Infrared Spectroscopic Study of the Isotopic Exchange of Lattice

44 Infrared Spectroscopic Study of the Isotopic Exchange of Lattice Hydroxyls in Synthetic Faujasites

Downloaded by CORNELL UNIV on August 19, 2016 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0121.ch044

C. F. HEYLEN and P. A. JACOBS Centrum voor Oppervlaktescheikunde en Colloidale Scheikunde De Croylaan 42 B-3030 Heverlee, Belgium

The hydroxyls of hydrogen-sodium faujasites with different sodium and aluminum content, and of LaX, LaY, and "deep-bed" calcined zeolites were exchanged with D in the 200400°C temperature range. The exchange was followed continuously by infrared spectrometry. On each sample, the different types of hydroxyls exchanged at the same rate, except for the one having the 3750 cm band. The activation energy for this process depended on the nature of the cation, on the degree of ion exchange, and on the Si/Al ratio. The X samples were the most active. 2

-1

T n f r a r e d s p e c t r o m e t r y has been w i d e l y used t o s t u d y t h e r e a c t i v i t y of t h e h y d r o x y l groups i n t h e s y n t h e t i c zeolites, X a n d Y (1). In h y d r o g e n - Y ( H Y ) samples, t h e h y d r o x y l groups absorb a t 3650 a n d 3550 c m . T h e h y d r o x y l s a t 3650 c m react i n 1:1 s t o i c h i o m e t r y w i t h bases. T h e r e a c t i v i t y of t h e h y d r o x y l s a t 3550 c m has been c o r r e l a t e d r e c e n t l y w i t h t h e p o l a r effects exerted b y t h e s u b s t i t u t i n g groups of t h e a m i n e molecules (2). I n L a - e x c h a n g e d X a n d Y zeolites, h y d r o x y l s absorb a t 3640 a n d 3530 c m " (1, 3). I n "deep-bed" calcined N H Y samples a n d i n a l u m i n u m - d e f i c i e n t H Y samples, h y d r o x y l b a n d s are o b s e r v e d a r o u n d 3680, 3650, 3620, a n d 3550 c m " (1, 4, 5). T h e h y d r o x y l g r o u p s a t 3680, 3620, a n d 3530 c m are n o t r e a c t i v e t o w a r d bases. A

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1

4

1

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F e w a u t h o r s considered t h e r e a c t i v i t y of h y d r o x y l groups a t c a t a l y t i c a l l y i n t e r e s t i n g t e m p e r a t u r e s . In situ i n f r a r e d spectroscopy s h o w e d t h a t i n t h e cumene c r a c k i n g r e a c t i o n the 3550 c m hydroxyls i n a H Y sample are o n l y affected a b o v e 3 2 5 ° C . T h e 3650 c m h y d r o x y l decreased i n i n t e n s i t y a t 2 5 0 ° C (6). D u r i n g the c r a c k i n g of hexane o n a s i m i l a r s a m p l e t h e g r a d u a l d e a c t i v a t i o n of t h e c a t a l y s t is a c c o m p a n i e d b y t h e progressive - 1

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490 Meier and Uytterhoeven; Molecular Sieves Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

44.

491

Isotopic Exchange of Hydroxyls

H E Y L E N A N D JACOBS

r e m o v a l of t h e h y d r o x y l groups. T h e r e a c t i o n caused t h e r e m o v a l of, first, t h e 3640 c m b a n d a n d , s u b s e q u e n t l y , t h e 3540 c m b a n d (7). T h e b e h a v i o r of t h e other types of h y d r o x y l groups has n o t y e t been investigated. T h e use of d e u t e r i u m is r e p o r t e d i n order t o s t u d y t h e r e a c t i v i t y of different h y d r o x y l groups o n oxide surfaces b y i n f r a r e d spectroscopy (8-10). I n h y d r o g e n X a n d Y samples, t h e exchange of D w i t h t h e surface h y d r o x y l s w a s used t o determine t h e h y d r o x y l c o n t e n t of t h e samples (11). T h e i n f r a r e d m e t h o d for i n v e s t i g a t i n g a p a r t i c u l a r h y d r o x y l g r o u p o n t h e surface w a s also used o n zeolites (12,13). T h e h y d r o x y l groups a t 3650 a n d 3550 c m i n H Y showed a n i d e n t i c a l r a t e of exchange w i t h p e r d e u teroethylene (13). T h e exchange of D w i t h t h e h y d r o x y l s i n H X , H Y , a n d C a H Y samples was also r e p o r t e d (12). -

