Molecular Sieve Zeolites-I

17 Structural Studies on Erionite and Offretite

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J. ALAN GARD and J. MERVYN TAIT University of Aberdeen, Aberdeen AB9 2UE, Scotland Structure analysis has confirmed the offretite model of Ben nett and Gard and has located cation and water sites, in cluding one K in each cancrinite cage. Electron diffraction of many samples showed that the type locality is unique to date for offretite, which is partly disordered. All natural erionites examined were ordered. No ordered synthetic erionite was observed. One sample of ordered synthetic offretite was identified as "sausage-shaped" particles. The proportion of erionite in disordered intergrowths with offre tite can, in theory, be estimated from intensities of reflec tions with 1 odd, but comparison of x-ray with electron diffraction data on the same samples suggests that x-ray estimates may be low if erionite domains are thin, due to gross broadening of lines with 1 odd. +

^

s t r u c t u r a l scheme for the a l u m i n o s i l i c a t e f r a m e of erionite w a s p r o p o s e d b y Staples a n d G a r d (16)

P6 /mmc, 3

and a =

13.26, c =

w i t h the h e x a g o n a l space g r o u p

15.12 A . Intensity d a t a f r o m x - r a y

r o t a t i o n gave a m e a n r e s i d u a l R =

0.33.

R i n g s of 6 t e t r a h e d r a

fiber are

s t a c k e d i n A A B A A C — s e q u e n c e ( F i g u r e l a ) , so that c o l u m n s of alternat i n g c a n c r i n i t e cages a n d h e x a g o n a l p r i s m s are c r o s s - l i n k e d w i t h single rings, to f o r m cavities w i t h a free d i a m e t e r of 6.3 A , s h a r i n g w i n d o w s 4.7 X 3.5 A . T h i s scheme has b e e n c o n f i r m e d a n d refined b y K a w a h a r a a n d C u r i e n ( J O ) for erionite f r o m M a z e , N i i g a t a , J a p a n [ S h i m a z u a n d Kawakami (15)].

T h e y also l o c a t e d one c a t i o n i n e a c h c a n c r i n i t e cage

a n d 2 peaks o n the axis of e a c h large c a v i t y , w h i c h they i n t e r p r e t e d as w a t e r molecules. P u b l i s h e d c a t i o n exchange studies (4, 6, 11, 14)

have

s h o w n that a residue of 2 K ions i n e a c h u n i t c e l l of erionite or Zeolite Τ +

— a disordered

synthetic erionite (1,

peratures b e l o w 3 0 0 ° C ; loss of K

3)—is

not e x c h a n g e a b l e at t e m

a b o v e 300° appears to cause p a r t i a l

+

d i s r u p t i o n of the frame.

S h e r r y (14)

therefore contains a K

i o n ; this w o u l d agree w i t h the s t r u c t u r a l w o r k

+

suggested that e a c h c a n c r i n i t e cage

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


17.

GARD A N D TAIT

Erionite

and

231

Offretite

Figure 1. Projections of the frames of (A) erionite and (B) offretite. Relative heights of the rings of 6 tetrahedra are marked. Some cation sites are shown as Κ, M, and N. m e n t i o n e d a b o v e (10).

Intensity data have been recorded w i t h a H i l g e r

A u t o m a t i c L i n e a r D i f f r a c t o m e t e r f r o m another s a m p l e of e r i o n i t e f r o m M a z e [ H a r a d a et al. ( 8 ) ] , a n d f u r t h e r refinement w i l l b e a t t e m p t e d . Offretite w a s d i s c o v e r e d b y G o n n a r d (7)

i n 1890 o n M t . S i m i o u s e ,

Montbrison, France. F r o m x-ray powder data, H e y a n d Fejer (9) that i t was i d e n t i c a l w i t h erionite.

