[acs symposium series] zeolite synthesis volume 398 || competitive role of organic and inorganic...

Chapter 40

Competitive Role of Organic and Inorganic Cations in Directing One-Dimensional

Zeolitic Structures ZSM-48 and EU-1

Girolamo Giordano1, Janos B. Nagy, Eric G. Derouane, Nicole Dewaele, and Zelimir Gabelica

Laboratory of Catalysis, Center for Advanced Materials Research, Facultés Universitaires Notre Dame de la Paix, Namur, 61 Rue

de Bruxelles, B-5000 Namur, Belgium

The Bis-quaternary ammonium ions (e.g. hexamethonium, HM++) favour the formation of two different one-dimensional zeolites, namely ZSM-48 and EU-1. The resulting structure essentially depends on the initial aluminium content in the starting hydrogel. The stability fields for both zeolites synthesized by using various reactant compositions have been established. Zeolite ZSM-48 is prepared from a silica hydrogel containing HM++ ions and alkali cations (Li, Na, and Κ), in presence or in absence of Al . For a higher in i t ia l Al content and increased crystallization time, zeolite EU-1 is obtained. The critical role of hexamethonium ions and inorganic cations on the crystallization rate of ZSM-48 was systematically studied. HM++ ions favor the ZSM-48 formation by interacting electrostatically with Al negative charges and stabilizing its structure by acting as pore fillers.

The s y n t h e s i s o f pure and h i g h l y c r y s t a l l i n e z e o l i t e s from a l l u m i n o s i l i c a t e hydrogels r e q u i r e s the st u d y o f the s i m u l t a n e o u s e f f e c t s o f d i f f e r e n t parameters i n v o l v e d i n the s y n t h e s i s . Most of these z e o l i t e s are prepared i n presence of organic d i r e c t i n g

Current address: Dipartimento di Chimica, Université della Calabria, Arcavacata di Rende, 1-87030 Rende (CS), Italy

0097-6156/89A)398-0587$06.00A) ο 1989 American Chemical Society

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

588 ZEOLITE SYNTHESIS

agents whose r o l e can be d r a s t i c a l l y i n f l u e n c e d by the a c t u a l composition of the hydrogel.

Recent work has p o i n t e d out t h e predominant t e m p l a t i n g r o l e of b i s - q u a t e r n a r y ammonium ions (e.g. hexamethonium i o n s ) i n d i r e c t i n g o n e - d i m e n s i o n a l z e o l i t i c s t r u c t u r e s namely z e o l i t e s ZSM-48 and EU-1, the f i r s t r e p r e s e n t a t i v e member of the EU0 fami l y ( 1 - 4 . ) .

Z e o l i t e s having ZSM-48 t o p o l o g y a l s o c r y s t a l l i z e from hydrogels c o n t a i n i n g other l i n e a r organic s t r u c t u r e d i r e c t i n g agents, such as diamines (UL) or v a r i o u s (poly)alkylamines (£).

Z e o l i t e ZSM-50, another member of the EU0 f a m i l y p o s s e s s i n g the topology of EU-1, a l s o c r y s t a l l i z e s i n presence of dibenzyldimethylammonium ions (2).

The framework of ZSM-48 i s composed of f e r r i e r i t e -type sheets, connected i n such a s p e c i f i c way as t o generate l i n e a r 10-membered r i n g channels. The s t r u c t u r e i s a random intergrowth of the Imma-Cmcm frameworks and contains 48-T atoms per u n i t c e l l (&).

Recently B r i s c o e et a l . (ϋ) d e s c r i b e d the framework t o p o l o g y o f z e o l i t e EU-1. I t c o n s i s t s o f a unidimensional 10-membered r i n g channel system with s i d e pockets formed at r e g u l a r i n t e r v a l s o f f the channels. The u n i t c e l l c o n t a i n s 112-T atoms and the framework symmetry i s Cmma.

The aim o f t h i s work i s t o e v a l u a t e t h e (competitive) r o l e of other i n g r e d i e n t s i n s t a b i l i z i n g p r e f e r e n t i a l l y one or the other s t r u c t u r e . The most i n t e r e s t i n g are the c a t i o n i c s p e c i e s , namely the a l k a l i and HM + + ions, p o t e n t i a l n e u t r a l i z i n g agents t o A10 2~ n e g a t i v e l y charged framework c e n t e r s . Indeed, a l k a l i c a t i o n s were shown t o p l a y an important r o l e i n the f o r m a t i o n o f many z e o l i t e s , e i t h e r as s t r u c t u r e d i r e c t o r s i n the n u c l e a t i o n p r o c e s s ( 1 Ω . - 1 2 . ) or as s t a b i l i z i n g m i n e r a l i z e r s during growth ( 1 1 , 1 2 . ) , thereby a f f e c t i n g the f i n a l s i z e , morphology and composition of the c r y s t a l l i t e s .

