Synthesis of zeolites under vapor atmosphere

219

Microporous Materials, 1 (1993) 219-222 Elsevier Science Publishers B.V., Amsterdam

Short Communication

Synthesis of zeolites under vapor atmosphere Effect of synthetic conditions on zeolite structure Masahiko Matsukata*, Norikazu Nishiyama and Korekazu Ueyama Department of Chemical Engineering, Faculty of Engineering Science, Osaka University, I-I Machikaneyama-cho, Toyonaka-shi, Osaka 560, Japan

(Received 20 December 1992; accepted 28 January 1993)

The present study found that ahrminosilicate gels were crystallized to ZSMJ, ferrierite, KZ-2 or analcime under a vapor atmosphere. The structure and crystallinity of the resultant zeolite significantly depended on the composition of the organic vapor as well as that of the parent gel. Keywords: synthesis; ZSM-5, ferrierite; analcime; vapor

Introduction

Experimental

Medium pore zeolites have been hydrothermally synthesized by using quaternary ammonium salts [1,2], amines [3-81 or other polar organic substances [9,10] as templates. Dong et al. [l&12] have first synthesized ZSM-5 from amorphous aluminosilicate gels in vapor of ethylenediamine (EDA), triethylamine (Et,N) and water. Their new synthetic method seems attractive because the following possibilities open up: (1) synthesis of zeolites with a SiOz/Al,03 ratio which is the same as that of the parent gel, (2) continuous production of zeolites because the gel is separated from the liquid, and (3) production of zeolites from amorphous gels which are arranged in the desired shape in advance. The objective of the present study is to confirm that various zeolites can be synthesized from aluminosilicate amorphous gels in a vapor of amine, alcohol and water.

A sodium silicate solution (Kant0 Chemical Co., Inc.) containing 35-38 wt% SiOz and 17-19 wt% NazO was used as the silica source. In some experiments, a colloidal silica (ST-S; Nissan Chemical Industries, Ltd.) containing 30.33 wt% SiOz and 0.42 wt% Na,O was mixed with the sodium silicate solution to vary the concentration of Na+ ions in the resultant gel. Anhydrous aluminium sulfate, Al,(SO& (Wako Pure Chemical Industries Co., Ltd.), was used as the alumina source. The parent aluminosilicate gel was prepared as follows (unless otherwise stated): Al,(SO& was dissolved in deionized water and mixed with the silica source. After a given amount of sulfuric acid was added to the mixture in order to adjust the pH of the gel, the mixture was dried at 343 K for 4 h and then rinsed with deionized water. Crystallization was carried out in a special autoclave which had a perforated partition in the middle of the vessel. A schematic diagram of the autoclave is shown in Fig. 1. The parent gel was

* Corresponding author.

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M. Matsukata

et al. / Microporous Mater. I (1993) 219-222

with Nz to prevent organic compounds from reacting with COZ and OZ. Then, the autoclave was heated to 453 K and kept at that temperature for 3 days. The parent gel in contact with vapor from the liquid crystallized into a zeolite. The product was rinsed with deionized water and dried at 363 K overnight. XRD and 27A1 NMR were used to characterize the product.

Results and discussion

Fig. 1. Schematic diagram of special autoclave: (a) thermocouple, (b) agitator, (c) Teflon vessel, (d) filter, (e) perforated plate, (f) amorphous gel and (g) solution.

placed on a Polyflon filter (PF20; Advantec Toyo Co.) made of polyethylene and this was set on the partition. Water, Et3N, EDA, 1-propanol and mixtures containing some of these liquids were tested as sources of the supply vapor. The liquid phase was poured into the bottom of the vessel. After the autoclave was sealed, internal air was replaced

Crystallization experiments were carried out by varying the concentration of Naf ions, the pH of the parent gel and the composition of the liquid phase supplying vapor. We confirmed that several types of zeolites were produced in the present synthetic method. Table 1 summarizes the crystallization results. Ferrierite was produced in a vapor of Et,N, EDA and Hz0 when the pH of parent gel was in the range of 9-l 1 and the molar ratio of Et3N to EDA was 5.3 (Runs 4 and 8). In the presence of steam (Run 3), steam and EDA (Run lo), or steam and Et,N (Run 1l), crystallization usually did not occur. These results reveal that coexistence of Et,N and EDA is essential at least for the crystallization of ferrierite. KZ-2 [13]

TABLE 1 Typical results of crystallization in vapor Run

Initial amorphous gel”

Liquid phase composition

Product

Analcime Ammonium Analcite Amorphous Ferrierite Ferrierite + ZSM-5 ZSM-5 ZSM-5 Ferrierite KZ-2 Amorphous Amorphous Amorphous

Composition

PH

1 2

14Na,O : Al,O, : 29Si02 14Na,O : Al,O, : 29Si02

12.0 12.0

Hz0 EDA: 5.3Et,N : 2.5H,O

3 4 5b

14Na,O : A1,O1 : 29Si0, 14Na,O : A&O, : 29Si0, 12Na,O : Al,O, : 26Si0,

11.0 11.0 9.3

Hz0 EDA: 5.3Et,N : 2.5H20 EDA : 5.3Et,N: 2.5H,O

6

6Na,O : Al,O, : 26Si02 15NazO:Al,0,:31Si0, 14Na,O : A&O, : 29Si0, 14Na,O : Al,O, : 29Si02 14Na,O : Al,O, : 29Si0, 14Na,O : Al,O, : 29Si0, 14Na,O: Al,O, : 29Si0,

10.9 9.6 9.5 9.6 9.9 9.9 10.0

EDA: 5.3Et,N: 2.5H,O I-PrOH : 2.0Et,N EDA: 5.3EtsN : 2.5H,O EDA: 17.3Et,N: 7.4H,O 2.5EDA: H,O Z.lEt,N: H,O 1.1 I-PrOH:H,O

7b.c

8 9 lob lib 12b

“Initial gel compositions and’ pH are the values before rinsing. Compositions are shown by using molar ratio. bGel was not dried before crystallization. ‘Synthesized at 433 K for 6 days.