Bennett and G a r d

f o u n d the c - s p a c i n g to b e h a l f that of erionite. rotation photographs

(I),

stated

however,

C o m p a r i s o n of x - r a y

( F i g u r e 2 ) a n d e l e c t r o n d i f f r a c t i o n patterns

(Fig

u r e 3 ) s h o w c l e a r l y that a l l reflections w i t h 1 o d d for erionite are absent f r o m the offretite patterns. S h e p p a r d a n d G u d e (13)

h a v e s h o w n since

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


232

MOLECULAR SIEVE ZEOLITES

1

Figure 2. X-ray rotation photographs of (A) erionite and (B) offretite. Reflections with I odd are absent from (B), showing that c is halved for offretite.

Figure

3.

Electron diffraction of hOl zones: (A) erionite, (B) offretite, offretite with streaks parallel to c* indicating disorder

(C)

that the o p t i c signs are different; offretite has negative, a n d erionite p o s i t i v e , e l o n g a t i o n . T h e y also gave accurate u n i t c e l l d i m e n s i o n s , a = c =

13.291,

7.582 A for offretite, a n d a c h e m i c a l analysis c o r r e s p o n d i n g to eel]

contents of K i . i C a i . i M g o . 7 S i i 2 . 9 A l 5 . 2 0 3 . o : 1 5 . 3 H 0 . B e n n e t t a n d G a r d p r o 6

2

p o s e d a structure for the offretite f r a m e i n w h i c h the rings of 6 t e t r a h e d r a are stacked A A B A A B — ( F i g u r e l b ) .

A n o r d e r e d offretite s h o u l d h a v e

channels w i t h free d i a m e t e r 6.3 A , a n d s h o u l d b e c a p a b l e of

sorbing

m u c h larger molecules or cations t h a n w o u l d erionite, b u t a v e r y s m a l l degree of s t a c k i n g d i s o r d e r w o u l d constrict the channels w i t h w i n d o w s i d e n t i c a l w i t h those i n erionite. T h e r e s u l t i n g cavities, h o w e v e r , w o u l d b e longer t h a n those of erionite, w i t h f a r - r e a c h i n g effects o n the d i f f u s i o n rates a n d other properties [ R o b s o n et al. (12)"].

Streaks p a r a l l e l to c*

o n e l e c t r o n d i f f r a c t i o n patterns of some flakes (e.g., F i g u r e 3 c ) i n d i c a t e d d i s o r d e r of this t y p e w h i c h w o u l d restrict the channels i n this w a y .


17.

Erionite

GARD A N D TAIT

and

233

Offretite

I n t e n s i t y d a t a h a v e b e e n c o l l e c t e d w i t h the H i l g e r A . L . D . for 363 i n d e p e n d e n t reflections f r o m a p r i s m of the M t . S i m i o u s e s p e c i m e n B . M . 68970. U s i n g a t o m i c coordinates d e r i v e d f r o m those of Staples a n d G a r d for

erionite, a r e s i d u a l R

=

0.34

was

obtained.

Three-dimensional

F o u r i e r syntheses a n d least squares refinement i m p r o v e d R to 0.15.

Dis

p l a c e m e n t s of t h e f r a m e atoms h a v e d i s t o r t e d b o t h the d o u b l e a n d single 6-rings to d i s t i n c t l y t r i g o n a l s y m m e t r y . O n e K i o n was i d e n t i f i e d i n e a c h +

c a n c r i n i t e cage.

R e m a i n i n g cations w e r e

accounted

for

by

partially

o c c u p i e d sites l o c a t e d o n the axes p a r a l l e l to c of the single 6-rings a n d Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch017

the large channels ( M a n d Ν i n F i g u r e l b ) . p r e t e d as w a t e r m o l e c u l e s

coordinated

S m a l l e r peaks w e r e i n t e r

to these cations; some w a t e r

m o l e c u l e s w e r e o c t a h e d r a l l y d i s p o s e d a r o u n d cations Ν to f o r m c o l u m n s p a c k i n g the large channels. R e f i n e m e n t is p r o c e e d i n g . S y n t h e t i c zeolites suitable for s i n g l e - c r y s t a l x-ray analysis u s u a l l y can be prepared only under special conditions

[see

e.g.,

Ciric

(5)].

