Mechanism of Nucleation and Crystallization of Zeolites from Gels

11 Mechanism of Nucleation and Crystallization of Zeolites from Gels a

Downloaded by UNIV QUEENSLAND on June 25, 2013 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0121.ch011

ALI CULFAZ and L. B. SAND Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Mass. 01609

In zeolite systems chosen for study diffusion in the liquid phase and crystal growth on the crystal-liquid interface were the two major steps in converting gels to mordenite, zeolites A and X, the former being the rate-determining step for mordenite and the latter for zeolite X crystallization. In the mordenite system the effect of seed crystals, with surface areas per unit mass different by an order of magnitude, demonstrated the mechanism of nu cleation on the seed crystal surfaces. The data support the hy pothesis that crystal growth of the zeolite occurs from the solution phase rather than in the gel phase.

Jj^ s t u d y was done t o i n v e s t i g a t e t h e m e c h a n i s m of t r a n s f o r m a t i o n of gels * * i n t o zeolites u n d e r a u t o c l a v i n g c o n d i t i o n s . P r e v i o u s w o r k o n t h i s s u b j e c t has been r e v i e w e d b y Z h d a n o v (1 ). K e r r 3) r e p o r t e d o n c r y s t a l l i z a t i o n of zeolites A a n d X i n specific systems i n w h i c h h e p o s t u l a t e d g r o w t h f r o m s o l u t i o n . B r e c k a n d F l a n i g e n (4) a n d M c N i c o l et al. (δ) c o n c l u d e d t h a t n u c l e a t i o n a n d c r y s t a l g r o w t h of t h e zeolite o c c u r w i t h i n the g e l phase. T h e a p p r o a c h here w a s t o d i s t i n g u i s h n u c l e a t i o n f r o m c r y s t a l g r o w t h effects b y v a r y i n g t h e v i s c o s i t y (or m o b i l i t y ) of t h e s o l u t i o n phase a n d b y a d d i n g seed c r y s t a l s of different e x t e r n a l surface areas a v a i l able for n u c l e a t i o n . Experimental T h e r e a c t a n t s u s e d f o r m o r d e n i t e synthesis were a n a m o r p h o u s s u b s t r a t e of n e a r - m o r d e n i t e c o m p o s i t i o n (Zeolex S-6-10, 0.91 N a 2 0 - A l 0 10.6 S i 0 - 7 . 4 H 0 , J . M . H u b e r C o . ) a n d t w o different t y p e s of s o d i u m s i l i 2

2

3

2

α

Present address: Department of Chemical Engineering, Middle East Technical University, Ankara, Turkey. 140 In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

11.

141

Zeolites from Gels

CULFAZ AND SAND

cate s o l u t i o n s ( N - s o d i u m s i l i c a t e , N a 2 0 - 3 . 3 3 S i 0 - 2 4 . 1 H 0 , a n d C - s o d i u m silicate, N a O - 2 . 0 6 S i 0 - 8 . 8 H 0 , P h i l a d e l p h i a Quartz Co.). Zeolites A a n d X were s y n t h e s i z e d u s i n g s o d i u m a l u m i n a t e (1.1 N a 0 - A l 0 - 3 H 0 ) , s o d i u m h y d r o x i d e , a n d a m m o n i u m - s t a b i l i z e d aqueous c o l l o i d a l s i l i c a s o l (Ludox-AS, Si0 -7.77 H 0 , D u Pont). Syntheses were r u n i n m o d i f i e d M o r e y - t y p e a u t o c l a v e s of 1 5 - m l c a p a c i t y a t autogenous pressure. F o r m o r d e n i t e synthesis, t h e r e a c t a n t s were m i x e d i n a m o r t a r a n d pestle i n t o a homogeneous m i x a n d l o a d e d i n t o t h e a u t o c l a v e s . F o r zeolite A a n d X s y n t h e s i s , separate s o d i u m a l u m i n a t e s o l u t i o n s a n d c o l l o i d a l s i l i c a sols were p r e p a r e d a n d m i x e d i n t h e a u t o claves. 2

2

2

2

2

2

2

2

3

2

2


125

O

200

400

600

700

TIME , HOURS

Figure 1. Crystallization curves of mordenite from a batch composition 8.5 Na20-AkOz-35 SiOï-182 H 0 as a function of temperature and NaCl content: filled symbols, no NaCl; open symbols, 4.5 moles of NaCl/mole AWz) 2

