Zeolite Synthesis - American Chemical Society

Chapter 16

Contribution of Propylammonium Species to the Stabilization of the MFI-Type Structure

Downloaded by UNIV OF LEEDS on May 18, 2016 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch016

J. Patarin, H. Kessler, M. Soulard, and J. L. Guth Laboratoire de Matériaux Minéraux, Unité Associée au Centre National de la Recherche Scientifique No. 428, Ecole Nationale Supérieure de Chimie, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France Of the numerous organic species leading to the MFI-structure type, the tetrapropylammonium cations are known to be the most efficient. However few thermodynamic data have been determined to corroborate this experimental result. Three highly siliceous MFI-type samples were synthesized by using a fluoride-containing neutral or slightly acidic medium in the presence of tetra-(TPA+), tri-(TRIPA+), or dipropylammonium (DIPA+) cations. Determination of their solution enthalpy in 25% HF enabled their standard enthalpy of formation to be calculated and hence the contribution of the organic species to the stabilization of the structure could be estimated. The results show, as expected, the following stabilization effects: DIPA+ = TRIPA+ < TPA+. The f a v o r a b l e i n f l u e n c e of organic molecules i n the s y n t h e s i s of MFI-type z e o l i t e s i s w i d e l y r e c o g n i z e d . F o r example. aluminiumcontaining ZSM-5 can be o b t a i n e d a l s o i n the absence of an o r g a n i c template ( L..2K but t h e s y n t h e s i s o f s i l i c a t e I seems t o r e q u i r e the p r e s e n c e o f an o r g a n i c m o l e c u l e i n t h e r e a c t i o n mixture (_3J_. Many s t u d i e s have been devoted t o d e t e r m i n i n g t h e e x a c t r o l e o f these organic species. Stucture d i r e c t i n g e f f e c t s , v o i d - f i l l e r e f f e c t s , and s t a b i l i z a t i o n o f s p e c i f i c secondary b u i l d i n g u n i t s i n t h e s o l u t i o n have been c o n s i d e r e d ( 4-6) . Numerous o r g a n i c s p e c i e s a r e known t o l e a d t o t h e c r y s t a l l i z a tion o f t h e MFI-type s t r u c t u r e ( 7 ) but t h e tetrapropylammonium c a t i o n s can be c o n s i d e r e d t o be the most s p e c i f i c . To our knowledge no thermodynamic data such as s t a n d a r d f o r m a t i o n e n t h a l p i e s (AfH°) and stabilization e n e r g i e s a t t r i b u t e d t o t h e o r g a n i c s p e c i e s have been published t o c o r r o b o r a t e t h i s e x p e r i m e n t a l o b s e r v a t i o n . The p u b l i shed thermodynamic d a t a (AfG°, A f H ° , A f S ° , Cp) a r e f o r n a t u r a l zeolites (8-11) o r f o r o r g a n i c - f r e e s y n t h e t i c z e o l i t e s . However, some data have been o b t a i n e d by c a l c u l a t i o n s u s i n g l a t t i c e energy m i n i m i z a t i o n and extended Hiickel t h e o r y ( 1_2) o r by s e m i - e m p i r i c a l methods based on a d d i t i o n of t h e thermodynamic f u n c t i o n s o f t h e o x i d e compo-

0097-6156/89/0398-0221$06.00A) o 1989 American Chemical Society Occelli and Robson; Zeolite Synthesis ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

