Synthesis and Characterization of Zeolite ZSM-20 - American

Chapter 37

Synthesis and Characterization of Zeolite ZSM-20 1

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D. E. W. Vaughan , M. M. J. Treacy , J. M. Newsam , K. G. Strohmaier , and W. J. Mortier Downloaded by UNIV OF ILLINOIS URBANA on October 3, 2014 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch037

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Exxon Research and Engineering Company, Route 22 East, Annandale, NJ 08801 Exxon Chemical Holland, B.V., P. O. Box 7335, 3000 HH Rotterdam, Netherlands 2

Syntheses of zeolite ZSM-20 from various Na OTEA O-Al O -SiO -H O gel compositions under a variety of crystallization conditions have been investigated. In particular, the influence of K cations, and the addition of seeds and nuclei have been studied. Products were characterized by chemical analyses, sorption measurements, infra-red spectroscopy, powder X-ray diffraction (PXD) and electron microscopy. Confirming e a r l i e r work, materials s i m i l a r to those described in the o r i g i n a l ZSM-20 patents are formed only from a narrow range of gel compositions. S t r u c t u r a l l y , however, such products are not phase-pure, comprising crystals of cubic and mixed cubic and hexagonal stackings of faujasite sheets. 2

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ZSM-20 (1) i s a l a r g e pore z e o l i t e t h a t has r e c e n t l y attracted i n t e r e s t because of i t s properties as a c r a c k i n g (2.) and h y d r o c r a c k i n g c a t a l y s t Q ) . I t i s one o f a s e r i e s o f m a t e r i a l s r e l a t e d s t r u c t u r a l l y t o f a u j a s i t e (FAUf ramework (4.) ) t h a t have been d e s c r i b e d as h a v i n g h e x a g o n a l symmetry, i n c l u d i n g CSZ-1 (ϋ) , ZSM-2 (ϋ.) , ZSM-3 (7_L, a n d t w i n n e d z e o l i t e Υ (£1_. T h e s e v a r i o u s m a t e r i a l s a l l have high sorption capacities for substituted aromatic m o l e c u l e s , a c h a r a c t e r i s t i c o f p o r e systems w i t h a p e r t u r e s d e f i n e d by 10 o r more T-atoms (T = t e t r a h e d r a l s p e c i e s , S i o r A l e t c . ) . Z e o l i t e CS?-1 was o r i g i n a l l y d e s c r i b e d a s having a hexagonal u n i t cell with a= 1 7 . 4 Â a n d c= 2 8.4Â (ϋ, i l ) , corresponding to that described f o rthe h e x a g o n a l v a r i a n t o f f a u j a s i t e ( l a b e l l e d h e r e b y framework code BSS) by B r e c k a n d o t h e r s (10-12) . More r e c e n t work (JL3.) has, h o w e v e r , d e m o n s t r a t e d t h a t CSZ-1 a d o p t s t h e FAU0097-6156/89/0398-O544$06.00/0 ο 1989 American Chemical Society In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Downloaded by UNIV OF ILLINOIS URBANA on October 3, 2014 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch037

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framework, b u t w i t h a slight rhombohedral distortion (possibly induced by s t r a i n a s s o c i a t e d with twin faults near the center of the very thin c r y s t a l l i t e s (JL4.) ) . Z e o l i t e ZSM-3 h a s a l s o b e e n d e s c r i b e d a s h a v i n g h e x a g o n a l symmetry, b u t w i t h o u t a d e f i n e d c - a x i s c o n s t a n t , reflecting t h a t sheets o f s o d a l i t e cages a r e connected along c i n b o t h hexagonal and cubic s t a c k i n g s i n a highly disordered m a n n e r (JJi) . No s t r u c t u r e h a s y e t b e e n p r o p o s e d f o r z e o l i t e Z S M - 2 . C h a r a c t e r i z a t i o n o f z e o l i t e ZSM-20 u s i n g n - d e c a n e h y d r o c r a c k i n g as a t e s t method i s consistent with i t possessing a 3-dimensional 1 2 - r i n g p o r e s y s t e m , a n d t h e PXD p a t t e r n h a s been i n d e x e d on t h e b a s i s o f a h e x a g o n a l u n i t c e l l w i t h a = -17.3Â a n d c = -28.6Â (17.), a s e x p e c t e d f o r a m a t e r i a l a d o p t i n g t h e BSS-framework (10-12). We describe here further studies of the c r y s t a l l i z a t i o n o f z e o l i t e ZSM-20, f o c u s i n g on m i n o r i t y factors t h a t p r o v e d t o be i m p o r t a n t i n developing a s u c c e s s f u l s y n t h e s i s . We o u t l i n e X - r a y p o w d e r d i f f r a c t i o n and electron microscopy data which illustrate that, s t r u c t u r a l l y , ZSM-20 c o m p r i s e s a f a u l t e d a n d i n t e r g r o w n m i x t u r e o f b l o c k s o f b o t h h e x a g o n a l (BSS) a n d c u b i c (FAU) s t a c k i n g s o f s h e e t s o f s o d a l i t e c a g e s (1£) . M i x e d p h a s e behavior i n a z e o l i t e synthesis system i s o f t e n r e f l e c t e d i n c o n s i d e r a b l e v a r i a b i l i t y i n t h e PXD p a t t e r n s (reflecting c h a n g e s i n t h e r e l a t i v e amounts o f t h e two ( o r more) p h a s e s f r o m one p r e p a r a t i o n t o t h e n e x t ) . The r e l a t i v e p r o p o r t i o n s o f t h e c u b i c a n d h e x a g o n a l c o m p o n e n t s i n ZSM-20 s a m p l e s , however, a r e found t o f a l l w i t h i n r e l a t i v e l y narrow bounds in both the present materials and those described p r e v i o u s l y i n t h e l i t e r a t u r e (1 16-22) . r