C r y s t a l l i z a t i o n was f o l l o w e d b y a n a l y z i n g t h e s o l i d p r o d u c t q u a n t i t a t i v e l y b y x - r a y p o w d e r d i f f r a c t i o n . P r e p a r e d m i x t u r e s of a s t a n d a r d s a m ple of m o r d e n i t e a n d t h e a m o r p h o u s s u b s t r a t e of m o r d e n i t e c o m p o s i t i o n were u s e d t o e s t a b l i s h a c a l i b r a t i o n c u r v e for t h e q u a n t i t y of m o r d e n i t e based o n the s u m m a t i o n of x - r a y p e a k i n t e n s i t i e s . F o r zeolites A a n d X , the u n r e a c t e d a l u m i n o s i l i c a t e gel was u s e d t o prepare m i x t u r e s w i t h s t a n d a r d samples of zeolites A a n d X f o r q u a n t i t a t i v e phase i d e n t i f i c a t i o n . C r y s t a l l i z a t i o n curves were o b t a i n e d b y a n a l y z i n g the s o l i d p r o d u c t f r o m a n u m b e r of i d e n t i c a l l y c h a r g e d a u t o c l a v e s k e p t a t t h e c r y s t a l l i z a -

In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

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t i o n t e m p e r a t u r e for different t i m e s . pressed as

( 7o conversion =

T h e extent of c o n v e r s i o n was ex

grams of solid product \ /

% zeolite

\

grams of reactant mixture/ Vin solid product/ — total conversion grams of reactant mixture


w i t h t o t a l c o n v e r s i o n b e i n g defined as t h e q u a n t i t y of z e o l i t e i n t h e s o l i d p r o d u c t w h e n t h e c o n c e n t r a t i o n of t h e l i m i t i n g r e a c t a n t reaches zero i n t h e l i q u i d phase.

Results and Discussion M o r d e n i t e C r y s t a l l i z a t i o n . M o r d e n i t e w a s s y n t h e s i z e d as a single c r y s t a l l i n e phase o v e r a n a r r o w t e m p e r a t u r e range of 9 0 ° - 1 3 5 ° C w i t h a fixed b a t c h c o m p o s i t i o n , 8.5 Ν 3 * 0 - Α 1 0 - 3 5 S i 0 - 1 8 2 H 0 (0), w i t h or w i t h o u t t h e a d d i t i o n of N a C l (4.5 moles p e r m o l e of A 1 0 ) . T h e c r y s t a l l i z a t i o n c u r v e s are s h o w n i n F i g u r e 1. O u t s i d e t h i s t e m p e r a t u r e r a n g e o n t h i s b a t c h c o m p o s i t i o n , c o e x i s t i n g phases s t a r t t o appear. T y p i c a l l y , t h e c r y s t a l l i z a t i o n c u r v e s are c h a r a c t e r i z e d b y a l o n g " i n d u c t i o n p e r i o d " f o l l o w e d b y a s l o w i n i t i a l c r y s t a l l i z a t i o n . T h e r a t e t h e n becomes fast u n t i l m o s t of t h e a m o r p h o u s m a t e r i a l is c o n v e r t e d i n t o t h e c r y s t a l l i n e phase. 2

3

2

2

2

3

Figure 2. Mordenite single cry stals of uniform morphology (8 X 8X8 /xmeters) used as seed. Crystalized from a batch com position of 8.5 NaiO-AUOz-SS Si0 -182 H2O-4.S NaCl at 120°C and 9 days. 2


11.

cuLPAz AND SAND

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Zeolites from Gels


T h e fast c o n v e r s i o n r a t e of a m o r p h o u s b a t c h i n t o m o r d e n i t e , once t h e c r y s t a l l i z a t i o n has s t a r t e d , i n d i c a t e s t h a t t h e r a t e - l i m i t i n g step i n t h e o v e r a l l process is t h e n u c l e a t i o n . T o s u b s t a n t i a t e t h i s , m o r d e n i t e w a s c r y s t a l l i z e d w i t h t h e same b a t c h c o m p o s i t i o n b u t w i t h t h e a d d i t i o n of seed

so

ol 0

1

I 4

I

I 8

I

I 12

I

i 16

I

ι 20

TIME , HOURS

Figure 3. The effect of seeding on crystallization rates of mordenite from a batch composition of 8.6 Na^O-AWr35 Si0 -182 H2O-4.5 NaCl as a function of temperature (3X2X8 [meter seed crystals) 2

