V., Amsterdam - Printed in The Netherlands

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SYl'iTHESES OF PENTASIL SILICA-ZEOLITES FROM NONAQUEOUS SYSTEMS

HUO QISHENG, FENG SHOUHUA AND XU RUREN Department of Chemistry, Jilin University, Changchun, China ABSTRACT

Three types of pentasil silica-zeolites, silicalite-l,ZSM-39 and ZSM-48, have been synthesized from organic solvents in the presence of specific templating agents or crystal seeds. The crystalline products were characterized by means of X-ray diffraction(XPD), infrared(IR), thermoanalysis and composition analysis. The kind of product was remarkably dependent on the contents of alkali and templating agents used in the reaction mixtures. The present results showed that not only the zeolites with 4- and 6-membered rings but also the zeolites with 5membered ring can be synthesized in nonaqueous media. INTRODUCTION Hydrothermal techniques are widely used in the synthesis of zeolite molecular sieves and zeolite-like materials. Especially the introduction of organic templating agents into the reaction mixture has developed many new types of molecular sieve zeolites including high-silica zeolites such as a series of pentasil materials and novel family of aluminophosphate molecular sieves (A1P04-n)(refs.l-3). In recent years, the synthesis of zeolites in nonaqueous systems was attracted extensive attention in the field of zeolite research. In 1985, Bibby and Dale first reported the syntheses of a silica-sodalite and aluminosilicate-sodalites over a wide range of Si/Al ratio from ethylene glycol or propanol solvent(ref.4), which was followed by a study on the framework structure of the silica-sodalite with encapsulated ethylene glycol (refs. 5,6). In 1987, Van Erp and his coworkers (refs.7) synthesized BaT, hydroxysodalite, and kaliophilite using such organic solvents as glycol, glycerol, sulfolane, DMSO, ethanol, pyridine and c647 alcohols. The investigations on the zeolite syntheses in nonaqueous media are scarce, and only a few zeolites were synthesized from nonaqueous systems and also the zeolites obtained were limited within those containing 4- and 6-membered rings. Recently, we have developed a improved method to synthesize the silicasodalite rapidly in ethylene glycol solvent and determined its framework structure by single crystal X-ray diffraction method (ref. 8). In the present paper, we report the exploring research for the syntheses of pentad-type silica zeolites (silicalite-1, ZSM-39 and ZSM-48) in nonaqueous solvents. EXPERIMENTAL A typical synthetic procedure was in following: according to a certain batch

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composition of starting mixture, sodium hydroxide was first dissolved in organic solvent or mixed solvent and then fumed amorphous silica was added with stirring. A mixture was formed, to which certain templating agent or crystal seed was added. Crystallization of the reaction mixture was carried out in a stainless steel autoclave at 18OoC under autogenous pressure. The crystalline products were filtered,washed with distilled water and dried at ambient temperature. The organic solvents used were: ethylene glycol(EG), butyl alcohol(BuOH), glycerol(GE), amyl alcohol and hexyl alcohol. The templating agents were tetramethylamnonium bromide(R1ABr), tetraethylamnonium bromide(Wr), tetrapropylammonium bromide(TF'ABr), or propylamine(PrNH2). The crystal seed was silica-sodalite. The composition of crystalline products were determined by chemical analysis. The crystalline products were identified on a RIGAKU D/max- IIIA diffractometer using Cu Ka radiation. The infrared spectra in the range 400-1400~m-~ were recorded on a Nicolet 5DX spectrometer using KBr pellet technique. Scanning electron micrographs were taken on a HITAWI X-650 scanning electron microscope. Thermogravimetric analysis was carried out using a SHIMADZU DT-30 thermobalance. The concentration of silica dissolved in initial mixture was determined by the yellow silicmlykdate method. Prior to the determination the initial mixture was stirred for 24 hrs at ambient temperature. RESULTS AND DISCUSSION Syntheses of pentasil-type silica zeolites The initial reactant composition, synthetic conditions and products in EG solvent are listed in Table 1. The kinds of crystalline products are critically dependent on the contents of NaOH and TPABr. Without TPABr in run 101, a silicasodalite was easily obtained, and with the increasing of the content of NaOH, la new crystalline silicate containing EG molecules, named phase B(unknown structure) formed. When certain amounts of TPABr were added into the initial reactant mixture of run 104 (for phase B), a pentasil-type zeolite (silicalite-1) was synthesized. It has been observed that even if certain amounts of TPAEk were added into the initial reaction mixture of m lOl(for silica-sodalite), we cann't obtain silicalite-1, which only accelarated the crystallization of the silicascdalite (ref.8). So, both basicity and templating agent are important for the formation of silicalite-I.It seems that beso'silica molar ratio for the initial reaction mixture has only a small influence oli the formation of zeolites. The zeolite ZSM-48 was synthesized from EG-BuOH solvent in the presence of N B r or silica-sodalite crystal seeds. The initial reactant compositions,,synthetic conditions and products in EG-BdH mixed solvent are listed in Table 2. If no M r or silica-sodalite crystal seeds were added, we didn't obtain zeolite ZSM-48, but only obtained silica-sodalite in lower basicity (run 201). ?he role