222

ZEOLITE SYNTHESIS

nents of the z e o l i t e ( 1_3) and on c o r r e l a t i o n s between thermodynamic data and structural properties (14). In order t o compare the e f f e c t of various organic species, t h r e e h i g h l y s i l i c e o u s MFI-type samples c o n t a i n i n g t e t r a - , t r i - and di-n-propylammonium c a t i o n s Here s y n t h e s i z e d a c c o r d i n g t o the new synthesis r o u t e t h a t He have d e v e l o p e d r e c e n t l y i n our laboratory ( 1 5 - 1 7 ) . In p l a c e of the u s u a l a l k a l i n e r e a c t i o n medium, our s y n t h e s i s uses a n e u t r a l o r s l i g h t l y a c i d i c r e a c t i o n medium i n the p r e s e n ce of f l u o r i d e . In such a medium, F~ a c t s as a s o l u b i l i z i n g agent of silica and of o t h e r o x i d e s o u r c e s , i f any are present, and enters into the c h a n n e l s of the s t r u c t u r e n i t h the o r g a n i c s p e c i e s . Generally, Hell-formed c r y s t a l s are o b t a i n e d without any undesirable a d d i t i o n a l phase. T h i s r o u t e i s p a r t i c u l a r l y i n t e r e s t i n g here because i t a l l o n s the i n c o r p o r a t i o n of t r i p r o p y l a m i n e and dipropylamine i n the c a t i o n i c form comparable t o the c a t i o n i c TPA s p e c i e s . A c c o r d i n g t o the IUPAC recommandations ( 1 8 ) the d e s i g n a t i o n s used f o r the samples are TPA[si]-MFI, TRIPA[si]-MFI and DIPA[si]-MFI. The s t a n d a r d e n t h a l p i e s of f o r m a t i o n of the samples Here o b t a i ned by s o l u t i o n c a l o r i m e t r y i n 25% HF; a l s o the s t a b i l i z a t i o n e f f e c t on the MFI-type s t r u c t u r e of the t h r e e o r g a n i c species could be determined. For comparison, an a l u m i n i u m - c o n t a i n i n g sample TPAJjSi, Al] -MFI Has a l s o s t u d i e d .


+

EXPERIMENTAL The products used f o r the c a l o r i m e t r i c measurements and for the synthesis of the MFI-type m a t e r i a l s Here h i g h p u r i t y reagents: 40% aqueous HF ( P r o l a b o ) ; ( n - C H ) N B r ( F l u k a , purum, 99%); (n-C H ) N ( Fluka, purum, > 98%); ( n-C H ) NH ( Fluka, purum, 99%); n-C H Br (Prolabo, Rectapur, > 97%); A1C1 , 6H 0 ( F l u k a , purum, > 99%); A 1 ( 0 H ) (Merck g i b b s i t e , pure, > 98%); S i 0 ( Degussa, A e r o s i l 1 3 0 , > 3

7

3

4

7

3

2

3

3

7

2

3

98.

7

3

2

5%).

SYNTHESIS The s t a r t i n g molar c o m p o s i t i o n s are g i v e n i n T a b l e I. The r e a c t i o n m i x t u r e Has heated a t 1 7 0 ° C i n a T e f l o n - l i n e d s t a i n l e s s s t e e l a u t o c l a v e f o r 15 t o 50 days depending on the sample.

Table

Sample

Si0

I. S t a r t i n g c h e m i c a l

2

A1C1

3

molar

(C H ) NBr (C H ) N 3

7

4

3

7

3

composition

( C H ) N H NH F 3

7

4

2

HF

H0 2

(40%)

TPA[SÎ]-MFI

1

TPAJjSi, Al] -MFI

1

TRIPA[Si]-MFI

1

/

DIPA[Si]-MFI

1

/

/

0.

033

0.

125

/

/

0.

5

/

30

0.

125

/

/

0.

5

/

30

/

1

/

/

2

30

/

/

1

/

2

30

Occelli and Robson; Zeolite Synthesis ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

16.

