Crystal Structures of Ultrastable Faujasites

21 Crystal Structures of Ultrastable Faujasites P. K. MAHER, F. D. HUNTER, and J. SCHERZER

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W. R. Grace & Co., Washington Research Center, Clarksville, Md. The crystal structures of 4 ammonium exchanged, heattreated faujasites were determined from x-ray powder data. Structure I, often called "decationated Y," has lost 15 framework aluminum atoms and 21 framework O atoms (bridging oxygen atoms) per unit cell, and 15 Al(OH) ions are present in the sodalite cages. Structure II, called ammonium—aluminum Y hydrate, shows a complete rehydroxylation of the vacant O positions. Structure III, called ultrastable Y, shows the same 15 framework aluminum atoms absent, and the removal of 25 O and 13 O framework oxygen atoms. Structure IV, which is a repetitive exchanged and heat-treated version of Structure III, has a mean Si-O bond length of 1.610 A, which indicates that little framework aluminum is present. (1)

+

2

(1)

(3)

(4)

TidTcDaniel a n d M a h e r ( 9 ) h a v e r e p o r t e d a n e w f o r m of t h e zeolite ^ f a u j a s i t e that is t h e r m a l l y stable at temperatures i n excess of 1 0 0 0 ° C . T h i s s t a b i l i t y is i n contrast w i t h other r e p o r t e d h y d r o g e n or " d e c a t i o n a t e d " faujasites, w h i c h are less stable t h a n the c a t i o n forms.

According

to these authors, the c o n v e r s i o n of faujasite to the h y d r o g e n f o r m leads to a p a r t i a l d e s t r u c t i o n of t h e c a t i o n exchange sites w h i c h has b e e n explained only b y an alteration i n the s i l i c a - a l u m i n a anionic framework. A m b s a n d F l a n k (2)

h a v e c o n c l u d e d o n t h e basis of l i m i t e d d a t a

that the t h e r m a l s t a b i l i t y of s y n t h e t i c faujasite is d e p e n d e n t o n l y o n t h e l e v e l of s o d i u m present.

T h e y f u r t h e r assert t h a t n o difference

exists

b e t w e e n d e c a t i o n a t e d Y a n d u l t r a s t a b l e materials. Kerr

( 7 ) r e p o r t e d that h y d r o g e n zeolite Y , h e a t e d 2 - 4 h o u r s at

7 0 0 ° - 8 0 0 ° C i n a n i n e r t atmosphere w h e r e t h e c h e m i c a l w a t e r r e m a i n s i n t h e e n v i r o n m e n t of t h e h y d r o g e n zeolite, y i e l d s a substance of u n u s u a l l y h i g h t h e r m a l s t a b i l i t y ( 1 0 0 0 ° C ) . H e s h o w e d that i n this zeolite a p p r o x i m a t e l y 2 5 % of t h e a l u m i n u m is present i n t h e c a t i o n i c f o r m . 266 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

21.

Ultrastable

MAHER E T AL.

267

Faujasites

K e r r ( 8 ) also n o t e d the r e m o v a l of a l u m i n u m f r o m s o d i u m Y z e o l i t e t h r o u g h the use of d i l u t e solutions of e t h y l e n e d i a m i n e t e t r a a c e t i c a c i d . H e o b s e r v e d that the r e m o v a l of u p to 5 0 % of the a l u m i n u m y i e l d s h i g h l y c r y s t a l l i n e p r o d u c t s of i m p r o v e d t h e r m a l stability a n d i n c r e a s e d s o r p t i v e c a p a c i t y . I n a m o r e recent a r t i c l e , K e r r ( β ) has s h o w n that 2 d i s t i n c t p r o d u c t s c a n b e o b t a i n e d b y the t h e r m a l d e c o m p o s i t i o n of a m m o n i u m Y at 760 t o r r a n d 500 ° C .

A c c o r d i n g to this a r t i c l e , the g e o m e t r y of the

zeolite b e d d u r i n g c a l c i n a t i o n determines the n a t u r e of the p r o d u c t .

Bed

geometries that i m p e d e the r e m o v a l of a m m o n i a f r o m the b e d y i e l d a n ultrastable p r o d u c t . H e f o u n d that u p o n c a t i o n exchange of this m a t e r i a l


u s i n g 0.1 Ν N a O H s o l u t i o n , the S i / A l r a t i o i n c r e a s e d f r o m 2.85 for the o r i g i n a l m a t e r i a l to 3.58 for the e x c h a n g e d m a t e r i a l . T h i s x - r a y s t r u c t u r a l i n v e s t i g a t i o n was u n d e r t a k e n i n a n effort

to

c l a r i f y the structure of the u l t r a s t a b l e Y zeolite. It was felt t h a t the loss of f r a m e w o r k a l u m i n u m , the existence of c a t i o n i c a l u m i n u m , a n d a l t e r ations i n the f r a m e w o r k structure c o u l d be r e v e a l e d b y this t e c h n i q u e e v e n t h o u g h p o w d e r d a t a , w h i c h are i n h e r e n t l y less accurate t h a n s i n g l e c r y s t a l d a t a , h a d to be u s e d .

