Infrared Structural Studies of Zeolite Frameworks

16 Infrared Structural Studies of Zeolite Frameworks

Downloaded by MONASH UNIV on May 19, 2013 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch016

EDITH M. FLANIGEN and HASSAN KHATAMI Union Carbide Corp., Linde Division Laboratory, Tarrytown Technical Center, Tarrytown, Ν. Y. 10591 HERMAN A. SZYMANSKI Alliance College, Cambridge Springs, Pa. 16403 Mid-infrared

spectroscopy has been applied to zeolite struc

tural problems. -1

to 1300 cm

The infrared spectrum in the region of 200

is a sensitive tool indicating structural features

of zeolite f r a m e w o r k s . Preliminary

interpretation

suggests

infrared specificity for zeolite structure type and group, and for structural subunits such as double rings and large pore openings.

It is proposed that the major structural

groups

present in zeolites can be detected from their infrared pat tern. This hypothesis is based on correlation of newly deter mined

infrared

spectra

of synthetic

zeolites with

x-ray

structure data for most of the known structural classes of zeolites. Other structural information obtained from infra red studies includes framework Si/Al composition, structural changes during thermal decomposition, ment during dehydration and

and cation move

dehydroxylation.

* " p h e m e t h o d s a p p l i e d to t h e d e t e r m i n a t i o n o f zeolite structures

have

b e e n the c l a s s i c a l c r y s t a l l o g r a p h i c t e c h n i q u e s o f x - r a y d i f f r a c t i o n a n d m o r e r e c e n t l y e l e c t r o n d i f f r a c t i o n . A s a result o f extensive x - r a y structure studies o n zeolites since a b o u t 1955, the f r a m e w o r k structures o f some 40 zeolites are k n o w n . A classification o f zeolite structure types a n d g r o u p s has b e e n p r o p o s e d b y S m i t h (43), F i s c h e r a n d M e i e r (18), a n d M e i e r (28).

T h e structure types a n d classes are b a s e d o n a s i m i l a r i t y i n f r a m e

w o r k t o p o l o g y a n d c o m m o n elements of s e c o n d a r y b u i l d i n g u n i t s w h i c h c o m p r i s e r i n g s o f t e t r a h e d r a , d o u b l e r i n g s , a n d larger s y m m e t r i c a l p o l y 201

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

202

MOLECULAR SIEVE ZEOLITES

1

h e d r a l u n i t s s u c h as the 18-tetraherda " c a n c r i n i t e " u n i t or t h e 24-tetrahedra truncated octahedron "sodalite" unit (28).

I t is difficult to deter-

m i n e a t o m i c positions i n the c r y s t a l structure of n e w zeolite species b y x - r a y t e c h n i q u e s because of the large u n i t cells a n d t h e l a r g e n u m b e r of p o s s i b l e w a y s of l i n k i n g t e t r a h e d r a . T h e p r o b l e m is m a g n i f i e d w i t h s y n t h e t i c zeolites w h e r e the s t r u c t u r a l investigator most f r e q u e n t l y is l i m i t e d to x - r a y p o w d e r d a t a o w i n g to the u n a v a i l a b i l i t y of l a r g e r single crystals. T h e object of this s t u d y was to a p p l y m i d - i n f r a r e d s p e c t r o s c o p y to zeolite s t r u c t u r a l p r o b l e m s w i t h the u l t i m a t e h o p e of u s i n g i n f r a r e d , a r e l a t i v e l y r a p i d a n d r e a d i l y a v a i l a b l e a n a l y t i c a l m e t h o d , as a t o o l

to

c h a r a c t e r i z e t h e f r a m e w o r k structure a n d p e r h a p s to detect the presence of t h e p o l y h e d r a l b u i l d i n g units present i n zeolite f r a m e w o r k s .

The

m i d - i n f r a r e d r e g i o n of t h e s p e c t r u m w a s u s e d ( 1300 to 200 c m " ) since


1

that r e g i o n contains the f u n d a m e n t a l v i b r a t i o n s of t h e f r a m e w o r k ( S i , A l ) 0

4

t e t r a h e d r a a n d s h o u l d reflect the f r a m e w o r k structure. I n f r a r e d d a t a

i n s i m i l a r s p e c t r a l regions h a v e b e e n p u b l i s h e d for m a n y m i n e r a l zeolites (30)

a n d a f e w s y n t h e t i c zeolites (23,

49, 50).

