Significant Parameters in the Synthesis of Large Alkaline-Free MFI

Chapter 24

Significant Parameters in the Synthesis of Large Alkaline-Free MFI-Type Zeolites and AFI-Type Aluminophosphates

Downloaded by UNIV OF IOWA on May 18, 2016 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch024

U. Müller, A. Brenner, A. Reich, and Κ. K. Unger Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, P. O. Box 3980, D-6500 Mainz, Federal Republic of Germany

Factorial experiments were successfully employed to determine significant synthesis variables allowing the crystallization of large AlPO -5 and ZSM-5 c r y s t a l s . Growth of AFI-type aluminophoshate up to 500 μm in length was achieved using a molar reaction composition of 0.5 Pr N - Al O - P O - 300 H O. Crystal size and yield were countercurrently affected by the water content during the synthesis . The alkaline-free crystallization of 300μmuniform MFItype zeolites at high conversion was possible in a batch of 6.5 (TPA) O - 282 (NH ) O - 96 SiO - 1400 H O. Decreasing water content and increasing ammonia concentration improved both crystal size and yield. Length growth rates reached 3.0 ± 0.6μm/h.Increasing the aluminium content caused a decrease in the size and y i e l d of ZSM-5 after four days along with a reduction in the crystal aspect r a t i o compared to aluminium-free runs. Preliminary results with alkaline-free preparations of DOH-,DDR-, MTN-, and MEL-type z e o l i t e s indicate, that large crystals with sharp p a r t i c l e size d i s t r i b u t i o n s are frequently observed in ammonia-based zeolite synthesis processes. 4

3

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2

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4 2

2

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Large c r y s t a l s o f molecular s i e v e m a t e r i a l s a r e o f profound i n t e r e s t both f o r academic s t u d i e s and s p e c i a l i n d u s t r i a l a p p l i c a t i o n s . I n v e s t i g a t i o n s regarding s i n g l e c r y s t a l s t r u c t u r e refinement ( 1 ) , the determination o f a n i s o t r o p i c e l e c t r i c a l , magnetic o r o p t i c a l p r o p e r t i e s (2), t h e d e s c r i p t i o n o f d i f f u s i o n processes (3Λ) o r t h e e l a b o r a t i o n o f i n t r i n s i c a d s o r p t i o n p r o p e r t i e s (5J>) a r e based on the use o f uniform l a r g e specimens with a d i s t i n c t morphology. Large z e o l i t e c r y s t a l s with a r a t h e r small n o n s e l e c t i v e e x t e r n a l s u r f a c e might be useful i n s h a p e - s e l e c t i v e c a t a l y s i s (Z) o r i n f l u i d i z e d - b e d r e a c t i o n s as b i n d e r - f r e e and s e l f - s u p p o r t i n g adsorbents. Moreover, a c e r t a i n c r y s t a l s i z e and shape i s r e q u i r e d f o r t h e manufacture o f 0097-6156/89/0398-0346$06.00/0 o 1989 American Chemical Society Occelli and Robson; Zeolite Synthesis ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