Experimental

- Syntheses

Z e o l i t e ZSM-20 i s s y n t h e s i z e d i n t h e N a 2 0 - T E A 2 0 - A l 2 C > 3 SÎ02-H20 composition system (TEA= tetraethylammonium cation), using t e t r a m e t h y l o r t h o s i l i c a t e (TMOS) or tetraethylorthosilicate (TEOS) a s t h e s i l i c a s o u r c e ( 1 ) . The l a t t e r i s t h e p r e f e r r e d s i l i c a s o u r c e i n m o s t r e c e n t l y published work (19-22). S y n t h e s e s b a s e d on a range o f silica sources demonstrate that ZSM-20 formation i s s e n s i t i v e t o t h e s p e c i f i c g e l composition, p r e p a r a t i o n and crystallization conditions. Minor changes i n these v a r i a b l e s can t o t a l l y i n h i b i t t h e growth o f c r y s t a l l i n e products, o r promote t h e c r y s t a l l i z a t i o n o f other z e o l i t e s s u c h a s b e t a o r h i g h s i l i c a c h a b a z i t e s ( h e r s c h e l l i t e ) (when r e s i d u a l TMOS i s n o t c o m p l e t e l y h y d r o l y z e d a n d e v o l v e d a s methanol, and remains i n the system during c r y s t a l l i z a t i o n ) . S e v e r a l groups have r e p o r t e d syntheses o f Z S M - 2 0 ( 1 9 - 2 2 ) a n d m o d i f i c a t i o n s o f E x a m p l e 19 o f t h e V a l y o c s i k U.S. P a t e n t ( 2 0 22) a r e d e s c r i b e d a s p r o v i d i n g t h e most r e l i a b l e r e s u l t s . O p t i m i z e d syntheses produce highly crystalline ZSM-20 i n a s l i t t l e as f o u r days. Z e o l i t e b e t a t y p i c a l l y r e p l a c e s ZSM-20 w i t h i n c r e a s i n g r

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

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reaction time. ZSM-20 i s m o r e a l u m i n u m d e f i c i e n t t h a n z e o l i t e Y, w i t h S i : A l r a t i o s o f > 3 . 5 , a n d t y p i c a l l y 4 . 2 , and i s t h e r e f o r e a p p r o p r i a t e l y compared w i t h h i g h silica F A U - f r a m e w o r k m a t e r i a l s s u c h a s C S Z - 3 (22.) a n d ECR-4 (21) prepared by d i r e c t synthesis from different cation c o n t a i n i n g s y s t e m s . H y d r o c a r b o n s o r p t i o n c a p a c i t i e s o f ZSM20 m a t e r i a l s , i n t h e r a n g e o f 17 - 2 0 w t . % , a r e m o r e s i m i l a r t o those o f t h el a t t e r high s i l i c a materials than t h a t t y p i c a l o f z e o l i t e Y. R e c e n t l y p u b l i s h e d r e p o r t s o f ZSM-20 s y n t h e s e s i n c l u d e e v a l u a t i o n s ( 2 0 , 2 1 ) o f t h e p a t e n t e x a m p l e s o f C i r i c (JL) a n d V a l y o c s i k (1£); i n v e s t i g a t i o n s o f t h e r o l e o f g e l s t r u c t u r e and composition (22.) ; a n d s t u d i e s o f pressure and t e m p e r a t u r e e f f e c t s (22.) . T h e p r o c e d u r e s u s e d b y C i r i c a n d Valyocsik are outlined i n Figure 1, a n d i l l u s t r a t e t h e p o t e n t i a l problems with r e p r o d u c i b i l i t y i n t h e former case.

Valyocsik Method

(tetraethoxysllane) Q^S^)

Crystallization 100*C12d

ι

ZSM-20

Ciric Method

(Tetramethoxysilane)

j MeOH-*— Steam Box

Crystallization 70-100°Cia-42d

Cold age Nucleation Step

F i g u r e 1. S c h e m a t i c c o m p a r i s o n s o f t h e C i r i c a n d V a l y o c s i k m e t h o d s f o r t h e s y n t h e s i s o f ZSM-20.

The i n t e r m e d i a t e s t a g e s o f t h e g e l a g i n g may b e v i e w e d a s n u c l e i i n c u b a t i o n p e r i o d s , and t h e presence o f even s m a l l a m o u n t s o f r e s i d u a l m e t h a n o l may i n f l u e n c e t h e f i n a l products. We h a v e e x a m i n e d b o t h t h e i n f l u e n c e s o n t h e crystallization products of potassium cations(an u n d i s c l o s e d i m p u r i t y i n some c o m m e r c i a l T E A p r o d u c t s ) , a n d t h e v a r i a b i l i t y i n p r o d u c t s d e r i v e d f r o m o p t i m i z e d ZSM-20 gel compositions seeded i na v a r i e t y o f ways. A l t h o u g h t h e o r i g i n a l ZSM-20 p a t e n t d e s c r i b e s s u c c e s s f u l s y n t h e s e s b a s e d o n TMOS a s a s i l i c a s o u r c e ( 1 ) / we h a v e b e e n unsuccessful in d u p l i c a t i n g t h e patent examples using presently