T h e r e is a n

extensive

literature o n i n f r a r e d spectra of s i l i c a , silicates, a n d a l u m i n o s i l i c a t e s H o w e v e r , n o systematic s t u d y of the i n f r a r e d characteristics of f r a m e w o r k s as r e l a t e d to t h e i r c r y s t a l structure has a p p e a r e d .

Figure 1. Infrared spectra of zeolites A, X, and Y and hydroxy sodalite (HS); Si/Al in X is 1.2, and in Y , 2.5


(17). zeolite


16.

FLANIGEN E T A L .

Infrared

Structural

Studies

203

Figure 2. Infrared spectra of zeolites B(F1), ΖΚ-5, Ω, and S; right hand por tion of figure represents a higher zeolite concentration in the wafer than in the left portion for Figures 2, 5, and 7 Experimental T h e m a j o r i t y of t h e i n f r a r e d t r a n s m i s s i o n s p e c t r a w e r e o b t a i n e d u s i n g t h e K B r w a f e r t e c h n i q u e ( 3 7 ) . S p e c t r a of at least 2 a n d often m o r e p r e p a r a t i o n s of e a c h z e o l i t e w e r e o b t a i n e d b e f o r e the s p e c t r u m w a s a c c e p t e d as b e i n g c h a r a c t e r i s t i c of t h e z e o l i t e species. S p e c t r a also w e r e o b t a i n e d u s i n g C s l w a f e r s a n d i n the case of s e v e r a l zeolites w i t h m i n e r a l o i l m u l l s a n d p u r e z e o l i t e s e l f - s u p p o r t e d w a f e r s , to e s t a b l i s h a n y m a t r i x effect. O n l y m i n o r s p e c t r a l v a r i a t i o n s w e r e o b s e r v e d a m o n g the s e v e r a l t e c h n i q u e s a n d m a t r i c e s . E x c e p t w h e r e o t h e r w i s e n o t e d , t h e spectra r e p o r t e d here are for h y d r a t e d zeolites i n K B r or C s l w a f e r s . A t y p i c a l w a f e r c o n c e n t r a t i o n w a s 0.5 m g o f zeolite i n 300 m g of K B r or C s l ; h o w e v e r , zeolite c o n c e n t r a t i o n sometimes w a s v a r i e d to o b t a i n t h e d e s i r e d a b s o r b a n c e or to increase the s e n s i t i v i t y to w e a k b a n d s . S p e c t r a w e r e d e t e r m i n e d w i t h a P e r k i n E l m e r M o d e l 621 d o u b l e b e a m g r a t i n g spec trometer. E s s e n t i a l l y i d e n t i c a l spectra w e r e o b t a i n e d u s i n g a P e r k i n E l m e r M o d e l 225 d o u b l e b e a m g r a t i n g spectrometer a n d a B e c k m a n M o d e l I R - 1 2 d o u b l e b e a m g r a t i n g spectrometer as w e r e o b t a i n e d w i t h the P - E 621 f o r zeolites A , X , a n d Y . A f e w spectra w e r e m e a s u r e d for d e h y d r a t e d zeolites b y a c t i v a t i n g the z e o l i t e p o w d e r s i n a i r at 3 5 0 ° C , r a p i d l y q u e n c h i n g i n t o d r y m i n e r a l o i l , a n d r u n n i n g the s p e c t r u m as a m i n e r a l o i l m u l l . D e h y d r a t i o n studies r e p o r t e d f o r C a - e x c h a n g e d Y z e o -


