Short Papers

Preliminary studies on the synthesis of alkaline-free large crystals of ZSM-5

U. Mueller and K. K. Un er Institut fiir Anorganische t!! hemie und Anal t&he Chemie,

J ohannes Gutenberg-Universitiit, P. 8 . Box

3980, 6 00 Mainz, FRG (Received 27 July 1987; accepted IO August 1987)

Single crystals of ZSM-5 were synthesized in three systems

containing Na+-TPA, Li+-TPA, and NH:-TPA, respective-

ly. Applying a reaction mixture of the molar composition

8TPA + 123 (NH&O + A1203 + 59 SiOz + 2280 HzO,

alkaline-free, homogeneous, and pure single crystals of

ZSM-5 were prepared up to a length of 350 Km. The crystal

size and yield were found to be dependent on the water

content of the starting reaction mixture and on the type of

aluminium source; for example, boehmite and aluminium-

triisopropylate.

Keywords: ZSM-5; single crystals; alkaline-free synthesis

INTRODUCTION

There has been an enormous number of studies reported on the synthesis of zeolite ZSM-5’-s; howev- er, only a few studies reported attempts to produce large crystals (see Table I). Besides being well suited for X-ray structural analysis” these single crystals can be used as model substances for investigating diffu- sion processes,‘**i3 catalytic studies,14 and sorption experiments. Because the large crystals exhibit a negligibly small external surface area compared to microcrystalline products, the intrinsic sorptive prop- erties can be estimated with high precision. I5

This paper describes a synthetic rule to produce large single crystals of ZSM-5 with high yield and narrow particle-size distribution. Three different reaction mixtures coded as A, B, and C were employed. The latter did not contain alkali reactants. On the basis of a 23-factorial design, the operational variables of the reaction mixture C were optimized to gain a high yield and large size of crystals.

EXPERIMENTAL

The compositions of the starting mixtures were as follows: -

system A: Aerosil TT600 (Degussa); sodium alumin- ate and sodium hydroxide, both of rea- gent grade (Merck); tetrapropylammo- nium bromide (TPABr) supplied by SER- VA; and deionized water; Ludox AS-40 (Du Pont); boehmite (PU- RAL SB, Condea), lithium hydroxide and ammonia solution (25% w/w); both of reagent grade (Merck); TPABr; and de- ionized water; and Ludox AS-40; PURAL SB; aluminium- triisopropylate and ammonia solution (32% w/w), both reagent grade (Merck); TPABr; and deionized water.

system B:

system C:

Crystallization was carried out in teflon-coated auto- claves of 100 ml vol at 453 K. Details of the reaction procedure using system A were described elsewhere.6 To avoid losses of ammonia and to prevent carbon dioxide absorption, the reaction components of mix- tures B and C were directly weighed into the beaker of the autoclave and afterward stirred intensively. The sequence of adding the components was TPABr, LiOH, aluminium source, Ludox AS-40, water, and ammonia solution. The autoclave was filled to 70% of the total volume in each case. After maintaining the reaction temperature of 453 K for 7 days, the products were filtered, washed to neutrality, and dried at 393 K. The crystal morphology was moni- tored by means of scanning electron microscopy (SEM) using a PHILIPS SEM 500. Cristallinity and phase composition were controlled by X-ray diffrac- tion (PHILIPS APD 15).

RESULTS AND DISCUSSION

In the reaction mixture A using Na+-TPA, the ratio

Table 1 Synthesis systems for the growth of large ZSM-5 crystals

Authors Cry&l size

System (Km) Ref.

Guth et a/. NH,HF2, NH4F, TPA 800 Hayhurst and Lee

4

Na, TPA 400 Mueller and Unger

5 NH4, TPA 350

Lermer et a/. Na, TPA This paper

280 van Koningsveld et al.

6

Na, TPA 230 7 von Ballmoos and Meier Na, TPA 200 Chao et a/.

8 Na, TPA 200

Nastro and Sand 9

Li, NH4, TPA 140 Fegan and Lowe

10

Amine, TPA 100 11

0 1988 Butterworth Publishers

154 ZEOLITES, 1988, Vol8, March

Short Papers

line phases were observed. The yielcl was 75%’ (w/w). Typically, all crystals obtained from this reaction mixture showed flakelike growth clistortion at the surface (see Figure 2).

Crystals of ZSM-5 having lengths of 140 + 10 ALIBI have already been synthesized, but with a much lower amount of (NH ,)?O. I” Synthesis of ZSM-5 and ZSM-11 crystals in a NH.7 -TPA system were first described by Bibby e/ .l.“’ and the latter were more intensively studied by Ghamami and Sand.” Using a reaction mixture of type C with a composition:

(IV) 8 TPA + 123 (NH.,)20 + AlpO,, + 59 SiOL, + 1040 Hz0

sodium-free single crystals of ZSM-5 were synthe- sized. The lath-shaped crystals were about 1 10 pm in length with a narrow-size distribution, and they were fairly free of growth defects (see Figtrre 3). The yielcl varied from 70 to 75% (w/w). Crystal size and yielcl were further enhanced by an optimization (2” facto- rial design) of the composition of the starting reaction

mixture, in particular, by adjusting the duration of crystallization, the water content, and the concentra- tion of TPABr. Crystals of 350 pm in length of a yielcl of 85% (w/w) were received applying a mixture of the following composition (see Figure 4):

