Phosphorus Substitution in Zeolite Frameworks

6 Phosphorus Substitution in Zeolite Frameworks

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EDITH M. FLANIGEN and ROBERT W. GROSE Union Carbide Corp., Linde Division Laboratory, Tarrytown Technical Center, Tarrytown, Ν. Y. 10591 Zeolites containing phosphorus in the tetrahedral site in the framework have been synthesized. Phosphorus incorpora tion in a variety of structural types of zeolite frameworks has been achieved: analcime, phillipsite, chabazite, Type A zeolite, Type L zeolite, and Type Β (P) zeolite. The syn theses and properties of some of the new aluminosilicophosphate zeolites are described. The synthesis technique in volves gel crystallization where incorporation of phosphorus is accomplished by controlled copolymerization and coprecipitation of all the framework component oxides, aluminate, silicate, and phosphate, into a relatively homogeneous gel phase. Subsequent crystallization of the gel is carried out at temperatures in the region of 80° to 210°C. Proof and mechanism of framework substitution of phosphorus is based on electron microprobe analysis, infrared spectroscopy, and other characterization. " p h e polymorphs of silica—quartz, tridymite, etc.—exist as infinite threedimensional frameworks formed by corner-sharing [Si0 ] tetrahedra. Tetrahedra of [A10 ] may, by isomorphous substitution, replace [Si0 ] to form aluminosilicates with the excess negative charge neutralized by an alkali or alkaline earth cation. Phosphorus (P ) also exhibits tetra hedral coordination with oxygen anions to form [ P 0 ] tetrahedra and complex three-dimensional frameworks. The space dimensions of [ P 0 ] and [Si0 ] are similar, and the oxygen chemistry of phosphorus is similar to that of silicon. It therefore seems possible that [ P 0 ] could isomorphously replace [Si0 ] in the silicate crystal framework. Few instances of isomorphous replacement of [Si0 ] by [ P 0 ] have been found in mineral silicates. The mineral viseite, containing [ P 0 ] in

/

4

4

4

5+

4

4

4

4

4

4

4

4

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

6.

Phosphorus

F L A N I G E N A N D GROSE

77

Substitution

a d d i t i o n to [ A 1 0 ] a n d [ S i 0 ] , has a structure analogous to a n a l c i m e 4

(10).

4

T h e m i n e r a l kehoeite is a n a n a l o g u e of the a n a l c i m e structure b u t

is a c o m p l e x z i n c a l u m i n o p h o s p h a t e c o n t a i n i n g [ A 1 0 ] a n d [ P 0 ] 4

(II).

4

P h o s p h a t e t e t r a h e d r a r e p l a c e some [ S i 0 ] i n g r i p h i t e , a p h o s p h a t e garnet 4

( 1 2 ) , a n d [ S i 0 ] r e p l a c e some [ P 0 ] 4

4

i n apatite ( 9 ) .

Barrer and M a r

s h a l l r e p o r t e d unsuccessful attempts to synthesize p h o s p h o r u s - c o n t a i n i n g zeolites ( 2 ) .

K u h l has r e p o r t e d the effect o f p h o s p h a t e c o m p l e x i n g of

a l u m i n u m i n zeolite c r y s t a l l i z a t i o n ( 7 )

a n d the synthesis of a z e o l i t e

Z K - 2 1 containing "intercalated" phosphate w i t h a crystal structure similar to zeolite A

(8).


A n u m b e r of c o m p o u n d s are r e l a t e d i n t h e i r c r y s t a l structures to the p o l y m o r p h s of s i l i c a (6).

