Characterization of Siliceous Zeolites Crystallized in the Presence of Trioctylamine. Part I. Synthesis and Crystal Properties*

P.J. Grobet et al. (Editors) /Innovation in Zeolite Materials Science © Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

CHARACTERIZATION OF SILICEOUS ZEOLITES CRYSTALLIZED IN TRIOCTYLAMINE. PART I. SYNTHESIS AND CRYSTAL PROPERTIES*

45

THE

PRESENCE

OF

M. L. OCCELLI, 1 S. S. POLLACK, 2 and J. V. SANDERS 3 1Unocal Corporation, P.O. Box 76, Brea, CA 92621 USA 2Dept. of Energy, PETC, P.O. Box 10940, Pittsburgh, PA 15236 USA 3CSIRO, Locked Bag 33, Clayton, 3168, Victoria, Australia

ABSTRACT Alumina-rich zeolites of the pentasi1 family [with 20 < (Si02/A1?03) <30J and siliceous mordenite crystals [with 9 < (SiO fAl 0) < 2uJ h'ave been Al 0 :xSiO : obtained from near stoichiometric hydroge1s of compofiti6n~ 1.5Na?0:2.2K?0:250H 20 containing four moles of trioctylamine ~et mo1~ A120~. For 'lalues "Of x ellua1 to 8, 10, 12, 15, 20, 24, 30 and 1000, anal c'lms , and magadiite analcime-offretite-mordenite, mordenite, ZSM-ll, ZSM-5 (NaSi70n(OH)3H20) were obtained after heating at 150-200°C for a period of four weeks. In hydrogels with SiO fAl 0 in the 12-20 range, the crystall ization of mordenite over ZSM-ll 2i s fa~ored while in the 20-25 range, the opposite is observed; ZSM-5 was obtained with x = 30, SEM, X-ray, elemental analysis and electron microscopy data indicate that the presence of trioctylamine generates crystals with unique morphologies and unit cell composition characteristics. INTRODUCTION Since Mobil workers reported the synthesis of ZSM-35 (ref. 1) and ZSM-5 (ref. 2) using organic amines as temp1ating agents, these weak bases have been employed in the crystalllzation of several aluminosilicates such as ZSM-4 (ref. 3), ZSM-ll (ref. 4), mordenite and ferrierite (ref. 3,5). In addition to zeolites, amines have been extensively used (at Union Carbide) by Wilson and coworkers (ref. 6) to synthesize crystalline aluminophosphates and by Lok et al. (ref. 7) in the preparation of crystalline silica-aluminophosphates, a new class of molecular sieves. A recent review on the use of organic additives in zeolite synthesis has been given by Lok et al (ref. 8). The role of organic amines is currently under study; Valyocsik and Rollmann (ref. 9) have proposed that protonated amines are templates similar to the quaternary ammonium cations fi rs t di scussed by Ba rrer and Denny (ref. 10). The pu rpose of th is paper is to examine the properties of the various crystalline phases obtained by varying the Si0 2/A1 203 ratio of hydrogels containing trioctylamine. *Based in part on a poster paper presented at the 7th IZA Meeting, Tokyo, 1986.