E l e c t r o n d i f f r a c t i o n patterns of crystals as s m a l l as 1 m i c r o n d i a m e t e r , h o w e v e r , c a n b e o b t a i n e d r e a d i l y . G i v e n s u i t a b l e means for o r i e n t i n g the crystals, electron d i f f r a c t i o n is p a r t i c u l a r l y u s e f u l for d e t e c t i n g d i s o r d e r e d i n t e r g r o w t h s of erionite a n d offretite, w h i c h w e r e Bennett and G a r d

(1)

shown

by

to b e difficult to d i s t i n g u i s h f r o m offretite

by

x-ray p o w d e r t e c h n i q u e s .

N a t u r a l samples d e s c r i b e d as erionite f r o m

12 localities a n d several s y n t h e t i c samples h a v e b e e n e x a m i n e d

with

e l e c t r o n m i c r o s c o p y a n d d i f f r a c t i o n to d e t e r m i n e t h e i r s t r u c t u r a l types a n d the degree of d i s o r d e r , i f any. S y n t h e t i c samples i n c l u d e d : Zeolite Τ f r o m L i n d e D i v i s i o n of U n i o n C a r b i d e ( 3 ) ; 3 samples of " e r i o n i t e " f r o m E s s o R e s e a r c h L a b o r a t o r i e s , B a t o n R o u g e , L a . ( 1 2 ) ; Z e o l i t e Τ f r o m the b a t c h p r e p a r e d a n d assessed b y S h e r r y (14).

T h e f o l l o w i n g conclusions

were d r a w n : ( a ) O n l y one n a t u r a l source of offretite, the t y p e l o c a l i t y i n F r a n c e , w a s i d e n t i f i e d . S o m e fragments w e r e d i s o r d e r e d . ( b ) A l l the other n a t u r a l samples w e r e f u l l y o r d e r e d erionite. N o s t r e a k i n g of reflections, p a r a l l e l to c* or o t h e r w i s e , w a s detected. ( c ) N o f u l l y o r d e r e d s y n t h e t i c erionite has b e e n o b s e r v e d yet. ( d ) O n e s a m p l e of f u l l y o r d e r e d s y n t h e t i c offretite w a s i d e n t i f i e d a m o n g the E s s o samples. It differs m o r p h o l o g i c a l l y f r o m a n y of the s y n t h e t i c d i s o r d e r e d erionites. T h e synthetic offretite is p a r t i c u l a r l y i n t e r e s t i n g , as it appears h a v e the o r d e r e d structure necessary for u n r e s t r i c t e d channels.

We

to do

not h a v e details of the m e t h o d of p r e p a r a t i o n . A l l d i f f r a c t i o n patterns (e.g., F i g u r e 4 a ) w e r e w e a k , b u t c o m p l e t e l y free f r o m spots w i t h 1 o d d or streaks. T h e p a r t i c l e s w e r e " s a u s a g e - s h a p e d " w i t h c - e l o n g a t i o n ure 4 b ) .

(Fig

T h e r o u n d e d shape suggested a c r y s t a l l i n e core enclosed i n a n

a m o r p h o u s l a y e r , b u t this w a s d i s c o u n t e d b y t a k i n g d a r k - f i e l d m i c r o graphs u s i n g o n l y d i f f r a c t e d b e a m s , so that the c r y s t a l l i n e regions a p -



234


1

Figure 4. Synthetic offretite: (A) Electron diffraction of the hOl zone; odd-l reflections are absent. (B) Typical micrograph of "sausage-shaped" particles with c-elongation. (C) Dark-field image using electrons diffracted by the bottom particle, showing that the outer layer is crystalline.

Figure 5. Electron tion of hOl zone of a of disordered synthetic ite; odd-l spots are and streaked parallel

diffraccrystal eriondiffuse to c*

p e a r e d b r i g h t . T h e b r i g h t outer l a y e r i n F i g u r e 4c is therefore c r y s t a l l i n e ; the t h i c k e r center is d a r k o w i n g to inelastic scatter. T h e other synthetic samples c o m p r i s e d laths. I n electron d i f f r a c t i o n patterns, spots w i t h 1 o d d w e r e a l w a y s diffuse a n d often streaked a l o n g c*

(e.g., F i g u r e 5 ) .