Experimental I n o r d e r to u n d e r s t a n d the s t r u c t u r a l changes w h i c h o c c u r , 4 differ ent samples, e a c h f r o m different stages i n the p r e p a r a t i o n of the u l t r a stable m a t e r i a l , w e r e s t u d i e d . T h e first s a m p l e w a s selected f r o m step 2 of P r o c e d u r e " A " o u t l i n e d b y M c D a n i e l a n d M a h e r ( 9 ) . T h i s s a m p l e was o b t a i n e d f r o m N a Y w h i c h h a d u n d e r g o n e a m m o n i u m sulfate ex c h a n g e to r e d u c e the s o d i u m o x i d e content to 2 . 5 % a n d t h e n h a d b e e n c a l c i n e d at 540 ° C for 3 hours i n a mufHe furnace. A n a l y s e s of this s a m p l e s h o w e d that its u n i t c e l l c o m p o s i t i o n was N a ( A 1 0 ) 5 3 ( S i 0 ) i 3 9 ( S t r u c ture I ) . T h e second s a m p l e was chosen f r o m step 3 of the p r o c e d u r e a n d consisted of a p o r t i o n of the first s a m p l e w h i c h h a d b e e n treated t w i c e w i t h a m m o n i u m sulfate s o l u t i o n at 100 ° C a n d t h e n o v e n - d r i e d . T h e u n i t c e l l c o m p o s i t i o n of this s a m p l e is ( N H , H ) . 5 N a o . 5 ( A 1 0 ) 5 3 ( S i 0 ) i 9 r a H ^ ( S t r u c t u r e I I ) . H y d r o g e n a n d / o r a m m o n i u m ions w e r e a s s u m e d to b e present i n this s a m p l e to b a l a n c e the charges o w i n g to u n c o m p e n s a t e d aluminum tetrahedra. T h e t h i r d s a m p l e ( S t r u c t u r e I I I ) was the u l t r a s t a b l e Y m a t e r i a l i t self, N a ( A 1 0 ) 3 ( S i 0 ) i 3 9 . It was o b t a i n e d b y c a l c i n a t i o n of the sec o n d s a m p l e at 870 ° C for 5 hours i n a mufHe f u r n a c e . T h e f o u r t h s a m p l e s t u d i e d ( S t r u c t u r e I V ) was a p o r t i o n of the u l t r a s t a b l e m a t e r i a l w h i c h was subjected to 2 a d d i t i o n a l cycles of 100 ° C a m m o n i u m sulfate treat m e n t f o l l o w e d b y c a l c i n a t i o n for 5 hours at 8 7 0 ° C . B y c h e m i c a l analysis, this m a t e r i a l h a d the same s i l i c a a n d a l u m i n a content as the second a n d t h i r d samples. T h e u n i t c e l l values w e r e 24.56, 24.59, 24.31, a n d 24.24 ± 0.02 A for structures I , I I , I I I , a n d I V , respectively. T h e space g r o u p w a s a s s u m e d 9

4

0 5

2

5

8

2

2

2

2

2

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

3

2

268

MOLECULAR SIEVE ZEOLITES Table I. Atom

Occupancy Parameter

Atomic

Coordinates Y

X

1

Ζ

Τ

0.0364(9) -0.1136(16) 0.1447(17) -0.0288(15) 0.3216(16) 0.0800(20) 0.1618(15) 0.5000

3.37(0.50) 5.64(2.07) 4.19(2.28) 0.08(1.53) 2.42(1.88) 4.02(2.51) 6.59(2.70) 5.38(11.78)

Structure I Si,Al Ol o 0 A l l (Sn) OHi(^in) N a i CSV)

0.92 (3)* 0.78(4) 1.00 1.00 1.00 0.46(4) 1.00 0.32(8)

-0.0529(7) 0.0000 0.0012(11) 0.1743(11) 0.1816(13) 0.0800(20) 0.1618(15) 0.5000

Si,Al Ol o 0 O4 A h (Sn) O H i (Sm) Ni (Sy)

1.00 1.00 1.00 1.00 1.00 0.42(5) 0.47(7) 0.37(12)

-0.0530(8) 0.0000 -0.0017(14) 0.1732(12) 0.1766(12) 0.0899(15) 0.1617(43) 0.5000

Si,Al Ol Oo 0 O4 Ah (S )

0.92(8) 1.00 1.00 0.74(7) 0.86(8) 0.46(4)

-0.0540(5) 0.0000 -0.0044(8) 0.1752(9) 0.1861(11) 0.0913(18)

Si,Al Oi o 0 04 All

1.00 1.00 1.00 0.87(9) 1.00 0.23(3)

-0.0532(4) 0.0000 -0.0041(7) 0.1745(6) 0.1809(6) 0.0806(22)

2

3

O4

0.1228(12) 0.1136(16) 0.0012(11) 0.1743(11) 0.1816(13) 0.0800(20) 0.1618(15) 0.5000


Structure II

2

3

0.1256(10) 0.1107(14) -0.0017(14) 0.1732(12) 0.1766(12) 0.0899(15) 0.1617(43) 0.5000

0.0371(7) -0.1107(14) 0.1404(17) -0.0315(15) 0.3230(17) 0.0899(15) 0.1617(43) 0.5000

1.39(0.38) 5.04(1.51) 4.78(1.56) 0.08(2.20) 0.58(1.89) 1.89(3.18) 4.34(8.92) 12.88(7.26)

0.0358(6) -0.1058(7) 0.1476(10) -0.0416(15) 0.3195(14) 0.0913(18)

2.95(0.22) 2.76(0.81) 3.50(0.79) 0.60(1.3) 5.51(1.2) 20.74(4.0)

0.0359(4) -0.1061(6) 0.1464(8) -0.0366(11) 0.3200(8) 0.0806(22)

1.90(0.15) 3.44(0.89) 3.14(0.96) 2.50(0.87) 0.84(0.83) 8.08(3.6)

Structure III

3

u

0.1261(6) 0.1058(7) -0.0044(8) 0.1752(9) 0.1861(11) 0.0913(18)

Structure I V

2

3

α

0.1262(4) 0.1061(6) -0.0041(7) 0.1745(6) 0.1809(6) 0.0806(22)

The values in parentheses are the estimated standard deviations.

to b e Fd3m i n a l l cases. T h e x - r a y i n t e n s i t y d a t a w e r e c o l l e c t e d o n a N o r e l c o p o w d e r d i f f r a c t o m e t e r e q u i p p e d w i t h a H a m n e r s o l i d state d e tection system u t i l i z i n g a scintillation detector a n d pulse height analyzer. T h e d a t a f o r t h e first 2 structures w e r e c o l l e c t e d u n d e r a n i t r o g e n a t m o s p h e r e , a n d t h a t f o r t h e latter 2 w e r e c o l l e c t e d u n d e r a p a r t i a l v a c u u m of 88 m m of H g . T h e areas of t h e x - r a y p e a k s w e r e o b t a i n e d b y t h e use of a planimeter. T h r e e - d i m e n s i o n a l F o u r i e r techniques a n d least-squares r e f i n e m e n t p r o c e d u r e s s i m i l a r to those o u t l i n e d b y S h o e m a k e r et al. ( 3 , 12) w e r e e m p l o y e d i n t h e s t r u c t u r e d e t e r m i n a t i o n s . Results The

p o s i t i o n a l a n d t h e r m a l p a r a m e t e r s f o r a l l 4 s t r u c t u r e s are g i v e n

i n T a b l e I. T h e standard deviations given i n this table w e r e c a l c u l a t e d


21.