1

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1

2

-

1


2

I n c o n t r a s t t o p r e v i o u s w o r k (12), i n the present paper t h e D exchange is followed c o n t i n u o u s l y w i t h the i n f r a r e d spectrometer a t r e a c t i o n t e m p e r a t u r e . S a m p l e s were selected t o c o m p a r e t h e a b i l i t y for d e u t e r a t i o n of a l l the t y p e s of h y d r o x y l groups r e p o r t e d i n s y n t h e t i c faujasites. 2

Experimental M a t e r i a l s . T h r e e s y n t h e t i c faujasites w i t h different S i / A l r a t i o s were o b t a i n e d f r o m t h e L i n d e C o . T h e c o n c e n t r a t i o n of t h e i m p u r i t y a l k a l i n e e a r t h cations was g r e a t l y reduced ( < 0 . 0 3 % b y weight) b y successive e x changes w i t h p u r i f i e d N a C l s o l u t i o n . T h e r e s u l t i n g samples were washed w i t h s l i g h t l y a l k a l i n e d i s t i l l e d water t o a v o i d d e c a t i o n a t i o n . I o n exchange w a s p e r f o r m e d w i t h N H C l - N a C l o r L a ( N 0 ) solutions of 0.1 t o t a l n o r m a l i t y , f o l l o w i n g the procedure d e s c r i b e d elsewhere (14). T h e a n h y d r o u s u n i t c e l l c o m p o s i t i o n of t h e samples is g i v e n i n T a b l e I . F 8 5 a n d F 5 5 are a c o m m o n X zeolite a n d Y zeolite, r e s p e c t i v e l y . S a m p l e F 5 5 / 7 0 was also c a l c i n e d a t 560° C u n d e r c o n d i t i o n s of deep-bed g e o m e t r y used b y K e r r (16). S u b s e q u e n t l y , t h e r e s i d u a l N a ions were exchanged w i t h 0.1N N H C 1 s o l u t i o n . T h e s a m p l e is d e n o t e d b y Y D B N H . P a r t of t h e F 5 5 / 7 0 s a m p l e was b a c k - e x c h a n g e d t o increase t h e C a content u p t o 0 . 2 0 % b y weight. T h e s a m p l e is denoted as F 5 5 / 7 0 . * T h e s i l i c a A e r o s i l was f r o m D e g u s s a . S i l i c a platelets f o r spectroscopic use were p r e h e a t e d i n a i r a t 800° C , as described elsewheer (16). T h e h y d r o g e n a n d d e u t e r i u m gases were f r o m J . T . B a k e r . T h e p u r i t y w a s 9 9 . 9 5 % a n d 9 9 . 5 0 % , r e s p e c t i v e l y . T h e gases were d r i e d c a r e f u l l y before use. Equipment. T h e s p e c t r a were recorded o n a B e c k m a n I R 1 2 s p e c t r o m eter i n t h e absorbance mode, w i t h l o w a m p l i f i e r g a i n a n d slit w i d t h s s m a l l e r t h a n 1.6 of the h a l f - b a n d w i d t h of the O H o r O D b a n d s . U n d e r these c o n d i t i o n s t h e a p p a r e n t o p t i c a l d e n s i t y of t h e O H b a n d s c o u l d be r e p r o d u c e d within ± 0 . 5 % . T o a v o i d errors f r o m s a m p l e e m i s s i o n a t t e m p e r a t u r e s h i g h e r t h a n 100°C, t h e s p e c t r a were scanned w i t h t h e chopper between s a m p l e a n d detector disconnected. T h e device for d e u t e r i u m exchange consisted of a c i r c u l a t i o n c i r c u i t w i t h a 2000-ml reservoir c o n t a i n i n g 9 6 % of t h e t o t a l v o l u m e of the s y s t e m . D c o u l d be c i r c u l a t e d o v e r t h e s a m p l e i n t h e i n f r a r e d c e l l b y u s i n g a m a g n e t i c p u m p . T h e p u m p speed w a s c a l c u l a t e d t o be h i g h enough t o e l i m i n a t e 4

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Meier and Uytterhoeven; Molecular Sieves Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

492

M O L E C U L A R SIEVES

t h e r a t e of c i r c u l a t i o n as a possible r a t e - l i m i t i n g f a c t o r (17). t u r e was k e p t c o n s t a n t w i t h i n ± 1 ° C . Table I.