PATARIN ET A L

223

Propylammonium Species

For t h e TRIPA[sij -MFI and DIPA[si]-MFI samples, the amines were f i r s t n e u t r a l i z e d w i t h HF; s e e d i n g (4-5 wt % of the s t a r t i n g Si0 ) with finely ground c r y s t a l s was necessary. In t h e case of the TRIPAfsi]-MFI sample, f o r example, the seeds were o b t a i n e d as follows. A f i r s t r e a c t i o n m i x t u r e c o n t a i n i n g t r i p r o p y l a m i n e was seeded with c r y s t a l s of a TPA[si]-MFI sample. A f t e r crystallization, new seeds were t a k e n from the o b t a i n e d c r y s t a l l i n e s o l i d f o r a second synthesis of TRIPA|Si]-MFI. T h e r e f o r e , the q u a n t i t y of seeds of TPA[siJ-MFI still p r e s e n t i n the second seeds and i n the final TRIPA[Si] -MFI sample was n e g l i g i b l e . The same procedure was used f o r the DIPAlSi]-MFI sample. The s y n t h e s i s of the l a t t e r was rather d i f f i c u l t s i n c e t h e MTT-type (19) z e o l i t e KZ-1 (20) forms e a s i l y i n the same s y n t h e s i s c o n d i t i o n s . Only two of f i f t e e n attempts yielded a X-ray pure DIPA[si]-MFI sample.


2

A f t e r h e a t i n g , the s o l i d s were f i l t e r e d , washed with water and d r i e d i n a i r a t 90°C. O p t i c a l and e l e c t r o n microscopy, powder X-ray diffraction, thermal a n a l y s i s and h i g h r e s o l u t i o n solid-state C and S i NMR s p e c t r o s c o p y were used t o check t h e p u r i t y of t h e samples. Chemical a n a l y s e s were performed by u s i n g atomic a b s o r p t i o n s p e c t r o s c o p y ( A l and S i ) and i o n - s e l e c t i v e e l e c t r o d e s ( F ~ and NH ) for F~. TPA , TRIPA and DIPA . The propylammonium cations were first t r a n s f o r m e d i n t o NH by h e a t i n g i n cone. H S0 (180°C, 2 days) i n the presence o f Se as a c a t a l y s t a f t e r t h e s o l i d s had been dissolved i n aqueous HF. The water c o n t e n t of the m a t e r i a l s was determined by thermogravimetry. The c h e m i c a l f o r m u l a per u n i t cell of the a s - s y n t h e s i z e d and of the c a l c i n e d samples i s g i v e n i n T a b l e II. 1 3

2 9

+

4

+

+

+

+

4

2

T a b l e I I . Chemical f o r m u l a per u n i t

4

cell

TPAJ^Si] -MFI

dehydrated

S i

9 6 °192

The o r g a n i c - f r e e [si]-MFI and H [ S i , A l ] - M F I samples were obtained by c a l c i n a t i o n of t h e a s - s y n t h e s i z e d samples performed i n a i r a t 550°C. The H[si,Al]-MFI sample was h y d r a t e d a t room temperature i n a


224

ZEOLITE SYNTHESIS

Hater

vapor atmosphere ( P / P Q = 0.80). p l e s a r e hydrophobic. The water of h y d r a t a t i o n of the tions o c c l u d e d i n the a s - s y n t h e s i z e d samples can be removed i r r e v e r s i b l y . the TRIPAÎjSi]-MFI sample i n argon at TRIPA[Si] -MFl" sample.

The

three other c a l c i n e d

sam-

t r i - and dipropylammonium c a TRI PA [sij-MFI and DIPA[Si]-MFI For i n s t a n c e , the heating of 240°C l e a d s to the dehydrated