m o r d e n i t e c r y s t a l s . A s seed, single c r y s t a l s of m o r d e n i t e w i t h u n i f o r m m o r p h o l o g y , 3 X 3 X 8 Mmeters ( F i g u r e 2) were used. T h e a m o u n t of seed c r y s t a l s used corresponds t o a n i n i t i a l c o n v e r s i o n l e v e l of 2 6 % . The c r y s t a l l i z a t i o n c u r v e s for m o r d e n i t e as a single phase were o b t a i n e d i n t h e b r o a d e r range of 6 0 ° ~ 3 0 0 ° C , a n d some are s h o w n i n F i g u r e 3. T h e i n d u c t i o n p e r i o d was t o t a l l y e l i m i n a t e d . T h e same b a t c h c o m p o s i t i o n i n t h e absence of m o r d e n i t e seed c r y s t a l s y i e l d e d m o r d e n i t e c o n v e r t i n g t o a n a l c i m e a n d q u a r t z a t t e m p e r a t u r e s i n excess of 140° C . T h e a c t i v a t i o n energies of t h e n u c l e a t i o n a n d c r y s t a l g r o w t h c a n b e d e t e r m i n e d f r o m t h e c r y s t a l l i z a t i o n curves a t v a r i o u s t e m p e r a t u r e s w i t h the same b a t c h c o m p o s i t i o n . A s s u m i n g t h a t t h e f o r m a t i o n of n u c l e i of a size s t a b l e e n o u g h n o t t o redissolve b u t t o g r o w i n t o a c r y s t a l is a n ener g e t i c a l l y a c t i v a t e d process, a n d since t h e n u c l e a t i o n process is r a t e - d e t e r -


144

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mining during the induction period, the apparent activation energy for nucleation, E , can be calculated b y : N

d In (1/0) En d(l/T) " R =

where θ is the induction time—i.e., the point on the crystallization curve where conversion to the crystalline phase is just starting (7). A similar analysis can be made for the crystallization rate i n deter mining an apparent activation energy for crystal growth, E ,


0

assuming

Figure 4- Dependence of conversion rate and induction period on temperature for mordenite: (O) no NaCl, (Δ) 4.5 moles of NaCl /mole Al 0 ) 2

Table I.

Activation Energies

Batch Composition, Na 0/Al O /Si0 / H 0/NaCl 2

2

z

2

2

8.5/1/35/182/— 8.5/1/35/182/4.5 2.5/1/1.7/150/—

Temp Range, °C 90-135 90-135 60-90

3

Nucleation and Crystal Growth Activation Energy, kcal (gram mole) Zeolite Type mordenite mordenite zeolite A

Nuclear tion, Ε

ή

Crystal Growth, E

24 16 12


0

15 14 19

11.

CULFAZ AND SAND

Zeolites from Gels

145


t h a t t h e r a t e - l i m i t i n g step is c r y s t a l g r o w t h . T h i s is m o s t n e a r l y t r u e w h e n t h e c o n v e r s i o n r a t e is h i g h e s t ; therefore, t h e c r y s t a l l i z a t i o n r a t e is d e n n e d as t h e r a t e of c o n v e r s i o n a t 5 0 % of t h e t o t a l c o n v e r s i o n l e v e l i n t e r m s of percent c o n v e r s i o n per h o u r . T h e results are s u m m a r i z e d i n F i g u r e 4 a n d T a b l e I . T h e a d d i t i o n of N a C l t o t h e b a t c h , w h i c h effectively increases the v i s c o s i t y of t h e s y s t e m a n d therefore cuts d o w n t h e m o b i l i t y of i o n i c species i n t h e l i q u i d phase, a p p a r e n t l y does n o t influence t h e a c t i v a t i o n energy for c r y s t a l g r o w t h b u t does decrease t h e g r o w t h r a t e b y m o r e t h a n twofold. M i c r o s c o p i c e v a l u a t i o n of t h e c r y s t a l s g r o w n i n seeded systems i n d i cates t h a t t h e single c r y s t a l s of seed g r o w o n l y p a r t i a l l y , a n d n e w a c i c u l a r c r y s t a l s are g r o w n s e p a r a t e l y f r o m t h e seed c r y s t a l s ( F i g u r e 5). Since

Figure 5. Acicular mordenite crystals grown at 200°C and 16 hours using the single-crystal seeds shown in Figure 2. (scanning electron micrographs courtesy of AMR Corp., Burlington, Mass.)