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a v a i l a b l e TMOS. T h e ZSM-20 p r e c u r s o r g e l s t r u c t u r e appears to p l a y an important r o l e i nb r i n g i n g i n t h e product, and m i n o r v a r i a t i o n s i n s o u r c e TMOS may b e a p r o b l e m . T h e TEOS s y n t h e s i s r o u t e i s more r e l i a b l e , r e f l e c t i n g t h e s i m p l i f i e d gelation process (Figure 1), less sensitivity t o v a r i a b i l i t y i n t h i s p a r t i c u l a r r e a g e n t , o r more c o n s i s t e n t reagent quality. The d i f f e r e n c e s between t h e u s e o f tetramethyland tetraethylorthosilicate are partly illustrated i n t h e experiments d e s c r i b e d below.A l l e x p e r i m e n t s w e r e c a r r i e d o u t i n T e f l o n (DuPont Co.) b o t t l e s a t 95° t o 100°C i n a s t e a m b a t h (TMOS a n d TEOS p r e p a r a t i o n s only) f o l l o w e d by c r y s t a l l i z a t i o n i n an a i r oven w i t h o u t stirring. +

The effect of K addition t o the basic synthesis (using d i f f e r e n t s i l i c a sources) on t h ev a r i o u s products a t h i g h l e v e l s o f c r y s t a l l i z a t i o n a t 100°C i s i l l u s t r a t e d i n F i g u r e 2 a n d T a b l e 1. S o d i u m a l u m i n a t e w a s t h e s o u r c e o f a l u m i n a . T h e b a s e s y n t h e s i s w i t h o u t K y i e l d e d g o o d ZSM-20 a f t e r 3 d a y s a t 100°C f o l l o w i n g a 3 d a y c o l d a g e a t r o o m temperature (22°C) . W h e n K was p r e s e n t , h i g h silica d i s o r d e r e d c h a b a z i t e s , o f t h e G v a r i e t y (2J1) , a n d z e o l i t e b e t a (2 6 , 2 7 ) w e r e t h e major products, with a minor d e v e l o p m e n t o f o f f r e t i t e ( p r o b a b l y L i n d e Τ (2_i) ) . S c a n n i n g e l e c t r o n m i c r o g r a p h s o f t h e s e p r o d u c t s a r e shown i n F i g u r e 2. C r y s t a l l i z a t i o n o f ZSM-20 a p p e a r s t o b e s u p p r e s s e d b y t h e presence o f e i t h e r K o r r e s i d u a l methanol i nt h e g e l , and p r o d u c t s u s u a l l y common a t l o n g e r c r y s t a l l i z a t i o n times then predominate. The u s e o f an e x t e r n a l n u c l e a t i o n s o l u t i o n (JIQ.) s i g n i f i c a n t l y i n c r e a s e s t h e N a 0 c o n t e n t o f the g e l , andpromotes t h e formation o f b e t a , c h aand g i s . +

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1

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TABLE K+ #

INFLUENCES

Gel Composition R 0 : N a 0 : K 0 : S i 0 :H 0 2

2

2

2

1 9.9 1.1 0 32 2 9.9 1.1 1.1 3 2 3 9.6 1.1 1.1 3 1 4 9.9 1.1 1.1 32 5 10.0 1.1 1.1 3 1 6 10.0 1.8 1.1 3 1 7 9.6 2.2 1.1 3 0 * D e t a i l s : C=cold

2

ON

1 ZSM-20

Details* C/S/Si

SYNTHESES Xtln time

3d 455 C, TEOS 28d 455 C, TMOS 38d 530 C, TMOS 500 28d C, TEOS 425 17d C, HS40 425 9d S, HS40 410 18d S, C a b a g e d ; S= s e e d e d ; S i = s i l i

Products

ZSM-20 cha cha»of f amorphous J3>cha β /5>cha>gis ca source

Z e o l i t e b e t a c h a r a c t e r i s t i c a l l y r e p l a c e s ZSM-20 a t l o n g a g e times i n t h e standard s y n t h e s i s (JL) - r e p r e s e n t e d b y experiment #1 i n T a b l e 1. I n most o f t h e s e syntheses z e o l i t e b e t a seems t o b e a n u n a v o i d a b l e l o w l e v e l i m p u r i t y . The e x p e r i m e n t s d e t a i l e d i n T a b l e 2 e x a m i n e t h e e f f e c t s o f various nucleation and seeding methods on ZSM-20

American Chemical Society Library 1155 16th St., N.W. In Zeolite Synthesis; D.C. Occelli,20038 M., et al.; Washington,

ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


ZEOLITE SYNTHESIS

F i g u r e 2. SEM o f ZSM-20 (a) and c o - c r y s t a l l i z a t i o n p r o d u c t s b e t a (b) a n d c h a w i t h o f f ( c ) .


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c r y s t a l l i z a t i o n s . T h e s e were c o n d u c t e d i n p o t a s s i u m f r e e systems, where t h e T E A was first treated a t room t e m p e r a t u r e w i t h a c i d washed c l i n o p t i l o l i t e t o remove any r e s i d u a l traces o f potassium c a t i o n s .