T h e s e substances c a n b e a r r a n g e d i n t o 3 cate

gories o n the basis of s t r u c t u r a l r e l a t i o n s h i p : s i m p l e analogues, stuffed d e r i v a t i v e s , a n d c o u p l e d d e r i v a t i v e s . A n e x a m p l e of a s i m p l e analogue of s i l i c a is g e r m a n i u m d i o x i d e . G e r m a n i u m has b e e n s u b s t i t u t e d for s i l i c o n successfully i n zeolite f r a m e w o r k s b y s e v e r a l researchers, as w e l l as g a l l i u m for a l u m i n u m ( I ) . NaAlSi0

4

E x a m p l e s of the stuffed d e r i v a t i v e s are

(high-carnegieite) and K A l S i 0

4

( k a l s i l i t e ) , w h e r e ions of a p

p r o p r i a t e size are i n t r o d u c e d into v a c a n t i n t e r s t i t i a l positions i n the S i 0

2

structure t y p e . T h e c o u p l e d d e r i v a t i v e s are r e p r e s e n t e d b y A 1 P 0 , G a P 0 , A l A s 0 , 4

4

4

F e P 0 , a n d others w h i c h y i e l d n e u t r a l f r a m e w o r k s w i t h similarities to 4

various s i l i c a c r y s t a l structures. T h e f o r m a t i o n of a n A l P 0 - t y p e c o m 4

p o u n d i n the zeolite synthesis g e l a p p e a r e d to b e a reasonable a p p r o a c h to the synthesis of p h o s p h o r u s - s u b s t i t u t e d zeolites.

Experiments there

fore w e r e i n i t i a t e d to a t t e m p t the i s o m o r p h o u s s u b s t i t u t i o n of [ P 0 ] 4

in

zeolite structures u s i n g the l o w - t e m p e r a t u r e a n d pressure h y d r o t h e r m a l g e l systems g e n e r a l l y e m p l o y e d i n zeolite synthesis i n the U n i o n C a r b i d e laboratories These

(4). experiments w e r e

successful i n s y n t h e s i z i n g a l u m i n o s i l i c o -

p h o s p h a t e zeolites w i t h the f o l l o w i n g types of zeolite f r a m e w o r k s : a n a l c i m e , c h a b a z i t e , p h i l l i p s i t e - h a r m o t o m e , T y p e A zeolite, T y p e L zeolite, a n d T y p e Β ( Ρ ) zeolite, a l l of w h i c h c o n t a i n e d significant amounts of phosphorus

(5-25 wt %

P 0 ) i n c o r p o r a t e d i n the c r y s t a l f r a m e w o r k . 2

3

Species r e l a t e d to the f e l s p a t h o i d s , sodalite a n d c a n c r i n i t e , w e r e also s y n t h e s i z e d a n d c o n t a i n e d p h o s p h a t e detected b y c h e m i c a l analysis. F r a m e w o r k s u b s t i t u t i o n was not v e r i f i e d for these m a t e r i a l s , as t h e y n o r m a l l y c o n t a i n v a r i o u s i n t e r c a l a t e d salts i n their structure. Zeolites s t r u c t u r a l l y analogous to g m e l i n i t e ( T y p e S ), m o r d e n i t e , T y p e X , a n d T y p e Y zeolites w e r e s y n t h e s i z e d i n the s o d i u m a l u m i n o s i l i c o p h o s p h a t e system b u t c o n t a i n e d o n l y s m a l l amounts of p h o s p h a t e ( < 5 w t % P2O5). I n this w o r k , c h a r a c t e r i z a t i o n of the p h o s p h o r u s - s u b s t i t u t e d species was

performed

o n l y o n those w h i c h c o n t a i n e d a p p r e c i a b l e amounts of p h o s p h o r u s ( > 5

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

78

M O L E C U L A R SIEVE ZEOLITES

wt %

P2O5)

1

i n a n attempt to r e d u c e possible m i s i n t e r p r e t a t i o n of the

d a t a o w i n g to the presence of extraneous phosphate. T h e n o m e n c l a t u r e u s e d t h r o u g h o u t this p a p e r designates the s t r u c t u r a l t y p e b y t h e letter of the most closely r e l a t e d p h o s p h o r u s - f r e e s y n t h e t i c zeolite as u s e d i n the U n i o n C a r b i d e laboratories (4, 5 ) .