t h e i n d u c t i o n p e r i o d was t o t a l l y e l i m i n a t e d b y seeding a n d since t h e seed c r y s t a l s h a v e caused t h e i n d e p e n d e n t g r o w t h of n e w c r y s t a l s i n a d d i t i o n t o t h e i r o w n g r o w t h , n u c l e a t i o n i n t h e seeded systems a p p a r e n t l y t a k e s p l a c e o n t h e surface of seed c r y s t a l s . T h u s , t h e c r y s t a l g r o w t h r a t e i n seeded s y s t e m s s h o u l d d e p e n d o n t h e i n i t i a l l e v e l of c o n v e r s i o n a n d t h e size a n d shape of seed c r y s t a l s . T h i s w a s i l l u s t r a t e d b y u s i n g 0.5-5-Mmeter c r y s t a l aggregates of m o r d e n i t e as seed i n a set of e x p e r i m e n t s w i t h v a r i a b l e


146

MOLECULAR

SIEVES


i n i t i a l c o n v e r s i o n l e v e l . I n F i g u r e 6 these c r y s t a l l i z a t i o n curves, u s i n g " s m a l l " seed c r y s t a l s (0.5-5 /^meters) w i t h i n i t i a l c o n v e r s i o n levels of 3, 9, a n d 2 4 % are c o m p a r e d w i t h t h e c r y s t a l l i z a t i o n c u r v e u s i n g t h e r e l a t i v e l y " l a r g e " ( 3 X 3 X 8 Mm) single c r y s t a l s of m o r d e n i t e as seed. T h e c r y s t a l -

O

20

40

60

80

TIME , HOURS

Figure 6. Effect of seeding on crystallization rates of mordenite from a batch composition of 8.5 Na 0-Al 0 -35 Si0 -18 2H 0 at 120°C: (A) no seed, (·) seeding with 3X3X8 μmeter crystals, ( Δ , • , O) seeding with 0.5-5 ^meter crystals) 2

2

3

2

2

l i z a t i o n r a t e increases as t h e i n i t i a l c o n v e r s i o n l e v e l , a n d therefore t h e t o t a l e x t e r n a l surface area o v e r w h i c h n e w c r y s t a l s c a n nucleate, is increased. T h e same c o n c l u s i o n is r e a c h e d b y o b s e r v i n g a h i g h e r c r y s t a l l i z a t i o n r a t e o b t a i n e d w h e n t h e seed c r y s t a l s are s m a l l e r . F o r t h e same i n i t i a l c o n v e r s i o n l e v e l t h e s m a l l seed c r y s t a l s p r o v i d e l a r g e r t o t a l e x t e r n a l surface a r e a for n u c l e a t i o n t h a n t h e large single c r y s t a l seeds. A s t h e c o n v e r s i o n r a t e t o m o r d e n i t e is p r o g r e s s i v e l y increased b y u s i n g l a r g e r a m o u n t s of seed c r y s t a l s , a n d as t h e n u c l e a t i o n process t a k e s place o n t h e seed c r y s t a l surfaces, t h e o v e r a l l c o n v e r s i o n process is l i m i t e d b y t h e r a t e a t w h i c h t h e soluble species i n t h e l i q u i d phase is t r a n s p o r t e d t o t h e c r y s t a l - l i q u i d interface. A t t h e same i n i t i a l c o n v e r s i o n l e v e l , s m a l l e r


11.

CULFAZ A N D SAND

147

Zeolites from Gels

seed c r y s t a l s p r o v i d e s n o t o n l y a l a r g e r t o t a l surface a r e a f o r n u c l e a t i o n b u t also a s h o r t e r average d i s t a n c e for t h e soluble species t o r e a c h t h e nearest c r y s t a l - l i q u i d interface before t h e y are i n c o r p o r a t e d i n t o t h e s t r u c t u r e of t h e g r o w i n g c r y s t a l .

T h e c r y s t a l l i z a t i o n rates for m o r d e n i t e r e

p o r t e d here d o n o t represent t h e r a t e a t w h i c h m o r d e n i t e - f o r m i n g c o m p o n e n t s c a n be i n c o r p o r a t e d i n t o t h e m o r d e n i t e f r a m e w o r k , b u t t h e y are d i f f u s i o n - l i m i t e d g r o w t h rates.