Assessment of the p r o p o r t i o n of erionite i n s u c h

i n t e r g r o w t h s is t e c h n i c a l l y i m p o r t a n t , as it affects

d i f f u s i o n rates a n d

c a t a l y t i c properties [ R o b s o n et al. ( 1 2 ) ] . T h e 10.1, 20.1, a n d 21.1 x-ray p o w d e r lines are q u i t e strong for o r d e r e d erionite, b u t t h e y w e r e either undetectable

or v e r y w e a k a n d diffuse for the other 2 E s s o samples.


17.

GARD

AND

Intensities of

TAIT

odd-1

Erionite

and

235

Offretite

spots o n electron

d i f f r a c t i o n patterns i n d i c a t e d

a

c o n s i d e r a b l e p r o p o r t i o n of erionite, w h i l e s t r e a k i n g s h o w e d the presence of l a m e l l a e less t h a n 50 A w i d e i n the c - d i r e c t i o n .

S h e r r y (14)

estimated

of erionite i n his sample of Zeolite T . I n electron d i f f r a c t i o n p a t

2-3%

terns of this a n d the L i n d e s a m p l e , the odd-1 spots w e r e elongated, not streaked, i n the c * - d i r e c t i o n .

but

P r e l i m i n a r y e s t i m a t i o n of these i n t e n s i

ties suggests a p r o p o r t i o n of erionite significantly h i g h e r t h a n 3%. causes of these discrepancies

must be investigated.

The

T h e proportion

erionite controls the i n t e g r a t e d i n t e n s i t y of e a c h spot w i t h 1 o d d ,

of but


e l o n g a t i o n p a r a l l e l to c* increases w i t h " t h i n n e s s " of o r d e r e d d o m a i n s of W h e r e l a m e l l a e are extremely

thin,

x - r a y lines b e c o m e so diffuse t h a t t h e y are i n d i s t i n g u i s h a b l e f r o m

erionite b e l o w a f e w h u n d r e d A .

back

g r o u n d , a l t h o u g h t h e y are s t i l l v i s i b l e as streaks w i t h e l e c t r o n diffraction. Independent

e v i d e n c e for this w a s o b s e r v e d b y B h a t t y et al. (2),

who

f o u n d that several n o r m a l l y strong lines for a n o r t h i t e , w h i c h w e r e absent o w i n g to t w i n n i n g f r o m x - r a y p h o t o g r a p h s

of c e r t a i n s y n t h e t i c

samples,

c o u l d be seen c l e a r l y w i t h electron d i f f r a c t i o n as pairs of spots j o i n e d b y streaks. A n x-ray estimate i n this case w o u l d be zero i n s t e a d of t h e t r u e 100%,

as the t w i n s are s t r u c t u r a l l y i d e n t i c a l . E l e c t r o n d i f f r a c t i o n i n t e n s i

ties also m u s t be treated w i t h c a u t i o n , h o w e v e r , as m u l t i p l e d i f f r a c t i o n c a n e n h a n c e w e a k reflections. Acknowledgment T h e authors t h a n k the B r i t i s h M u s e u m ( N a t u r a l H i s t o r y ) , K . H a r a d a , H . E . R o b s o n , a n d H . S. S h e r r y for specimens a n d a d v a n c e i n f o r m a t i o n , L . I n g r a m a n d B . G . C o o k s l e y for c o l l e c t i n g the A . L . D . i n t e n s i t y d a t a , a n d H . F . W . T a y l o r for his interest i n this w o r k a n d for

advice

o n the structure analysis.