46

EXPERIMENTAL All crystallization reactions were performed at 150-200°C for 7d, in 750 ml teflon-lined autoclaves equipped with a magnetic stirring mechanism. Gels into a were prepared by dissolving commercial grade NaA10 (containing 25% H 20) 2 mixed NaOH-KOH alkaline solution. Following trioctylamine (C24H51N) addition, colloidal silica (Ludox HS-40) was introduced dropwise; the gel formed was first allowed to cold age for 10h and then placed in the autoclave for crystallization. After calcination at 600°C/10h in air. crystals were reacted with a 1M NH 4N03 solution; H-zeol ites were obtained by heating the NH 4-exchanged crystals in air at 500°C for 10h. Removal of occluded trioctylamine (TOA) was followed by Differential Scanning Calorimetry (DSC); Thermogravimetric Analysis (TGA) measurements were carried out with a DuPont lOgO thermal analyzer using high purity nitrogen or oxygen as purge gases and heating rates of 10°C/min. Products formed during calcination were examined by GC-MS using a Varian 1700 Chromatograph and a DuPont 21-491 Mass Spectrometer. Samples were pyrolyzed at 100°C increments over the 100°-400°C temperature range using a coiled probe. X-ray diffraction studies were performed using a Rigaku computer controlled diffractometer equipped with both a receiving graphite monochromator to obtain monochromatic CuKa radiation and a scintillation detector (ref. 11). Electron diffraction patterns were obtained with a JEOL 100 CX transmission electron microscope fitted with a top entry two-axis tilting stage and a UHR objective pol piece (C = 0.7 mm). In this situation, electron diffraction s patterns can be obtained from crystals tilted by about ± 30° from the horizontal. Experimental details have been discussed elsewhere (ref. 12). RESULTS AND DISCUSSION Synthesis By heating hydrogels of composition A1203:xSi02:1.5Na20:2.2K20:250H20 (in the presence of 4 moles of trioctylamine per mole of A1 at 150-200°C 203), crysta 11 i ne phases were obta i ned that were controlled by the gel Si0 2/ A12°3 ratio; results have been summarized in Table 1. Scanning electron micrographs (SEM) are shown in Figure 1; x-ray data is given in Table 2. The SEM in Figure la shows the For x = 6.0, analcime is formed. characteristic cubo-octahedral and trapezohedral symmetry typical of analcime crystals seen in natural deposits (ref. 13). Crystal intergrowth was observed about 10~m in several of the samples studied. Crystal size varied from 2~m'to ° ° and the unit cell size (a was 13.692 A (esd = 0.004A). Small amounts of K o) and TOA are incorporated into the structure and only ~20% of the Na ions can be removed by NH (Table 1, sample No.1); the crystal Si0 2/A1 203 ratio 4-exchange

47

Figure 1. Scanning electron micrographs for: (A) Analcime; (B) AnalcimeMordenite mixtures; (C) (Na,K,TOA)-Mordenite, sample No.2; (0) (Na,TOA)Mordenite, sample No.4; (E) Siliceous (Na,K,TOA)-Mordenite, sample No.6; (F) (Na,TOA)-ZSM-ll, sample No.7; (G) (Na,K,TOA)-ZSM-ll; (H) (Na,K,TOA)ZSM-ll large batch, sample No.8; (I) (Na,K,TOA)-ZSM-5, sample No. 10; (J) (Na,K)-ZSM-5 seed, (K) (Na,K)-ZSM-ll seeded, sample No.9; and (L) Magadiite, sample No. 11.

48

TABLE 1. BET surface area and crystal composition (per A1 mole) before and after 203 NH 4-exchange and calcination. S Gel x No. Value --

Before Si0 2 Na 20 5.0 1.1 9.2 0.38 8.4 0.41 13.3 0.84

Exchange ~ (TOA)2 0

6 1. 0.03 2. 12 0.67 3. 15 0.51 4. 15 0.0 5. 15 6. 20 17.3 0.58 0.53 7. 24 20.0 0.78 0.0 8. 24 21.1 0.49 0.50 21.2 0.61 0.49 9. 24 27.1 0.47 0.43 10. 30 14.0 1.0 11. 1000 *Less than O. 01 ; Q Quartz;

0.01 0.28 0.33 0.08 0.00 0.10 0.25 0.22 0.00 0.23

After Exchange Si0 2 Na 20 ~ 4.7 0.82 0.03 10.6 * * 9.5 0.29 0.03 13.3 * 0.0 10.4 0.03 * 16.9 * * 19.9 * * 21.4 * * 20.1 * * 28.2 * *

Area Phase(s) m2/g Present 440 293 432 441 409 359 390 336 357 17

Analcime Mordenite + Q Mordenite Mordenite Mordenite Mordenite ZSM-ll + ZSM-5 ZSM-ll + M ZSM-ll ZSM-5 Magadiite

M = Mordenl te.