CALORIMETRIC MEASUREMENTS S o l u t i o n c a l o r i m e t r y was performed at 298. 2±0.1 Κ by u s i n g a C-80 d i f f e r e n t i a l f l u x c a l o r i m e t e r manufac t u r e d by Setaram. The energy e q u i v a l e n t of the c a l o r i m e t r i c s i g n a l was determined by e l e c t r i c c a l i b r a t i o n . The reliability of the equipment was checked by the d i s s o l u t i o n of t r i s - ( hydroxymethyl) aminomethane (THAM). Agreement w i t h i n 0.4% with the p u b l i s h e d value of +17.75 kJ. mol" ( 21 ) was o b t a i n e d . Both c e l l s ( F i g u r e 1), f o r sample and r e f e r e n c e , made of Kel-F, were d e s i g n e d and manufactured i n our l a b o r a t o r y (22). They c o n s i s t of a body (a) ( i n n e r d i a m e t e r : 17 mm) f i t t e d i n t o the lower part with a t r o u g h ( b) and i n the upper p a r t with a p l u g ( c ) . The whole i s h e l d t o g e t h e r by two b r a s s r i n g s (d,e) which are screwed i n t o the body. The t i g h t n e s s i s ensured by two V i t o n 0 - r i n g s ( f ) . The volume a v a i l a b l e t o HF i s about 6 ml. For the d e t e r m i n a t i o n of the e n t h a l p i e s of d i s s o l u t i o n of so l i d s i n HF, a 5. 5 ml a l i q u o t of 25% HF was p l a c e d i n the sample c e l l and the a c i d was covered with a t h i n l a y e r ( h) of p a r a f f i n o i l ( Prolabo, Rectapur) which i s i n e r t t o HF. The Kel-F c a p s u l e ( g) con t a i n i n g the s o l i d was p l a c e d on the o i l layer. S u f f i c i e n t buoyancy was ensured by the l a t t e r ; any a t t a c k of the sample powder by HF vapor o r by the s o l u t i o n was thus avoided. The r e f e r e n c e c e l l con t a i n e d the same volume of HF than the sample c e l l . The heat of s o l u t i o n of t r i propylamine and of d i p r o p y l a m i n e in HF was determined by u s i n g the same c e l l with some s l i g h t m o d i f i c a t i o n s . I n s t e a d of u s i n g the sample c a p s u l e , the amine was i n t r o d u c e d i n the empty lower trough which was then c l o s e d with a T e f l o n sphe re. Afterwards, the HF was poured i n t o the volume above the sphere. A t h i n V o l t a l e f g r e a s e l a y e r on the sphere ensured a t i g h t s e a l . The heat of r e a c t i o n between t r i p r o p y l a m i n e and p r o p y l bromide was determined by u s i n g the s t a n d a r d commercial stainless steel c e l l s from Setaram. In a l l types of measurements, complete mixing of the reactants was ensured by c o n t i n u o u s t u m b l i n g of the c a l o r i m e t e r block.


1

RESULTS AND

DISCUSSION 1 3

According t o c h e m i c a l a n a l y s i s ( T a b l e II) and CP C MAS NMR spec t r o s c o p y , i t can be c o n c l u d e d t h a t the t h r e e propylammonium cations are o c c l u d e d as i o n p a i r s with F~ i n the c h a n n e l s of the structure of the TPA[Si]-MFI, TRIPA[Si] -MFI and DIPA j"sij-MFI samples. In the case of the two l a t t e r samples, the o r g a n i c c a t i o n s are hydrated ( T a b l e I I ) ; i t w i l l be seen l a t e r t h a t the water m o l e c u l e s c o n t r i b u t e s i g n i f i c a n t l y to the f o r m a t i o n e n t h a l p y of both m a t e r i a l s . Also, CP C MAS NMR s p e c t r o s c o p y shows f o r the DIPA S i -MFI sample a s m a l l amount of TRIPA b e s i d e the DIPA + c a t i o n s (molar TRIPA /DIPA 1 3

+


+

+


16.

PATARIN ET AL.

Propyhmmonium Species

Figure 1. Sample c e l l : a, body; b, trough; c, plug; d, e: b r a s s r i n g s ; f, O-rings; g, c a p s u l e ; h, p a r a f f i n o i l l a y e r ( 2 2 ) .


225

226

ZEOLITE SYNTHESIS +

~ 0.10); d i s p r o p o r t i o n a t i o n of DIPA c o u l d have o c c u r e d under the synthesis c o n d i t i o n s (23). Thermochemical c y c l e s ( F i g u r e 2) i n v o l v i n g the f o r m a t i o n o f compounds (α-quartz, g i b b s i t e , amines, tetrapropylammonium bromide, etc.), t h e d i s s o l u t i o n o f t h e s e compounds and o f the MFI-type sam p l e s i n 25% HF, and t h e d i l u t i o n o f aqueous HF a l l o w the c a l c u l a t i o n of t h e s t a n d a r d e n t h a l p y o f f o r m a t i o n o f t h e samples. As an example, i n T a b l e I I I a r e g i v e n the r e a c t i o n s and t h e corresponding e n t h a l p i e s used f o r t h e d e r i v a t i o n o f t h e s t a n d a r d f o r m a t i o n e n t h a l p y o f the TRIPA[Si]-MFI sample.