MAHER ET A L .

Table II. Position

OCD 0

. a n d J i . are t h e o b s e r v e d a n d c a l c u l a t e d c a

c

intensities. For

S t r u c t u r e I , w h i c h w i l l b e t e r m e d s o d i u m - a l u m i n u m Y b y us

a n d has b e e n t e r m e d " d e c a t i o n a t e d " Y b y R a b o a n d others ( 11, 13),

an

o c c u p a n c y factor of 0.92 for the f r a m e w o r k S i , A l sites i n d i c a t e s the loss

Figure 1. Projection of the sodalite cage for faujasite showing the avaihble nonframework sites. Site 5 is in the center of the 12-membered ring and is not shown here.


270

MOLECULAR SIEVE ZEOLITES

of 15.4 a l u m i n u m ions f r o m t h e f r a m e w o r k .

T h i s n u m b e r agrees

w i t h the 14.7 a l u m i n u m cations p e r u n i t c e l l f o u n d to o c c u p y S (see

F i g u r e 1 f o r a d e f i n i t i o n of the s i t e s ) . A l s o , 21 0

{1)

n

1

well sites

o x y g e n atoms

p e r u n i t c e l l h a v e b e e n r e m o v e d f r o m t h e f r a m e w o r k b y the 540 ° C c a l cination.

Site S

m

is o c c u p i e d c o m p l e t e l y b y h y d r o x y l groups.

atoms p e r u n i t c e l l r e s i d i n g i n S

v

T h e a l u m i n u m cations l o c a t e d i n S at 2.03 A a n d 3 f r a m e w o r k 0 octahedral complex. minum ion in S

n

( 3 )

T h e 5.1

sites w e r e a s s u m e d to b e s o d i u m ions. n

sites are c o o r d i n a t e d to 3 h y d r o x y l s

oxygens at 2.68 A to f o r m a d i s t o r t e d

O f the 3 h y d r o x y l groups c o o r d i n a t e d to e a c h a l u -

sites, 2 are s h a r e d w i t h another S

n

aluminum ion and


the other is n o t s h a r e d . Table III. Atom Set Si,Al-0 i) Si,Al-0 Si,Al-0 Si,Al-0 M e a n Value Al )-0 Al -OH ) (

( 2 )

( 3 )

( 4 )

( 1

( 1 )

( 3 )

( 1

Metal to Oxygen Bond Distances, A

Structure 1.75(4) 1.67(4) 1.62(4) 1.71(4) 1.69 2.68(6) 2.03(6)

I

Structure

II

Structure

1.73(3) 1.62(4) 1.63(4) 1.62(4) 1.65 3.02(5) 1.77(11)

III

Structure

1.61(3) 1.64(2) 1.60(3) 1.65(3) 1.62 3.28(6)

IV

1.62(2) 1.61(2) 1.61(2) 1.60(2) 1.61 2.85(3)

A s seen i n T a b l e I I I , the m e a n S i , A l - 0 b o n d distance of 1.69 A is r e l a t i v e l y l o n g c o m p a r e d to the values of 1.635 a n d 1.644 A o b t a i n e d b y E u l e n b e r g e r et al. (3) f o r N a Y a n d O l s o n a n d D e m p s e y (10) gen faujasite.

for hydro-

B o t h of these materials h a d s o m e w h a t l o w e r s i l i c a - t o -

a l u m i n a ratios t h a n o u r s o d i u m - a l u m i n u m Y sieve. A p r o j e c t i o n of the sodalite cage for this structure ( F i g u r e 2 ) shows t h a t the cage is d i s t o r t e d as c o m p a r e d w i t h the projections o b t a i n e d for t h e other structures ( F i g u r e 3 ) . T h e r e l a t i v e l y l o n g S i , A l - 0 b o n d lengths, the d i s t o r t i o n of the sodalite cage, a n d the loss of 2 2 % of the b r i d g i n g 0 D o x y g e n atoms (

e x p l a i n the i n s t a b i l i t y of this m a t e r i a l at h i g h e r temperatures. I n S t r u c t u r e I I , w h i c h w e c a l l a m m o n i u m - a l u m i n u m Y h y d r a t e , the o c c u p a n c y factors for a l l the f r a m e w o r k positions w e r e u n i t y . Site S is o c c u p i e d b y 13.4 a l u m i n u m ions, a n d S sites are filled b y 15.0 h y d r o x y l groups p e r u n i t cell. T h e 5.9 ions l o c a t e d i n S sites are t h o u g h t to b e a m m o n i u m ions. T h e ( a p p r o x i m a t e l y ) 2 a l u m i n u m ions present p e r sodalite cage are c o o r d i n a t e d to the same 2 h y d r o x y l groups f r o m S m sites at a distance of 1.77 A . T h e nearest f r a m e w o r k oxygens are 3 0 oxygens at 3.02 A . T h e m e a n S i , A l - 0 b o n d l e n g t h is 1.65 A . n

i n

v

( 3 )

T h e o c c u p a n c y parameters f o r u l t r a s t a b l e Y , S t r u c t u r e I I I , s h o w the absence of the same 15.4 a l u m i n u m ions as i n S t r u c t u r e I, b u t 25.0 0 ( 3 )



21.