B y u s i n g s m a l l e r a n d s m a l l e r seed c r y s t a l s

t h e c r y s t a l l i z a t i o n r a t e w o u l d b e increased t o a l e v e l s u c h t h a t t h e l i m i t i n g step w o u l d be t h e a c t u a l r a t e a t w h i c h t h e soluble species w h i c h are r e a d i l y a v a i l a b l e a t t h e c r y s t a l - l i q u i d i n t e r f a c e are i n c o r p o r a t e d i n t o t h e f r a m e


work.

100

80

Figure 7. Crystallization curves of zeolite X from a batch composition 4 NosO-AWz-^ S1O2-2OO H 0 at 90° C: (O) no seed crystals; (Δ) 0.55 μΤΜίβτ seed crystals, 29% initial conversion; (•) 30-70 μmeter seed crystals, 15% initial con version 2

S y n t h e s i s of Z e o l i t e X . Z e o l i t e X was c r y s t a l l i z e d f r o m a b a t c h of o v e r a l l c o m p o s i t i o n 4 N a g O - A l - A - ô S i O - 2 0 0 H 0 a t 9 0 ° C (8). The c r y s t a l l i z a t i o n c u r v e i s s h o w n i n F i g u r e 7. A f t e r a n i n d u c t i o n p e r i o d of 2.4 hours, zeolite X w a s f o r m e d r a p i d l y as a single phase a t a c o n v e r s i o n 2

2


148

MOLECULAR SIEVES

r a t e of 5 5 % p e r h o u r . T h e c r y s t a l l i z a t i o n of zeolite X c o n t i n u e d u n t i l t h e c o n v e r s i o n l e v e l reached 7 1 % of the t o t a l c o n v e r s i o n c a l c u l a t e d o n the basis of c o n v e r t i n g a l l of t h e a l u m i n a i n the o r i g i n a l b a t c h i n t o zeolite X h a v i n g a s i l i c a t o a l u m i n a r a t i o of three. T h e same b a t c h c o m p o s i t i o n

100


80

Figure 8. Crystallization curves for zeolite A from a batch composition 2.5 Na 0-Al 0$-1 .7 Si0 -150 H 0: (solid curves) no seed crystals, (broken curve) 0.5-5 μmeter seed crystals, 25% in itial conversion 2

2

2

2

w a s seeded w i t h s m a l l c r y s t a l s (0.5-5 Mmeters) of zeolite X a n d w i t h large single c r y s t a l s of zeolite X ( 3 0 - 7 0 μτα) c o n t a m i n a t e d b y a s m a l l a m o u n t of a zeolite Β phase p r e p a r e d b y t h e m e t h o d of C h a r n e l l (9) c o r r e s p o n d i n g t o i n i t i a l c o n v e r s i o n l e v e l s o f 29 a n d 1 5 % , r e s p e c t i v e l y . A s t h e i n d u c t i o n p e r i o d a n d c o n v e r s i o n r a t e were unaffected b y t h e i n c l u s i o n of seed c r y s t a l s , t h e c o n v e r s i o n d a t a w e r e t r e a t e d b y c o n s i d e r i n g t h e seed c r y s t a l s as i n e r t species a n d were p l o t t e d as t h e c o n v e r s i o n of t h e a m o r p h o u s p a r t of


11.

CULFAZ AND SAND

149

Zeolites from Gels

t h e o r i g i n a l b a t c h i n t o zeolite X as t h e single c r y s t a l l i n e phase ( F i g u r e 7). I n t h i s s y s t e m , w h i c h is c o n s i d e r a b l y m o r e d i l u t e t h a n t h e m o r d e n i t e s y s t e m , d i f f u s i o n a l l i m i t a t i o n s were n o t expected t o p l a y a m a j o r role.

As

t h e i n d u c t i o n p e r i o d was n o t affected b y t h e presence of seed c r y s t a l s ,

TEMP, 90


IOOO

e

C

75

I

60

I

I

\

100

10

< tr. CO

0C

S ζ

.0

ο ο

1.0

\

^*Δ

Δ

2.6

2.7

2.θ 2.9 ( Ι / Τ ) ΙΟ , Κ 3

β

0.1

3.0 _ Ι

Figure 9. Dependence of conversion rate and induction period on temperature for zeolite A from a batch composi tion 2.5 Νθ2θ-Α1 Ο -1.7 SiO -150 H 0 2

ζ

2

2

r e a c t i o n s i n t h e gel a n d l i q u i d phases are b e l i e v e d t o be t a k i n g p l a c e before conversion to zeolite X starts. S y n t h e s i s of Z e o l i t e A.