Besides t h e i r obvious r o l e as templates or s t r u c t u r e d i r e c t i n g agents (13.) or as s t a b i l i z i n g pore f i l l e r s Qrl!) the organic c a t i o n s w i l l a l s o compete with a l k a l i i o n s f o r the s t a b i l i z a t i o n o f the n e g a t i v e l y charged framework (1Û, 11,1!) .

The p r e s e n t approach c o n s i s t s i n examining the s t r u c t u r e and c o m p o s i t i o n o f s e l e c t e d c r y s t a l l i n e z e o l i t e s o b t a i n e d by h e a t i n g under a p p r o p r i a t e c o n d i t i o n s hydrogels having the general composition:

x M 20 y HMBr2 ζ A l 2 0 3 60 S i 0 2 3000 H 20

by s y s t e m a t i c a l l y v a r y i n g the i n i t i a l c a t i o n i c , organic and A l content t o d e f i n e the fundamental r o l e of HM + +

i o n s i n e a c h s y s t e m , a n d t o u l t i m a t e l y o p t i m i z e t h e o p e c i f i c 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 f o r each z e o l i t e .

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40. GIORDANO ET AL. Competitive Role ofOrganic and Inorganic Cations 589

Experimental

A s e r i e s of hydrogels having the f o l l o w i n g molar composition :

χ M 20 y HMBr2 ζ A 1 2 0 3 60 S i 0 2 3000 H 20

(where HMBr 2 stands f o r hexamethonium bromide; M= L i , Na or K; 0<x<12.5; 0<y<25 and 0<z<2) was prepared by mixing the a p p r o p r i a t e amounts of the f o l l o w i n g commercial i n g r e d i e n t s : fumed s i l i c a ( A e r o s i l S e r v a ) f aluminium hydroxyde (Serva), a l k a l i hydroxyde (Janssen Chimica) , hexamethonium bromide monohydrate (Janssen Chimica) and d i s t i l l e d water.

The r e a c t a n t s were c a r e f u l l y admixed i n t h e f o l l o w i n g o r d e r : A l ( O H ) 3 , MOH, HMBr 2, H 20 and S i 0 2 . The g e l was t r a n s f e r r e d i n t o a 60 ml T e f l o n - l i n e d Morey-type a u t o c l a v e s , and heated at 200 ± 2 °C, under autogeneous p r e s s u r e , i n s t a t i c c o n d i t i o n s . At predetermined times, the autocl a v e s were removed from the oven and quenched t o room temperature i n c o l d water. The r e a c t i o n products were f i l t e r e d , thoroughly washed with c o l d d i s t i l l e d water and d r i e d overnight at 105 °C.

The i d e n t i f i c a t i o n of the s o l i d phases and the determination of t h e i r c r y s t a l l i n i t i e s were c a r r i e d out by X-ray powder d i f f r a c t i o n (XRD), u s i n g a P h i l i p s PW 1349/30 X-ray d i f f r a c t o m e t e r (Cu-KCC r a d i a t i o n ) . The c r y s t a l l i n i t y of each sample was eval u a t e d by u s i n g as standard the most c r y s t a l l i n e a s - s y n t h e s i z e d ZSM-48 from which the r e s i d u a l amorphous phase was f u r t h e r removed by u l t r a s o n i c treatment (15.) . A l k a l i and A l contents were determined by proton induced γ-ray emission (PIGE) (lu) or atomic a b s o r p t i o n , while the amount of org a n i c and water molecules was eval u a t e d by thermal a n a l y s i s ( S t a n t o n R e d c r o f t St 780 combined TG-DTA-DTG the r m o a n a l y z e r ) . The amount of d e f e c t groups i n the s t r u c t u r e s was c a l c u l a t e d from s o l i d s t a t e MAS 2 9Si-NMR (15.) .

Results and D i s n n a a i n n

Influence of the i n i t i a l A l content P r e l i m i n a r y a d j u s t m e n t s o f N a 2 0 and HMBr 2

c o n c e n t r a t i o n s d e f i n e d g e l compositions y i e l d i n g each phase i n re p r o d u c i b l e c o n d i t i o n s (see l a t e r ) . The values were :

Na 20 5 HMBr2 f o r ZSM-48 Na 20 10 HMBr2 f o r EU-1.