24. MULLERETAL.

Large Alkaline-Free Zeolites and Aluminophosphates

347

zeolite-membranes (8) o r t h e employment o f m o l e c u l a r s i e v e s as s u b s t r a t e s f o r semiconductors ( 9 ) . However, d u r i n g t h e c r y s t a l l i z a t i o n o f z e o l i t e s and r e l a t e d m a t e r i a l s , complex multicomponent mixtures, e.g. o f s i l i c a , alumina, m i n e r a l i z e r s , water and o r g a n i c templates, a r e hydrothermal 1y r e a c t e d . N u c l e a t i o n and growth o f c r y s t a l s can be dependent upon chemical composition as well as k i n e t i c s o r e q u i l i b r i u m c o n d i t i o n s e x i s t i n g i n t h e s o l i d , l i q u i d , and g a s phase. Given these c o n s i d e r a t i o n s , the most e f f i c i e n t method o f s t u d y i n g the impact on the r e s u l t s when two o r more s y n t h e s i s parameters , h e r e a f t e r c a l l e d " f a c t o r s " , were t o be changed i s obtained by f a c t o r i a l experiments (10) . A c c o r d i n g l y , a t r i a l i s designed where s e t s o f d i f f e r e n t s y n t h e s i s v a r i a b l e s are arranged i n s p e c i f i c treatment combinations, e n a b l i n g an assessment o f t h e e f f e c t s o f changing t h e l e v e l o f a f a c t o r independently o f a l l others and p o s s i b l e i n t e r a c t i o n e f f e c t s . Thus t h e r e q u i r e d i n f o r m a t i o n i s e x t r a c t e d with a p r e - s e l e c t e d degree o f s t a t i s t i c a l c e r t a i n t y a t a minimum expenditure o f e f f o r t and c o s t s . I f s i g n i f i c a n t e f f e c t s a r e e l u c i d a t e d , they can be d i r e c t l y employed as s t a r t i n g values t o f u r t h e r improve s y n t h e s i s by means o f c e n t r a l composite design o r S i m p l e x - v a r i a t i o n procedures, f i n a l l y y i e l d i n g optimum c o n d i t i o n s f o r t h e d e s i r e d response, r e g a r d i n g c r y s t a l s i z e , morphology or product y i e l d . T h i s study aims t o demonstrate, t h a t s t a t i s t i c f a c t o r i a l design can be used i n order t o determine s i g n i f i c a n t compositional parameters i n the r a p i d growth o f l a r g e h i g h - s i l i c a ZSM-5 z e o l i t e (11) and A l P 0 - 5 aluminophosphate c r y s t a l s (12.13). 4

Experimental Z e o l i t e ZSM-5. Z e o l i t e samples were c r y s t a l l i z e d from a g e l containing colloidal s i l i c a (Ludox AS-40), d e i o n i z e d water, a l u m i n i u m t r i i s o p r o p y l a t e (ATIP, Merck), as source o f aluminium, and tetrapropylammonium bromide, (TPABr, A l d r i c h ) . Ammonia s o l u t i o n s were prepared by s a t u r a t i n g a thermostated aqueous s o l u t i o n with gaseous NH (98% p u r i t y ) . Contents o f 25%, 32%, and 47% w/w o f ammonia were obtained and g r a v i m e t r i c a l l y c o n t r o l l e d . The components were added i n the sequence: TPABr, S i 0 , alumina source, water and ammonia s o l u t i o n . The mixture was v i g o r o u s l y a g i t a t e d , s e a l e d and l e f t f o r f o u r days a t a temperature o f 453 Κ t o r e a c t . Li-NH -ZSM-5 was grown using a procedure d e s c r i b e d elsewhere (14.15). 3

2

4

Aluminophosphate A l P Q - 5 . A l P 0 - 5 was obtained from compositions c o n t a i n i n g pseudoboehmite (Pural SB, Condea) which was added t o aqueous phosphoric a c i d (Merck, 85%) and d e i o n i z e d water. F i n a l l y , t r i p r o p y l a m i n e ( A l d r i c h ) was c o n t i n u o u s l y added t o t h e s t i r r e d s o l u t i o n . The c r y s t a l l i z a t i o n time was l i m i t e d t o 72 hours. C r y s t a l l i z a t i o n was c a r r i e d out with 50 ml o f r e a c t i o n mixtures in 100 ml s t e e l a u t o c l a v e s l i n e d with T e f l o n under s t a t i c c o n d i t i o n s . A l l i s o l a t e d products were c h a r a c t e r i z e d b y X-ray d i f f r a c t i o n , scanning e l e c t r o n microscopy, and e l e c t r o n microprobing (Camebax, CAMECA). S e l e c t e d samples were employed f o r n i t r o g e n a d s o r p t i o n and m i c r o c a l o r i m e t r y a t 77 K. A f t e r c a l c i n a t i o n a t 823 K, c a t a l y t i c a c t i v i t y and s e l e c t i v i t y o f HZSM-5 samples were monitored using the d i s p r o p o r t i o n a t i o n o f ethylbenzene as a t e s t r e a c t i o n . The 4

4

American Chemical Society Library 1155 16th St., N.W. Washington, Occelli and Robson;D.C. Zeolite20036 Synthesis ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