Ultrastable

MAHER ET A L .

Figure

a n d 13.4 0 ) (4

2.

Projection

271

Faujasites

of the sodalite cage for num Y (Structure I)

o x y g e n atoms r a t h e r t h a n the 21 0

f r o m the f r a m e w o r k .

sodium-alumi

( υ

atoms are m i s s i n g

T h e loss of a t o t a l of 38.4 oxygen atoms p e r u n i t

c e l l represents the r e m o v a l of 10%

of the f r a m e w o r k o x y g e n atoms p r e s

ent i n the faujasite structure. Sites S

n

are filled b y 14.7 atoms p e r u n i t

c e l l w h i c h , as d i s p l a y e d b y t h e h i g h t h e r m a l p a r a m e t e r o b t a i n e d the e l o n g a t e d p e a k i n the e l e c t r o n d e n s i t y m a p , s e e m to b e

and

displaced

f r o m the t h r e e - f o l d axis. W h e n a p o s i t i o n off this axis w a s a s s u m e d for these atoms, a m o r e reasonable t e m p e r a t u r e p a r a m e t e r a n d a distance of 1.91 A c o r r e s p o n d i n g to a n a l u m i n u m - o x y g e n species are o b t a i n e d . I n S t r u c t u r e I V , w h i c h is t e r m e d h i g h - s i l i c a Y , the f r a m e w o r k

occu

p a n c y factors s h o w that the r e p e a t e d c a l c i n a t i o n a n d b o i l i n g a m m o n i u m sulfate treatment has r e s t o r e d a l l the f r a m e w o r k atoms except for of the Ο ( ) o x y g e n atoms. Sites S 3

n

12.5

are o c c u p i e d b y 7.4 ions p e r u n i t c e l l .

T h e s e ions, w h o s e i d e n t i t y is n o t c e r t a i n , h a v e 3 f r a m e w o r k 0

( 3 )

oxygens

as nearest n e i g h b o r s at a distance of 2.85 A . T h e m e a n S i , A l - 0 b o n d distance of 1.610

(8)

A is o n l y 1 σ greater t h a n the v a l u e of 1.603

r e p o r t e d b y Jones f o r a p u r e S i - O b o n d l e n g t h

(5).


A


272


•1

Figure 3.

01

Projection

Ql

1

01

of the sodalite cage for high-silica Y (Structure IV)

Discussion T h e s t r u c t u r e o b t a i n e d f o r the s o d i u m - a l u m i n u m Y sieve is i n g o o d agreement w i t h other e x p e r i m e n t a l results w h i c h h a v e b e e n

reported.

T h i s m a t e r i a l w a s m a d e u n d e r the p r e s c r i b e d c o n d i t i o n s for p r o d u c i n g " d e c a t i o n a t e d " Y . H o w e v e r , as o u r d a t a h a v e s h o w n , this m a t e r i a l c o n tains a l u m i n u m cations w h i c h w e r e d e r i v e d f r o m the f r a m e w o r k a l u m i n u m . H e n c e , i t is a p p a r e n t w h y w e p r e f e r the n a m e s o d i u m - a l u m i n u m Y to " d e c a t i o n a t e d " Y . M c D a n i e l a n d M a h e r ( 9 )

r e p o r t e d a decrease i n

the i o n exchange c a p a c i t y of " d e c a t i o n a t e d " Y sieves.

I n v i e w of o u r

results, this decrease p r o b a b l y results f r o m the r e m o v a l of a l u m i n u m , w h i c h was s u b s e q u e n t l y i o n - e x c h a n g e d s i l v e r ions u s e d i n t h e i r experiments.

framework

b y the s o d i u m

or

T h e l o w e r i n g of the a m o u n t of

f r a m e w o r k a l u m i n u m w o u l d result i n f e w e r a l u m i n u m t e t r a h e d r a w h o s e n e g a t i v e charges m u s t b e b a l a n c e d a n d h e n c e a decrease i n the i o n exchange

capacity.

K e r r (6)

has s h o w n t h a t d u r i n g the t h e r m a l d e c o m p o s i t i o n of a m -

m o n i u m Y z e o l i t e at 5 0 0 ° C there is a loss of a l u m i n u m i f a " d e e p b e d " geometry

is e m p l o y e d .

I n the p a r t i c u l a r m a t e r i a l that K e r r s t u d i e d ,

s o d i u m h y d r o x i d e t r e a t m e n t of the " d e e p b e d " s a m p l e l e d to the increase


21.

MAHER E T A L .

Ultrastable

273

Faujasites

of t h e S i / A l r a t i o f r o m 2.85 i n t h e o r i g i n a l a m m o n i u m zeolite t o 3.58. S o d i u m h y d r o x i d e treatment of o u r s o d i u m - a l u m i n u m Y s a m p l e r e s u l t e d i n a n e w S i / A l r a t i o of 3.19 a c c o r d i n g t o c h e m i c a l analyses. T h i s n u m b e r is s o m e w h a t s m a l l e r t h a n t h e ratio of 3.62 w h i c h w e get f r o m t h e x - r a y results i f w e take into a c c o u n t t h e r e m o v a l of 15 f r a m e w o r k

aluminum

atoms, b u t is c o n s i d e r a b l y h i g h e r t h a n t h e r a t i o of 2.62 i n t h e o r i g i n a l material. K e r r ' s p o s t u l a t i o n o f t h e f o r m a t i o n of A l ( O H )

2

species as p a r t o f

+

the m e c h a n i s m f o r a l u m i n u m r e m o v a l agrees w i t h o u r x - r a y


\

/,!

v

AI

\

Si

+ NHΘ

Si

/

Al

AI

v

/

J

Si

>>

V

4 2

4

Si

2 Al (OH)® J O O ^ A

Si

X\

+ Al (OH)|

\ / Si /

(NH ) S0« H,0

HE

V

Si

C STEP 3

Oj H,0

C

χ.