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TABLE 1 The initial reactant compositions, synthetic conditions and products in run

101 102 103 104 105 106 107

Reactants(mo1e) NaOH Si02 EG TPABr

1.0 1.0 1.2

1..5 1.5 2.0 3.0

2.0 2.0 1.5 2.0 2.0 2.0 2.0

40 40 40 40 40 40 40

Crystallizationa time(days)

0

0.3 0.3 0 0.3 0.3 0.3

3 2 10 10 25 25 25

Product silica-sodalite silica-sodalite silica-sodalite B silicalite-1 silicalite-1 amorphous

a Crystallization temperature 180OC. TABLE 2 The initial reactant compositions, synthetic conditions and products in EG-BuOH mixed solvent Reactants (mole) Crystallizationa Product run NROH sio2 EG BUOH m r time( days) 201 0.5 2 20 12 0 10 silica-sodalite 202b 1.0 2 20 12 0 45 amorphous 1.0 2 20 12 0 50 ZSM-48 203 204 1.0 2 20 12 0.1 25 ZSM-48 a Crystallization temperature 180OC. b Silica-sodalite crystal seeds added(0.X in weight of total reactants). of crystal seeds is probably favourable for the nucleation of ZSM-48. It had been seen that one kind of zeolite formed from the synthetic system having another type of zeolite seeds. One example is the synthesis of zeolite ZSM-5 in the presence of mordenite, zeolite-Y, zeolite-B or ZSM-50(refs. 9-11). An investigation for this is being made. In the synthetic system for zeolite ZSM-48, the BLOH of the mixed solvents can be replaced by amyl alcohol or hexyl alcohol. The zeolite ZSM-39 was prepared from the mixed solvents of BuOH-GE (see Table 3). To obtain zeolite ZSM-39, we used EG-BuOH as mixed solvent and also added TABLE 3 Synthetic conditions and products for zeolite ZSM-39. Reactants(mole) Crystallizationa run NaOH Si02 BUOH GE PrNH2 time(days)

8 5 2 16 3Olb 0.5 8 3 0.5 2 16 302 303 0.5 2 16 8 0 a Crystallization temperature 180OC. b 0.1 mole 'IMABr and 0.1 mole TEABr added.

60

100

60

Product ZSM-39 ZSM-39 amorphous

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PrW2. Without PrNH2, no crystalline product was obtained, so PrNH2 molecules seem to be much favourable to the formation of zeolite ZSM-39 in nonaqueous systems. Characterization of silica-zeolite All samples of silica zeolites obtained from nonaqueous systems have higher crystallinity and have considerable particle size. Their scanning electron micrographs are shown in Figure 1. The scanning electron micrograph of a typical zeolite ZSM-48 shows large growth aggregates composed of small prisms. Silicalite-1 is "a dumbbell" in shape. The zeolite ZSM-39 shows incomplete octahedra growth aggregates. The X-ray powder diffraction patterns of as-made silicalite-l(a), ZSM-39(b), and ZSM-48(c) are shown as Figure 2 . Table 4 lists the unit cell compositions of selected pentasil-type silica zeolites. TABLE 4 The unit cell compositions of selected pentasil-type silica zeolites Zeolite Unit cell composition

For investigating the guest molecules in the pentasil-type silica zeolites, the thermal analyses were made in flowing nitrogen with the temperature range of 20-10OO0C. The results showed that most of the EG and TPABr molecules lost from the framework of silicalite-1 (105) over the temperature range of 100-600°C. The silica ZSM-39(301) lost PrNH2 molecules over the range of 100-700°C. The silica ZSM-48(203) began to loss weight at 100°C and completly lost BuOH molecules until 60OoC. All frameworks did not collapse in structure at 1000°C by X-ray analysis. The IR spectra of silicalite-l(a), ZSM-39(b) and ZSM-48(c) are bhown in Figure 3. The silicalite-1 has characteristic absorptions of external asymnetric stretching(1224cm- 1), internal asymnetric stret~hing(l095cm-~),symnetric stretbhing (783cm-'), double ring (558cm-I) and bend (445cm-I) vibrations (ref. 1 2 ) . The bands at 1092, 786, 558 and 466cm-1 for ZSM-48 are assigned to asymnetric stretching, symnetric stretching, double ring and Si-0 bend vibrations, respectively. The asymnetric stretching, symnetric stretching and Si-0 bend vibrations for silica ZSM-39 appeared at 1115, 787 and 47Ocm-', respectively. Some characteristics of nonaqueous systems An organic compound which was used as medium for zeolite synthesis should possess higher boiling point and stability to alkali. The measurement of the electric conductivity was made to characterize the basicity of organic solution. Table 5 lists the results of the measurements of

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Silicalite-I (a)

Silicalite-1 (b)

ZSM-39

ZSM-48

Fig. 1 Scanning electron micrographs of silicalite-1, ZSM-39 and ZSM-48.

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I (C)

Degree, 28 Fig.2 X-ray diffraction patterns of of silicalite-l(a), ZSM-39(b) and ZSM-48(c).