TABLE NUCLEATION


Composition:

INFLUENCES

2 ON ZSM-20

SYNTHESES

9.7 (TEA) 0 : 1.14Na 0: A 1 0 : 2 4 . 2 S i 0 :

S e e d i n g mode O.lg ZSM-20 X t a l s 0.1g FAU-Y X t a l s I d age 23°C 2d age 23°C 5d age 23°C l i d age 23°C ns= no sample;

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370H O. 2

C r y s t a l l i z a t i o n Products 8d 5d 3d 2d am am am am fi>fau fc>fau am am am β am ns ZSM-20 Ζ5Μ-2 0>β am ns ns β am" ns ns β ns ns am= amorphous p r o d u c t s ;

C o l d a g i n g (1) i s a c o m p e t i t i v e n u c l e i b r e e d i n g s t e p w h i c h c l e a r l y has an optimum t i m e p e r i o d f o r ZSM-20, a f t e r which promoters o f z e o l i t e b e t a predominate. Attempts t o i n d u c e c r y s t a l l i z a t i o n by a d d i t i o n o f c r y s t a l l i n e p r o d u c t s o f ZSM-20 o r t y p e - Y , w i t h o u t any c o l d a g i n g s t e p , f a i l e d to demonstrate any s e e d i n g e f f e c t s . I n t h e s e c a s e s b e t a was the primary product. The ZSM-20 products characteristically show a morphology o f t w i n n e d and i n t e r g r o w n " h e x a g o n a l " p l a t e s o r s q u a s h e d o c t a h e d r a about 0 . 1μ i n d i a m e t e r (similar t o those observed for a p o t a s s i u m " p l a t e l e t f a u j a s i t e " (J1L) ) , w i t h t h e a d d i t i o n a l f e a t u r e o f h a v i n g many c r y s t a l s g r o w i n g o u t f r o m t h e p l a t e s u r f a c e . The p l a t e s have an a s p e c t r a t i o o f about 3, and a r e sometimes a g g l o m e r a t e d i n t o s m a l l s p h e r u l e s .

Experimental - C h a r a c t e r i z a t i o n of Synthesis Products Chemical a n a l y s i s and s o r p t i o n d a t a . Chemical analyses (ICP-AES) o f h i g h l y c r y s t a l l i n e a n d p u r e ZSM-20 m a t e r i a l s g i v e S i / A l r a t i o s i n t h e range o f 3.7 ( T a b l e 2) t o 4.7 (Table 1 ) . Na/Al ratios o f 0.7 a r e t y p i c a l , as a r e ( N a + T E A ) / A l r a t i o s o f a b o u t 1.1. S i n g l e p o i n t n-hexane s o r p t i o n c a p a c i t i e s a t 40 t o r r a n d 23°C, a f t e r b u r n o f f o f t h e TEA a t 550°C i n a i r f o r 3 h o u r s , a r e i n v a r i a b l y i n t h e r a n g e o f 18% t o 20% wt. - v a l u e s t y p i c a l f o r h i g h s i l i c a d i r e c t l y s y n t h e s i z e d f a u j a s i t e t y p e p r o d u c t (24.) . Infra-red spectroscopy. I.R. s p e c t r a a r e f r e q u e n t l y u s e d to i d e n t i f y s t r u c t u r a l components i n z e o l i t e s , and t o compare i d e n t i t i e s . F i g u r e 3 compares t h e I.R. s p e c t r a f o r


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t h e a m m o n i u m e x c h a n g e d f o r m s o f Y, Z S M - 2 0 a n d ZSM-3. T h e f i r s t two a r e i d e n t i c a l i n a l l e s s e n t i a l characteristics, e x c e p t f o r m i n o r p e a k b r o a d e n i n g a n d a weak s h o u l d e r a t - 9 2 0 c m . " i n t h e ZSM-20 s p e c t r u m . T h e s e a r e i n d i s t i n c t c o n t r a s t t o t h e s p e c t r u m f o r ZSM-3, w h i c h , t h o u g h having the e s s e n t i a l f e a t u r e s o f t h e other two s p e c t r a , i s h i g h l y degraded, probably reflecting a high level of disorder, e v e n t h o u g h m o r p h o l o g i c a l l y i t w a s s i m i l a r t o ZSM-20 i n crystal size distribution.


1

Powder X-ray d i f f r a c t i o n . P o w d e r X - r a y d i f f r a c t i o n (PXD) data were measured on an automated Siemens D500 d i f f r a c t o m e t e r u s i n g C u KOC r a d i a t i o n f r o m a f i n e - f o c u s Xr a y t u b e o p e r a t i n g a t 1200W, a n d w i t h 1° i n c i d e n t b e a m divergence s l i t s . Samples were g e n e r a l l y measured after f u l l e q u i l i b r a t i o n w i t h a t m o s p h e r i c m o i s t u r e . T y p i c a l PXD p a t t e r n s a r e s h o w n i n F i g u r e 4, a n d l i k e t h e scanning e l e c t r o n micrographs, they give t h e impression o f a pure p h a s e , e v e n when c o c r y s t a l l i z e d w i t h o t h e r z e o l i t e s , such as b e t a , shown i n F i g u r e 4b. C o m p a r i s o n b e t w e e n t h e PXD p a t t e r n o b s e r v e d f o r a t y p i c a l ZSM-20 m a t e r i a l ( F i g u r e 4 a ) w i t h t h a t c a l c u l a t e d on t h e b a s i s o f d i s t a n c e l e a s t squares optimized atomic c o o r d i n a t e s f o r t h e BSS f r a m e w o r k ( F i g u r e 5a) i l l u s t r a t e s t h a t t h e observed peak p o s i t i o n s a r e i n g e n e r a l reproduced b y a h e x a g o n a l c e l l (l 11) w i t h a = 17.37Â a n d c = 28.50Â. However, t h e d i s t r i b u t i o n s of reflection intensities are c l e a r l y d i f f e r e n t b e t w e e n t h e o b s e r v e d a n d s i m u l a t e d PXD p a t t e r n s , w i t h t h e presence o f s e v e r a l broad peaks being a particular feature of the ZSM-20 pattern. The d i s c r e p a n c i e s c a n n o t be e x p l a i n e d on t h e b a s i s o f e i t h e r s l i g h t d e v i a t i o n s from t h e i d e a l framework geometry o r t h e scattering c o n t r i b u t i o n s o f t h e n o n - f r a m e w o r k s p e c i e s . The observed p a t t e r n i s , however, reproduced reasonably well when modelled as a simple sum o f c u b i c (FAU) and hexagonal(BSS) components i n t h e a p p r o x i m a t e r a t i o BSS:FAU = - 2 - 2.5 (1£) ( F i g u r e 5 c ) . r