"Fig u r e 1" shows the c r y s t a l l i n i t y v a r i a t i o n f o r ZSM-48 and EU-1 z e o l i t e s , as a f u n c t i o n of the i n i t i a l

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3 ι I f 1 1 1 2

x mole A\2O3/60 S1O2

Figure 1. V a r i a t i o n of the percentage of c r y s t a l l i n i t y of z e o l i t e s ZSM-48 and EU-1 as a fu n c t i o n of the AI2O3 content i n the f o l l o w i n g precursor g e l phases: · = ZSM-48 5Na 20 5HMBr2 x A l 2 0 3 60SiO 2 3000H 2O, (200°C, 66 h) . • = EU-1 10Na2O 10HMBr2 x A l 2 0 3 60SiO 2 3000H 2O, (200°C, 120 h) . 0 = EU-1 + ZSM-48 (30%) Q = EU-1 + ZSM-48 (40%) + α-quartz and c r i s t o b a l i t e .

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40. GIORDANO ET AL. Competitive Role of Organic and Inorganic Cations 591

A l content (expressed i n mole AI2O3 per 60 mole S1O2), i n each g e l system. Nearly 100% c r y s t a l l i n e ZSM-48 was o b t a i n e d i n A l - f r e e g e l systems. The c r y s t a l l i n i t y f u r t h e r markedly decreases u n t i l the upper l i m i t of 1 AI2O3, above which no ZSM-48 c r y s t a l s c o u l d be detected, even f o r longer r e a c t i o n times.In the A l - f r e e 10 Na 20 10 HMBr2 hydrogel, ZSM-48, c r i s t o b a l i t e and α-quartz are the o n l y c r y s t a l l i n e phases detected, c o n f i r m i n g t h a t EU-1 can not be s t a b i l i z e d i n such a system (2.) . For 0.5 AI2O3 about 40% c r y s t a l l i n e EU-1 was detected along with ZSM-48 and smaller amount of c r i s t o b a l i t e and α-quartz, and f o r 1 AI2O3 EU-1 and ZSM-48 are the only c r y s t a l l i n e phases. EU-1 i s the only phase present f o r 1.5 AI2O3, but over t h i s value i t s c r y s t a l l i n i t y s t a r t s t o decrease, i n agreement with the w e l l e s t a b l i s h e d i n h i b i t i n g r o l e o f l a r g e amounts o f A l i n t h e c r y s t a l l i z a t i o n r a t e of many z e o l i t e s (11).

Influence of HMBr2

The amount of HM"1""1" ions i n the i n i t i a l h y d r o g e l d r a s t i c a l l y i n f l u e n c e s the nature of the z e o l i t e formed and i t s c r y s t a l l i z a t i o n k i n e t i c s . Pure and h i g h l y c r y s t a l l i n e ZSM-48 i s formed f o r a HMBr2 molar c o n c e n t r a t i o n c l o s e t o 2.5 ("Figure 2"). For h i g h e r HMB r 2 c o n t e n t s t he c r y s t a l l i n i t y shows a s l i g h t decrease, probably due to a marked m o d i f i c a t i o n of the hydrogel composition and/or of the s o l u b i l i t y of the va r i o u s r e a c t i v e s pecies, induced by the excess of organic molecules. For HM + + concentrations l y i n g between 1 and 2.5 mole, dense S1O2 pol y m o r p h i c phases coc r y s t a l l i z e w i t h ZSM-48, w h i l e f o r lower H M + +

c o n c e n t r a t i o n s , e s s e n t i a l l y below 0.5 mole, ZSM-5 was found t o be predominant z e o l i t i c phase. T h i s l a t t e r o b s e r v a t i o n confirms once more t h a t Na + ions r e a d i l y i n i t i a t e the formation of 5-1 SBU i n h i g h l y s i l i c e o u s hydrogels (11,1£) .

Our i n v e s t i g a t i o n s l e a d us t o propose the f o l l o w i n g optimum composition t o o b t a i n 100% c r y s t a l l i n e ZSM-48 a f t e r 48 h:

Na 20 2.5 HMBr2 0-0.5 A 1 2 0 3 60 S i 0 2 3000 H 20

The optimum c r y s t a l l i n i t y of EU-1 was found i n the 15-20 HM + + molar range and f o r 1.5 AI2O3 per 60 S1O2 ("Figure 3").

Furthermore we c o u l d d e f i n e more a c c u r a t e l y the appro x i m a t e g e l c o m p o s i t i o n i n which pure EU-1 c r y s t a l l i z e s with a r e l a t i v e l y f a s t r a t e :

10 Na20 17.5 HMBr2 1.5 A1 20 3 60 S i 0 2 3000 H20

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80 -

2 60 -Φ > k. Ο ^ 4 0 -

20 -

1 3 5 χ mole HMBr2/60 S1O2

Figure 2. V a r i a t i o n of the percentage of c r y s t a l l i n i t y of z e o l i t e ZSM-48 synthesized from:5Na 20 xHMBr2 0.5Al 20 3 60SiO 2 3000H2O gels (200 °C, 66 h) , as a fu n c t i o n of HMBr2 content 0 = ZSM-48 + c r i s t o b a l i t e .