Anhydrous Unit Cell Composition of the Samples

Sample

Unit cell composition

YDBNH4 F55/70 F55/40 F49/70 F49/41 F85/45 LaY LaX


The tempera

Na .4

(NH )n

Nan.6

(NH )37.4

Naœ.o

(NH4)

0

%

Α1 (Α1 -χ0 ) (A10 ) .o β

4

1

2

4

2

(Si0 W

52

2

2

2

2

Naw.9

(NH )34.3

2

(NH ) .

2

(A10 ) .i (A10 ) .i

(SiOz)144

Na s.9 Na46.6

(NH )38.

2

(AlO )85.0

(Si0 )io7

Naio.23

Lai2.9

Naio.so

La .7o

(A10 ) .o (A10 ) .o

4

4

20

4

2

49

2

49

(Si0 )

2 144

2

2

24

68. 0 40. 0 69. 9 41. .1 45. 2 70 .0 87 .0

(Si0 )l37 (Sl0 )l37

55

(AlO )55.0

22

Exchange

2

55

(Sl0 )l37

2

85

(SiO )l07

2

2

χ — 0.31, determined by NaOH extraction (4).

a

Techniques. P l a t e l e t s of a p p r o x i m a t e l y 30 X 26 m m , w e i g h i n g 3 to 4 m g / c m , were p r e p a r e d b y p r e s s i n g t h e p o w d e r e d samples at 7 tons for 2 m i n u t e s . T h e s e were p l a c e d i n t h e i n f r a r e d c e l l , e v a c u a t e d at r o o m t e m p e r a t u r e u n d e r a v a c u u m of 1 0 ~ t o r r , a n d h e a t e d s l o w l y t o 4 0 0 ° C (18). T h e samples were t h e n cooled a n d h e a t e d a g a i n a t r e a c t i o n t e m p e r a t u r e . B e f o r e e a c h r u n , t h e h y d r o x y l s p e c t r a were s c a n n e d a t r o o m t e m p e r a t u r e a n d r e a c t i o n t e m p e r a t u r e . T h e s p e c t r o m e t e r w a v e l e n g t h scale w a s l o c k e d a t t h e m a x i m u m of t h e o p t i c a l d e n s i t y of t h e h y d r o x y l (deuteroxyl) b a n d , a n d t h e decrease (increase) of t h e O H ( O D ) b a n d m a x i m u m was r e c o r d e d c o n t i n u o u s l y as a f u n c t i o n of t i m e . N o s h i f t i n t h e m a x i m u m of t h e o p t i c a l d e n s i t y o c c u r r e d d u r i n g t h e r e a c t i o n . F o r m o s t of t h e reactions t h e pressure of D w a s 100 t o r r . T h e t e m p e r a t u r e r a n g e f r o m 200° t o 4 0 0 ° C w a s i n v e s t i g a t e d i n i n t e r v a l s of 5 0 ° C . T h e exchange d a t a for each h y d r o x y l b a n d were e v a l u a t e d f o l l o w i n g a first-order equation: 2

6

2

—In (χ

—

Χα,) =

— In (xo —

kt

(1)

Xœ)

T h e v a l u e of t h e a t o m f r a c t i o n H (of t h e O H + O D ) , i n i t i a l l y , a t e q u i l i b r i u m , and a t t i m e t, i s d e n o t e d b y x , x , a n d x r e s p e c t i v e l y . A l l o w a n c e w a s m a d e for t h e fact t h a t t h e a p p a r e n t o p t i c a l densities of the h y d r o x y l a n d c o r r e s p o n d i n g d e u t e r o x y l g r o u p s are different b y as m u c h as 1 0 % . T h e excess of D was a t least 5-fold, so t h a t t h e v a r i a t i o n of t h e different t y p e s of h y d r o x y l s c o u l d be e v a l u a t e d s e p a r a t e l y (17). F r o m E q u a t i o n 1 the charact e r i s t i c slope p a r a m e t e r is o b t a i n e d (19) : 0

m

}

2

fcimin- ) = R(2N + N )/2N N 1

B

a

g

(2)