The f i r s t m a i n f e a t u r e i n t h e PXD p a t t e r n s contains contributions from the 0 1 0 ( 2 9 a l c = 5.88°), 0 0 2 (6.20°) a n d 0 1 1 (6.64°) r e f l e c t i o n s from t h e hexagonal c o m p o n e n t (BSS), a n d f r o m t h e 1 1 1 r e f l e c t i o n o f t h e c u b i c component (FAU) w h i c h occurs at (6.25°), effectively c o i n c i d e n t w i t h 0 0 2 x ( F i g u r e 5) . T h e l o w e r a n g l e data a r e a f f e c t e d b y s p r e a d i n g o f t h e i n c i d e n t beam b e y o n d t h e sample, and c o n t a i n s i g n i f i c a n t c o n t r i b u t i o n s from t h e nonframework components. Nevertheless, the relative intensities of the first three peaks provide a rough q u a n t i t a t i v e measure o f t h e r e l a t i v e amounts o f t h e c u b i c (FAU) a n d h e x a g o n a l (BSS) c o m p o n e n t s . As i l l u s t r a t e d i n Figure 5c, optimal agreement between t h e observed and s i m u l a t e d p a t t e r n s i s o b t a i n e d f o r a r a t i o BSS:FAU = - 2.5. Approximately t h i s same d i s t r i b u t i o n of intensities i s C

h e



37. VAUGHAN ET AL.


F i g u r e 3. C o m p a r a t i v e i n f r a - r e d s p e c t r a f o r ammonium exchanged Y-FAU, ZSM-20 a n d ZSM-3.

10000

7500,

w 5000. o O 2500. -

4.00 22.071

9.00 9.817

24.00 29.00 14.00 19.00 3.705 3.076 6.320 4.667 Two - Thêta / D - Spacing

34.00 2.935

F i g u r e 4. O b s e r v e d powder X - r a y d i f f r a c t i o n p a t t e r n s f o r a t y p i c a l ZSM-20 m a t e r i a l ( a ) a n d a b e t a c o n t a m i n a t e d product(b).


551

552

ZEOLITE SYNTHESIS

COUNTS


253S0.0

5070.0

Ill

68680.0

_ .

17170.0

_ .

III

I

I III

0.00

5.71

III II

I

I

II

IIIIIIUI III

II

II

I

III

I II

I II I I

I I

II

II

II

II

II II

I

I II II II I II I II I I I I I I II II II II II I I I III II l l l l l l l l III Ι Ι Ι Ι Ι Μ Μ Η Ι Ι Ι Η Η Μ Μ Η Π

1.43

17.14

22.86

28.57

34.29

Two

40.00

Theta

F i g u r e 5. C a l c u l a t e d powder X - r a y d i f f r a c t i o n p r o f i l e s f o r t h e FAU (a) a n d BSS frameworks (b) and t h e sum o f t h e s e two components i n t h e r a t i o BSS:FAU = 3 . 0 (c) w h i c h a p p r o x i m a t e s o b s e r v e d p r o f i l e s f o r z e o l i t e ZSM-20 m a t e r i a l s (lower v e r t i c a l b a r s - p o s i t i o n s o f a l l o w e d reflections).


37. VAUGHAN ET AL.


553


r e p o r t e d f o r a l l ZSM-20 p r e p a r a t i o n s ( 1 . 1 4 - 2 0 ) . Zeolite ZSM-20 t h u s comprises intergrown b l o c k s o f c u b i c and hexagonal stackings of f a u j a s i t e sheets, but i n r e l a t i v e amounts t h a t f a l l w i t h i n q u i t e n a r r o w bounds. T h i s l i m i t e d variability i n t h e r e l a t i v e c o n c e n t r a t i o n s o f t h e two components r e f l e c t s p a r t l y t h e r e l a t i v e l y n a r r o w window o f compositions a n d c o n d i t i o n s u n d e r w h i c h ZSM-20 c a n be c r y s t a l l i z e d . I n a d d i t i o n , we s u s p e c t t h a t i t a l s o r e f l e c t s t h e manner i n w h i c h t h e c u b i c a n d h e x a g o n a l components i n t e r g r o w i n t h i s system. A l t h o u g h t h e c u b i c and h e x a g o n a l components s e p a r a t e l y form b l o c k s extended over s e v e r a l u n i t c e l l s , they are coherently intergrown. Symptomatic of this stacking b e h a v i o r , t h e peak w i d t h s i n t h e measured PXD p a t t e r n s a r e i n d e x - d e p e n d a n t ( F i g u r e 4 ) . The 1 0 3 x r e f l e c t i o n a t 11.0° i s , f o r example, c o n s i d e r a b l y b r o a d e r t h a n t h e a d j a c e n t 1 1 Ohex r e f l e c t i o n ( F i g u r e 4) . The p a t t e r n o f p e a k widths illustrated i n Figure 4 i s t y p i c a l of a l l previously reported PXD p r o f i l e s (17.20.22) and i t i s a second c h a r a c t e r i s t i c o f ZSM-20 m a t e r i a l s . A f u l l t r e a t m e n t o f t h e e f f e c t s o f c o h e r e n t , c l u s t e r e d f a u l t i n g on t h e s i m u l a t e d PXD d a t a (2J1) r e p r o d u c e s q u a n t i t a t i v e l y t h e p a t t e r n o f peak w i d t h s and i n t e n s i t i e s o b s e r v e d f o r ZSM-20 m a t e r i a l s , a n d c o r r o b o r a t e s t h e i r d e s c r i p t i o n as f a u l t e d m i x t u r e s o f c u b i c and h e x a g o n a l s t a c k i n g s o f f a u j a s i t e s h e e t s i n t y p i c a l r e l a t i v e c o n c e n t r a t i o n s B5S:FAU o f 2 t o 2.5:1. The r e s u l t o f s u c h a c a l c u l a t i o n i n t h e 20 r a n g e 4° t o 19° i s compared i n F i g u r e 6 w i t h t h e experimental X-ray d i f f r a c t i o n p a t t e r n o f a s e e d e d ZSM-20 p r o d u c t ( T a b l e 2 ) . U s i n g a v a l u e f o r α = -0.7 (α = BSS I(BSS+FAU) ) , t h e e x p e r i m e n t a l intensity r e l a t i o n s h i p s a r e c l o s e l y matched. he