20 -

5 15 25 x mole HMBT2 / 60 S1O2

Figure 3. V a r i a t i o n of percentage of c r y s t a l l i n i t y of z e o l i t e EU-1 synthesized from: 10Na2O xHMBr2 1.5Al 20 3 60SiO 2 3000H2O gels (200 °C, 7 days), as a fu n c t i o n of HMBr2 content • = EU-1 • = EU-1 + α-quartz 0 = EU-1 + ZSM-48 (t r a c k s ) .

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c r y s t a l l i z a t i o n of dense phases f o r low co n c e n t r a t i o n s and general i n h i b i t i o n of c r y s t a l l i z a t i o n f o r high HM + +

contents. I t i s i n t e r e s t i n g t o note t h a t between 5 and 10 HM+ + , ZSM-48 c o - c r y s t a l l i z e s with EU-1. A s p e c i f i c composition of both z e o l i t e s c o u l d not be measured but i t seems reasonable t o suppose that t h i s ZSM-48 phase i s not r i c h e r i n A l than those c r y s t a l l i z e d from S i - r i c h e r g e l s , as most of the A l i s probably u t i l i z e d t o b u i l d up the EU-1 framework.

Influence of NaOH c o n c e n t r a t i o n . The minimun Na 20 content (mole/60 mole S i 0 2 ) t o

i n i t i a t e the c r y s t a l l i z a t i o n o f ZSM-48 and EU-1 i s r e s p e c t i v e l y 2.5 and 7.5, w h i l e t h e h i g h e s t c r y s t a l l i n i t y f o r each z e o l i t e i s observed f o r 5 and 10 mole Na 20 r e s p e c t i v e l y ("Figure 4") . Because added as NaOH, a l a r g e r amount of N a + may a l s o i n d i r e c t l y i n c rease the c r y s t a l l i z a t i o n through the more pronounced m o b i l i z i n g e f f e c t of the OH" ions (JL2.) , but a l s o , more d i r e c t l y by s t a b i l i z i n g the f i r s t n u c l e i (IQ.,11) . The l a r g e r amount of Na + needed t o a c c e l e r a t e the growth of an A l - r i c h e r m a t e r i a l (here EU-1) suggests t h a t , i n both systems, N a + i s at l e a s t as e f f i c i e n t as HM + + i n the r o l e of counterion t o framework A l negative centers, i n agreement t o what i s u s u a l l y observed f o r z e o l i t e s s y n t h e s i z e d i n presence of both Na + and organic c a t i o n s (JUL,UL) . Note t h a t above these Na 20 optimum v a l u e s , dense phases l i k e α-quartz or c r i s t o b a l i t e s t a r t t o c r y s t a l l i z e i n both systems, as alr e a d y observed i n a previous study (2) . Indeed as soon as the maximum amount of z e o l i t e i s formed the system i s d e p l e t e d i n A l and merely behaves as usual Na-Si hydrogels.

Influence of the n a t u r e of a l k a l i c a t i o n s on t h e o p t i m a l s y n t h e s i s p r o c e d u r e f o r ZSM-48.

The d i f f e r e n t a l k a l i c a t i o n s a f f e c t n u c l e a t i o n and growth of z e o l i t e s i n various ways, independently or i n competition with the other organic c a t i o n i c s p e c i e s . In p a r t i c u l a r , s m a l l e r hydrated s t r u c t u r e - f o r m i n g c a t i o n s (towards water) l i k e L i + or Na + r e a d i l y favour, along t h e o r g a n i c t e m p l a t e s , the f o r m a t i o n o f r e g u l a r s t r u c t u r e d a l u m i n o s i l i c a t e p r e c u r s o r s or SBU, and e s s e n t i a l l y i n f l u e n c e the n u c l e a t i o n process. S t r u c t u r e -b r e a k i n g c a t i o n s l i k e K + induce l e s s r e a d i l y s t a b l e p r i m i t i v e b u i l d i n g u n i t s , but can act as s t a b i l i z i n g m i n e r a l i z e r s during growth (11,19).

We have checked such a behaviour by r e p l a c i n g Na +

i o n s by L i + and K +, i n the g e l s g i v i n g ZSM-48 i n "optimum y i e l d " , namely

M 20 2.5 HMBr2 χ A l 2 0 3 6 0 s i 0 2 3 0 0 0 H 2 °

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Figure 4. Percentage of c r y s t a l l i n i t y f o r z e o l i t e s ZSM-48 and EU-1 as a fu n c t i o n of Na 20 content i n the g e l . Curve a: ZSM-48 synthesized from:

xNa 20 5HMBr2 0.5Al 2O 3 60SiO 2 3000H2O; curve b: EU-1 synthesized from:

xNa 20 10HMBr2 1.5A1 20 3 60SiO 2 3000H2O; curve c: α-quartz and/or c r i s t o b a l i t e c o - c r y s t a l l i z e d with