348

ZEOLITE SYNTHESIS

p a r t i c l e s i z e d i s t r i b u t i o n was o b t a i n e d u s i n g o p t i c a l microscopy on 300 t o 800 i n d i v i d u a l c r y s t a l s . R e s u l t s and D i s c u s s i o n S y n t h e s i s of l a r g e AFI-tvpe c r y s t a l s . For these s t u d i e s of the c r y s t a l l i z a t i o n of l a r g e AFI-type aluminophosphate c r y s t a l s , the r e a c t i o n temperature T, the c o n c e n t r a t i o n o f t r i p r o p y l a m i n e Pr N, and the amount o f water were chosen as o p e r a t i o n a l v a r i a b l e s . S y n t h e s i s runs were performed with each of these " f a c t o r s " at a high (+) and a low (-) l e v e l , f o r molar compositions with b P r N - A 1 0 - P 0 - c H 0 as i n d i c a t e d in Table I: 3

3

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5

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3

2


Table I. Compositional F a c t o r s and L e v e l s i n v e s t i g a t e d f o r the S y n t h e s i s of ΑΙΡΟ^-δ c r y s t a l s Factor

High Level

Α: Τ (Κ) B:

C:

423 0.5 50

453 3.0 300

ProN

H0 2

Low Level

J

Table II summarizes the 2 p o s s i b l e treatment combinations. Run (1) denotes a s y n t h e s i s with a l l f a c t o r s at t h e i r lowest l e v e l . Product y i e l d s , see Table II , and maximum c r y s t a l s i z e s along the (001) a x i s ( T a b l e I I I ) r e p r e s e n t mean values from d u p l i c a t e d s e t s o f each t r i a l . The " e f f e c t " column l i s t s the impact of a f a c t o r , p o s i t i v e or n e g a t i v e , on the response, v i z . product y i e l d and c r y s t a l l e n g t h , f o r the case t h a t the l e v e l o f t h i s f a c t o r i s r a i s e d from a medium to a high l e v e l . C a l c u l a t i o n procedures have been d e s c r i b e d i n the l i t e r a t u r e (10). Table I I . Treatment Combinations f o r the I n f l u e n c e of D i f f e r e n t F a c t o r s on the A l P 0 - 5 Product Y i e l d A

Combination

Factor A

Factor Β

1 a b ab c ac be abc

423 453 423 453 423 453 423 453

0.5 0.5 3.0 3.0 0.5 0.5 3.0 3.0

Factor Yield C % w/w 50 50 50 50 300 300 300 300

85 17 42 34 3 9 18 8

Effect 27.0 -10.0 - 1.5 5.5 -17.5 9.0 5.0 - 9.5

Significance 95% + -

F i n a l l y , a l l e f f e c t s were e v a l u a t e d by "Student t - t e s t " and " F - t e s t " methods, in order t o check whether these e f f e c t s were simply due t o experimental e r r o r r a t h e r than being s t a t i s t i c a l l y s i g n i f i c a n t . D e c i s i o n s are based on a c e r t a i n t y o f at l e a s t 95% . S i g n i f i c a n t

Occelli and Robson; Zeolite Synthesis ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

24.

MULLER ET AL.


349

v a r i a b l e s i n t h e f o l l o w i n g t a b l e s have been marked (+) i n t h e l a s t column. R e f e r r i n g t o Table I I , f a c t o r C, t h e water content, o b v i o u s l y s t r o n g l y i n f l u e n c e s the y i e l d o f AlP0 -5. T h i s e f f e c t i s negative i n s i g n which means t h a t i n c r e a s i n g t h e water content d u r i n g t h e c r y s t a l l i z a t i o n causes a s i g n i f i c a n t decrease i n y i e l d . I t should be noted, t h a t t h i s r e s u l t i s s t r i c t l y v a l i d o n l y f o r the experimental c o n d i t i o n s and compositions as l i s t e d in Table I . 4

Table I I I . Treatment Combinations f o r the I n f l u e n c e o f D i f f e r e n t F a c t o r s on the A l P 0 - 5 C r y s t a l S i z e