is somewhat higher than that typically reported for this zeolite (ref. 13). For values of x between 6 and 12. mixtures containing several crystalline phases are evident from X-ray analysis of the calcined samples. For x = 8. analcime with minor amounts of offretite is obtained. If the x value is increased from 8 to 10. co-crystallization of offretite, analcime, and mordenite occurs. A mordenite-analcime mixture is shown in Figure lb. At higher x-values. instead of offretite. mordenite was obtained from this type of gel at K20/Na20 ~ 1.47. At a higher SiO Z/A1 203 ratio (12
49

100R'==---------------

96 92

~88 I-

~_--~

84

J: ~ 80

w

==

76

72

----~ ~_--~

68 44.6

45.0 45.5 TWO THETA ANGLE

Figure 2. X-ray diffractograms of (A) Mobil ZSM-5; (B) (Na,TPA)-ZSM-5 with x = 90; (C) (Na,K,TOA)-ZSM-5; (0) (Na,K)-ZSM-ll and (E) (Na,K, TOA)-ZSM-ll.

45.8

~_-~

640~~~--"-~~L~~~-_::~~~~-I

200 400 600 800 TEMPERATURE (0C)

10'00

Figure 4. TGA Profile for: (A) (Na,K, TOA)-Mordenite; (B) (Na,TOA)Mordenite; (C) (Na,K,TOA)-ZSM-5 and (0) Analcime.

Figure 3. OSC profile for: (A) (Na,K,TOA) ZSM-5; (B) (Na,K,TOA)-ZSM-ll; (C) (Na,TOA)Mordenite and (0) Analcime.

By increasing the starting gel Si0 2/A1 203 ratio from 20 to 30 (while keeping the TOA/A1 203 ratio constant), crystal s become more sil iceous, then ZSM-ll and ZSM-5 appear. The pattern in Figure 2 (Sample 8, Tables 1 and 2) is similar to ZSM-5 except that in the doublet at 45°_46° two theta, the lower angle peak is slightly weaker than that at higher angle, whereas in ZSM-5 (or sil ical ite), these peaks are about equal in intensity. The doublet is easily seen for crystals obtained from a gel with x = 30 (Samples 9 and 10, Table 1), while in crystals obtained from gels with x = 24, the lower angle peak of the doublet is definitively weaker, see Figure 2. As with mordenite, after replacing all Na with K ions, gel s with x = 24 did not crystall ize after heating at l75°C/l week. Replacing all K with Na ions (Sample 9, Table 1)

TABLE 1 - X-RAY DIFFRACTION DATA FOR SEVERAL OF THE C~YSTALS

As $ynthes lZed

Analcime

UJ!l-

-d 11. 30

I

5.60 4.84 3.80 3.66 3.58 3.424 3.241 3.060 1.919 1.795 1.685 1.499 1.411 1.110 1.164 2. III 1.019 I. 938 I. 900 I. 865 1.739 I. 711 1.685 1.666 1.614 1.591 1.493

91 II I 5 3 I DO 1 2 51 5 11 10 5 5 I I I I 5 6 11 3 4 1 1 4 1

Ce l cined (600 CC)

i

~

6.31 5.57 4.82 3.82 3.630 3.57 3.339 3.110

1 100# 8 I 7 1 54 1

1.901 1.786 1.665 2.479 1.405 1.210 1.149

10 2 6 8 1 3 1

1.004

1

1.883 I. 850 1.725

3 1 4

1.647 1.601

I. 580 1.464

Semple 2

13.71 10.31 9.13 6.62 6.41 6.10 5.87 5.81 4.54 4.25 4.14 4.00 3.95 3.85 3.789 3.634 3.553 3.481 3.397 3.289 3.111 3.098 2.934 1.897

Sample 4

!!

-.!.L.i£ 41 11 68 16 19 4 II 19 44 25 3 100 10 7 36 10 7 96 60 38 93 13 7 30

t

t

13.50 10.11 9.03 6.55 6.37 6.02 5.77 5.09 4.51 4.14 3.98 3.832 3.760 3.627 3.461 3.384 3.280 3.215 3.200 3.083 2.889

1 I 1 I

has been noted for ZSM-S, the low angle lines have a higher rel a ti ve intensity after cel ctne t ton than before.

