Molecular Sieve Zeolites-I - American Chemical Society

3 Stages of Zeolite Growth from Alkaline Media

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R. AIELLO, R. M . BARRER, and I. S. KERR Physical Chemistry Laboratories, Imperial College, London S.W. 7, England A study has been made of stages of aggregation from alka line aluminosilicate solutions. Appropriate mixtures con taining M O, Al O , SiO , and H O (where M = Li, Na, or K) were made with sufficient water and strength of alkali that the solids initially dissolved to give clear liquids. These liquids were heated at 80°C without stirring. Solids appeared, the evolution of which was followed by electron microscopy and electron and x-ray diffraction. The solid phase appeared initially as laminae, mostly amorphous. After longer heating, the solids contained thin laminae and thicker, broken laminae which seemed to be evolving into larger particles. At this stage, the x-ray pattern showed clear arcs caused by zeolites. Finally, the laminae were completely replaced by zeolites, nucleation of which ap peared to be heterogeneous. 2

2

3

2

2

Τ Tnder suitably alkaline conditions and with a sufficient volume of ^ water, it is possible to dissolve aluminosilicate gels to form clear liquids free of any residual solids. Such liquids are of interest because from them one may hope to examine the first stages of zeolite crystalliza tion. The question of homogeneous vs. heterogeneous nucleation (7,8) of zeolite crystals may be studied usefully when clear liquids provide the reaction mixture. For these reasons, we have examined the first solids to appear from such liquids and have followed their subsequent evolution. Experimental Limpid liquids were obtained by dissolving a small quantity of amorphous silica powder and freshly prepared aluminum hydroxide (total weight of oxides about 2 to 3 grams) in 1 liter of hot I N Na, K, 44 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

Growth

AIELLO E T A L .

from Alkaline

Media

45

o r L i h y d r o x i d e s o l u t i o n . T h e S i 0 : A l 0 m o l a r ratios w e r e a b o u t 4. T h e l i q u i d s so p r e p a r e d w e r e filtered a n d e a c h w a s d i v i d e d i n t o 4 p a r t s , w h i c h w e r e p u t i n p l a s t i c bottles i n a n o v e n at 80 ° C w i t h o u t s t i r r i n g . A f t e r a s o m e w h a t v a r i a b l e i n t e r v a l , u s u a l l y of s e v e r a l h o u r s , there w a s p r e c i p i t a t i o n of solids. T h e bottles w e r e r e m o v e d , one at a t i m e at i n tervals, f r o m the o v e n , a n d the solids w e r e s e p a r a t e d f r o m the l i q u i d b y c e n t r i f u g a t i o n a n d w a s h e d . A l i t t l e of the m a t e r i a l s u s p e n d e d i n w a t e r was p l a c e d o n grids for s u b s e q u e n t e l e c t r o n m i c r o s c o p i c e x a m i n a t i o n , a n d the r e m a i n d e r was d r i e d f o r x - r a y s t u d y . B e c a u s e so l i t t l e w a s n e e d e d for t h e e l e c t r o n m i c r o s c o p e , i t w a s p o s s i b l e to o b t a i n samples f o r this e x a m i n a t i o n c o r r e s p o n d i n g to shorter r e a c t i o n times t h a n w e r e i n v o l v e d i n c o l l e c t i n g the first samples for x - r a y e x a m i n a t i o n .


2

Electron

2

3

Microscopy

T h e first solids to f o r m w e r e t h i n b o u y a n t p a r t i c l e s w h i c h t e n d e d to c i r c u l a t e t h r o u g h the l i q u i d b y c o n v e c t i o n . A s t h e y a g e d , t h e y b e c a m e denser a n d settled at the b o t t o m of the vessel. T h e f r e s h l y f o r m e d solids c o u l d , because of t h e i r b o u y a n c y , b e g e l - l i k e , w i t h a c o n s i d e r a b l e w a t e r content. I n a l l cases c o n s i d e r e d , these f r e s h l y f o r m e d p a r t i c l e s a p p e a r e d u n d e r the e l e c t r o n m i c r o s c o p e to consist m a i n l y of l a m e l l a e s u c h as are s h o w n i n F i g u r e s Ι Α , 2 A , a n d 3. A s the r e a c t i o n t i m e i n c r e a s e d , i n a d d i t i o n to the t h i n flakes m a n y t h i c k e r a n d b r o k e n ones w e r e o b s e r v e d

(Figures

4 a n d 5 ) , as w e l l as some t h i c k particles or conglomerates w h i c h w e r e

Figure 1.

Laminae with the appearance of a smectite from solutions ing Na +

Figure 2.