Figure 1 Product of reaction system A: ZSM-5 crystals largely intergrown (scale bar = 100 pm)

of TPA to OH- was systematically varied between the limits of 0.5 (I) to 6.4 (II). The corresponding compositions of the starting reaction mixtures were:

(1) 60 TPA + 60 Na20 + A&O:< + 22 SiO? + 3300 H20

(11) 154 TPA + 12 Nay0 + AlzOzr + 22 SiOy + 3300 Hz0

The product obtained from mixture I was pure analcime. With increasing the content of TPABr, the yield of ZSM-5 increased. Reaction mixture II gave a yield of 95% of ZSM-5 crystals up to a length of 240 pm; however, the products were largely intergrown (see Figure I).

Reaction system B using a composition of:

(III) 8 TPA + 74 (NH.,)20 + 3 L&O + Al.,0z3 + 59 SiO? + 750 Hz0

yielded crystals of ZSM-5 of 190 + 20 pm (see Figure 2). Small amounts of amorphous gel were removed by dissolution with sodium hydroxide. No other crystal-

Figure 2 Product of reaction system B: ZSM-5 crystals with distorted surfaces (scale bar = 10 pm)

W) 8 TPA + 123 (NH a)20 + A120:< + 59 SiO? + 2280 HyO

Replacing PURAL SB by aluminium-triisopl-opylate, the yield increased up to 95%; however, the crystal size diminished to about 80 pm (see F~KI~,-(J 5).

CONCLUSIONS

Reaction mixtures and conditions were Morkecl out to synthesize alkaline-free single crystals of ZSM-5 up to a length of 350 pm. Crystallization occurrecl at a high yield of 85% (w/w), ancl the products hacl a pure phase composition. The water content of the reaction mixture as well as the solubility of the aluminium

Figure 3 Product of reaction system C: ZSM-5 crystals, alkaline-free using a composition IV (scale bar = 100 pm)

ZEOLITES, 1988, Vol8, March 155

Figure 4 Large ZSM-5 crystals using an optimized reaction composition V (scale bar = 10 pm)

component exerted a notable influence on the crystal properties described. The crystals obtained in system C showed a high morphological homogeneity in comparison with products synthesized in Na+-TPA and Li+-TPA systems.

The materials synthesized serve as candidates for high-resolution sorption measurements. Adsorption studies of nitrogen and organic vapors on such HZSM-5 showed that single crystals gave rise to distinct hysteresis effects. Fine gradations in some structural characteristics of the zeolite lattice help to explain the results from sorption experiments.18

ACKNOWLEDGEMENTS We wish to thank Dr. G. T. Kokotailo for his helpful discussions and advice during his stay at Mainz in September 1986. Financial support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

REFERENCES 1 Argauer, R. J. and Landolt, G. R. US Pat. 3 702 886 (1972)

Figure 5 ZSM-5 crystals obtained with an optimized starting composition using aluminium-triisopropylate as aluminium source (scale bar = 100 pm)

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Lok, B. M., Cannan, T. R., and Messina, C. A. Zeolites 1983,3, 282, and references given therein Olson, D. H. et al. J. hys. Chem. 1981, 85, 2238-2243 Guth, J. L., Kessler, H.. and Wev. R.. in Studies in Surface Science and Cata/y&, vol. 28, (ids. i’. Murakami, A. lijima, and J.W. Ward) Elsevier, Amsterdam, 1986, pp. 121-128 Hayhurst, D. T. and Lee, J. C. in ibid., pp. 113-120 Lermer, H. et a/. Zeolites 1985, 5, 131-134 van Koningsveld, H., van Bekkum, H., and Jansen, J. C. Acta Ciyst. 1987, B 43, 127-l 32 von Ballmoos, R. and Meier, W. M. Nature 1981, 289, 782 Chao, K.-J. et al. Zeolires 1986, 6, 35 Nastro, A. and Sand, L. B. Zeolites 1983, 3, 57-62 Fegan, S. G. and Lowe, B. M. J. Chem. Sot., Faraday Trans. 1 1986, 82, 801 Prinz, D. and Riekert, L. Ser. Bunsenges. Phys. Chem. 1986, go,413417 Billow, M. et al., Studies in Surface Science and Catalysis Vol. 28 (Eds. Y. Murakami, A. lijima, and J. W. Ward) Elsevier, Amsterdam, 1986, pp. 579-586 Chen, N. Y., Kaeding, W. W., and Dwyer, F. G. J. Am. Chem. Sot. 1979,101, 6783 Mueller, U. and Unger, K. K. Fortschr. Mineral. 1986, 64(l), 128 Bibby, D. M., Milestone, N. B., and Aldridge, L. P. Nature 1980,285, 30 Ghamami, M. and Sand, L. B. Zeolites 1983, 3, 155 Mueller, U. and Unger, K. K., in Studies in Surface Science and Catalysis, vol. 39 (Eds. K. K. Unger et a/.), Elsevier, Amsterdam, 1988, pp. 101-108

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