Literature Cited (1) Bennett, J. M., Gard, J. Α., Nature, London 1967, 214, 1005. (2) Bhatty, M. S. Y., Gard, J. Α., Glasser, F. P., Mineral. Mag. 1970, in press. (3) Breck, D. W., Acara, Ν. Α., U. S. Patent 2,950,952 (1960). (4) Chen, N. Y., Rosinski, E. J., Wilson, J. R., Jr., private communication to H. S. Sherry, 1969. (5) Ciric, J., Science 1967, 55, 689. (6) Eberley, P. E., Jr., Am. Mineralogist 1964, 49, 30. (7) Gonnard, F., Compt. Rend. 1890, 111, 1002. (8) Harada, K., Iwamoto, S., Kihara, K., Am. Mineralogist 1967, 52, 1785. (9) Hey, M. H, Fejer, Ε. E., Mineral. Mag. 1962, 33, 66. (10) Kawahara, Α., Curien, H., Bull. Soc. Franc. Mineral. Crist. 1969, 92, 250. (11) Peterson, D. L., Helfferich, F., Blytas, G. C., J. Phys. Chem. Solids 1965, 26, 835. (12) Robson, H. E., Hamner, G. P., Arey, W. F., Jr., ADVAN. CHEM. SER. 1971, 101, 607.


236


1

(13) Sheppard, R. Α., Gude, A. J., III, Am. Mineralogist 1969, 54, 875. (14) Sherry, H. S., Troc. Intern. Conf. Ion Exchange, London, 1969, 1970, press. (15) Shimazu, M., Kawakami, T.,J.Japan.Assoc. Mineral. Petrol. Econ. Geol. 1967, 57, 68. (16) Staples, L. W., Gard, J. Α., Mineral. Mag. 1959, 32, 261. RECEIVED February 10, 1970.


Discussion W . H . Flank ( H o u d r y L a b o r a t o r i e s , M a r c u s H o o k , P a . 1 9 0 6 1 ) : S o m e m i c r o g r a p h s of offretite crystallites h a v e b e e n o b s e r v e d i n w h i c h the ends a l o n g the " c " axis a p p e a r e d as sharp i r r e g u l a r t e r m i n a t i o n s , l i k e the f r a c t u r e d e n d of a b u n d l e of p r i s m a t i c needles. T h e o v e r - a l l shape w a s sausage-like. T h i s supports G a r d ' s c o n c l u s i o n f r o m the d a r k - f i e l d m i c r o graphs t h a t the outer l a y e r , as w e l l as the c r y s t a l l i t e core, is c r y s t a l l i n e rather than amorphous. W . Sieber a n d W . M . Meier ( E i d g e n o s s i s c h e T e c h n i s c h e H o c h s c h u l e , Zurich):

A new

m e m b e r of

the c h a b a z i t e

group,

tentatively

named

L O S O D , has b e e n s y n t h e s i z e d i n o u r l a b o r a t o r y . T h e synthesis m i x t u r e contains s o d i u m a n d o r g a n i c cations, b u t o n l y s o d i u m is b u i l t i n t o the structure. T h e synthetic zeolite is h e x a g o n a l ( a =

12.91 a n d c =

10.54

Â ) , a n d its f r a m e w o r k is b a s e d o n a n A B A C s t a c k i n g sequence of single 6 - m e m b e r e d rings ( W . T h o n i a n d W . M . M e i e r , i n p r e p a r a t i o n ) . J . A . G a r d : T h i s suggests that t w o d i s t i n c t m e c h a n i s m s of synthesis are i n v o l v e d . D i s c r e t e c a n c r i n i t e cages m a y f o r m a r o u n d K

+

ions d u r i n g

synthesis of erionite, offretite, a n d zeolite L a n d act as precursors w h i c h condense w i t h s i m i l a r units to f o r m d o u b l e 6-rings a n d single r i n g s w h e r e the c o l u m n s cross-link. K

+

ions are a p p a r e n t l y n o t essential for synthesis

of structures c o m p r i s i n g o n l y 6-rings, as they cannot b e m a d e b y d e n s i n g w h o l e c a n c r i n i t e cages.


con-

Molecular Sieve Zeolites-I

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