Electron Microscopy. S e v e r a l s a m p l e s were e x a m i n e d b y t r a n s m i s s i o n e l e c t r o n microscopy (TEM) i n a P h i l i p s 430T o p e r a t i n g a t 300 kV. Samples were p r e p a r e d by u l t r a s o n i c a l l y d i s p e r s i n g t h e c a l c i n e d z e o l i t e i n e t h a n o l , and c o l l e c t i n g t h e d i s p e r s e d z e o l i t e c r y s t a l l i t e s on a s t a n d a r d 200 mesh 3mm Cu g r i d c o v e r e d w i t h a t h i n (-20 nm) amorphous carbon f i l m . High r e s o l u t i o n e l e c t r o n microscopy shows d i r e c t l y t h a t ZSM-20 i s an i n t e r g r o w t h o f t h e c u b i c a n d h e x a g o n a l modes o f s t a c k i n g o f f a u j a s i t e s h e e t s ( F i g u r e 7 ) . T h e r e a r e q u a l i t a t i v e s i m i l a r i t i e s w i t h CSZ-1 a n d CSZ-3 m a t e r i a l s ( 1 3 1 4 ) . As f o r CSZ-1 and CSZ-3, ZSM-20 c r y s t a l l i t e s adopt a h e x a g o n a l t a b u l a r m o r p h o l o g y w i t h an a s p e c t ratio, p l a t e l e t w i d t h t o t h i c k n e s s , o f -3:1, compared w i t h -8:1 for CSZ-1 a n d -4:1 f o r CSZ-3. U n l i k e CSZ-1 a n d CSZ-3, h o w e v e r , t h e ZSM-20 p l a t e l e t s t e n d t o i n t e r g r o w , with p l a t e l e t normals mutually i n c l i n e d a t -70°. r

T h e r e i s a h i g h d e n s i t y o f t w i n n i n g i n most o f t h e ZSM-20 p l a t e l e t s , w i t h -65% o f t h e FAU (111) p l a n e s b e i n g twinned t o produce a c r y s t a l l i t e which i s predominantly



554

ZEOLITE SYNTHESIS

ZSM-20

J

4

Calculation α = 0.70

JI U L· 7

10

13

16

19

2 theta (°) F i g u r e 6. E x p e r i m e n t a l X - r a y d i f f r a c t i o n p a t t e r n o f a ZSM-20 m a t e r i a l c o m p a r e d w i t h a p a t t e r n c a l c u l a t e d u s i n g t h e c o h e r e n t f a u l t i n g m o d e l (28). The v a l u e α r e p r e s e n t s the p r o b a b i l i t y that successive (111) p l a n e s w i l l interconnect v i a a mirror operation rather than through a n i n v e r s i o n . T h u s (X=0 r e p r e s e n t s p u r e F A U , a n d CC=1 r e p r e s e n t s p u r e BSS. ZSM-20 h a s CC=0 .7 .




37. VAUGHAN ET AU

F i g u r e 7. E l e c t r o n m i c r o g r a p h o f a t y p i c a l ZSM-20 c r y s t a l l i t e a g g r e g a t e . R e g i o n s o f b o t h h e x a g o n a l ABAB (BSS) a n d c u b i c A B C A B C . . . (FAU) s t a c k i n g a r e e v i d e n t


ZEOLITE SYNTHESIS

556


h e x a g o n a l {BSS) i n s t a c k i n g c h a r a c t e r . In CSZ-1, a b o u t 10% o f t h e (111) p l a n e s a r e t w i n n e d ( H J i ) . However, i n ZSM20, some o f t h e i n t e r p e n e t r a t i n g c r y s t a l l i t e s t e n d t o have a s i g n i f i c a n t l y l o w e r t w i n d e n s i t y (see F i g u r e 7 ) . T h i s arises because hexagonal stacking sequences cannot i n t e r p e n e t r a t e c o h e r e n t l y when c r y s t a l a x e s a r e i n c l i n e d . However, the unfaulted cubic FAU-stacking can i n t e r p e n e t r a t e c o h e r e n t l y when c r y s t a l l i t e s a r e mutually r o t a t e d by -7 0°. The interpénétrant g r o w t h may t h u s promote t h e o c c u r r e n c e o f t h e c u b i c s t a c k i n g , as s u g g e s t e d by t h e stacking i n the crystallite that protrudes from the i n t e r g r o w n c r y s t a l l i t e i n F i g u r e 7.