Table II

i n Ref. 5 contains a d e s c r i p t i o n of the s y n t h e t i c zeolites d e s c r i b e d here. F o r the a l u m i n o s i l i c o p h o s p h a t e zeolites, these letter designations are p r e fixed

b y Ρ to i n d i c a t e t h a t the z e o l i t e f r a m e w o r k contains

phosphorus

s u b s t i t u t e d i n the t e t r a h e d r a l ( S i , A l ) site. F o r e x a m p l e , the p h o s p h a t e z e o l i t e s t r u c t u r a l l y r e l a t e d to T y p e A z e o l i t e is d e s i g n a t e d Ρ—A; P—R zeo lite is the p h o s p h a t e z e o l i t e r e l a t e d to zeolite R , a s y n t h e t i c s o d i u m Downloaded by UNIV OF MINNESOTA on June 4, 2013 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch006

a l u m i n o s i l i c a t e zeolite w i t h a c h a b a z i t e t y p e f r a m e w o r k structure T h e a l u m i n o s i l i c o p h o s p h a t e zeolites w i l l be a b b r e v i a t e d to

(5).

phosphate

zeolites or p h o s p h o r u s - s u b s t i t u t e d zeolites t h r o u g h o u t this p a p e r . Synthesis T h e synthesis t e c h n i q u e i n v o l v e s g e l c r y s t a l l i z a t i o n w h e r e i n c o r p o r a t i o n of p h o s p h o r u s is a c c o m p l i s h e d b y c o n t r o l l e d c o p o l y m e r i z a t i o n a n d c o p r e c i p i t a t i o n of a l l the f r a m e w o r k c o m p o n e n t oxides, a l u m i n a t e , silicate, a n d p h o s p h a t e , into a r e l a t i v e l y h o m o g e n e o u s g e l phase.

Subsequent

c r y s t a l l i z a t i o n of the g e l is c a r r i e d out at temperatures i n the r e g i o n of 80° to 210 ° C .

T y p i c a l compositions of the gels i n moles are g i v e n i n

T a b l e I, a n d the synthesis p r o c e d u r e is d e s c r i b e d b e l o w for the major phosphate zeolite species. Zeolite P - C (Analcime Structure T y p e ) . Z e o l i t e P - C was c r y s t a l l i z e d f r o m s o d i u m a l u m i n o s i l i c o p h o s p h a t e gels p r e p a r e d b y s i m u l t a n e o u s l y Table I.

Typical Synthesis Conditions for Crystallizing Phosphorus-Substituted Zeolites

Beactant Composition Zeolite P-C w G R A L Β (Ρ)

Na O 2

KO

a

2

a

>0.5 >0.5 >0.5 >1.2 >1.8

>1.0

>0.4

Al 0 2

3

1.0 1.0 1.0 1.0 1.0 1.0 1.0

in

Moles

Si0

PO

HO

0.6 1.6 1.0 1.8 1.6 1.5 0.6

0.5 0.5 0.5 0.9 1.1 1.0 0.7

> 55 >110 >110 >110 >110 >110 >110

2

2

b

2

a

Crystallization Temp., °C

Crystallization Time, Hrs.

210 150 150 125 125 175 200

160 68 116 94 45 166 70

Values for N a 0 , K 0 , and H 0 are slightly higher than the values shown and undetermined because of unknown quantities absorbed on the precipitated hydrous aluminophosphate gel. a

2

2

2



6.

Phosphorus


79

Substitution

Figure 1. Partial reaction composition diagram. Projection of the Na 0, Al 0 , Si0 P0, H 0 system at 100°-125°C. Na 0 + Si0 + P 0 = 100 mole %. Al O = 12-20 mole % of the total anhydrous gel composition; mole H 0/Al 0 is constant (= 110). A solid colloidal silica ("Cah-O-Sil") is the silica source. 2

2

5

2

3

2>

2

2

9

2

2

5

2

2

s

3

Figure 2. Same as Figure 1 with a crystallization temperature of 125°-150°C and an aqueous colloidal silica source ("Ludox"). Al 0 = 17-23 mole %. 2