2 Η,Ο

\ y \

ft

3

B

% Sr

+ NH

Si

STE

A

/

/

/>

,°Γ

Η

Si

Si

+

Η,Ο

Si

2 Al ( O H ) ®

+

Si

Al

Si

STEP 1

+ NH

9 ^

ΑΚΟΗ)I©

AI-O

+

w

+ 2 H0 2

G

Al-O®

>

AIO(OH)

+

, 0 Si

Al

Si

STEP 3 Figure 4. Proposed mechanism for the structures studied; percentages are based on the total aluminum content Structure I « Structure II ^ Structure III «

60% A + 11% C + 28% D 72% A + 28% Ε 49% A + 28% G + 23% H


findings.

274


1

H o w e v e r , i n v i e w of the loss of 2 2 % of the f r a m e w o r k 0 D o x y g e n atoms (

w h i c h w e o b s e r v e d , w e f e e l that the m e c h a n i s m for a l u m i n u m r e m o v a l m a y be s o m e w h a t different f r o m that g i v e n b y K e r r . T h e m e c h a n i s m as w e e n v i s i o n i t is g i v e n i n R e a c t i o n I of F i g u r e 4 a n d depends u p o n the r e a c t i o n of a m m o n i u m ions w i t h the f r a m e w o r k 0 D oxygens w h i c h are (

c o n v e n t i o n a l l y the b r i d g i n g oxygens.

U p o n h e a t i n g to h i g h e r t e m p e r a

tures, p r o t o n a t i o n a n d the subsequent r e m o v a l of these o x y g e n atoms as w a t e r occur. b y steam.

T h e s e steps leave the a l u m i n u m ions accessible to attack

H e n c e , a c c o r d i n g to this r e a c t i o n a n d our x-ray results, the

structure of s o d i u m - a l u m i n u m Y contains 21 S i 0 , 15 A l ( O H ) \ a n d 3


9 Na

+

+

2

( t o t a l of 4 5 ) species or ions p e r u n i t c e l l to b a l a n c e t h e 15 S i 0 " 4

a n d 32 A 1 0 ~ ( t o t a l 47) groups. 4

T h e r e m a i n i n g 6 a l u m i n u m atoms p e r

u n i t c e l l w o u l d be i n v o l v e d i n n e u t r a l A 1 0

groups.

3

M c D a n i e l a n d M a h e r h a v e f o u n d t h a t Step 3 of t h e i r p r o c e d u r e for m a k i n g u l t r a s t a b l e Y is e x t r e m e l y i m p o r t a n t . T h e y n o t e d t h a t treatment of the 5 4 0 ° C c a l c i n e d , l o w - s o d i u m oxide m a t e r i a l ( 3 %

Na 0) 2

with a

s o l u t i o n of a m m o n i u m sulfate at 1 0 0 ° C for a p r o l o n g e d p e r i o d w a s essen t i a l to the s t a b i l i z a t i o n step. I n r e p e a t e d experiments i n w h i c h t h i s m a t e r i a l was subjected to o n l y 2 cycles of 15 to 20 m i n u t e s e a c h of b o i l i n g a m m o n i u m sulfate treatment, the m o l e c u l a r sieve c o l l a p s e d u p o n h i g h t e m p e r a t u r e ( 8 1 0 ° to 9 2 7 ° C ) c a l c i n a t i o n ( 9 ) . O u r s t r u c t u r a l results o n the a m m o n i u m - a l u m i n u m Y ( S t r u c t u r e I I ) m a t e r i a l are i n complete agreement w i t h the a b o v e

findings.

The

com

plete o c c u p a n c y of a l l Ο D positions indicates t h a t the a m m o n i u m sulfate (

treatment serves not o n l y to r e m o v e the r e m a i n i n g s o d i u m ions b u t also to r e h y d r o x y l a t e ( F i g u r e 4, R e a c t i o n I I , Step 1 ) the t r i - c o o r d i n a t e d s i l i c o n atoms. E v i d e n t l y this r e a c t i o n is difficult to affect, a n d the 15-minute treatments are not sufficient to r e h y d r o x y l a t e the m a t e r i a l . S i n c e the 0 u (

oxygens are the p r i s m or b r i d g i n g oxygens, it is u n d e r s t a n d a b l e t h a t h i g h t e m p e r a t u r e c a l c i n a t i o n w o u l d result i n the loss of the s t r u c t u r e w h e n 2 2 % of t h e m are absent.

W e h a v e r e p e a t e d M c D a n i e l a n d M a h e r ' s ex

periment a n d found that the s o d i u m - a l u m i n u m Y (Structure I )

sieve

w h i c h has u n d e r g o n e o n l y t w o 1 5 - 2 0 m i n u t e treatments i n b o i l i n g a m m o n i u m sulfate has a surface area of 300 m / g r a m at 810 ° C a n d less t h a n 2

10 m V g r a m at 927 ° C i n spite of almost c o m p l e t e r e m o v a l of

sodium

oxide. T h e s e values are i n s t r i k i n g contrast to the 700 m / g r a m w h i c h 2

is t y p i c a l of the u l t r a s t a b l e Y sieve.

W e h o p e that f u t u r e x - r a y studies

of the sieve, w h i c h has u n d e r g o n e o n l y t w o 1 5 - m i n u t e a m m o n i u m s u l fate treatments, w i l l v e r i f y t h a t the v a c a n t 0 ι > sites h a v e not b e e n (

filled

i n this m a t e r i a l . Since the structure of u l t r a s t a b l e Y ( S t r u c t u r e I I I ) shows the loss of 15 a l u m i n u m atoms, i t is t h o u g h t t h a t the l a c k of vacancies i n the S i , A l sites i n the a m m o n i u m - a l u m i n u m Y ( S t r u c t u r e I I ) sieve is o w i n g to


21.

Ultrastable

MAHER ET A L .