Discussion As i s d i s c u s s e d e l s e w h e r e (JJL) , t h e c u b i c (FAU) and h e x a g o n a l (BSS) stackings of sheets of s o d a l i t e cages d i f f e r i n t h e c h a r a c t e r o f t h e symmetry o p e r a t i o n t h a t r e l a t e s s u c c e s s i v e sheets along the [lll] or [001] . P a i r s o f s o d a l i t e cages w i t h i n t h e s h e e t s a r e i n b o t h c a s e s r e l a t e d ( a p p r o x i m a t e l y ) by i n v e r s i o n c e n t e r s a t t h e c e n t e r s of the hexagonal prisms. In t h e c u b i c c a s e , successive sheets along [ l l l ] a r e a l s o r e l a t e d by i n v e r s i o n c e n t e r s at the centers of the hexagonal prisms. In the hexagonal(BSS) form (10-12), these i n v e r s i o n c e n t e r s are r e p l a c e d by m i r r o r p l a n e s t h a t b i s e c t t h e h e x a g o n a l p r i s m s a l o n g [001] . A s t e r e o v i e w o f t h e BSS framework b a s e d on d i s t a n c e l e a s t squares optimized atomic coordinates (which a r e g i v e n e l s e w h e r e ) i s shown i n F i g u r e 8. The g e o m e t r i e s o f t h e p o r e s y s t e m s i n t h e FAU and BSS frameworks d i f f e r s i g n i f i c a n t l y ( F i g u r e 8 ) . In t h e former, s u p e r c a g e s have four 12-ring apertures arranged tetrahedrally, interconnecting adjacent supercages i n a face-centered c u b i c a r r a y . In c o n t r a s t two t y p e s o f s u p e r c a g e s o c c u r i n BSS. The l a r g e r , which form s t r a i g h t channels along [001] , have f i v e 12-ring apertures (Figure 9). The s m a l l e r have t h r e e 1 2 - r i n g a p e r t u r e s and p r o v i d e lateral connections between c h a n n e l s . These d i f f e r e n c e s i n the s u p e r c a g e c o n f i g u r a t i o n s a r e l i k e l y t o be r e f l e c t e d i n significant differences in sorption and catalytic p r o p e r t i e s . There i s t h e r e f o r e a s i g n i f i c a n t i n c e n t i v e f o r attempts to synthesize materials that have a larger p r o p o r t i o n of the hexagonal s t a c k i n g than i s found i n ZSM20 m a t e r i a l s . c u b i c

h e x

c u b i c

h e x

h e x

The l i m i t e d v a r i a t i o n o b s e r v e d i n t h e r e l a t i v e p r o p o r t i o n s o f t h e c u b i c and h e x a g o n a l components i n ZSM20 z e o l i t e s must be r e l a t e d t o c r y s t a l l i z a t i o n c o n d i t i o n s . Z e o l i t e ZSM-20 can be made r e p r o d u c i b l y p r o v i d e d t h a t t h e recommended conditions are strictly followed. The syntheses are p a r t i c u l a r l y s e n s i t i v e t o c h a r a c t e r of the r e a g e n t s u s e d , and t o r e s i d u a l a l c o h o l i n t h e g e l . T h i s l a t t e r v a r i a b l e may be r e s p o n s i b l e f o r a d e g r e e o f non-



37. VAUGHAN ET AL.


F i g u r e 8. S t e r e o v i e w o f t h e BSS framework drawn as s t r a i g h t l i n e s connecting adjacent t e t r a h e d r a l v e r t i c e s . A t o m i c c o - o r d i n a t e s a r e b a s e d on d i s t a n c e l e a s t s q u a r e s optimized values.

F i g u r e 9. O u t l i n e s o f t h e s u p e r c a g e s i n t h e FAU framework (A), and o f t h e two d i f f e r e n t s u p e r c a g e s i n t h e BSS framework (B and C ) . The l a r g e r c a g e s (B) a r e connected i n a continuous f a s h i o n , forming s t r a i g h t channels along the c r y s t a l l o g r a p h i c c d i r e c t i o n .


557

558

ZEOLITE SYNTHESIS


r e p r o d u c i b i l i t y i n c r y s t a l l i z a t i o n rates i n otherwise i d e n t i c a l g e l s . Reaction times are apparently optimized when t h e c o l d a g e s t e p i s some 2 t o 4 d a y s . As i l l u s t r a t e d h e r e , t h e form and p e r f e c t i o n o f t h e l a y e r s t a c k i n g s i n ZSM-20 m a t e r i a l s c a n be c a t e g o r i z e d b y b o t h p o w d e r X - r a y d i f f r a c t i o n a n d , more d i r e c t l y , b y h i g h resolution lattice imaging. Spatially resolved measurements o f c o m p o s i t i o n s and, p e r h a p s , o f framework o r non-framework c o m p o s i t i o n a l z o n i n g a r e a l s o feasible. D e t a i l s o f t h e r e l a t i o n s h i p between s y n t h e s i s c o n d i t i o n s and c r y s t a l l i z e d s t r u c t u r e may y e t g u i d e a t t e m p t s t o make t h e p u r e h e x a g o n a l form (BSS). Acknowledgments We t h a n k J . Quodomine f o r t h e I . R . s p e c t r a , P. K w i a t e k f o r t a k i n g t h e SEM m i c r o g r a p h s r e p r o d u c e d h e r e , and A. J . Jacobson f o r h e l p f u l d i s c u s s i o n s .