3

a d d i n g aqueous solutions of s o d i u m m e t a s i l i c a t e a n d p h o s p h o r i c a c i d to a n aqueous s o l u t i o n of A 1 C 1 w i t h a g i t a t i o n . T h e p H of the p r e c i p i t a t i n g s o l u t i o n was a d j u s t e d to 7.5 b y t i t r a t i o n w i t h c o n c e n t r a t e d N a O H s o l u tion. T h e resultant precipitate was separated b y v a c u u m filtration, washed w i t h d i s t i l l e d w a t e r , a n d p l a c e d i n a T e f l o n - l i n e d stainless steel autoclave. A p r e d e t e r m i n e d a m o u n t of N a O H s o l u t i o n w a s a d d e d . T h e g e l w a s c r y s t a l l i z e d at a b o u t 1 7 5 ° - 2 1 0 ° C a n d autogenous pressure for 9 0 - 1 6 0 hours. M a x i m u m p h o s p h o r u s contents of 25 w t % were achieved in zeolite P - C . 3

P2O5


80


1

Zeolite P - W (Phillipsite-Harmotome Structure T y p e ) . T h e P - W synthesis g e l was p r e p a r e d b y t i t r a t i n g a n aqueous s o l u t i o n of A 1 C 1 a n d p h o s p h o r i c a c i d w i t h c o n c e n t r a t e d K O H s o l u t i o n to a p H of 7.5. T h e p r e c i p i t a t e w a s filtered, w a s h e d w i t h d i s t i l l e d w a t e r , a n d t h e n b l e n d e d w i t h " L u d o x , " a n aqueous s i l i c a sol, a n d K O H s o l u t i o n . T h e r e a c t i o n m i x t u r e was c r y s t a l l i z e d at 1 5 0 ° - 1 7 5 ° C a n d autogenous pressure for a b o u t 72 h o u r s . T h e use of a s i l i c a sol as the s i l i c a source appears to f a v o r the f o r m a t i o n of P - W zeolite over coexisting phases s u c h as P - G or P - L zeolites. P h o s p h o r u s contents u p to 20 w t % Ρ 2 θ w e r e f o u n d i n zeolite P - W . Zeolite P - R and P - G (Chabazite Structure T y p e ) . Z e o l i t e P - G was c r y s t a l l i z e d f r o m p o t a s s i u m a l u m i n o s i l i c o p h o s p h a t e gels p r e p a r e d b y the same p r o c e d u r e u s e d i n the p r e p a r a t i o n of P - W g e l . Zeolite P - R was c r y s t a l l i z e d i n the s o d i u m system b y u s i n g N a O H i n p l a c e of K O H . T h e reactant g e l was c r y s t a l l i z e d at 1 2 5 ° - 1 7 5 ° C a n d s a t u r a t e d w a t e r v a p o r pressure for 4 8 - 1 2 0 hours. Z e o l i t e P - G c o n t a i n i n g u p to 21 w t % P 0 , a n d zeolite P - R c o n t a i n i n g u p to 16 w t % P 0 w e r e synthesized. Zeolite P - A ( A Structure T y p e ) . T h e reactant c o m p o s i t i o n for P - A z e o l i t e was p r e p a r e d i n the same m a n n e r as t h a t for the synthesis of P - W or P - R zeolites u s i n g N a O H s o l u t i o n as the t i t r a n t a n d solvent. P - A z e o l i t e also was c r y s t a l l i z e d f r o m s o d i u m a l u m i n o s i l i c o p h o s p h a t e gels p r e p a r e d b y simultaneous a d d i t i o n of N a A 1 0 - N a O H s o l u t i o n a n d s o l u t i o n to a n a g i t a t e d aqueous s l u r r y of " C a b - O - S i l , " a c o l l o i d a l s i l i c a p o w d e r . T h e synthesis g e l was c r y s t a l l i z e d at 1 0 0 ° - 1 5 0 ° C a n d autogenous pressure for 2 4 - 9 6 hours. T h e " C a b - O - S i l " s i l i c a source favors the c r y s t a l l i z a t i o n of P - A z e o l i t e over zeolites s u c h as P - R or P - B . Z e o l i t e P - A c o n t a i n i n g u p to 10 w t % P 0 was p r e p a r e d . Zeolite P - L ( L Structure T y p e ) . Zeolite P - L w a s s y n t h e s i z e d f r o m a l u m i n o s i l i c o p h o s p h a t e gels p r e p a r e d b y t h e p r o c e d u r e d e s c r i b e d for z e o lites P - W a n d P - G u s i n g K O H s o l u t i o n as the source of base. T h e use of a s o l i d s i l i c a source s u c h as " C a b - O - S i l " facilitates the f o r m a t i o n of P - L 3