204


1

l i t e u s i n g s e l f - s u p p o r t e d w a f e r s w e r e c a r r i e d out w i t h a c e l l a n d t e c h n i q u e essentially t h e same as t h a t d e s c r i b e d b y A n g e l l a n d Schaffer ( J ) . T h e s p e c t r a l r e s o l u t i o n is b e t t e r t h a n 5 c m " a n d the e s t i m a t e d a c c u r a c y ± 5 c m " u s i n g the same t e c h n i q u e a n d i n s t r u m e n t , b u t c a n b e as h i g h as ± 1 0 c m " w i t h other m e a s u r e m e n t v a r i a t i o n s . A l l of t h e s y n t h e t i c zeolites i n v e s t i g a t e d w e r e p r e p a r e d i n this l a b o r a t o r y w i t h the e x c e p t i o n of the Z e o l o n p r o d u c t a n d Z K - 5 , a n d w e r e f u l l y c h a r a c t e r i z e d i n terms of c h e m i c a l c o m p o s i t i o n , x - r a y , a n d a d s o r p t i o n p u r i t y . A l l represent z e o l i t e contents of greater t h a n 9 0 % a n d c o n t a i n e d n o c r y s t a l l i n e i m p u r i t i e s detectable b y x - r a y p o w d e r d i f f r a c t i o n analysis. T h e N a " Z e o l o n " u s e d w a s o b t a i n e d f r o m t h e N o r t o n C o . , a n d the e x p e r i m e n t a l s a m p l e of Z K - 5 w a s p r e p a r e d b y K . R . M u l l e r at t h e U n i o n C a r b i d e E u r o p e a n R e s e a r c h Associates L a b o r a t o r y i n Brussels, B e l g i u m . I n the t h e r m a l d e c o m p o s i t i o n studies of A , X , Y , a n d L zeolites, p o w d e r samples of e a c h z e o l i t e w e r e h e a t e d i n a m b i e n t a i r f o r 16 h o u r s at i n c r e a s i n g temperatures to y i e l d a series of t h e r m a l d e c o m p o s i t i o n p r o d ucts w i t h successively l o w e r r e s i d u a l zeolite x - r a y c r y s t a l l i n i t y . T h e h e a t e d p o w d e r s w e r e h y d r a t e d at r o o m t e m p e r a t u r e a n d r u n as K B r w a f e r s to o b t a i n t h e i r i n f r a r e d patterns. 1

1


1

Results I n f r a r e d s p e c t r a w e r e o b t a i n e d o n t h e s y n t h e t i c zeolites A , N - A , X , Υ, Β ( P I ) , K Z - 5 , o m e g a ( Ω ) , S, R , G , D , T , L , W , s y n t h e t i c analogues of mordenite ("Zeolon"), a n d analcime ( C ) , a n d for the related synthetic

1200

1000

800

600

400

200 Crrr

Figure 3.

800

600

400

200

1

Infrared spectra of zeolites R, G, and D


FLANIGEN E T A L .

Infrared

Structural

Studies


16.


205

206

M O L E C U L A R SIEVE ZEOLITES

Table I.

1

Infrared Spectral

Si0

2

Zeolite

AW*

A Ca A N-A N-A X Y Y La Y Y e x

e x


BCD Hydroxy sodalite (HS) Ω ZK-5 R G D S Τ Hydroxy cancrinite (HC) L C Zeolon

Asym. Stretch 1050vwsh 1055vwsh

Sym. Stretch 742vwsh 750vwsh 750vwsh 746m 760m 784m 790m 789m 772mwsh

660vw 705vwsh 665vw 675vw 698vw 690wsh 668m 686m 714m 705m 718m 670mw 738mw

729m

701mw

660m

805mw

722mw 730mw 678w 696wsh 711w 722mw

690vwsh

1.88 1.9 3.58 6.01 2.40 3.42 4.87 5.0 5.63 2.8

1090vwsh 1130vwsh 1131vwsh 1151vwsh

2.0

1096vwsh

1030s 1044s 971s 985s 1005s 1006s 1017s 9951000s 986s

7.7 6.0 3.25 5.44 4.62 2.5

1130wsh 1158wsh 1136mwsh 1138mwsh 1184mwsh 1140wsh

1024s 1048s 1007s 1027s 1018s 1020s

7.0 2.0

1156wsh 1095mw

1059s 1035msh

1010s 1000s

771w 755w

718w

6.0 4.0 9.95

1162vwsh 1216w

1012s 1180vwsh

1015s 952s 1046s

3.6

1128msh

767mw 740m . 40m 795\ , 772/ 7861 756/

721mw 686wb 715\ . 690f 691mwb

1060msh 1135msh 1130msh 1135msh 1130msh 1105mw8h

995s

890vwb 738w 720w 755wsh 770vwsh

w b

W

1006s

642vwsh

w b

K

m w b

Figure 6. Infrared spectra of zeolites A and N-A; numbers in parenthesis are Si/Al values


16.