ZSM-48; curve d: α-quartz c o - c r y s t a l l i z e d with EU-1. D

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with two d i f f e r e n t A l contents (x= 0 or 0.5). The so ob t a i n e d c r y s t a l l i z a t i o n k i n e t i c curves o f ZSM-48 i n absence ("Figure 5a") and i n presence ("Figure 5b") of A l were compared f o r each c a t i o n i c system. In a l l three cases, the c r y s t a l l i z a t i o n was found f a s t e r i n absence of A l , i n agreement with what was g e n e r a l l y observed f o r (M) ZSM-5 ( 2 Ώ . ) . In a d d i t i o n , the i n d u c t i o n p e r i o d v a r i e s i n the f o l l o w i n g order:

L i < Na < K, s u g g e s t i n g t h a t the s t r u c t u r e - f o r m i n g L i + and Na +

b e t t e r favour the ZSM-48 n u c l e a t i o n process than K +. The f u r t h e r growth r a t e s f o r the t h r e e systems appear comparable ("Figure 5a").

Table I. Cation and A l contents of four ZSM-48 samples s y n t h e s i z e d from 5 M 20 2.5 HMBr 2 (0 or 0.5)Al 2O 3 60 S i 0 2 3000 H 20 a f t e r 48 h

Sample M +/u.c. HM + +/u.c. Al/u.c . a b a

Na-ZSM-48 0.05 1.0 (Na+Al)ZSM-48 0.20 1.0 0.59

K-ZSM-48 0.22 1.1 (K+Al)ZSM-48 0.23 1.1 0.62

a: atomic absorption; b: TG-DTA

The amounts of i n c o r p o r a t e d a l k a l i c a t i o n s remain low (Table I) and these c a t i o n s o n l y n e u t r a l i z e the defe c t SiO~ negative charges f o r A l - f r e e samples. Note tha t the HM + + content f o r each sample i s s i m i l a r , t h i s s t r o n g l y suggesting that the e s s e n t i a l s t a b i l i z a t i o n of the framework i s achieved by the pore f i l l i n g a c t i o n , as i n the s i m i l a r system y i e l d i n g Nu-10 (14.) . However, t h i s f i l l i n g i s not completely a c h i e v e d by the o r g a n i c s (about 85%), because, f o r s t r u c t u r a l reasons, about one HM + +/u.c. i s the maximum p o s s i b l e amount t h a t can be incorporated i n the ZSM-48 framework (see below).

S i m i l a r k i n e t i c s trends are observed i n presence of aluminium ("Figure 5b") with the d i f f e r e n c e t h a t Na + i s a l s o i n c o r p o r e t e d during growth, i n s i m i l a r amount than K +, both probably a c t i n g t o a l i m i t e d extent, as A10 2~ counterions.

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Time (h)

Figure 5 . C r y s t a l l i z a t i o n k i n e t i c s of z e o l i t e ZSM-48 i n presence of L i + , Na + and K + ions, without A l (a) and i n presence of 0.5 mole A I 2 O 3 i n the g e l (b) : 5Na 20 2.5HMBr2 (0 or 0.5)Al2C>3 60SiO 2

3000H2O.

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C o m p e t i t i v e r o l e o f Na+ and HM++ s p e c i e s Unit c e l l composition of t y p i c a l z e o l i t e s prepared

from d i f f e r e n t Na + b e a r i n g hydrogels are r e p o r t e d i n Table I I .

The constant Na/Al r a t i o s measured f o r two ZSM-48 samples c r y s t a l l i z e d from two d i f f e r e n t g e l compositions at d i f f e r e n t s y nthesis times and from which the r e s i d u a l amorphous phase was removed by u l t r a s o n i c c l e a n i n g , confirms t h a t Na + ions are c o n t i n u o u s l y i n c o r p o r a t e d d u r i n g growth. In n e i t h e r case they can n e u t r a l i z e t o t a l l y the A l bearing negative charges, suggesting that the HM + + ions a l s o p a r t i c i p a t e i n t h i s n e u t r a l i z a t i o n p r o c e s s . N e v e r t h e l e s s , the amount of o r g a n i c ions was found t o be remarkably constant, as i n the case of the other a l k a l i systems (Table I ) .

S i m i l a r y , i n sample 4, about one HM + + was again found occluded per u n i t c e l l of ZSM-48. However sample 4 contains a s l i g h t l y l a r g e r amount of N a + / u . c , and t h i s may be due to the l a r g e r Na 20 content c h a r a c t e r i z i n g i t s hydrogel p r e c u r s o r (Table II) . T h i s suggests t h a t Na +

i o n s probably do not p l a y t h e i r n e u t r a l i z i n g r o l e as counterions t o A l . At l e a s t our o b s e r v a t i o n confirms t h a t , i n our sy n t h e s i s c o n d i t i o n s , Na + do not b r i n g A l to the s t r u c t u r e .