4

Combination

Factor A

Factor Β

Factor C

Size /zm

Effect


423 453 423 453 423 453 423 453

0.5 0.5 3.0 3.0 0.5 0.5 3.0 3.0

50 50 50 50 300 300 300 300

98 25 30 13 500 140 135 350

161.4 -29.4 -29.4 78.4 119.9 6.9 9.4 64.9

Significance 95% + -

Regarding the c r y s t a l s i z e i n Table I I I , i t was observed t h a t again f a c t o r C, t h e amount o f water i n t h e s y n t h e s i s mixture e x e r t s a strong i n f l u e n c e . However, high water c o n c e n t r a t i o n s a r e conducive to t h e growth o f l a r g e c r y s t a l s , s i n c e t h e e f f e c t i s p o s i t i v e . R e s u l t s obtained so f a r i l l u s t r a t e , t h a t e i t h e r high product y i e l d s or l a r g e c r y s t a l s o f AlP0 -5 can be prepared by t h e method under i n v e s t i g a t i o n . Within t h e boundaries o f these treatment combina t i o n s , n e i t h e r t h e s y n t h e s i s temperature n o r t h e c o n c e n t r a t i o n o f t r i p r o p y l a m i n e proved t o be s i g n i f i c a n t parameters f o r the growth o f l a r g e AlP0 -5 c r y s t a l s , t h e hexagonal r o d - l i k e shape o f l a r g e c r y s t a l s o f AFI-type i s i l l u s t r a t e d i n F i g u r e 1, whereas the norma l i z e d p a r t i c l e s i z e d i s t r i b u t i o n o f a t y p i c a l sample i s d e p i c t e d i n F i g u r e 2. A s i m i l a r c r y s t a l morphology has a l r e a d y been r e p o r t e d by Wilson e t a l . (13) using tetrapropylammonium c a t i o n s as an o r g a n i c template. A d s o r p t i o n p r o p e r t i e s o f l a r g e AFI-type c r y s t a l s are c o n s i s t e n t with t h e micropore s t r u c t u r e which have been d i s c u s s e d elsewhena 4

4

(16)(6).

S y n t h e s i s o f l a r g e ZSM-5 C r y s t a l s . P r e l i m i n a r y s t u d i e s l e d t o t h e i n v e s t i g a t i o n o f a s y n t h e s i s mixture with a molar composition expressed in oxide r a t i o : 6.5 (ΤΡΑ)οΟ - b (NH ) 0 - c Al 0o - Si0 a H 0. Table IV i l l u s t r a t e s the f a c t o r s which were examinea. 4

2

2

2


2

ZEOLITE SYNTHESIS


350

F i g u r e 1.

Scanning E l e c t r o n Micrograph of Large A l P 0 - 5 C r y s t a l s ( s c a l e bar: 10 μπι). 4

30

1

Ξ θ1 2

10-i 0 J-

Γ ο

F i g u r e 2.

TJTTTTJTT

TTJTTTTJT

rTJTTTTJT

20 40 60 R e l a t i v e C r y s t a l L e n g t h (QQJ)

τ 80

100 ( % )

P a r t i c l e S i z e D i s t r i b u t i o n of Large A l P 0 - 5 Crystals. 4


24. MULLERETAL.

Large Alkaline-Free Zeolites and Aluminophosphates 351

Table IV. Compositional F a c t o r s and L e v e l s f o r the S y n t h e s i s o f ZSM-5 C r y s t a l s Factor

High

A: HoO B: ( N R ) 0 C: A l ^ 4

Level

1400 141 1

3200 282 0

2

Low Level


Product y i e l d , see Table V, was found t o be s i g n i f i c a n t l y dependent upon t h e ammonia content. High c o n c e n t r a t i o n s caused i n c r e a s e s i n the y i e l d o f ZSM-5. Table V. Treatment Combinations f o r the I n f l u e n c e o f D i f f e r e n t F a c t o r s on the ZSM-5 Product Y i e l d Combination