FLANIGEN E T A L .

Infrared

Structural

207

Studies

D a t a f o r S y n t h e t i c Zeolites Cm~

7a

Dbl. Rings

508vwsh 500wsh 500wsh 504mwsh

464m 460m 474m 475m 458ms 460ms 455ms 450ms 456ms

600m

406w

435ms 461ms


Pore Opening?

TO Bend

550ms 542ms 572ms 581ms 560m 564m 572m 565m 575m

610mw 572m 625m 632m 631m

508mw 515m 513m 518mb

595sh/ 623mw 624m

606m 615vw 621w 637mw

378ms 376m 385m 393m 365m 372m 380m 382m 383m 380mwsh

260vwb?

250vwb? 260vwb? 315vwsh

282vwb?

432ms

372m

451ms 445m 452m 460m 459m 448m

426m 408m 415m 424ms

467ms 458ms

433ms 429ms

474ms 442ms 448ms

435wsh 410msh

408wsh 370vwsh 378vwsh 376vwsh 370vwsh

mb

575w 567m

498mw

580wsh 571\ 555/ 590wb

512vwsh

483vwsh

410vwsh 390mw

366wsh 353wb

375vwsh 370vwsh

432ns

375vwsh

° s = strong; ms = medium strong; m = medium; mw = medium weak; w = weak; vw = very weak; sh = shoulder; b = broad.

f e l s p a t h o i d phases, h y d r o x y sodalite ( H S ) a n d h y d r o x y c a n c r i n i t e ( H C ) . T h e I R spectra a r e s h o w n i n F i g u r e s 1 - 6 , a n d s p e c t r a l f r e q u e n c i e s l i s t e d i n T a b l e I . C a t i o n a n d f r a m e w o r k c o m p o s i t i o n s a n d references d e s c r i b i n g t h e i r synthesis a n d properties a r e g i v e n f o r a l l of t h e zeolites i n T a b l e I I . S t r u c t u r a l characteristics b a s e d p r i n c i p a l l y o n M e i e r ' s ( 2 8 ) a n d Barrer's ( 2 ) reviews are c o m p i l e d i n T a b l e I I I a n d a summary of s t r u c t u r a l elements a n d b u i l d i n g u n i t s i n z e o l i t e f r a m e w o r k s g i v e n i n T a b l e I V . T h e d e f i n i t i o n of s e c o n d a r y b u i l d i n g u n i t s ( S B U ) a n d b u i l d i n g b l o c k s u s e d h e r e is n o t as precise as that o f M e i e r (28), a n d there is some m i n o r v a r i a t i o n f r o m M e i e r ' s s t r u c t u r a l classification. T h e zeolites w e r e chosen to represent a s p e c t r u m of s t r u c t u r a l types a n d S B U a n d p o l y h e d r a l b u i l d i n g u n i t s i n t h e f r a m e w o r k s as w e l l as a r a n g e o f S i , A l f r a m e w o r k compositions. C o r r e l a t i o n of t h e i n f r a r e d spectra w i t h z e o l i t e s t r u c t u r e has l e d u s to p r o p o s e t h e f o l l o w i n g i n t e r p e r t a t i o n s a n d hypotheses.

E a c h zeolite

species has a t y p i c a l i n f r a r e d p a t t e r n . I n a d d i t i o n , there a r e often g e n e r a l


208


1

s i m i l a r i t i e s a m o n g t h e s p e c t r a of zeolites w i t h t h e same s t r u c t u r a l t y p e a n d i n t h e same s t r u c t u r a l g r o u p . T h e i n f r a r e d s p e c t r a of zeolites i n the 1 3 0 0 - 2 0 0 c m " r e g i o n a p p e a r to consist o f 2 classes of v i b r a t i o n s : those 1

c a u s e d b y i n t e r n a l v i b r a t i o n s of t h e f r a m e w o r k T 0