T a b l e I I I : Thermochemical scheme f o r t h e d e r i v a t i o n o f t h e s t a n d a r d e n t h a l p y o f f o r m a t i o n o f t h e TRIPAfjSi]-MFI sample

REACTIONS

AH°(kJ)

(1)

9 6 S i ( s ) + 96 0 ( g ) — >

(2)

96cc-Si0

(3)

Β —>

(4)

2H (g) + 2F (g) — >

(5)

4 H F U ) + 13. 3 H O U ) — >

(6)

2N (g) + 36C(s) + 42H ( g) — >

(7)

4(C H ) NU)

( 8)

96Si0 a-quartz

2

-874501136

2

+ 19453. 5HF · 64810. 0H O — >

2

A

2

4HF( I)

2

- 1214.2H.0

4HF · 13.3H 0

2

3

7

+ A —>

3

-

2

4( C3H7) N U )

2

Β

- 244.7 ±4.5

19449. 5HF»64796. 7 H 0 + 4 H F » 1 3 . 3H 0 — > 1 9453.5HF •64810.0H 0

26 22

2

0

22

=0

25

-2286. 6±0. 3

27

2

( 9)

25

70. 60±0. 02 25

- 828.6 ±4.0

3

2

8

+1 3623. 7±93. 2 22

2

2

24

-1 3016. 6±1 7. 3

C + 19449. 5HF · 64802. 0H O

2

Ref

19449.5HF»64802.0H O — > 19449.5HF«64796.7H 0 +5. 3H 0 (£) 2

2

2

( 10) 4 0 ( g )

+ 8H (g) — >

2

8H 0(A)

2

2

Δ H ° ( T R I P A [ S i ] -MFI) = Δ Η ° + Δ Η ° Γ

9

10

+ ΔΗ° + ΔΗ° + ΔΗ° + ΔΗ° +ΔΗ° + ΔΗ° + 4

5

8

1

6

2

ΔΗ°7+ΔΗ°3 = -91487.6 ± 165.8 kJ. mol" A = 96H SiF 2

6

18877.5HF

1

65002.0H O 2

Β = 4£(C H7) NH+J(aq)-»-4F"~(aq)+96H SiF »18873. 5HF»65002. 0H 0 3

3

2

C =[(C H ) NH]4Si9 0 3

7

3

6

1 9 2

F4( H 0) 2

6

2

8



16. PATARIN ET AL.

A H°(Z)

Elements

As-synthesized or

f

•

calcined

( S i , 0 , H , C, F , N ,. . . ) 2

2

in


2

sample ( Z)

2

Σ A

F

H°( compounds)

q u a r t z , amino compounds, g i b b s i t e , . . .

Δ

Σ

H

2

s i F

3

6 ( aq) + A 1 F " 6

Δ Η°(Ζ) Γ

= Σ

(a

q

)

3 Ο 1

Γ

H

z

s o l . °< >

Η°(compounds)

+propylammonium

Δ ΗΟ(ΟΟΠΦ.

A

) + Σ

A

G

O

L

( a

Η°(

q

)

+F~

( a q )

comp. ) -

.

Δ

Η

δ

ο1. °

( ζ )

F i g u r e 2. Thermochemical c y c l e c o n s i d e r e d f o r t h e d e r i v a t i o n o f the s t a n d a r d f o r m a t i o n e n t h a l p y o f t h e MFI-type samples ( Z ) .