~A",

Pentas i 15

Mordeni tes

i

.!L!Q... 28 18 100 59 12 4 25 5 48 5 80 8 12 7 92 48 8 38 34 2 29

.!!

Zeolan 900

lJ.59 10.17 9.11 6.60 6.41 6.02 5.79 5.07 4.53 4.15

~ 33 8 64 56 21 1 20 1 41 I

4.00 3.835 3.772 3.642 3.467 3.390

71 18 11 I 100 56

3.218 3.105 3.138 2.94 2.89

68 45 10 10 29

11. 15 9.96

-.!.L.i£ 100 74

7.45

2

6.69 6.43 5.99 5.70 5.38

8 7 15 7 12 I

5.00 4.60 4.36 4.17

6 1

4.00 3.83

3 97

3.74

46

3.65

22

3.46

2

3.32

6

3.05 3.00

5 9

1.73

1

1.48 2.41 1.008 1.995

3 1 4 8

5.58

8

I

-Cr i s tobe l i te

1.871 1.449

Samp I p

Sample 8

Sample 7

i

tOuartz or Mordeni te and Quartz. *Mordeni te

01 0

UNDER STUOY (SEE TABLE I FOR SAMPLE IDENTIFICATION AND ELEMENTAL COMPOSITION)

!!

11.18 10.04 9.76 9.11*

.!L!Q... 100 55 14 14

7.49 6.72 6.37 6.00 5.75 5.59 5.37 5.13 5.01 4.62 4.524.37 4.27

3 7 9 13 6 10 3 3 7 4 9 7 4

3.98* 3.85 3.75 3.66

17 60 28 20

3.46* 3.37 3.32 3.22* 3.05 2.99 2.87 2.79 2.74 2.61 2.50 2.090 2.060 2.015 1.996 1.957 1.763 1.671 1.663

17 7 4 4 7 7 3 2 1 1 4 1 I 4 6 3 2 3 3

i

9

.!L.!.2.

Sample 10

M0011 Z5M-5

!!

!lli

i

lL.l2... 100 62 14

11.18 10.04 9.76

100 70 10

11.33 10.04 9.76

100 71 lJ

11.18 10.04 9.76

9.02 7.46 6.75 6.37 6.00 5.71 5.60 5.37 5. I 3 5.01 4.61

2 4 8 9 11 9 12 4 4 5 5

9.06 7.49 6.72 6.38 6.02 5.73 5.59 5.38 5.13 5.01 4.62

3 3 8 8 17 9 12 3 3 6 6

9.02 7.46 6.70 6.37 6.00 5.71 5.58 5.37 5.15 5.01 4.62

4.37 4.27

9 6

4.37 4.28 4.10 4.01

9

Ib+

4.37 4.27

10

4.01

3.85 3.73 3.65 3.49 3.45 3.37 3.33

70 32 18 5 8 5 8

3.85 3.74 3.65 3.49 3.45 3.35 3.31

62 24 18 4 6 5 9

13

3.06 2.99

7 13

4.02

12

3.85 3.75 3.65

60 30 15

3.46 3.35 3.31

6 8 6

2.99

10

2.80 2.74 2.61 2.50 2.090 2.080 2.017 I. 996 1. 957 1.763 1.671 1.663

2 4 3 4 4 3 4 6 4 4 4 4

-

3.05 2.99 2.87 2.79 2.74 2.61 2.49 2.090 2.080 2.017 1.997 I. 956 1. 763 1.671 1.663

11 I 2 3 4

11 2 2 6 7 3 3 3 3

2.79 2.74 2.61 2.495 2.095 2.080 2.017 I. 996 1. 957 1.760 1.671 1.663

I 2 5 12 15 9 12 2 1 5 6

1 3 1 2 2 2 9 8 I 1 1 1

51

produced instead crystals with x-ray diffraction patterns similar to the pattern used by Kokotailo and coworkers (ref. 15) to describe ZSM-ll; 0 0 0 0 diffraction lines at d = 6.37A, 5.71A, 4.27A and 3.65A are attributed to the presence of a small amount of ZSM-5 impurities. SEM data is shown in Figures 1G-1K.