M. Matsukata

et al. / Microporous

Mater. I (1993) 219-222

was obtained instead of ferrierite when the molar ratio of Et,N to EDA was increased from 5.3 to 17.3 (Run 9), indicating that the type of zeolite structure depended on the molar ratio of Et3N to EDA. In Et,N, EDA and H,O vapor, ZSM-5 and a mixture of ZSM-5 and ferrierite were obtained when the molar ratio of Na,O to AlzO, was 6 and 12, respectively, as shown in Runs 5 and 6. Taking into account that a pure phase of ferrierite was obtained at a Na,O/Al,O, ratio of 14, we considered that ZSM-5 was produced at lower concentrations of Na in the parent gel. ZSM-5 was, however, synthesized using Et,N and l-PrOH at a high Na,O/Al,O, ratio of 15 in the parent gel, as shown in Run 7. As in the ferrierite synthesis in a vapor of Et,N, EDA and HzO, coexistence of Et3N and l-PrOH was found to be essential to synthesize ZSM-5, because no crystallization was observed under a I-PrOH atmosphere, as shown in Run 12. While ferrierite was formed in the pH range 9-l 1 as described above, analcime was produced in steam; ammonium analcite having a similar type of structure to analcime [14,15] was produced at pH 12 in vapor of Et,N, EDA and H,O. Thus, the pH of the parent gel is another factor that governs the structure of the resultant zeolite. The *‘Al MAS NMR spectra were taken for ferrierite and ZSM-5 synthesized in Runs 4 and 6, as shown in Fig. 2. The occurrence of one major line in the spectra shows the predominance of tetrahedrally coordinated aluminum. It gave no 55.7

(4

221

peak at 0 ppm, indicating the absence of octahedral aluminum. Figure 3 shows *‘Si MAS NMR spectra for ferrierite and ZSM-5. The Si02/A1203 ratio was determined from these spectra as 25 both for ferrierite and ZSM-5. It should be noted that the ratio for ZSM-5 was in good agreement with the ratio of the parent gel. These results reveal that the parent gel was sufficiently crystallized and all Al3 + ions were incorporated in the framework of ZSM-5. Thus, we consider that zeolites with the same Si02/A1203 ratio as that of the parent gel can be synthesized by this method. On the other hand, while it was suggested from the *‘Al NMR spectrum that all Al3 + ions were incorporated in the framework, the Si02/A1203 ratio of ferrierite determined from the *‘Si NMR spectrum was slightly smaller than that of the parent gel. This result implied that part of Si remained uncrystallized under the experimental conditions employed. Figure 4 compares the compositions of the parent gels used in Runs 4, 6 and 7 with typical ones of gels which have been used in hydrothermal synthesis. The gel compositions used by Xu et al. [ 1l] is shown together. It is noteworthy that ZSM5 with a low Si02/A1203 ratio of 25 was obtained in this method even at a Na20/Si02 ratio of 0.48 which was higher than those used in the conventional hydrothermal synthesis. The present study confirmed the usefulness of the synthetic method under a vapor atmosphere for the production of various zeolites. We expect that this synthetic method offers promising pros-

I 55.2

Tetrahedral

04

Tetrahedral

(4

(b) i

ferrierite

ZSM-5

Fig. 2. “Al NMR spectra of ferrierite (Run 4) and ZSM-5 (Run 6). Chemical shift was calibrated by using Al,(SO,),.

Fig. 3. 29Si NMR spectra of ferrierite (Run 4) and ZSM-5 (Run 6). Chemical shift was calibrated by using TMS.

M. Matsukata et al. / Microporous Mater. I (1993) 219-222

222

’

I

’

I

’

I

References

I

’

’

ZSMQ: Vapor phase method”) 0

ZSMQ: Hydrothermal synthesis”’

0

ZSMQ: This work

A

Feniertte: Hydmthenal

cl

Ferrterite: This work

16W

synthesis4)

I

0.0

0.1

0.2

0.3

0.4

Nan0 / SiOn [ mol

0.5 /

0.6

mol ]

Fig. 4. Compositions of parent gels for synthesis of ZSM-5 and ferrierite. Figures given in the neighborhood of each plot correspond to the reference numbers.

pects for (1) synthesis of zeolites possessing the same SiOZ/Al,03 ratio to that of the parent gel, (2) continuous production of zeolites, and (3) production of zeolites shaped in advance, as mentioned in the introduction.

Acknowledgements We wish to express our appreciation for a Grantin-Aid for General Scientific Research by The Ministry of Education, Science and Culture.

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