Crystallite laminae and electron diffraction

patterns

In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

contain

46

M O L E C U L A R SIEVE ZEOLITES

Figure grown

1

Figure 4. Gaps developing in lameUar material

3. Lamellae from liquids containing Li


+

Figure 5.

A further stage in the nucleation of zeolite

probably composed

Figure 6. Final stage showing crystats of Na-Pl and basic sodalite

m a i n l y of zeolites.

A t s t i l l l o n g e r r e a c t i o n times,

the t h i n l a m i n a e b e c a m e less n u m e r o u s , a n d the t h i c k b r o k e n ones w e r e p r e d o m i n a n t . F i n a l l y , at the longest times, the l a m e l l a e p r a c t i c a l l y d i s a p p e a r e d a n d w e r e r e p l a c e d b y crystals of zeolite, s u c h as those i n F i g u r e 6 w h i c h w e r e i d e n t i f i e d b y x - r a y d i f f r a c t i o n as N a - P l ( 3 ) a n d b a s i c s o d a lite (6).

A l t h o u g h the f o r m a t i o n a n d e v o l u t i o n of the l a m e l l a e seemed

to b e s i m i l a r i n a l l the cases e x a m i n e d , t h e i r n a t u r e a p p e a r e d to b e to some extent a f u n c t i o n of the c a t i o n present, as s h o w n b e l o w . Electron

Diffraction

by

F i g u r e 3 shows

Lamellae

t y p i c a l freshly f o r m e d l a m e l l a e g r o w n f r o m

the

l i q u i d s c o n t a i n i n g L i . A l l the l a m e l l a e e x a m i n e d s h o w e d o n l y the diffuse +

halos c h a r a c t e r i s t i c of a n e a r l y a m o r p h o u s structure. A l a r g e m a j o r i t y of the l a m i n a e f r e s h l y g r o w n f r o m l i q u i d s c o n t a i n i n g K phous.

+

also w e r e a m o r -

H o w e v e r , a f e w of these, w h i c h a l r e a d y s h o w e d signs of

the

a g i n g r e f e r r e d to i n the p r e v i o u s section a n d c o n t a i n e d s m a l l p a r t i c l e s ( F i g u r e 7 A ) , gave patterns s u c h as that i n F i g u r e 7 B , w i t h a b r o a d arc i n the r a n g e d =

2.88-2.93A.

T h i s corresponds w i t h the strongest d i f -

f r a c t i o n f o u n d i n the c h a b a z i t e - l i k e phase K - G of B a r r e r a n d B a y n h a m


3.

Growth

AIELLO E T A L .

Figure

7.

from Alkaline

Laminae

47

Media

grown from liquids ing K

contain-


+

(2).

X - r a y diffraction showed

t h a t this phase w a s present, a n d i t is

c o n c l u d e d t h a t K - G forms the d a r k p a r t i c l e s seen i n F i g u r e 7 A . T h e lamellae g r o w n from the liquids containing N a

+

also c o m p r i s e d

m a i n l y a m o r p h o u s structures w i t h diffuse halos, b u t there w e r e 2 m i n o r exceptions.

A f e w l a m i n a e s u c h as those i n F i g u r e 1 A h a v e t h e a p p e a r -

a n c e of a smectite a n d i n fact g i v e e l e c t r o n d i f f r a c t i o n patterns l i k e those i n F i g u r e s in

a n d 1 C , t a k e n r e s p e c t i v e l y f r o m t h i n a n d t h i c k e r parts of

the same l a m e l l a . T h e latter p a t t e r n also appears to s h o w r o t a t i o n a l s l i p . T h e d-spacings are g i v e n i n T a b l e I. T h e y c a n b e i n d e x e d as the hkffs from a hexagonal unit cell w i t h a = a =

5.24A a n d b =

5.24A o r a m o n o c l i n i c u n i t c e l l w i t h

9.08A, s i m i l a r to t h a t f o r m i c a s a n d c l a y m i n e r a l s .

T i l t i n g t h e l a m e l l a e r e v e a l e d h e a v y f a u l t i n g i n layers p a r a l l e l to the b a s a l p l a n e , a n d i t w a s therefore i m p o s s i b l e to d e t e r m i n e c. A f e w o t h e r l a m i n a e p r o d u c e d patterns s u c h as those i n F i g u r e s 2 B a n d 2 C . F i g u r e 2 C shows the p a t t e r n n o r m a l for m a n y s u c h crystallites. F i g u r e 2 B shows t h e p a t t e r n f r o m the l a m i n a e i n F i g u r e 2 A , a n d i n d i cates a t y p e of e l e c t r o n d i f f r a c t i o n p a t t e r n w h i c h occurs w h e n there is a s t r o n g l y p r e f e r r e d o r i e n t a t i o n p a r a l l e l to the s u p p o r t i n g

Table I.