The crystallization of materials with pentasil structures seems to require the presence of Al. In fact, for x ~ 1000, instead of sil ical ite, magadi ite formation was observed; see Table 1, Sample No. 11. The rosetta morphology of the crystals is shown in Figure lL. Similar results have been reported by Gatti and coworkers (ref.16) in their study of the use of triethanolamine in the synthesis of ZSM-5 crystals. Magadiite was obtained also when all Na was replaced by K ions. Thermal Analysis Analcime has a simple DSC profile characterized by a broad endotherm with minimum at about 280°C representing a 12% weight loss from water removal; Figure 3. In contrast, the mordenites and pentasil crystals show a more complex DSC profile due to TOA occlusion. After an initial broad endotherm with minimum at about 75°C representing water desorption, the pentasils show a second (weaker) endotherm at ~210°C resulting from losses of TOA. The GC-MS analysis of the pyrolyzate obtained in this temperature interval (100-200°C) showed the presence of TOA with minor amounts of dioctylamine and octanol. In the corresponding TGA profile, TOA desorption is indicated by a change in slope at ~lOO°C; at 215°C, a cumulative 12% weight loss is observed, Figure 4. Betw~en 215°C and 600°C, there is an additional 4.5% weight reduction from the oxidative decomposition of occluded TOA. This mode of TOA removal is represented by a single (broad) exotherm in the DSC profile with a peak maximum at 350°-370°C; a temperature somewhat lower than that used to remove quaternary ammonium cations. In mordenites, the change in slope in the TGA profile occurs between 200 and 300°C; the larger weight losses are attributed to their greater water loading. Electron Diffraction Of the 18 crystals (obtained from a gel with x = 15, Sample 4, Table 1) examined by electron diffraction, all but one were consistent with the mordenite structure; crystals are plates that tend to be thin in the ~ direction. In contrast, natural mordenite crystals are laths elongated along the c direction. Particles are mostly lumps of crystal aggregates with occasional protruding straight edges, Fig. 1. The disorder shown by natural mordenite is not present in these samples. If disordered, no streaks would occur on the hko net but spots would show at the forbidden 2n-l positions, and these spots are not present (ref. 14). Therefore, this is a well-crystallized (Na,K, TOA)-mordenite with morphology and channel arrangements as shown in

52

Figure 5. Examination of 24 crystals (obtained from a gel with x = 20, Sample 6, Table 1) indicate the presence of mainly (Na,K,TOA)-mordenite with probably some cristobalite and possibly some other unidentified crystalline components. Mordenite morphology resembled that obtained from gels with x = 15. From gels with x = 24 (in the presence of both Na and K), particles are obtained that are aggregates of rectangularly shaped crystal s identified by electron diffraction to be ZSM-ll essentially free from ZSM-5; see Sample 8, Table 1 and Figure 6. While slabs of ZSM-5 intergrown into ZSM-ll can be seen in lattice images (ref. 17), the presence of such faults or intergrown crystals is more readily detected by examination of electron diffraction patterns taken down [010]. The absence of odd order spots or streaks in the

[100]

r

12 RING APERTURE

J---~

[001]

~[010]

8 RING APERTURE

o

Figure 5. Transmission electron micrographs (a) show that crystals of (Na,K,TOA)-Mordenite are elongated plates (1 x 0.5 micron) with tapered or serrated ends, and thinner in the third dimension. Electron diffraction (b) identifies the crystallographic axes (d), from which it can be deduced that the large (12-rings) channels run across the plates, the smaller (8 rings) channels run along the plates (c), and there are no channels through the shortest dimension.

