Zeolite Synthesis - American Chemical Society

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Chapter 19

Crystal Growth Regulation and Morphology of Zeolite Single Crystals of the MFI Type 1

J. C. Jansen, C. W. R. Engelen , and H. van Bekkum Downloaded by UNIV OF AUCKLAND on May 8, 2015 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch019

Department of Organic Chemistry, Delft University of Technology, Julianalaan 136, 2628 BL Delft, Netherlands

Crystal growth phenomena in zeolite MFI formation have been monitored. Two new single crystal forms of z e o l i t e s of the MFI type are reported. Pyramidal single crystals were found to grow at the surface of gel spheres, the formation of which is thought to be induced by the decomposition of tetrapropyl­ ammonium ion during zeolite synthesis and by the presence of t r i v a l e n t metal ions. The pyramidal crystals are shown to be precursors of the cube-shaped ZSM-5 single crystals described earlier. Another morphology known for MFI-type single c r y s t a l s , the elongated prismatic habit is shown to transform into a shelf-shape morphology when increasing amounts of boric acid are added to the synthesis mixture.

S y n t h e s i s procedures t o o b t a i n l a r g e z e o l i t e c r y s t a l s a r e well developed (1,2). In p a r t i c u l a r much a t t e n t i o n has been p a i d t o t h e s y n t h e s i s o f ZSM-5 c r y s t a l s (3-6). Elongated p r i s m a t i c ( F i g . l a ) and cubic-shaped orthorhombic ( F i g . lb) ZSM-5 c r y s t a l s o f s i z e s between 2-50 /zm were r e p o r t e d i n t h e f i r s t r e c i p e s (7) i n t h e patent l i t e r a t u r e . L a t e r on, systematic s t u d i e s have l e d t o e x c e l l e n t s y n t h e s i s p r e s c r i p t i o n s f o r t h e growth o f l a r g e c r y s t a l s o f t h e p r i s m a t i c (8) as well as o f t h e orthorhombic form ( 9 ) . The s y n t h e s i s parameters which a r e dominant i n t h e c r y s t a l l i z a t i o n o f pure ZSM-5 s i n g l e c r y s t a l s , a r e s t i l l under study (10,11). 1

Current address: Exxon Chemical Holland BV, P.O. Box 7335, 3000 HH Rotterdam, Netherlands 0097-6156/89A)398-0257$06.00/0 ο 1989 American Chemical Society In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

ZEOLITE SYNTHESIS

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Figure 1. Four different single c r y s t a l forms of ZSM-5. (a) Elongated prismatic; (b) cubic-shaped orthorhombic. Continued on next page.

In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

JANSENETAL.

Crystal Growth Regulation

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19.

Figure 1. Continued, (c) Pyramidal shaped and (d) shelfl i k e shaped.

In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ZEOLITE SYNTHESIS

A f u l l understanding o f z e o l i t e growth p r i n c i p l e s i s d i f f i c u l t because hydrothermal 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 takes p l a c e i n heterogeneous r e a c t i o n media. Domains d i f f e r i n g i n composition and i n v i s c o s i t y e x i s t i n the same r e a c t i o n mixture and can g i v e r i s e t o d i f f e r e n t products due to l o c a l d i f f e r e n c e s i n s u p e r s a t u r a t i o n , i n ion t r a n s p o r t v e l o c i t y , e t c . For t h i s reason i t i s o f t e n d i f f i c u l t to c o r r e l a t e the c r y s t a l shape and type to the s t a r t i n g s y n t h e s i s parameters because the c r y s t a l morphology, composition and s i z e w i l l r e f l e c t the l o c a l c r y s t a l growth c o n d i t i o n s . So f a r o n l y the c r y s t a l growth h i s t o r y o f c r y s t a l s with the elongated p r i s m a t i c form i s well d e s c r i b e d . The o b j e c t i v e o f our s t u d i e s i s t o i d e n t i f y l o c a l c r y s t a l growth c o n d i t i o n s which l e a d t o d i f f e r e n t c r y s t a l forms o f ZSM-5 by i n f l u e n c i n g n u c l e a t i o n and growth behaviour. In t h i s paper we r e p o r t on two new morphologies ( F i g . l c , Id) o f s i n g l e c r y s t a l s o f the MFI type. Growth h i s t o r y as well as r e l a t i o n t o the morphologies r e p o r t e d e a r l i e r ( F i g . l a , b) w i l l be d i s c u s s e d . Experimental M a t e r i a l s . Table I l i s t s the s t a r t i n g chemicals t o g e t h e r with the c o n c e n t r a t i o n o f the main i n o r g a n i c i m p u r i t i e s . Table I. Inorganic impurity contents ( i n ppm)of source chemicals a p p l i e d Al S i 0 , A e r o s i l 200, Degussa * S i 0 , FO Optipur, Merck NaOH, Merck aq. NaOH, Suprapur, Merck * TPA.Br, Janssen 2

440

110

10

90

3

< 0.01 < 5 < 0.05

0.004

0.2

< 10"

2

R e g u l a r l y used

Fe

Cr

Ti

< 5 < 0.05 0.2

0.18

chemicals.

S y n t h e s i s . Two types o f s y n t h e s i s f o r m u l a t i o n s were a p p l i e d . The f i r s t one i s the s y n t h e s i s procedure as d e s c r i b e d by Lermer et a l . (9) r e s u l t i n g i n l a r g e c u b i c ZSM-5 c r y s t a l s ( F i g . l b ) with composition (molar r a t i o ) i n the c l e a r s t a r t i n g s o l u t i o n as f o l l o w s : Si0 A1 0 Na 0 TPA 0 H0 (I) 12