Mechanism o f HM++ a c t i o n A l l the ZSM-48 samples s y n t h e s i z e d from the above

envisaged g e l systems, accomodate about one HM + + per u n i t c e l l , t h i s corresponding to about 85% of the t o t a l pore f i l l i n g . By c o n t r a s t , the A l c o n c e n t r a t i o n can be d i f f e r e n t from one sample t o a n o t h e r , as i t s i n c o r p o r a t i o n i s governed by the i n i t i a l A l content i n the g e l , p r o v i d e d i t i s not too important. However, c o n s i d e r i n g the framework charge balance, at l e a s t p a r t of the HM + + ions must a l s o act as A l c o u n t e r i o n s . We t h e r e f o r e propose the f o l l o w i n g model t o e x p l a i n the r o l e of HM + + ions i n d i r e c t i n g syntheses of z e o l i t e s with l i n e a r channel systems such as ZSM-48 and EU-1.

During the f i r s t r e s t r u c t u r a t i o n of the s i l i c a t e or S i - r i c h a l u m i n o s i l i c a t e complexes p r i o r t o the z e o l i t i c n u c l e a t i o n , t h e HM + + e n t i t i e s p l a y a s t r u c t u r e s t a b i l i z i n g r o l e . By t h e i r p a r t i c u l a r l i n e a r shape, they favour the formation of channel systems. Simultaneously, they can a l s o n e u t r a l i z e one AIO2"" negative center of the a l u m i n o s i l i c a t e complex by i t s p o s i t i v e — N + ( C H 3 ) 3 ends. Note th a t t h i s does not exclude the formation of a c e l l i n v o l v i n g o n l y one (or l e s s ) A l , t h a t then i n t e r a c t s o n l y with one p o s i t i v e l y charged end of the template. The other p o s i t i v e end w i l l be s o l i c i t a t e d o n l y i f enough A l i s a v a i l a b l e i n the g e l , up t o a maximum of 2 Al per one HM++

f i.e. per unit c e l l .

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Tabl

e II. Na

ture

cry

stal

lini

ty an

d ch

emic

al c

ompo

siti

on o

f va

riou

s ze

olit

es s

ynth

esiz

ed i

n pr

esen

ce of Na

+

and HM"1"

1" io

ns

Samp

le

AI2

O3

/S

1O

2 Sy

nthe

sis

Soli

d ph

ase

Comp

osit

ion

per

unit

ce

ll

a Po

re

fill

ing

(gel

) ti

me,(

h)

(%cr

ysta

l.)

Al

Na

H20

HM++

Si

OR

(%)

b b

c d

e £

1 0

48

ZSM-

48(9

7)

η. ,d.

n. ,d.

1. ,80

0. 98

11

. .1

82

2 0, .008

3 66

ZSM-

48(8

1)

0, .78

0, .24

2 .31

1, .01

10. .6

85

» 0, .008

3 90

ZSM-

48(7

5)

0, .72

0, .24

2 .25

1. .00

10. .1

84

3 0, .008

3 48

ZSM-

48(9

3)

0. .60

0, .20

2, .97

1, .04

-87

If

0, .0083

66

ZSM-4

8(97

) 0. .67

0, .24

2, .96

1. .05

-88

4 0. .0083

48

ZSM-

48(8

3)

0. .74

0, .49

3, .42

0. .96

10. .9

80

5 0. .0250

120

EU-1 (8

0)

2, .10

0, .44

7. .40

1, .30

3. ,5

g Co

rres

pond

ence

be

twee

n sa

mple

nu

mber and gel

comp

osit

ion:

5 Na

20

5 Na

20

5 Na

20

10 Na

20

5 HM

Br2

5 HM

Br2

2.5

HMBr

2

5 HM

Br2

0.5

Al203

0.5

A1

20

3

0.5

A1

20

3

60

Si0 2

60

Si0 2

60

Si0 2

60

Si0 2

3000 H

20

3000 H

20

3000 H

20

3000 H

20

10 N

a20

10 HMB

r 2

1.5 A1

2C>3

60 S

i02

3000 H

20

a For

sake of

comp

aris

on,

one

unit

ce

ll of EU-1 is as

sume

d to ha

ve 4

8 Τ

atom

s b

Eval

uate

d by

PIGE

c

Eval

uate

d by TG

-DTA

d

Eval

uate

d by TG

-DTA a

nd am

moni

a ti

trat

ion

e Ev

alua

ted by

29Si-NMR

f Pe

rcen

tage of

fill

ing as

calc

ulat

ed by

cons

ider

ing the

leng

th of one HM

++ i°

n equ

al t

o 14

.05 Â, and by

cons

ider

ing the

tota

l ch

anne

l le

ngth of one ZS

M-48

uni

t ce

ll

equa

l to

16.8 Â.

g The

tota

l le

ngth of the

tort

uous

ch

anne

l sy

stem of EU

-1 i

s not

know

n.