5

2

2

H3PO4

5

2

2

5

Figure 3. Same as Figure 1 with a crystalliza tion temperature of 150°C and a "Cab-O-Sil" silica source. Al O = 14-18 mole %. 2

s


5

6.


Phosphorus Substitution

81

zeolite r a t h e r t h a n P - W or P - G zeolite. T h e g e l was c r y s t a l l i z e d at 1 5 0 ° 175 ° C a n d autogenous pressure for 7 2 - 1 7 0 hours. Z e o l i t e P - L c o n t a i n i n g u p to 19 w t % P 0 was s y n t h e s i z e d . Zeolite P - B (B or Ρ Structure T y p e ) . Z e o l i t e P - B was c r y s t a l l i z e d f r o m c o p r e c i p i t a t e d gels u s i n g N a O H s o l u t i o n as the t i t r a n t a n d " L u d o x " c o l l o i d a l s i l i c a sol. T h e g e l w a s c r y s t a l l i z e d at 1 5 0 ° - 2 0 0 ° C for 4 5 - 7 2 hours. P h o s p h o r u s contents u p to 23 w t % P 0 w e r e a c h i e v e d i n P - B zeolites. 2

5


2

5

Figure 4. Partial reaction composition dia gram. Projection of the K 0, Al 0 , Si0 P 0 , H 0 system at 150°C~ K 0 + Si0 + Ρ JO. = 100 mole %. Al 0 = 24-42 mole % of the total anhydrous gel composition; mole H 0/Al 0 constant (= 110). "Ludox" is the silica source. 9

2

5

2

2

2

2

2

2

3

2f

2

3

3

Figure 5. Same as Figure 4 with a crystalliza tion temperature of 175°C and a "Ludox" or "Cab-O-Sil" silica source. Al 0 = 12-25 mole %. 2

3


82


Table II.

T y p i c a l X - R a y Powder Diffraction


P-C

P-W

d, A

I/Io

d, A

I/Io

5.64 4.87 3.68 3.44 3.27 2.93 2.81 2.70 2.51 2.37 1.91 1.87 1.75 1.72 1.70

80 16 6 100 3 45 6 14 13 8 8 5 12 3 3

10.2 8.3 7.2 5.40 5.07 4.51 4.31 4.11 3.68 3.25 3.19 2.96 2.80 2.75 2.69 2.57 2.46 2.20 2.08 1.79 1.78 1.73

18 42 61 17 29 27 23 19 18 71 100 45 16 39 18 23 10 8 4 5 6 8

Figure 6.

1

Optical photomicrographs

of phosphate zeolites

Plate 1 Zeolite P-C (12.9 wt % P O ) 200X Plate 3 Zeolite P-B (21.1 wt % P O ) 200X Plate 2 Zeolite P-C (17.5 wt % P O ) 150X Plate 4 Zeolite P-W (14.3 wt % P O ) 600X 2

2

s

s


2

s

2

s

6.