Z e o l i t e A was c r y s t a l l i z e d f r o m a b a t c h of

o v e r a l l c o m p o s i t i o n 2.5 Ν ^ Ο - Α 1 0 - 1 . 7 S i O - 1 5 0 H 0 a t 60, 75, a n d 9 0 ° C 2

(10).

3

2

2

T h e same s y s t e m w a s seeded w i t h zeolite A c r y s t a l s of 0 . 5 - 5 Mmeter

size a t a n i n i t i a l c o n v e r s i o n l e v e l of 2 5 % a n d c r y s t a l l i z e d a t 6 0 ° C .

As

w i t h t h e c r y s t a l l i z a t i o n of zeolite X f r o m seeded s y s t e m s , t h e d a t a were t r e a t e d b y i g n o r i n g t h e presence of seed c r y s t a l s . c u r v e s are s h o w n i n F i g u r e 8.

T h e crystallization

D u r i n g the induction time period i n the

unseeded s y s t e m , c r y s t a l l i z a t i o n w a s t a k i n g p l a c e a t a s l o w r a t e i n t h e seeded s y s t e m , b o t h a t 6 0 ° C .

A f t e r this slow crystallization period the

crystallization rate reached 2 2 % per hour at the 5 0 % conversion level


150

MOLECULAR SIEVES


in the seeded system as compared with 12% per hour conversion rate at the same conversion level in the unseeded system. Figure 9 shows the de pendence of the conversion rate and induction period on temperature for zeolite A synthesis. The reactions in the gel and liquid phases which precede the crystallization of zeolite X both in the seeded and unseeded systems are also apparently taking place in the zeolite A crystallization. The shorter induction period for zeolite A as compared with zeolite X at the same temperature makes this initial step not as overridingly significant for zeolite A as it is for zeolite X which had identical induction periods for both the seeded and unseeded systems. The doubling of the crystallization rate of zeolite A by the use of seed crystals of 0.5-5-Mmeter size presumably can be further increased by the use of still smaller crystals as seed. Conclusions This study showed that the overall crystallization processes for mor denite, zeolite X, and zeolite A were similar. However, the physical prop erties of the crystallizing system determine the rate-limiting step for a particular zeolite synthesis. In the case of mordenite in which both the viscosity of the batch composition and the morphology of seed crystals were varied, it was observed that diffusion in the liquid phase was the ratedetermining step. For zeolite X the actual growth rate on the crystalliquid interface was the rate-limiting factor as shown by identical con version rates for the seeded and unseeded systems. For zeolite A in the system chosen, both processes influenced the conversion rate. It was possible for two of the systems chosen that the nucleation and crystallization activation energies could be determined separately by distinguishing the induction period and crystal growth period in the overall crystallization process. Of the two hypotheses proposed for zeolite crystallization, in the gel phase or from the solution phase, the data support the latter hypothesis for crystal growth with the crystal-liquid surface enhancing the nucleation process in seeded systems. The precise mecha nism of nucleation in unseeded systems remains to be determined. Literature Cited 1. 2. 3. 4.

Zhdanov, S. P., ADVAN. CHEM. SER. (1971) 101, 20. Kerr, G. T., J. Phys. Chem. (1966) 70, 1047. Kerr, G. T., J. Phys. Chem. (1968) 72, 1385. Breck, D. W., Flanigen, Ε. M., "Molecular Sieves," pp. 47-61, Society of Chemical Industry, London, 1968. 5. McNicol, B. D., Pott, G. T., Loos, R. K., J. Phys. Chem. (1972) 76, 3388. 6. Sand, L. B., "Molecular Sieves," pp. 71-77, Society of Chemical Industry, London, 1968. 7. Hsu, A. C. T., A.I.Ch.E. J. (1971) 17, 1311.


11. CULFAZ AND SAND

Zeolites from Gels

151

8. Zhdanov, S. P., "Molecular Sieves," pp. 62-70, Society of Chemical Industry, London, 1968. 9. Charnell, J. F., J. Crystal Growth (1971) 8, 291. 10. Myrsky, Ya. V., Mitrofanov, M . G., Popkov, B. M., Bolotov, L. T., Ruchko, L. F., "Zeolites, Their Synthesis, Properties and Utilization," p. 192, Nauka, Moskow-Leningrad, 1965.


RECEIVED December 4, 1972.


Mechanism of Nucleation and Crystallization of Zeolites from Gels

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