e

w h e r e R i s t h e l e a k r a t e ( a t o m s / m i n ) or t h e r a t e of t r a n s f e r a t w h i c h D flows b e t w e e n e q u i v a l e n t sites i n D a n d O D g r o u p s . N* i s t h e n u m b e r of h y d r o x y l g r o u p s e x c h a n g i n g w i t h N d e u t e r i u m molecules. N w a s d e t e r m i n e d w i t h t h e a i d of t h e i n t e g r a t e d i n t e n s i t y of t h e h y d r o x y l b a n d s (20) a n d was c h e c k e d b y mass s p e c t r o m e t r y . T h e e x p e r i m e n t s w e r e so a r r a n g e d t h a t N 26). It has been suggested (18) that the amount of extra-lattice aluminum is proportional to the hydroxyl band around 3600 c m . Careful examination of the hydroxyl spectrum of the H - N a faujasites shows the presence of the 3600 cm"* band and, therefore, of extra-lattice aluminum. The concentration is higher in the X than in the Y zeolites (18). The leak rate (R) shows the same sequence. On the other hand the LaY sample shows the highest activity, indicating the promoting effect of the L a ions on the leak rate. The activation energy of the exchange process changes with the nature of the cation, the degree of cation exchange, and the presence of extralattice aluminum. The intrinsic activity of the different samples as de termined by the activation energy seems to be influenced by these param eters. Further work is in progress to determine supplementary parameters as the temperature of pretreatment on H Y , the degree of cation exchange, the pretreatment temperature for other cations, and the simultaneous presence of several polyvalent cations. 2 +

4

+

+

4

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1

3 +

Acknowledgment P.A.J. acknowledges a grant from the National Science Foundation (N.F.W.O. Belgium). C.H.F. acknowledges a grant from I.W.O.N.L. (Belgium). We acknowledge support from the Belgian Government (Dienst voor Programmatie van het Wetenschapsbeleid). We are grateful to J . B. Uytterhoeven, E . A. Lombardo, and W. K . Hall for helpful dis cussions and suggestions. Literature Cited 1.

Ward, J. W., ADVAN. CHEM. SER. (1971) 101, 380.

2. 3. 4. 5.

Jacobs, P. Α., Theng, Β. K. G., Uytterhoeven, J. B., J. Catalysis (1972) 26, 191. Bolton, A . P., J. Catalysis (1971) 22, 9. Jacobs, P. Α., Uytterhoeven, J. B., J. Catalysis (1971) 22, 193. Beaumont, R., Pichat, P., Barthomeuf, D., Trambouze, Y., Proc. Fifth Int. Congr. Catalysis (1972) paper 19. 6. Ward, J. W., J. Catalysis (1968) 11, 259. 7. Bolton, A . P., Bujalski, R. L., J. Catalysis (1971) 23, 331. 8. Carter, J. L., Luchessi, P. L., Cornell, P., Yates, D. J. C., Sinfelt, J. H., J. Phys. Chem. (1965) 69, 3070. 9. Fry, D. L., Mohan, P. V., Lee, R.W., J. Opt. Soc. Amer. (1960) 50, 321. 10. Peri, J. B., Hannan, R. B., J. Phys. Chem. (1960) 64, 1526.


MOLECULAR SIEVES


500

11. Uytterhoeven, J. B., Christner, L. G., Hall, W. K., J. Phys. Chem. (1965) 69, 2117. 12. Imanaka, T., Okamoto, Y., Takahata K., Teranishi, S., Bull. Chem. Soc. Japan (1972) 45, 366. 13. Cant, N. W., Hall, W. K., J. Catalysis (1972) 25, 161. 14. Theng, B. K. G., Vansant, E., Uytterhoeven, J. B., Trans. Faraday Soc. (1968) 64, 3370. 15. Kerr, G. T., J. Catalysis (1969) 15, 200. 16. Van Cauwelaert, F. H., Jacobs, P. A. Uytterhoeven, J. B., J. Phys. Chem. (1972) 76, 1434. 17. Fripiat, J. J., Gastuche, M. C., Brichard, R., J. Phys. Chem. (1962) 66, 805. 18. Jacobs, P. Α., Uytterhoeven, J. B., J.C.S. Faraday 1 (1973) 69, 373. 19. Cheselske, F. J., Wallace, W. E., Hall, W. K., J. Phys. Chem. (1959) 63, 505. 20. Uytterhoeven, J. B., Jacobs, P. A., Makay, K., Schoonheydt, R., J. Phys. Chem. (1968) 72, 1768. 21. Angell, C. L., Schaffer, P. C., J. Phys. Chem. (1965) 69, 3463. 22. Sheppard, C. W., Householder, A. S., J. Appl. Phys (1951) 22, 510. 23. Fripiat, J. J., Catalysis Rev. (1971) 5, 269. 24. Heylen, C. F., Jacobs, P. Α., to be published. 25. Mestdagh, M. M., Stone, W. E., Fripiat, J. J., J. Phys. Chem. (1972) 76, 1220. 26. Ward, J. W., J. Catalysis (1970) 18, 348. RECEIVED November 29, 1972.


Infrared Spectroscopic Study of the Isotopic Exchange of Lattice

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