Electron Diffraction D a t a

0

dohJA

hkl

vs vs vw m vs

4.50 2.61 2.27 1.71 1.52 1.31 1.26 1.04 0.99 0.87

100 110 200 210 300 220 310 320 410 330

S

a n d this

from the Lamina in Figure IB

Int.

w vw vw vw

film

° Indexed on a hexagonal unit cell with a — 5.24A.

American Chemical Society Librsry

In Molecular Sieve 1155Zeolites-I; 16th St,Flanigen, N.W. E., et al.; Advances in Chemistry; American Chemical DC, 1974. mi—hi— t w no Society: 9 n Washington, mc

48


1

film is t i l t e d w i t h respect t o t h e i n c i d e n t b e a m . d - S p a c i n g s f r o m F i g u r e s 2 B a n d 2 C are s h o w n i n T a b l e I I . T h e y c o r r e s p o n d to the same as yet unidentified material having a hexagonal unit cell w i t h a = c =

7.05A a n d

6.47A.

X-Ray

Examination

T h e x - r a y d i f f r a c t i o n patterns of the solids after they h a d b e g u n to e v o l v e t o w a r d s the stage of t h i c k e r , b r o k e n l a m e l l a e h a v i n g the a p p e a r ance of those i n F i g u r e s 4 or 7 A s h o w e d lines w h i c h o c c u r i n the p a t Downloaded by GEORGE MASON UNIV on July 7, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch003

terns of v a r i o u s zeolites.

T h e reflections w e r e i n i t i a l l y v e r y w e a k b u t

b e c a m e p r o g r e s s i v e l y m o r e intense as the r e a c t i o n t i m e i n c r e a s e d .

In

solids f o r m e d f r o m l i q u i d s c o n t a i n i n g N a , z e o l i t e N a - P a n d b a s i c s o d a +

lite w e r e the final c r y s t a l l i n e constituents, b u t for short r e a c t i o n times there w e r e v e r y w e a k reflections f o u n d i n the patterns of L i n d e A a n d faujasite.

Solids d e r i v e d f r o m

liquids containing K

+

soon

reflections of K - G , w h i l e those f r o m l i q u i d s c o n t a i n i n g L i

developed +

developed

reflections w h i c h c o r r e s p o n d e d w i t h lines i n the zeolite L i - A of B a r r e r and White (5).

I n g e n e r a l , these d i f f r a c t i o n studies w e r e m a d e o n p r o d -

ucts f u r t h e r e v o l v e d f r o m the f r e s h l y f o r m e d l a m e l l a e t h a n those u s e d f o r the electron d i f f r a c t i o n , t h o u g h there was some o v e r l a p .

Discussion T h e f o r m a t i o n of the zeolites f r o m clear l i q u i d s d i d not o c c u r as a d i r e c t s h o w e r of crystals, as w o u l d be the case for e x a m p l e w i t h r o c k salt crystallites f r o m a s u p e r s a t u r a t e d s o l u t i o n . T h u s , h o m o g e n e o u s n u c l e a t i o n was not apparent.

Instead, a r a t h e r c o m p l e x

evolution

took

p l a c e , a l w a y s h e r a l d e d b y the a p p e a r a n c e of a m o r p h o u s l a m e l l a e . C r y s tallites w h i c h w e r e n o t zeolites o c c a s i o n a l l y a p p e a r e d as a d d i t i o n a l t r a n sient species—e.g., l a y e r silicates s u c h as smectites, or the u n k n o w n phase of T a b l e I I . Zeolites t h e n b e g a n to a p p e a r as crystallites i n assoc i a t i o n w i t h the l a m e l l a e , a l t h o u g h f r e s h , zeolite-free l a m e l l a e also seemed to be f o r m i n g at the same t i m e . W h e r e zeolite crystals w e r e associated w i t h l a m e l l a e , the latter soon d e v e l o p e d holes a n d gaps a n d ( F i g u r e 4 ) gave the i m p r e s s i o n t h a t the l a m e l l a r m a t e r i a l was b e i n g

consumed.

F r o m the f o r e g o i n g e v i d e n c e , the n u c l e a t i o n of zeolites is almost cert a i n l y heterogeneous

under our conditions.

T h e l a m i n a e m a y f e e d the

a l k a l i n e s o l u t i o n a n d t h e s o l u t i o n the g r o w i n g zeolites, u n t i l e v e n t u a l l y the l a m i n a e d i s a p p e a r . T h e sequence of the a b o v e processes recalls the p r i n c i p l e first p o i n t e d out b y O s t w a l d , t h a t i n a l l reactions the most stable state m a y


3.

AIELLO E T A L .

Table II.