228

ZEOLITE SYNTHESIS

The standard f o r m a t i o n e n t h a l p y of many compounds ( H 0 ( £ ), (C H7)3N ( , e t c . ) t a k i n g p a r t i n the c y c l e s are t a k e n from the literature. The s t a n d a r d e n t h a l p y of f o r m a t i o n of TPABr ( t a k i n g part i n the c y c l e s r e l a t i v e t o the TPAJjSi]-MFI and T P A [ s i , Al] -MFI samples i s not a v a i l a b l e ; t h e r e f o r e , i t had t o be determined. Follo wing the s y n t h e s i s of tetraalkylammonium bromides and i o d i d e s ( 2 8 ) , the r e a c t i o n of f o r m a t i o n of TPABr Has c a r r i e d out i n butanone on s t a r t i n g w i t h t r i p r o p y l a m i n e and p r o p y l bromide. The o t h e r r e a c t i o n s t h a t were considered a r e the d i s s o l u t i o n of TPABr, ( ( ^ 7 ) 3 ^ and C H.7Br i n butanone. The v a l u e o b t a i n e d f o r A H°( TPA Br) i s -322. 9± 1.0 kJ. m o l " . 2

3

3

f

1


STANDARD SOLUTION ENTHALPY The measured s t a n d a r d s o l u t i o n e n t h a l p y of α-quartz and of the a s - s y n t h e s i z e d and the c a l c i n e d MFI-type sam p l e s a r e as f o l l o w s : Sample ( per

Asol.H° 96 T 0 ,

(kJ) T=Alv Si)

2

α-quartz

-13245. 1±48. 0

T P A [ s i ] -MFI

-12653. 0±89. 0

TRIPAJjSi] -MFI

-13623. 7±93. 2

T R I P A [ s i ] -MFI, DIPA[Si]

dehydrated

-1 3527. 5±91.2 -13688. 6±25. 9

-MFI

TPAJjSi, Al] -MFI

-12628. 8±26. 8

H[Si,

Al] -MFI

-13054. 8±29. 5

[Si]

-MFI

-1 3250. 8±86. 5

The s t a n d a r d d e v i a t i o n of the mean i s e x p r e s s e d by (Tj= VS( χ^-χ) / n ( n-1 ), nhere Σ ( χ ^ - χ ) i s the sum of the squares of the d e v i a t i o n s from the mean v a l u e χ and η the number of measure ments ( 30). The s o l u t i o n e n t h a l p y of α-quartz found here ( A o l . ° "137.97 ±0.52 kJ. m o l " S i 0 ) i s s l i g h t l y l a r g e r than the v a l u e p u b l i s h e d by Johnson e t a l . ( 8) (-135.59±0.18 kJ. m o l " ) . For our f u r t h e r calcu l a t i o n s we have chosen t h i s p u b l i s h e d v a l u e s i n c e our q u a r t z sample c o n t a i n e d t r a c e s of c r i s t o b a l i t e . There i s a s 4% d i f f e r e n c e betneen our v a l u e of the solution enthalpy of the h i g h l y s i l i c e o u s c a l c i n e d [ s i ] -MFI sample and the v a l u e p u b l i s h e d r e c e n t l y by Johnson e t a l . ( 29) f o r the dissolution i n 24. 456 HF of a sample of s i l i c a l i t e I p r e p a r e d i n a l k a l i n e medium i n the absence of f l u o r i d e (-144.93±0.18 k J / S i 0 f o r a S i 0 / H F r a t i o equivalent to the r a t i o used h e r e ) . Such a difference could be r e l a t e d t o the n a t u r e of the samples and t o morphology differences. Our c a l c i n e d sample c o n t a i n e d t r a c e s of f l u o r i n e nhereas the s i l i c a 2

2

H

=

S

1

2

1

2

2


16.

PATARIN ET AL.