The Na

and Al

cont

ents for sa

mple 3 at

(4 8 h)

wer

e ev

alua

ted by

atom

ic

abso

rpti

on

Ν ES

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The f i n a l s t r u c t u r e so genereted i s a Cmcm-Imma inte r g r o w t h (&) i n which the Cmcm u n i t i s only able to accomodate two A l at st a b l e p o s i t i o n s .

For l a r g e r A l g e l concentrations r i n g s i n v o l v i n g an even number of Τ atoms (e.g. four membered ring s ) w i l l be p r e f e r e n t i a l l y f a v o u r e d and the f i n a l s t r u c t u r e s t a b i l i z e d by the HM + + ions w i l l be d i f f e r e n t i n terms of geometry and c o n c e n t r a t i o n of s t a b l e Τ s i t e s f o r aluminium (1£) . EU-1 i s one example of such a s t r u c t u r e , s t a b i l i z e d by HM + + ions under the p a r t i c u l a r c o n d i t i o n s d e s c r i b e d .

For i n t e r m e d i a t e A l c o n c e n t r a t i o n s i n the g e l phases, one can suppose t h a t both s t r u c t u r e s coc r y s t a l l i z e , each i n c o r p o r a t i n g the appropiate amount of A l .

As a c o n c l u s i o n , HM + + i o n s are not e x c l u s i v e templates f o r a given s t r u c t u r e but w i l l s t a b i l i z e an a l u m i n o s i l i c a t e s t r u c t u r e that i s p r e l i m i n a r i l y favoured by other v a r i a b l e s such as the A l content i n the g e l . They w i l l a c t p a r t l y as co u n t e r i o n s t o the neg a t i v e framework, p a r t l y as pore f i l l e r s . O b v i o u s l y , they e x c l u s i v e l y act as pore f i l l e r s i n the A l fr e e g e l s , i n which a l k a l i c a t i o n s can be pre s e n t ( t h i s work) or absent (2) .

In ZSM-48 the presence of HM + + generates a marked number of s t r u c t u r a l S i — Ο — R d e f e c t groups (up t o 11 SiOR/ u.c.) (R = H, M + or HM+ + ), as measured by 2 9Si-NMR (Table I I ) . In c o n t r a s t , when a l i n e a r diaminoalkane i s used as template a s m a l l e r amount of de f e c t groups i s measured (about 3.5 SiOR/u.c.) (21) . The d i f f e r e n c e between t h e s e two v a l u e s , about 8 SiO R / u . c , can be e a s i l y e x p l a i n e d by c o n s i d e r i n g the a c t u a l s i z e of the bul k y t e r m i n a l trimethylammonium groups. Being l a r g e r (6.9 Â) than the average ZSM-48 channel diameter (about 5.3*5.6 Â ) , they are accomodated w i t h i n the s t r u c t u r e by c r e a t i n g 4 SiOR groups at each end of the channel that r e s u l t from an empty Τ p o s i t i o n ("Figure 6") . Such d e f e c t groups l i n k e d t o empty Τ p o s i t i o n s have a l s o been det e c t e d i n high s i l i c a ZSM-5 (15.) .By c o n t r a s t few s t r u c t u r a l d e f e c t s are detected i n the EU-1 framework. T h i s i s e a s i l y e x p l a i n e d by c o n s i d e r i n g t h a t the si d e pockets r e s u l t i n g from the h i g h t o r t u o s i t y o f the s t r u c t u r e more e a s i l y accomodate the t e r m i n a l trimethylammonium groups of the HM + + i o n .

Conclusion

The framework of z e o l i t e ZSM-48 can be o r i e n t e d by hexamethonium (HM + +) templates i n v a r i o u s g e l systems h a v i n g d e f i n e d A l c o n c e n t r a t i o n s . The HM + + i o n s

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Figure 6.Schematic l o c a l i z a t i o n of hexamethonium ions i n ZSM-48 channel s t r u c t u r e , generating SiO" defects near the terminal trimethylammonium groups of the template.