Growth

from Alkaline

Electon Diffraction D a t a


Int. m m vw s vw vw s vs m vw m vw vw vw vw VS w s, b r m, br w, b r w, b r a

a

à/A Figure 2 B 6.14 3.52 3.08 2.85 2.40 2.22 2.15 2.02 1.89 1.76 1.75 1.34 1.25 Figure 2 C 3.56 3.23 2.83 2.32 1.90 1.50 1.29 1.15

49

Media from U n k n o w n Material hkl 100 110 111 102 112 202 003 300 212 220 203 313 403

301, 400, 411, 311,

110 002 102 210 212 312, 303 005, 322 420

Indexed on the hexagonal unit cell with a = 7.05A, c = 6.47A.

n o t b e r e a c h e d at once, b u t that first a succession of i n t e r m e d i a t e a n d less stable states tends to b e t r a v e r s e d .

E x a m p l e s of this b e h a v i o r i n

h y d r o t h e r m a l systems i n c l u d e t h e l o w - t e m p e r a t u r e f o r m a t i o n of cristob a l i t e i n s t e a d of q u a r t z f r o m excess s i l i c a ( 4 ) , the f o r m a t i o n of h i g h t e m p e r a t u r e d i s o r d e r e d p o t a s h felspar u n d e r c o n d i t i o n s w h e n t h e stable phase is t h e o r d e r e d felspar s t r u c t u r e ( 2 ) , a n d the i n i t i a l f o r m a t i o n of N a - m o r d e n i t e f r o m s i l i c a - r i c h h i g h l y a l k a l i n e aqueous a l u m i n o s i l i c a t e gels, w h i c h crystals t h e n d i s p r o p o r t i o n a t e i n t o a n a l c i t e a n d q u a r t z ( I ) . T h e s e latter species are stable u n d e r s u c h a l k a l i n e c o n d i t i o n s .

This be-

h a v i o r signifies a g e n e r a l t e n d e n c y f o r less stable species to nucleate m o r e r a p i d l y t h a n stable ones so that k i n e t i c considerations c a n i n i t i a l l y o u t w e i g h t h e r m o d y n a m i c ones.

T h e O s t w a l d l a w of successive

trans-

formations correlates, at least i n p a r t , w i t h t h e s i m p l e x i t y p r i n c i p l e of J . R . G o l d s m i t h ( 9 ) , a c c o r d i n g to w h i c h phases t e n d to a p p e a r i n t h e o r d e r of d e c r e a s i n g s i m p l e x i t y o r entropy.

F o r instance, t h e d i s o r d e r e d

felspar r e f e r r e d to a b o v e is i n a state of h i g h e r s i m p l e x i t y t h a n its o r d e r e d counterpart.

R e a d y nucleation m a y be favored b y h i g h simplexity or

e n t r o p y , b u t energy as w e l l as e n t r o p y changes u l t i m a t e l y d e t e r m i n e the r e l a t i v e stabilities of t h e phases a n d so t h e final p r o d u c t .


50


1

Literature Cited (1) Barrer, R. M., J. Chem. Soc. 1948, 2158. (2) Barrer, R. M., Baynham, J. W., J. Chem. Soc. 1956, 2882. (3) Barrer, R. M., Baynham, J. W., Bultitude, F. W., Meier, W. M., J. Chem. Soc. 1959, 195. (4) Barrer, R. M., Marshall, D. J., J. Chem. Soc. 1964, 485. (5) Barrer, R. M., White, E. A. D.,J.Chem. Soc. 1951,1267. (6) Barrer, R. M., White, E. A. D.,J.Chem. Soc. 1952, 1561. (7) Breck, D. W., Flanigen, Ε. M., "Molecular Sieves," p. 47, Society of the Chemical Industry, London, 1968. (8) Ciric, J., J. Colloid Interface Sci. 1968, 28, 315. (9) Goldsmith, J. R., J. Geol. 1953, 61, 439. Downloaded by GEORGE MASON UNIV on July 7, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch003

RECEIVED

November 13, 1969.

Discussion

John Turkevich (Princeton University, Princeton, N. J. 08540) : What were the conditions of centrifugation, and what types of particles could not be driven down? R. Aiello: The conditions of centrifugation were about 4000 rpm for many hours, until the solution was clear and practically all the suspended particles were separated. W. Sieber (Inst, fur Kristallographie und Pétrographie, ΕΤΗ, Zurich): Did you ever examine the behavior on heating of the filtrate from the amorphous lamellae? Is it excluded that formation of lamellae and formation of zeolites are independent phenomena? R. Aiello: We did not examine the behavior of the filtrate from the lamellae on heating. We cannot exclude that formation of lamellae and zeolite are independent.


Molecular Sieve Zeolites-I - American Chemical Society

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