229

l i t e I sample s t u d i e d by Johnson e t a l . ( 2 9 ) was p r e p a r e d i n a l k a l i n e medium i n the presence o f TPAOH, which may have c o n t a i n e d the usual KOH i m p u r i t y . Such an a l k a l i n e compound, which s t i l l may be present in the c a l c i n e d s o l i d c o u l d l e a d t o an i n c r e a s e i n the solution heat. The c r y s t a l s i z e of our sample (80x40x20 gm ) Has much larger than the s i z e (4um) of the sample s t u d i e d by Johnson e t a l ( 29). 3

STANDARD ENTHALPY of FORMATION The s t a n d a r d e n t h a l p i e s of forma t i o n o f the a s - s y n t h e s i z e d and the c a l c i n e d samples a r e as f o l l o n s : H° ( k J per 9 6 T O 2 )


Sample

TPA[si]-MFI

-89925. 0±163. 5

TRIPA[Si] -MFI

-91487. 6±165. 8

TRIPA[Si] -MFI

-89297. 2±164. 7

DIPA[Si] -MFI

-91 308. 3±1 39. 5

TPA[Si, Al]-MFI

-89317. 0±136. 0

H[Si,

-95976. 2±138. 4

Al]-MFI

[Si] -MFI

-87216. 6±1 62. 1

The u n c e r t a i n t y i c ) of Δ^Η° g i v e n above i s e q u a l t o t h e square root of the sum of the s q u a r e s of t h e s t a n d a r d d e v i a t i o n s of the means f o r the i n d i v i d u a l r e a c t i o n s t a k i n g p a r t i n t h e thermochemical cycle considered \/Σ σ χ ^ ( 30). The e n t h a l p y term can be c o n s i d e r e d here as g i v i n g a direct measure o f the l a t t i c e energy. Comparison of the A H ° values ac c o u n t s f o r the v a r i a t i o n s of l a t t i c e energy and hence f o r the s t a b i l i t y of the s t r u c t u r e o f the samples. The a s - s y n t h e s i z e d TPAjjSi] -MFI sample appears t o be slightly more s t a b l e than the a l u m i n i u m - c o n t a i n i n g TPA[si, Al]-MFI sample. T h i s r e s u l t i s i n agreement n i t h the s e m i - e m p i r i c a l c a l c u l a t i o n s of Ooms et a l . ( 12) n h i c h shon t h a t i n the absence of nater, the aluminiumr i c h samples a r e l e s s s t a b l e than the p u r e l y s i l i c e o u s ones. Honever the o b s e r v e d d i f f e r e n c e betneen t h e A H ° v a l u e s i s s m a l l because the aluminium c o n t e n t o f the TPAJj3i, Al] -MFI sample i s not very high ( S i / A l = 31). On t h e o t h e r hand, i n agreement n i t h the nork o f B a r r e r ( 31 ), i t i s found f o r the c a l c i n e d samples t h a t the H [ s i , A l ] - M F I sample i s more s t a b l e than the h i g h l y s i l i c e o u s [si] -MFI one; t h e h y d r a t i o n of the compensating c a t i o n s i n c r e a s e s the s t a b i l i t y of the structure. The AfH°= -908.5±1.7 kJ. mol"" S i 0 f o r the [Si]-MFI sample i s s l i g h t l y l a r g e r ( a b s o l u t e value) than the v a l u e d e t e r m i n e d f o r s i l i c a l i t e I by Johnson e t a l . ( 29) by f l u o r i n e - c o m b u s t i o n c a l o r i m e t r y (-905.20 ±0.84 kJ. mol" S i 0 ) . V i e i l l a r d ( 14) has p u b l i s h e d a s m a l l e r value (-900.45±0.28 kJ. mol" S i 0 ) n h i c h Has not d e t e r m i n e d calorimetrit

2

f

f

1

2

1

2

1

2


230

ZEOLITE SYNTHESIS

cally but s e m i - e m p i r i c a l l y by u s i n g correlations between thermodynamic d a t a ^ a n d s t r u c t u r a l p r o p e r t i e s such as mean S i - 0 bond l e n g t h , mean S i O S i a n g l e and t h e p o l a r i z a b i l i t y o f S i and 0. The magnitude o f A f H ° f o r t h e a s - s y n t h e s i z e d DIPA[Si]-MFI and TRIPA [Si]-MFI samples i s l a r g e r than f o r t h e T P A f s i ] - M F I sample; t h i s o b s e r v a t i o n i s unexpected. I n f a c t AfH° t a k e s i n t o account the e n t h a l p y o f f o r m a t i o n o f t h e water o c c l u d e d i n t h e DIPA[si]-MFI and TRIPA [ S i ] - M F I samples. The AfH° of both dehydrated samples a r e s l i g h t l y d i f f e r e n t , and t h e o r d e r o f i n c r e a s i n g magnitude o f AfH° i s then as expected:


DIPA[si]-MFI

dehydr.

s T R I P A [ s i ] - M F I dehydr. < T P A [ S Î ] - M F I .

A good e s t i m a t e o f t h e c o n t r i b u t i o n o f t h e o r g a n i c s p e c i e s the s t a b i l i z a t i o n o f t h e a s - s y n t h e s i z e d samples may be o b t a i n e d c o n s i d e r i n g t h e f o l l o w i n g i n i t i a l and f i n a l s t a t e s :

+

[Si]-MFI( s) t 4 T P A ( aq)+4F"( aq)

to by

> T P A [ s i ] - M F K s)

[Si]-MFI(s>+4TRIPA+(aq)+4F"(aq)+8H 0( £)

> TRIPA [ S i ] - M F K s)

2

+

[Si]-MFI(s)+4.8DIPA (aq)+4.8F~(aq)+6.5H OU) 2

> DIPA Csi] -MFK s)

By u s i n g t h e f o l l o w i n g s t a n d a r d f o r m a t i o n e n t h a l p i e s t h a t o b t a i n e d from v a r i o u s thermochemical c y c l e s ( t h i s work): +

were

1

Af H° ( T P A ( a q ) , F"( aq) ) = - 527.9±1.1 kJ. m o l " AfH° ( TRIPA ( aq), F~( aq) ) = - 604.0±1.5 kJ. m o l " AfH° ( D I P A ( a q ) , F"( aq) ) = - 571.211.2 kJ. m o l " +

+

1

1

1

the ΔΗ° o f s t a b i l i z a t i o n a r e -596.8±230.3 kJ. m o l " , +431.6±231.9 kJ. mol" and + 508. 0±21 3. 9 kJ. m o l " f o r t h e TPAJjSi] -MFI, TRIPA[si]MFI and D I P A [ s i ] - M F I samples r e s p e c t i v e l y . I t a p p e a r s t h a t t h e TPA F i o n p a i r o n l y c o n t r i b u t e s s i g n i f i c a n tly t o t h e s t a b i l i z a t i o n o f t h e MFI s t r u c t u r e . T h i s result agrees with the observed s p e c i f i c i t y of the t h r e e organic species with respect t o t h e M F I - s t r u c t u r e type. The tetrapropylammonium species l e a d t o t h e MFI-type s t r u c t u r e alone, whereas t h e two o t h e r species l e a d a l s o t o t h e s t r u c t u r e t y p e s MEL ( 32) and MTT r e s p e c t i v e l y . 1

1

CONCLUSION The d e t e r m i n a t i o n o f t h e s t a n d a r d e n t h a l p y o f f o r m a t i o n o f t h e as-synthesized and c a l c i n e d h i g h l y s i l i c e o u s MFI-type samples made it p o s s i b l e t o e s t i m a t e t h e i n t e r a c t i o n between t h e framework and the o r g a n i c s p e c i e s . T h i s i n t e r a c t i o n i s s i g n i f i c a n t i n t h e case o f the TPAF s p e c i e s o n l y , due presumably t o t h e i r neat f i t i n t o t h e channels. F o r t h e a l u m i n i u m - c o n t a i n i n g sample, t h e s t a b i l i z i n g e f f e c t o f water m o l e c u l e s , when o c c l u d e d i n t h e c h a n n e l s , was eviden ced.


16. PATARIN ET AL.


231


LITERATURE CITED

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RECEIVED December 22, 1988


Zeolite Synthesis - American Chemical Society

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