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s t a b i l i z e the z e o l i t i c s t r u c t u r e i n formation and, by t h e i r p a r t i c u l a r l i n e a r shape, t h e y f a v o u r t h e generation of the channel system. In a d d i t i o n , they a l s o n e u t r a l i z e the negative charges of the s t r u c t u r e , l i n k e d e i t h e r t o S i - 0 - A l ~ e n t i t i e s or t o S i - 0 ~ d e f e c t groups. Because the complete f i l l i n g by the HM + + ions represents one HM + + per u n i t c e l l , the maximum number of A l atoms th a t can be introduced i n t o the framework, i s t h e r e f o r e e q u a l t o two. I n t e r e s t i n g l y because o f s t e r i c i n t e r a c t i o n s , the HM + + ions introduce defect groups i n t o the s t r u c t u r e , t he amount of which can be e a s i l y r a t i o n a l i z e d by supposing the presence of two missing Τ s i t e s per u n i t c e l l . Note that i f ZSM-48 i s formed i n presence o f polymethylenediamines, much l e s s d e f e c t groups are intro d u c e d i n the s t r u c t u r e . A l k a l i c a t i o n s p l a y a secondary r o l e and probably n e u t r a l i z e the Si-0"~ defect groups.

A higher A l content i n the hydrogel i s a predominant v a r i a b l e t h a t leads t o a d i f f e r e n t l y arranged A l - r i c h e r EU-1 framework. HM + + s t a b i l i z e t h i s framework as counterio n s along with the a l k a l i c a t i o n s and a l s o as pore f i l l i n g agents, but do not i n i t i a t e i t s n u c l e a t i o n . The more open, t o r t u o u s pore s t r u c t u r e t h a t r e s u l t s , accomodates the HM + + ions e a s i l y , without much s t e r i c c o n s t r a i n t , and the EU-1 s t r u c t u r e c o n t a i n s a f a r smaller number of S i - 0 ~ defects than ZSM-48.

Literature cited 1. Casci, J.L.; Whittam, T.V.; Lowe, B.M. Proc. 6th

Intern, Zeolite Conference, 1984, p 894. 2. Dodwell, G.W.; Denkewicz, R.P.; Sand, L.B. Zeolites

1985, 5, 153. 3. Dewaele, N.; Gabelica, Ζ.; Bodart, P.; B.Nagy, J.;

Giordano, G.; Derouane E.G. Stud. Surf. Sci. Catal. 1988, 37, 65.

4. Casci, J.L. Stud. Surf. Sci. Catal. 1986, 28, 215. 5. Araya, Α.; Lowe, B.M. J. Catal. 1984, 85, 135. 6. Chu, P. Eur. Patent 23 089, 1981 and U.S. Patent

4 397 827, 1983. 7. Kaeding, W.W. Eur. Patent 219 271, 1987. 8. Schlenker, J.L.; Rohrbaugh, W.J.; Chu, P.; Valyocsik,

E.W.; Kokotailo, G.T. Zeolites 1985, 5, 355. 9. Briscoe, N.A.; Johnson, D.W.; Shannon, M.D.;

Kokotailo, G.T.; McCusker, L.B. Zeolites 1988, 8, 74. 10. Gabelica, Ζ.; Blom, N.; Derouane, E.G. Appl. Catal.

1983, 5, 227 and references cited therein. 11. Gabelica, Z.; Derouane, E.G.; Blom, N. In Catalytic

Materials: Relationship between Structure and Reactivity: White,Τ.Ε., Jr. et al., Eds.; ACS Symposium

Dow

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Series No. 248; American Chemical Society: Washington, DC, 1984; p 219.

12. Nastro, Α.; Gabelica, Z. ; Bodart, P.; B.Nagy, J . Stud. Surf. Sci. Catal. 1984, 19, 131.

13. Lok, B.M.; Cannan, T.R., Messina, C.A. Zeolites 1983,3, 252.

14. Pellegrino, C.; Aiello, R.; Gabelica, Z. In ACS Symposium Series "Advances in Zeolite Synthesis" (this book) and references cited therein.

15. B.Nagy, J.; Bodart, P.; Colette, H.; El Hage-Al Asswad, J.; Gabelica, Z. ; Aiello, R.; Nastro, Α.; Pellegrino, C. Zeolites 1988,8, 209.

16. Debras, G.; Derouane, E .G. ; Gilson, J .P . ; Gabelica, Z. ; Demortier, G. Zeolites 1983,3, 37.

17. Nastro, Α.; Colella, C.; Aiello, R. Stud. Surf. Sci. Catal. 1985, 24, 39.

18. Bellussi, G.; Perego, G.; Carati, Α.; Cornaro, U.; Fattore, V. Stud. Surf. Sci. Catal. 1988, 37, 37.

19. Guth, J.L.; Caullet, P. J . Chim. Phys. 1986, 83, 155. 20. Rollman, L.D. In Zeolites, Science and Technology;

Ribeiro, F.R. et al., Eds.; M. Nijhoff, Den Haag, 1984, p 109.

21. Dewaele, N. Ph.D. Thesis, Namur University, Namur, 1988.

22. Van Santen, R.A.; Keijsper, J.; Ooms, J.; Kortbeek, A.G.T.G. Stud. Surf. Sci. Catal. 1986, 28, 169.

RECEIVED February 18, 1989

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