Literature Cited 1. Ciric, J. U.S. Patent 3 972 983, 1976 (Mobil Oil Corp.). 2. Ciric, J. U.S. Patent 4 021 331, 1977 (Mobil Oil Corp.). 3. Weitkamp, J . ; Ernst, S.; Cortes-Corberan, V.; Kokotailo, G. In 7th. Intl. Zeolite Conf. Posters; Japan Assoc. Zeolites, Tokyo, 1986; 239. 4. Meier, W. M. and Olson, D. H., Atlas of Zeolite Structure Types 2nd. Edn.; Butterworths: Surrey UK, 1987. 5. Barrett, M. G.; Vaughan, D. E. W. U.S. Patent 4 309 313, 1982 (W. R. Grace Co.). 6. Ciric, J. U.S. Patent 3 411 874, 1968 (Mobil Oil Corp.). 7. Ciric, J. U.S. Patent 3 415 736, 1968 (Mobil Oil Corp.). 8. Audier, M.; Thomas, J. M.; Klinowski, J.; Jefferson, D. Α.; Bursill, L. A. J. Phys. Chem. 1982, 86, 581584. 9. Millward, G. R.; Thomas, J. M.; Ramdas, S.; Barlow, M. T. In Proc. Sixth Int. Zeolite Conf.; Olson, D . ; Bisio, A. Eds.; Butterworths: Surrey UK, 1984; pp. 793-802. 10. Breck, D. W. Zeolite Molecular Sieves; J.Wiley: New York, 1974 (reprinted R.E.Krieger: Malabar FL, 1982) pp. 56-58. 11. Moore, P. B.; Smith, J. V. Mineralog. Mag. 1964, 35, 1008-1014. 12. Breck, D. W.; Flanigen, Ε. M. In Molecular Sieves; Barrer, R. M. Ed.; Soc.Chem.Ind.: London, 1968; pp.4761.


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13. Treacy, M. M. J.; Newsam, J . M.; Beyerlein, R. A.; Leonowicz, M. E . ; Vaughan, D. E. W. J.Chem.Soc.Chem.Comm. 1986, 1211-1214. 14. Treacy, M. M. J.; Newsam, J . M.; Vaughan, D. E. W.; Beyerlein, R. Α.; Rice, S. B . ; DeGruyter, C. B. In Microstructure and Properties of Catalysts: Treacy, M. M. J.; Thomas, J . M.; White, J . M. Eds.; Mater. Res. Soc. Symp. Proc. No. 111; Materials Research Society: Pittsburgh, PA, 1988; pp. 177-190. 15. Kokotailo, G T.; Ciric, J . In Molecular Sieve Zeolites 1; Flanigen, E. M.; Sand, L. B. Eds.; Amer. Chem. Soc. Adv. Chem. Ser. No. 101; American Chemical Society: Washington, DC, 1971; pp. 109-121. 16. Weitkamp, J.; Ernst, S.; Kumar, R. Appl. Catal.; 1986, 27, 207-210. 17. Derouane, E . ; Dewaele, N . ; Gabelica, Z.; Nagy, J . B. Appl. Catal.; 1986, 28, 285-293. 18. Newsam, J . M.; Treacy, M. M. J.; Vaughan, D. E. W.; Strohmaier, K. G.; Mortier, W. J . J. Chem. Soc. Chem.Comm.; 1989, in press. 19. Valyocsik, E. W. European Pat. APPL. 12 572, 1983 (Mobil Oil Corp.). 20. Ernst, S.; Kokotailo, G. T.; Weitkamp, J . Zeolites; 1987, 7, 180-182. 21. Ernst, S.; Kokotailo, G. T.; Weitkamp, J . In Innovation in Zeolite Materials Science; Grobet, P. J . et a l . Eds.; Elsevier: Amsterdam, 1987; pp. 29-36. 22. Dewaele, Ν.; Maistriau, L . ; Nagy, J . B . ; Gabelica, Z.; Derouane, E. G. Appl. Catal.; 1988, 37, 273-290. 23. Vaughan, D. E. W.; Barrett, M. G. U.S. Patent 4 333 857, 1982(W. R. Grace Co.). 24. Vaughan, D E. W. U.S. Patent 4 714 601, 1987 (Exxon Research and Engineering Co.). 25. Barrer, R. M.; Baynham, J . W. J.Chem.Soc.(London); 1956, 2882. 26. Wadlinger, R. L.; Kerr, G. T. U.S. Patent 3 308 069, 1967 (Mobil O i l Corp.); (reissued No. Re.28 341, 1975). 27. Treacy, M. M. J.; Newsam, J . M. Nature; 1988, 332, 249-251. 28. Treacy, M. M. J.; Newsam, J . M.; Vaughan, D. E. W.; Deem, M. W. in preparation, 1988. 29. Gard, J . A . ; Tait, J . M. In Molecular Sieve Zeolites 1; Flanigen, Ε. M.; Sand, L. B. Eds.; Amer. Chem. Soc. Adv. Chem. Ser. No. 101; American Chemical Society: Washington, DC, 1971; pp. 230-236. 30. Vaughan, D. E. W; Edwards, G. C.; Barrett, M. G. U.S. Patent 4 340 573, 1982 (W.R.Grace Co.). 31. Edwards, G. C.; Vaughan, D. E. W.; Albers, E. W. U.S. Patent 4 175 059, 1979 (W.R.Grace Co.). RECEIVED

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Synthesis and Characterization of Zeolite ZSM-20 - American

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