275

Faujasites

w a t e r m o l e c u l e s or a m m o n i u m ions o c c u p y i n g positions near these holes. I n the s t r u c t u r e of a m m o n i u m - a l u m i n u m Y , there are 13 A l ( O H ) per unit cell.

2 +

ions

B a s e d o n the 38 f r a m e w o r k a l u m i n u m atoms f o u n d i n

S t r u c t u r e I I I , a charge b a l a n c e c a l c u l a t i o n for S t r u c t u r e I I shows that there are o n l y 12 n e g a t i v e charges w h i c h m u s t b e c o m p e n s a t e d .

These

r e m a i n i n g 12 n e g a t i v e charges w o u l d b e b a l a n c e d b y 12 a m m o n i u m ions. Six of these a m m o n i u m ions are l o c a t e d i n S

v

sites. U p o n h e a t i n g this

s a m p l e , the loss of a m m o n i a w o u l d result i n the e v e n t u a l p r o t o n a t i o n of 12 m o r e 0

( 3 )

atoms ( F i g u r e 4, Step I of R e a c t i o n I I I ) .

P r o t o n a t i o n of

Ο 3 ) r a t h e r t h a n a n y of the other o x y g e n atoms w o u l d b e p r e f e r r e d since (

O l s o n a n d D e m p s e y h a v e c o n c l u d e d that i n h y d r o g e n faujasite ( J O ) 32 Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch021

protons are l o c a t e d o n 0

atoms a n d the r e m a i n d e r o n 0 D atoms.

( 3 )

(

S u c h p r o t o n a t i o n easily w o u l d e x p l a i n the results o b t a i n e d for u l t r a stable Y ( S t r u c t u r e I I I ) .

H i g h - t e m p e r a t u r e c a l c i n a t i o n of the

ammo

n i u m - a l u m i n u m sieve results i n the d e h y d r o x y l a t i o n of the s i l a n o l groups to f o r m w a t e r a n d h y d r o x y l groups w h i c h c o u l d react w i t h the A l ( O H )

2 +

species to f o r m a m o r p h o u s a l u m i n a as suggested b y R e a c t i o n I I I , Steps 2 a n d 3, of F i g u r e 4. T h u s , a p p r o x i m a t e l y 27 0

( 3 )

atoms a n d 15 0

atoms

( 4 )

p e r u n i t c e l l w o u l d b e lost o n the basis of the p r o p o s e d m e c h a n i s m s . e x p e r i m e n t a l results s h o w t h e r e m o v a l of 25 0

( 3 )

a n d 13 0 ) ( 4

The

atoms.

I n t e r p r e t a t i o n of these results shows that for the u l t r a s t a b l e Y sieve, l i t t l e or n o c a t i o n i c species are n e e d e d to b a l a n c e the f r a m e w o r k charges. T h e a b o v e reactions ( F i g u r e 4, Steps 2 a n d 3 of R e a c t i o n I I I )

would

result i n 15 S i 0 " a n d 26 A 1 0 " groups i n the f r a m e w o r k w h i c h w o u l d 4

4

b e b a l a n c e d b y the 42 S i 0 the 42 o x y g e n atoms.

3

+

groups p e r u n i t c e l l c r e a t e d b y the loss of

T h i s m a t e r i a l w o u l d h a v e m o r e of a L e w i s a c i d

surface r a t h e r t h a n a B r o n s t e d a c i d t y p e a n d r e h y d r o x y l a t i o n is n o t a c h i e v e d easily. T h e f o r m a t i o n of p r e d o m i n a n t l y L e w i s a c i d a n d base sites w o u l d e x p l a i n the l o w i o n e x c h a n g e a b i l i t y o b s e r v e d b y M c D a n i e l a n d M a h e r i n this m a t e r i a l . B y r e p e a t e d a m m o n i u m sulfate treatments at 100 ° C a n d h i g h - t e m p e r a t u r e c a l c i n a t i o n at 870 ° C , i t is c o n c e i v a b l e t h a t e v e n t u a l l y a m a j o r i t y of the a l u m i n u m c a n be r e m o v e d .

H o w e v e r , to g i v e s t a b i l i t y to the s t r u c

ture, i t is l o g i c a l that transport of s i l i c a f r o m another p o r t i o n of the s a m p l e s h o u l d occur.

T h e results of these 2 p h e n o m e n a are d e p i c t e d b y the

structure f o u n d for the h i g h - s i l i c a Y s a m p l e s t u d i e d ( S t r u c t u r e I V ) . absence of a p p r o x i m a t e l y 12 0 be present.

( 3 )

atoms means that 12 S i 0

3

+

The

groups m u s t

H e n c e , it is possible that there are s t i l l a p p r o x i m a t e l y 12

a l u m i n u m atoms p e r u n i t c e l l present i n the f r a m e w o r k . T h e close agree m e n t of the average ( S i , A l ) - 0 b o n d of 1.610 ( 8 ) A to the v a l u e of 1.603 A g i v e n b y Jones for a p u r e S i - O b o n d supports the r e m o v a l of a m a j o r i t y of the f r a m e w o r k a l u m i n u m . T h e o c c u p a n c y

factor of u n i t y for

the f r a m e w o r k t e t r a h e d r a l sites indicates t h a t these sites m u s t h a v e b e e n


276


r e f i l l e d b y s i l i c o n atoms.

S i n c e these reactions w e r e p e r f o r m e d

under

h y d r o t h e r m a l c o n d i t i o n s w h i c h f a c i l i t a t e the t r a n s p o r t of s i l i c a these suppositions are q u i t e reasonable.

1

(14),

C h e m i c a l analyses s h o w that

the u l t r a s t a b l e Y m a t e r i a l , h i g h - s i l i c a Y , a n d a m m o n i u m - a l u m i n u m Y a l l h a v e essentially the same s i l i c a a n d a l u m i n a content.