4

t e t r a h e d r o n , the

p r i m a r y b u i l d i n g u n i t i n a l l zeolite f r a m e w o r k s , w h i c h t e n d to b e i n s e n s i t i v e to v a r i a t i o n s i n f r a m e w o r k s t r u c t u r e , a n d v i b r a t i o n s r e l a t e d to exter n a l l i n k a g e s b e t w e e n t e t r a h e d r a w h i c h are sensitive to t h e f r a m e w o r k structure a n d to the presence of some S B U a n d b u i l d i n g b l o c k p o l y h e d r a s u c h as d o u b l e r i n g s a n d the large p o r e openings. to A 1 0 T0

4

N o v i b r a t i o n s specific

t e t r a h e d r a o r A l - O b o n d s are assigned b u t r a t h e r v i b r a t i o n s of

groups a n d T - O b o n d s w h e r e t h e v i b r a t i o n a l f r e q u e n c i e s represent

4


t h e average S i , A l c o m p o s i t i o n a n d b o n d characteristics of t h e c e n t r a l Τ cation.

T h e p r o p o s e d i n f r a r e d assignments are p r e s e n t e d i n d e t a i l i n

T a b l e V a n d i l l u s t r a t e d w i t h the i n f r a r e d s p e c t r u m of zeolite Y i n F i g u r e 7. T h e b a n d s assigned to i n t e r n a l t e t r a h e d r a l v i b r a t i o n s are s h o w n i n t h e Table II.

Compositions of Synthetic Zeolites Ref.

Zeolite

Cation*

A N-A X Y HS ( H y d r o x y Sodalite) ZK-5 B(P1) Omega (Ω) S R G D Τ L HC ( H y d r o x y cancrinite) W Zeolon C

Na TMA , Na Na Na Na

2 2.5-6.0 2.0-3.0 >3-6 2-3

{15, 31) {5) {16, 32) {11, 16) U, 8)

Na, D D O Na Na, T M A Na Na Κ K, Na K, Na Κ; K , N a Na

4-6 2-5 5-12 4.6-5.9 3.5-3.7 2-6 4.6-5.0 6.4-7.4 5.2-6.9 2.0

{22) {33) {6, 19) {10) {35) {3) {12) {13)

Κ Na Na

3.3-4.9 10-11 2-6

6

{14, {8)

{34)

{41)

{38,

39)

° Cation composition as synthesized. T M A = tetramethyl ammonium ion, ( C H ^ N * . D D O = ( C H i N ) = [l,4-dimethyl-l,4-diazoniacyclo (2.2.2.) octane] *. 6

c

8

8

2

16)

2 +

2

2


16.

Infrared

FLANIGEN E T A L .

Structural

Studies

209

figures w i t h a f u l l l i n e d r a w i n g , a n d those to e x t e r n a l l i n k a g e m o d e s w i t h a broken line. T h e first class of v i b r a t i o n s c o m m o n to a l l zeolites a n d assigned to i n t e r n a l t e t r a h e d r o n v i b r a t i o n s i n c l u d e s the 2 most intense b a n d s i n the s p e c t r u m , the strongest at 9 5 0 - 1 2 5 0 c m " a n d the other of m e d i u m i n t e n 1

sity at 420--500 c m " . W e p r o p o s e as a m o d e l f o r c o m p a r i s o n a n d a s s i g n 1

m e n t of i n t e r n a l t e t r a h e d r a l m o d e s the c o m p r e h e n s i v e w o r k of L i p p i n c o t t et al. (26)

o n the i n f r a r e d spectra of the p o l y m o r p h s of s i l i c a . T h e p r i

m a r y b u i l d i n g u n i t of a S i 0

4

tetrahedron linked i n a three-dimensional

t e t r a h e d r a l f r a m e w o r k i n the silicas is analogous to zeolite f r a m e w o r k s , a n d serves as a p o i n t of reference.

Lippincott's S i - O vibrations become


T - O v i b r a t i o n s i n o u r assignments. A f t e r L i p p i n c o t t , the strongest v i b r a tion i n the 950-1250 c m "

1

r e g i o n is assigned to a T - O stretch i n v o l v i n g

m o t i o n p r i m a r i l y associated w i t h o x y g e n atoms, or a l t e r n a t e l y d e s c r i b e d as a n a s y m m e t r i c s t r e t c h i n g m o d e

Infrared Structural Studies of Zeolite Frameworks

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