83

Phosphorus Substitution

F L A N I G E N AND GROSE

D a t a for Phosphate Zeolites P - C , P - W , P - R , P - G


P-G

P-R

d, A

I/Io

d, A

I/Io

9.46 6.97 5.61 5.10 4.72 4.53 4.36 4.15 4.02 3.90 3.62 3.48 3.25 3.14 2.95 2.92 2.71 2.64 2.54 2.33 2.11 1.89 1.82 1.73

100 21 17 21 10 5 74 7 9 43 28 16 12 10 95 53 9 19 14 9 7 8 14 12

9.46 6.94 5.59 5.09 4.72

100 29 10 32 9

-

-

2.94

-

-82

2.71 2.62 2.53 2.32 2.10 1.89 1.82 1.73

-

-

5 11 8 5 8 8 9 6

76 5 8 24 32 16 10

4.35 4.11 4.00 3.90 3.63 3.47 3.25

T h e f o r m a t i o n of t h e a l u m i n o s i l i c o p h o s p h a t e g e l r e q u i r e s a r e a c t i v e f o r m of p h o s p h o r u s s u c h as p h o s p h o r i c a c i d f o r its i n c o r p o r a t i o n into t h e g e l s t r u c t u r e a n d zeolite f r a m e w o r k .

T h e m e r e presence of a p h o s p h a t e

salt s u c h as s o d i u m m e t a p h o s p h a t e i n t h e reactant g e l w i l l n o t result i n p h o s p h o r u s i n c o r p o r a t i o n i n t h e zeolite c r y s t a l lattice. T e r n a r y r e a c t i o n d i a g r a m s s h o w i n g t h e regions of g e l c o m p o s i t i o n f o r s y n t h e s i z i n g t h e p h o s p h a t e zeolites are s h o w n i n F i g u r e s 1-3 f o r t h e s o d i u m a l u m i n o s i h c o p h o s p h a t e zeolites, a n d i n F i g u r e s 4 a n d 5 f o r t h e analogous p o t a s s i u m system. Properties G e n e r a l l y , t h e p h o s p h a t e zeolites c r y s t a l l i z e i n t h e f o r m of l a r g e , near-single crystals of t h e o r d e r of 100 μ i n size.

H o w e v e r , for zeolite

P - A , t h e c r y s t a l size w a s of t h e o r d e r of 1 to several μ. S i n g l e - c r y s t a l measurements w e r e therefore possible f o r most of t h e p h o s p h a t e zeolites. P h o t o m i c r o g r a p h s of several of t h e p h o s p h a t e zeolite crystals are s h o w n i n F i g u r e 6.


84


1

T y p i c a l x - r a y p o w d e r d i f f r a c t i o n d a t a for the p h o s p h o r u s - s u b s t i t u t e d zeolites are g i v e n i n T a b l e s I I a n d I I I . U n i t c e l l d i m e n s i o n s h a v e

been

d e t e r m i n e d for several of the p h o s p h a t e zeolites a n d c o m p a r e d w i t h t h e s t r u c t u r a l l y r e l a t e d p h o s p h o r u s - f r e e zeolites. T h e u n i t c e l l d i m e n s i o n of c u b i c P - C zeolite ( 13.2 w t % P 0 ) was f o u n d to b e 13.75 A f r o m s i n g l e 2

5

c r y s t a l precession x - r a y p h o t o g r a p h s . z e o l i t e C has a n a = wt %

P 0 ) 2

elsewhere

5

A single c r y s t a l of the

analogous

13.73 A . T h e c r y s t a l s t r u c t u r e of zeolite P - C ( 13.2

has b e e n d e t e r m i n e d b y B i r l e et al. a n d w i l l b e r e p o r t e d

(3).

A single c r y s t a l of P - W zeolite ( 16.5 w t % P 0 ) was e x a m i n e d b y 2

5


precession x - r a y p h o t o g r a p h s a n d f o u n d to b e t e t r a g o n a l , w i t h u n i t c e l l Table III.

T y p i c a l X - R a y Powder Diffraction D a t a for Phosphate Zeolites P - A , P - L , P - B ( P )

P-A d, A 12.2 8.6 7.07 5.48 4.99 4.33 4.08 3.87 3.69 3.54 3.40 3.28 2.96 2.89 2.74 2.68 2.62 2.50 2.45 2.36 2.24 2.17 2.14 2.10 2.07 2.05 2.02 1.92 1.89 1.85 1.83 1.73