T h i s i n d i c a t e s that

the t h e r m a l treatments h a v e c a u s e d the r e m o v e d a l u m i n u m to f o r m some t y p e of i n s o l u b l e , p o l y m e r i c a l u m i n a c o m p o u n d w h i c h w o u l d not

be

r e m o v e d b y the a m m o n i u m sulfate treatments at 100 ° C . Acknowledgment


W e t h a n k R . M . B a r r e r for his v a l u a b l e c o m m e n t s a n d P . H . E m m e t t for his h e l p f u l discussions. W e are i n d e b t e d to the A n a l y t i c a l R e s e a r c h Department

for

chemical

analyses.

N R C - 1 2 F o u r i e r p r o g r a m (1)

Computer

a n d P O W O W (4)

programs

used

were

least squares p r o g r a m .

C o m p u t a t i o n s w e r e d o n e o n the U n i v a c 1108 c o m p u t e r at the U n i v e r s i t y of

Maryland.

Literature Cited (1) Ahmed, F. G., "NCR Crystallographic Programs for the IBM/360 Sys tem," National Research Council of Canada, Ottawa, 1968. (2) Ambs, W. J., Flank, W. H., J. Catalysis 1969, 14, 118. (3) Eulenberger, G. R., Shoemaker, D. P., Keil, J. G., J. Phys. Chem. 1967, 71, 1812. (4) Hamilton, W. C., POWOW, Brookhaven National Laboratory, Brookhaven, New York, 1962. (5) Tones, J. B., Acta Cryst. 1968, Β 24, 355. (6) Kerr, G. T., J. Catalysis 1969, 15, 200. (7) Kerr, G. T., J. Phys. Chem. 1967, 71, 4155. (8) Ibid., 1968, 72, 2594. (9) McDaniel, C. V., Maher, P. K., Conf. Mol. Sieves, Society of Chemical Industry, London, 1967. (10) Olson, D. H., Dempsey, E., J. Catalysis 1969, 13, 221. (11) Rabo, J. Α., Pickert, P. E., Boyle, J. E., U. S. Patent 3,130,006 (1964). (12) Seff, K., Shoemaker, D. P., Acta Cryst. 1967, 22, 162. (13) Uytterhoeven, J. B., Christner, L. G., Hall, W. K., J. Phys. Chem. 1965, 69, 2117. (14) Wyart, J., Sabatier, G., Compt. Rend. 1954, 238, 702. RECEIVED March 24, 1970.

Discussion Hans Villiger ( M a r t i n s w e r k G m b H ,

Bergheim, Germany):

r a t h e r p u z z l e d b y the s m a l l t e m p e r a t u r e factor of 0

3

I

am

w h i c h is persistent

t h r o u g h o u t Structures I—III. C o u l d y o u c o m m e n t o n this situation?


21.

MAHER E T A L .

Ultrastable

277

Faujasites

F . D . H u n t e r : I don't r e c a l l that i t w a s a l w a y s the 0 factor w h i c h was l o w .

3

temperature

I do r e m e m b e r t h a t i n e a c h s t r u c t u r e there w a s

one o x y g e n w h o s e t e m p e r a t u r e factor was u n u s u a l l y l o w .

Generally, i n

the structures, the first five observations h a d m e a s u r e d values w h i c h w e r e l o w e r t h a n the c a l c u l a t e d ones. T h i s is p r o b a b l y o w i n g to e x t i n c t i o n a n d a b s o r p t i o n . I f the d a t a w e r e c o r r e c t e d for these t w o factors, a l l the t e m p e r a t u r e factors p r o b a b l y w o u l d h a v e refined i n t o the e x p e c t e d

values.

D . H . Olson ( M o b i l R e s e a r c h & D e v e l o p m e n t C o r p . , P r i n c e t o n , N . J.) : T h e results r e p o r t e d here are the best s t r u c t u r a l d a t a to date p e r t a i n i n g to the s t r u c t u r a l transformations o c c u r r i n g d u r i n g the p r e p a r a t i o n of u l t r a -


stable faujasite. H o w e v e r , I f e e l the w a r n i n g p r e s e n t e d e a r l i e r b y J . V . S m i t h s h o u l d be k e p t i n m i n d . T h e l a r g e s t a n d a r d deviations of the p o p u l a t i o n parameters w h i c h give site o c c u p a n c i e s

a n d vacancies s h o u l d b e

c o n s i d e r e d w h i l e d e r i v i n g a m e c h a n i s t i c p i c t u r e f r o m the s t r u c t u r a l d a t a . D . J . C . Yates ( E s s o R e s e a r c h C o . , L i n d e n , N . J . 0 7 0 3 6 ) : T h e t e r m " c a l c i n a t i o n " is u s u a l l y t a k e n to m e a n h e a t i n g i n a i r b u t i t c o u l d b e i m p o r t a n t to k n o w i f static a i r or m o v i n g a i r is u s e d . F o r instance, i f static air is u s e d , t h e n one is h e a t i n g the zeolite i n a m i x t u r e of a m m o n i a a n d w a t e r w h i c h w e r e i n t r o d u c e d i n t o t h e zeolite b y the a m m o n i u m sulfate exchange. F . D . H u n t e r : T h e h e a t i n g was d o n e i n a mufHe f u r n a c e . W e t h i n k that w e are s i m u l a t i n g the d e e p - b e d c o n d i t i o n s d e s c r i b e d b y K e r r . P. K . Maher: W e h a v e e x a m i n e d the c a l c i n a t i o n treatment u n d e r c o n t r o l l e d atmospheres a n d h a v e f o u n d that this static mufHe t r e a t m e n t is the same as t r e a t m e n t i n l o w p a r t i a l pressure steam. J . B. Uytterhoeven ( U n i v e r s i t y L e u v e n , 3030 H e v e r l e e , B e l g i u m ) : I n Structures I a n d I I , t h e presence of h y d r o x y l s o n S - I I I positions is p o s t u l a t e d ; i n Structures I I I a n d I V , h y d r o x y l s b e l o n g i n g to A I O ( O H ) o n Site I I are s h o w n . D o y o u h a v e i n f r a r e d or other d a t a w h i c h d e m o n strate a different n a t u r e for these h y d r o x y l s ? J . Scherzer: Since w e c a n expect that O H groups a t t a c h e d to n o n f r a m e w o r k a l u m i n u m w i U absorb i n the same g e n e r a l r e g i o n of the I R s p e c t r u m w h e r e a b s o r p t i o n b a n d s of s t r u c t u r a l h y d r o x y l groups of f a u jasite-type zeolites occur, t h e i r i d e n t i f i c a t i o n w o u l d b e difficult because of possible b a n d o v e r l a p p i n g . T h i s is true e s p e c i a l l y for materials w i t h S t r u c t u r e I I I a n d I V since w e h a v e f o u n d that t h e i r I R s p e c t r a s h o w a rather b r o a d b a n d i n the 3600 c m "

1

region.