53

Figure 6. Electron micrograph of (Na,K,TOA)-ZSM-ll, sample 8, Table 1. The white arrows indicate positions at which spots or streaks appear when ZSM-5 is present in the crystal. hOO rows of the ZSM-ll diffraction pattern can be taken as evidence for the absence of ZSM-5 intergrowths or faults (refs. 17,18). Figure 6 is an electron diffraction pattern from a crystal of sample 8, Table 1. The white arrows indicate the type of positions at which spots or streaks would indicate the presence of ZSM-5 in this crystal. Other crystals gave similar diffraction patterns, so we conclude that this sample is essentially pure ZSM-ll. The crystals' Si0 2/A1 203 ratio is about 21, which is significantly lower than that usually reported for zeolites of the pentas il family. There is a second phase represented by crystals lath shaped and heavily, faulted (probably mordenite), which could not be identified. Electron diffraction analysis of crystals from gels with x = 30 (Sample 10, Table 1) reveal the material to be mostly (Na,K,TOA)-ZSM-5 with morphology and related channel system as shown in Figure 7. Crystal morphology is different from that of typical (Na, TPA)-ZSM-5, since the relative sizes in the ~ and ~ axis are interchanged, so that the direction of the crystals is along the ~ axis rather than the more usual ~ axis. The relative lengths of straight and tortuous channels are also interchanged (Figure 7).

54

tl:

0

ll:

[010]

[100]

[001]

X

[001]

~

Figure 7. Crystals of (Na,K,TOA)-ZSM-5 are about l~m in length and appear to have two different shapes in electron micrographs (b). Electron diffraction (a) identifies the crystallographic axes shown in (c). From this it seems likely that these two shapes are different projections of the one form. From the orientation given by electron diffraction it can be seen that there are no channels along the length of the crystals, and that the straight and tortuous channels are normal to the planar and serrated faces respectively.

55

SUMMARY Siliceous mordenite crystals and Al-rich pentasils can be synthesized from near stoichiometric hydrogels containing trioctylamine together with Na+ and K+ ions. Instead of spheroids, the pentasils crystallize as agglomerates of rectangularly shaped crystals irregular in size and shape, thus facilitating the forming of these particles into extrudates with the crush strength resistance required for catalytic evaluation in pilot plant units. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

J. C. Plank, E. J. Rosinski and M. K. Rubin, U.S. Pat. 4,016,245 (1977). M. K. Rubin, E. J. Rosinski and J. C. Plank, U. S. Pat. 4,151,189 (1979). M. R. Klotz, U. S. Patent 4,377,502 (1983). L. D. Rollman, U. S. Patent 4,108,881 (1978). W. J. Ball and D. G. Stewart, U.S. Patent 4,376,104 (1983). S. T. Wilson, B. M. Lok and E. M. F1anigen, U. S. Pat. 4,310,440 (1982). B. M. Lok, C. A. Messina, R. L. Patton, R. T. Gajek, T. R. Cannan and E. M. Flanigen, European Patent 0103117 (1984). B. M. Lok, T. R. Cannan and C. A. Messina, Zeolites 1983, 3, 282. E. W. Va1yocsik and L. D. Rollmann, Zeolites 1985, 5, 123. R. M. Barrer and P. J. Denny, J. Chern. Soc., 1961, 971. M. L. Occelli, R. A. Innes, S. S. Pollack and J. V. Sanders, Zeolites, 7, 3, 265 (1987). J. V. Sanders, M. L. Occelli, R. A. Innes and S. S. Pollack, Proc. 7th Int. Conf. Zeolites, Tokyo, p. 429 (1986). F. A. Mumpton and W. C. Ormsby, in "Natural Zeolites, Occurrence, Properties, and Use," L. B. Sand and F. A. Mumpton, Eds., Pergamon Press, 1978, p. 113. J. V. Sanders, Zeolites, 5, 81, 1985. G. T. Kokotai10, P. Chu, S. K. Lawton and W. L. Meier, Nature, 275, 119 (1978). F. Gatti, E. Moretti, M. Padovan, M. Solari and V. Zamboni, Zeolites, 6, 4, 312 (1986). G. R. Millward, S. Ramndas and J. M. Thomas, J. Chern. Soc. Faraday, Trans. 2, 79, 1075 (1983). K. Foger, J. V. Sanders and D. Seddon, Zeolites, 4, 339 (1984).