Factor A

Factor Β

Factor C

Yield % w/w


1400 3200 1400 3200 1400 3200 1400 3200

141 141 282 282 141 141 282 282

1 1 1 1 0 0 0 0

76.0 1.4 83.2 88.4 47.5 42.2 95.2 94.8

Significance 95%

Effect 66.1 - 9.4 24.3 10.6 3.8 7.9 0.8 - 9.5

+ -

High ammonia c o n c e n t r a t i o n s a r e n o t o n l y r e s p o n s i b l e f o r maximum product y i e l d s but t o g e t h e r with low water and aluminium concentra t i o n s , they appear f a r more important f o r t h e growth o f l a r g e c r y s t a l s (see Table V I ) . Figure 3 presents a scanning e l e c t r o n micrograph o f l a r g e uniform NH^-ZSM-5 c r y s t a l s . Compared t o a p r e v i o u s l y s y n t h e s i z e d Li-NH -ZSM-5, s e e F i g u r e s 4 and 5, t h e p a r t i c l e s i z e d i s t r i b u t i o n o f s o l i t a r y c r y s t a l s from the a l k a l i n e f r e e composition was found t o be markedly narrow, see F i g u r e 6, which h i n t s a t a s h o r t n u c l e a t i o n p e r i o d . I t i s obvious from Table VI, t h a t a high water content leads t o a decrease i n the s i z e o f the crystals. The treatment combination "be" o f Table VI was chosen i n order t o monitor the growth k i n e t i c s o f NH -ZSM-5. Table VII summarizes the r e s u l t s and compares the growth r a t e s with the data found by v a r i o u s other i n v e s t i g a t o r s with d i f f e r e n t systems. Strong i n f l u e n c e s o f OH" c o n c e n t r a t i o n on growth r a t e s have a l r e a d y been observed by Hou e t a l . f o r NH4-TPA mixtures (17) and by Lowe (20) and Hayhurst e t a l . (18) f o r Na-TPA systems. The l a t t e r group recorded even f a s t e r c r y s t a l l i z a t i o n and s h o r t e r i n d u c t i o n p e r i o d s i n N a - f r e e s y n t h e s i s 4

4

+


ZEOLITE SYNTHESIS


352

F i g u r e 3.

F i g u r e 4.

Scanning E l e c t r o n Micrograph o f Large NH -ZSM-5 C r y s t a l s ( s c a l e b a r : 100 μπι). 4

Scanning E l e c t r o n Micrograph o f Large Li-NH -ZSM-5 C r y s t a l s ( s c a l e b a r : 100 μπι). 4


24.

M U L L E R

ET

AL.



30 ^ -20-;

0 -= j I I I I I II II j I II H I I I I j l l l l | l l l l | I H I | I I H | l l l l

0

20 40 60 Relative Crystal Length (QQI)

jllll |

80

100 (%)

F i g u r e 5. P a r t i c l e S i z e D i s t r i b u t i o n o f Large Li-ZSM-5 Crystals.

30-3 Ξ20Ι >*

ο i«

h

φ

0-3

j I I I I [ I M I [ I I M j I I I 1 1 M j I I I I j I I I I j I M I j 11 11 j I I I I j

0

20 40 60 80 100 Relative Crystal Length (001) (* )

F i g u r e 6. P a r t i c l e S i z e D i s t r i b u t i o n o f Large NH -ZSM-5 Crystals. 4


353

354

ZEOLITE SYNTHESIS

p r o c e s s e s . With an a l k a l i n e - f r e e , h i g h l y a c t i v e composition o f 6.5 (TPA)oO - 282 (NH ) 0 - 96 S i 0 - 1400 HoO i t was p o s s i b l e t o r a p i d l y grow l a r g e ana uniform c r y s t a l s a t a maximum c o n v e r s i o n . 4

2

2


Table VI. Combinations f o r t h e I n f l u e n c e o f D i f f e r e n t F a c t o r s on t h e C r y s t a l S i z e o f ZSM-5 Combination

Factor A

Factor Β

Factor C

Size μπι


1400 3200 1400 3200 1400 3200 1400 3200

141 141 282 282 141 141 282 282

1 1 1 1 0 0 0 0

105 18 232 123 133 122 285 225

Effect

Significance 95%

155.5 -33.3 60.8 - 9.0 36.0 15.8 2.8 - 3.5

+ + -

+ -

Upon a d d i t i o n o f aluminium, i t c o u l d be seen t h a t n o t o n l y t h e c r y s t a l s i z e f o r a g i v e n r e a c t i o n time tended t o be s m a l l e r compared to an aluminium-free s y n t h e s i s r u n , s e e Table V I , b u t t h a t t h e c r y s t a l morphology was s i g n i f i c a n t l y a f f e c t e d . Table V I I .