G . T . Kerr ( M o b i l Research & Development Corp., Princeton, N . J. ) : I n y o u r p a p e r y o u s a i d , " M c D a n i e l a n d M a h e r r e p o r t e d a decrease i n the i o n exchange c a p a c i t y of ' d e c a t i o n a t e d ' Y sieves. I n v i e w of our r e sults, this decrease p r o b a b l y results f r o m the r e m o v a l of f r a m e w o r k a l u m i n u m , w h i c h was s u b s e q u e n t l y i o n - e x c h a n g e d b y the s o d i u m or silver ions u s e d i n t h e i r e x p e r i m e n t s . " I c a n find n o t h i n g i n the M c D a n i e l a n d


278


1

M a h e r p a p e r w h e r e t h e y s h o w e d r e m o v a l of a l u m i n u m f r o m the zeolite b y i o n exchange.

Please c l a r i f y this p o i n t .

F . D . H u n t e r : I t h i n k w e s a i d " p r o b a b l y " this o c c u r r e d .

However,

w e t h i n k that o u r S t r u c t u r e I I I p r o v i d e s the a n s w e r to the l o w ion-exc h a n g e a b i l i t y w h i c h M c D a n i e l a n d M a h e r observed. W. H . F l a n k ( H o u d r y Laboratories, Marcus Hook, Pa. 19061): Ambs a n d F l a n k w e r e s o m e w h a t m i s q u o t e d i n y o u r p a p e r w h e n i t stated that faujasite s t a b i l i t y was c l a i m e d b y us to be d e p e n d e n t level.

only on sodium

W e c l a i m e d that a continuous d i s t r i b u t i o n of materials existed

w h o s e r e l a t i v e p r o p e r t i e s are a f u n c t i o n of s o d i u m l e v e l . T h i s v i e w w a s


m o r e c l e a r l y d e f i n e d a n d discussed i n a n exchange of letters i n a recent issue of / . Catalysis.

W e r e c o g n i z e the existence of differences i n degree

r a t h e r t h a n differences i n k i n d . S t r u c t u r e I ( N a , A l Y ) is c l a i m e d u n s t a b l e at h i g h e r temperatures. W e p r e p a r e d a n u m b e r of samples of this t y p e a n d f o u n d t h e m to be g e n e r a l l y q u i t e stable, w i t h collapse temperatures h i g h e r t h a n 9 5 0 ° C . W e d i d n ' t use "Step 3" at a l l . P e r h a p s y o u get d e g r a d a t i o n at

810°-

927° because y o u u s e d a p a r t i a l "Step 3" c o m p r i s i n g b r i e f exchange. S i l i c a transport u n d e r h y d r o t h e r m a l conditions is c i t e d to

support

some m e c h a n i s t i c postulations r e g a r d i n g S t r u c t u r e I V . W h y s h o u l d the e x p l a n a t i o n for the o c c u p a n c y factor i n S t r u c t u r e I V be q u a l i t a t i v e l y different t h a n for S t r u c t u r e I I , since S t r u c t u r e I V o n l y r e c e i v e d a n i n tensification of the treatment g i v e n S t r u c t u r e I I ?

T h e t y p e of

hydro-

t h e r m a l e n v i r o n m e n t present c a n h a v e a n i m p o r t a n t b e a r i n g o n this s i l i c a transport p h e n o m e n o n .

I n v i e w of y o u r use of a m m o n i u m sulfate, d i d

y o u i n fact achieve the conditions for transport c i t e d b y W y a r t a n d Sabatier? R e s i d u a l sulfate w o u l d be e x p e c t e d to b e q u i t e persistent i n s u c h a system. A f u r t h e r p o i n t r e g a r d i n g S t r u c t u r e I V is that w e h a v e f o u n d that the l a t t i c e p a r a m e t e r is a s m o o t h f u n c t i o n of the degree of c a l c i n a t i o n severity, so that i t m i g h t be e x p e c t e d to b e s m a l l e r t h a n the lattice p a r a m e t e r for S t r u c t u r e I I I o n that basis alone. F . D . H u n t e r : Y o u h a v e several questions w h i c h I w i l l t r y to answer. I t h i n k y o u are c o m p a r i n g S t r u c t u r e I I a n d S t r u c t u r e I V . T h e s e structures are q u i t e different.

S t r u c t u r e I I r e s u l t e d f r o m a 540 ° C c a l c i n a t i o n a n d

t h e n a r e h y d r a t i o n o w i n g to the a m m o n i u m sulfate treatment. S t r u c t u r e I V r e s u l t e d f r o m r e p e a t e d 100 ° C a m m o n i u m sulfate exchanges a n d c a l c i n a t i o n at 870 ° C . H e n c e , y o u are t r y i n g to c o m p a r e a h y d r a t e d sieve to a c a l c i n e d or d e h y d r a t e d one.

A l s o , since the f r a m e w o r k a l u m i n u m s are

still m i s s i n g i n S t r u c t u r e I I I , t h e y s h o u l d be m i s s i n g i n I I .


Crystal Structures of Ultrastable Faujasites

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