Fig.3 Infrared spectra of silicalite-l(a), ZSM-39(b) and EM-48(c)

.

electric conductivities of various NaOH-EG solutions and NaOH-H20 solution as a reference. From Table 5, we can see that the electric conductivity of NaOH-EG solution (No.1) is much less than that of NaOH-H20 solution(No.5). This showed that some of NaOH exist in the form of ionpair in organic solvent, which led to the lower effective basicity in this solution. The concentrations of silica dissolved in starting mixtures were analysized (Table 6) to be very low. As the content of NaOH increased from 0.5 to 2.0 mole, the concentration of silica increased from 5.4~10-~ to 1.2x10-2mole/l. Even at crystallization temperature, the concentration of silica in nonaqueous system subh )as in FG solvent was also very low compared to hydrothermal system (ref. 13)

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we know that the polymerization degree of silicate mainly depends on the concentration of silicate and basicity of solution (ref.14). Therefore, the silicate species in nonaqueous system have very different structure and polymerization degree from those in aqueous system. In addition, the possible interaction between silicate species and organic solvnet should be considered.

As

TABLE 5

The electric conductivities of various NaOH-EG and NaOH-H,O solutions No.

NaOH (mole)

solvent NaOH (mole) apparent concentration (mole/l) 40EG

0.22

1 .o

40EG

0.44

1.5

4OEG 40EG 126H20

0.66

1

0.5

2

3 4 5

2 .O 0.5

0.88

0.22

electric conductivity

(US) 1 .9x103 3. 9x103 4.2xI03 5. 7xI03 3.0~10~

TABLE 6 The concentrations of silica dissolved in various solutions. No.

NaOH

batch canposition(mo1e) Si02 solvent

2 3 4

1 .o

2 2

1.5

2

2 .O

5

0.5

2 2

1

0.5

40EG

40EG 40EG 4OEG

12m20

Si(mole/l) 5. ~ x I O - ~ 8.1x10m3 9.2~10-~ 1.2x10-2 1.2x10-1

Some organic templating agents used in nonaqueous systems have the same effect of structure-directingas in aqueous systems, but a limit of the kinds of used organic templating agents was observed and a suitable content of soluble silica was required. This was driven from the fact of the synthesis of silicalite1 by using 1.5 mole NaOH (corresponding to 9.2~10-~ Si02 mole/l) and certain amounts of "F'ABr. But under the condition of relatively less amounts of NaOH and in the presence of TPABr, we cann't obtain desired product. No all ternplating agents, which are effective in aqueous solution, can be used in nonaqueous systems. The attempt to use some other ternplating agents for the synthesis of silica zeolites in EG solvent did not succeed.

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CONCLUSIONS The increase of content of NaOH in the initial mixture composition from which the silica-sodalite was crystallized and the introduction of specific templating agent, TF'ABr, led to the formation of the silicalite-1. The silica ZSM-39 and ZSM-48 can be synthesized in the presence of effective templating agents or crystal seeds from mixed organic solvents. The crystallization of pentasil silica zeolites was critically dependent on the kind of organic solvnet, the basicity of reaction mixture and added templating agent. The present results showed that not only silica clathrasils (rafs. 4,15,16) but zeolites containing 4-, 5- and 6membered rings can be obtained from nonaqueous media as well. REFERENCE 1 D.W. Breck, Zeolite Molecular Sieves, John Wiley, New York, 1974. 2 R. M. Barrer, Hydrothermal Chemistry of Zeolites, Academic Press, New York, 1982. 3 S.T. Wison, B.M. Lok C.A. Messina, T.R. Cannan and E.M. Flanigen, J. Am. Chem. SOC., 104(19823 1146. 4 D.M. Bibby and M.P. Dale, Nature, 317(1985) 157. 5 R.H. Meinhold and D.M. Bibby, Zeolites, 6(1986) 427. 6 J.W. Richardson, Jr., J.J. Pluth, J.V. Smith and W.J. Dytrych, J. Phys. Chem., 92(1988) 243. 7 W.A. van Erp, H.W. Kouwenhoven and J.M. Nanne,Zeolites, 7(1987) 286. 8 Feng Shouhua, Xu Jianing, Xu Ruren Yang Guangdi, Chen Zhongguo and Li Genpei, Chem. J. Chinese Univ,(English Ed. 4(1988) 9. 9 Zhou Jiansheng, Hua Xue Tong bao, 6(1988) 29. 10 R. Mostowitz and L.B. Sand, Zeolites, 3(1983) 219. 11 Chu Pochen. La Pierre and Rene Bernard, EP 170, 486 (1986). 12 J.C. Jansen, F.J. van der Gang and H. van Bekkum, Zeolites, 4(1984) 369. 13 Feng Shouhua, Suhitted for Publication. 14 R.K. Iler, The Chemistry of Silica, Wiley, New York, 1979,p131. 15 J.V. Smith, Chem. Rev., 88(1988) 149. 16 F. Liebau, H. GIes, R.P. Gunawardane adn B. Marler, Zeolites, 6(1986) 373.

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