Comparison o f C r y s t a l Growth Rates

System 1.9 3.8 12.8 6.5 2.4

(TPA)o0-1.3 NaoO-96 SiOo-960 HoO (TPA)oO-96 SiOo-960 HoO (TPA)oO-192 (NR )oO-96 SiOo-2400 HoO (TPA)oO-282 (NH )oO-96 SiOo-1400 HoO (TPA) 0-3.4 Na 0-96 Si0 -3500 HoO-384 EtOH 4

4

2

2

2

Rate μπι/h

Reference

1.3 2.2 0.6 3.0 2.0

19 21 16 Table VI 20

With i n c r e a s i n g aluminium content d u r i n g t h e r e a c t i o n , t h e product c r y s t a l s became more g l o b u l a r i n shape. Table V I I summarizes t h e i n f l u e n c e o f A l with r e s p e c t t o t h e aspect r a t i o , d e f i n e d as t h e r a t i o o f c r y s t a l l e n g t h (001) t o c r y s t a l width (100). Concerning c r y s t a l h a b i t s i n Na-TPA compositions, no i n f l u e n c e o f A l - c o n c e n t r a t i o n was observed by Mostowicz and Berak (22). Hayhurst e t a l . (18) r e p o r t e d a dependency o f product aspect r a t i o s on t h e a l k a l i n i t y i n sodium c o n t a i n i n g r e a c t i o n mixtures. C o n t r a r i l y , o b s e r v a t i o n s o f NH^-ZSM-S r e a c t i o n s g i v e n i n Table VIII c l e a r l y i n d i c a t e , t h a t even a d u p l i c a t e d amount o f ( N H ) 0 , runs " c " and "be", has no s t a t i s t i c a l s i g n i f i c a n t impact on t h e aspect r a t i o . 4

2


24.

MULLERETAL.


Table V I I I . Influence o f Aluminium Content on C r y s t a l Morphology f o r NH -ZSM-5


4

Combination

Factor A

Factor Β

Factor C

Aspect Ratio

Effect


1400 3200 1400 3200 1400 3200 1400 3200

141 141 282 282 141 141 282 282

1 1 1 1 0 0 0 0

3.13 1.27 3.71 2.06 7.69 9.99 6.20 6.90

5.12 -0.06 -0.40 -0.17 2.59 0.81 -0.74 -0.23

Significance 95%

-

+ -

Microprobe a n a l y s i s o f HZSM-5 samples from a Li-NFiVTPA system (sample A ) , see Figure 7, gave r i s e t o a c h a r a c t e r i s t i c composi t i o n a l zoning o f A l i n t h e outer r i m o f the c r y s t a l s . HZSM-5 from a l k a l i n e - f r e e processes (sample B ) , see Figure 8, had a more homo geneous aluminium d i s t r i b u t i o n throughout t h e c r y s t a l s . E v a l u a t i n g t h e c a t a l y t i c s h a p e - s e l e c t i v i t i e s o f these m a t e r i a l s by use o f t h e d i s p r o p o r t i o n a t i o n o f ethylbenzene (23.24) a t 523 Κ a t a conversion o f 2% i n d i f f e r e n t i a l r e a c t o r mode, i t was observed that l a r g e r c r y s t a l s o f sample A gave 85% para-diethylbenzene and 15% meta-diethylbenzene. The s m a l l e r c r y s t a l s o f sample Β with t h e smoother aluminium g r a d i e n t y i e l d e d 96% para-diethylbenzene and only 4% meta-isomer. In a second s e r i e s , samples o f crushed l a r g e c r y s t a l s with mean s i z e s o f 1-10 μπι were examined. No increase i n a c t i v i t y was observed as i s expected when t h e r e a c t i o n i s c o n t r o l l e d by t h e d i f f u s i o n l i m i t a t i o n o f molecules i n t h e l a r g e c r y s t a l s . However, t h i s treatment c r e a t e d larger non-selective external s u r f a c e area and hence a s m a l l e r s e l e c t i v i t y o f 87% p a r a - d i e t h y l benzene f o r sample Β was recorded. These r e s u l t s , a t l e a s t f o r t h e t e s t r e a c t i o n a p p l i e d , a r e encouraging f o r t h e f e a s a b i l i t y o f l a r g e c r y s t a l s as c a t a l y s t s . Thus, t h e advantages o f t h e c r y s t a l l i z a t i o n o f NH -ZSM-5, v i z . l a r g e uniform c r y s t a l s , maximum conversion a t high growth r a t e s and smooth A l - z o n i n g p r o f i l e s with o n l y few e x t e r n a l s u r f a c e a c t i v e s i t e s were s u c c e s s f u l l y combined f o r t h e one-step manufacture o f a HZSM-5 c a t a l y s t , see Figure 9, d i r e c t l y grown as a s h e l l on pre-shaped s i l i c a beads (25). 4

Summary and Conclusion The amount o f water present during t h e s y n t h e s i s o f l a r g e AFI-type aluminophosphate c r y s t a l s was found t o be o f s i g n i f i c a n t importance. However, y i e l d o f A l P 0 - 5 and c r y s t a l s i z e were c o u n t e r c u r r e n t l y i n f l u e n c e d . I t f o l l o w s t h a t a t l e a s t with t r i p r o p y l a m i n e , e i t h e r few l a r g e c r y s t a l s o r maximum conversions i n t o small p a r t i c l e A l P 0 - 5 i s possible. With regard t o MFI-type z e o l i t e s , s t a t i s t i c f a c t o r i a l design proved t o be extremely h e l p f u l . For a l k a l i n e - f r e e systems, f a c t o r s 4

4


355

ZEOLITE SYNTHESIS


356

SILICON

ALUMINIUM

40

80

120

160

200

m

Figure 7. E l e c t r o n Microprobe A n a l y s i s Across a ZSM-5 C r y s t a l of Sample A (bulk a n a l y s i s S i / A l = 6 5 ) .

0

20

40

60

80

urn

F i g u r e 8. E l e c t r o n Microprobe A n a l y s i s Across a ZSM-5 C r y s t a l of Sample Β (bulk a n a l y s i s S i / A l = 4 2 ) .



24.

MULLER ET AL.

F i g u r e 9.


Scanning E l e c t r o n Micrograph of a Fragment of an A l k a l i n e - F r e e HZSM-5 S h e l l Grown on a Pre-Shaped S i l i c a P e l l e t ( s c a l e bar: 10 μπ\).


357


358

ZEOLITE SYNTHESIS

were d e t e c t e d which enable the r a p i d s y n t h e s i s o f large uniform 2SM5 c r y s t a l s o u t o f r e a c t i o n compositions with high ammonia and low water c o n t e n t s . Aluminium a f f e c t s t h e c r y s t a l aspect r a t i o . Moreover, f o r t h e ammonia based r e a c t i o n mixtures, a more homo geneous A l - g r a d i e n t a c r o s s t h e HZSM-5 c r y s t a l i s o b t a i n e d , which assures improved s h a p e - s e l e c t i v e behavior i n t h e c a t a l y t i c conver sion o f e t h y l benzene. Using o r g a n i c t e m p l a t i n g molecules o t h e r than TPABr, s e v e r a l s y n t h e s i s c h a r a c t e r i s t i c s remained. With aminoadamantane, l a r g e DOH-type c r y s t a l s (see F i g . 10) c o u l d be synthe s i z e d as well as l a r g e ZSM-58 (DDR-type) f o l l o w i n g a d d i t i o n o f aluminium. Tetramethylammoniurn n u c l e a t e d l a r g e c r y s t a l s o f ZSM-39 (MTN-type) and tetrabutylammoniurn f a v o r e d t h e s y n t h e s i s o f uniform MEL-type z e o l i t e s . Independent o f t h e template, a l l these ammonia based c r y s t a l l i z a t i o n processes had a high product y i e l d , narrow p a r t i c l e - s i z e d i s t r i b u t i o n and a r a p i d growth. F a c t o r i a l experiments can s u c c e s s f u l l y serve t o determine s i g n i f i c a n t s y n t h e s i s parameters f o r aluminophosphates and z e o l i t e s . Future s t u d i e s w i l l a l s o focus on t h e u n d e r l y i n g mechanisms o f t h e n u c l e a t i o n and growth o f h i g h - s i l i c a z e o l i t e s o u t o f a l k a l i n e - f r e e ammonia c o n t a i n i n g r e a c t i o n mixtures.

F i g u r e 10. Scanning E l e c t r o n Micrograph o f Large C r y s t a l s o f DOH-Type ( s c a l e - b a r : 100 μπι). Acknowledgments F i n a n c i a l support was obtained by Deutsche Forschungsgemeinschaft. We are g r a t e f u l t o Dr. J . D. G r i b b i n and Dipl.-Chem. H. R e i c h e r t f o r help in p r e p a r i n g the manuscript. Literature 1. 2. 3. 4.

Cited

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24. MULLER ET AL. Large Alkaline-Free Zeolites and Aluminophosphates 359

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February 17, 1989


Significant Parameters in the Synthesis of Large Alkaline-Free MFI

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