P-L I/Io 100 89 57 35 5 16 57 8 81 5 32 68 92 22 16 11 49 11 8 5 3 14 8 5 5 14 2 12 7 5 5 18

d, A 16.0 8.0 7.55 6.09 5.86 4.65 4.47 4.37 3.96 3.68 3.51 3.32 3.22 3.09 3.05 2.93 2.88 2.82 2.69 2.64 2.53 2.50 2.46 2.44 2.32 2.30 2.22 2.06 1.96 1.88

P-B I/Io

d, A

I/Io

100 4 8 18 4 29 9 6 28 9 19 15 31 24 5 28 4 4 24 8 9 4 4 5 3 3 9 3 2 6

7.08 5.01 4.96 4.44 4.10 4.04 3.53 3.34 3.20 3.13 2.71 2.68 2.66 2.53 2.20 1.98 1.68

58 58 45 7 57 17 5 6 100 57 37 38 22 8 5 6 7


6.

FLANIGEN

Phosphorus

A N D GROSE

Table I V .

P - A Zeolite U n i t Cell Dimensions, a vs.

P 2 O 5 Wt Wt


N a F o r m of P - A Z e o l i t e

Ca

e x

85

Substitution

%

% a,

P2O5

5.2 6.2 6.4 6.6 6.7 6.8 6.9 7.3 7.7 8.7 9.1 10.2

F o r m of P - A Zeolite

12.249 12.243 12.246 12.237 12.236 12.235 12.232 12.242 12.235 12.237 12.235 12.232

6.3 8.0 8.6

A

db ± ± ± ± ± db ± ± db ± ±

0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005

12.237 =fc 0.005 12.251 db 0.005 12.220 ± 0.005

12.34 12.32 ) vs. P2O5 2

L

\

12.30 12.28 , 12.26 12.24

a vs. P

:

DASI IED LI JES IN DICAT ILIMI" S OF ANAL rTICAL ACCU ^ACY 6 %P 0 2

8

10

12.22

12

5

Figure 7. Si0 content vs. P,0 content and unit cell dimension (a) vs. P 0 content of P-A zeolite 2

2

5

5

d i m e n s i o n s of a = 20.17 A a n d c = 10.03 A . A n alternate t e t r a g o n a l c e l l w i t h a = 14 A was also consistent w i t h t h e x - r a y d a t a . A s i n g l e c r y s t a l of p h o s p h o r u s - f r e e T y p e W zeolite w a s n o t a v a i l a b l e f o r c o m p a r i s o n . B a s e d o n p o w d e r d a t a , z e o l i t e W has b e e n i n d e x e d o n a c u b i c u n i t c e l l with a =

20 A b y D . W . B r e c k ( u n p u b l i s h e d r e s u l t s ) . Steinfink (14)

reports a n o r t h o r h o m b i c u n i t c e l l w i t h a =

9.96 A , b =

14.25 A , a n d

c = 14.25 A f o r the m i n e r a l z e o l i t e p h i l l i p s i t e , a n d S a d a n a g a et al. ( 13 ) f o u n d a m o n o c l i n i c u n i t c e l l f o r t h e r e l a t e d m i n e r a l zeolite h a r m o t o m e w h i c h deviates o n l y s l i g h t l y f r o m t h e o r t h o r h o m b i c p h i l l i p s i t e c e l l .


86


Table V . Phosphate Zeolite P-L

2 ( S i 0 ) , has not b e e n i d e n t i f i e d 3

2

2

w i t h a n y specific z e o l i t e because of t h e d i f f i c u l t y i n p r o v i n g the existence of a t e t r a h e d r a l c o n f i g u r a t i o n s u c h as ( H 0 ) ~ . T h i s t e t r a h e d r a l u n i t has 3

2

b e e n p r o p o s e d as o c c u p y i n g t e t r a h e d r a l sites i n the s t r u c t u r e of viseite a n d kehoeite, the m i n e r a l p h o s p h a t e analogues of a n a l c i m e (10,

11).

M e c h a n i s m 5 is a possible means of s u b s t i t u t i o n u t i l i z i n g the r e p l a c e m e n t of a l u m i n a r a t h e r t h a n s i l i c a , b u t is not p r o b a b l e because of t h e excess alumina

(or silica deficiency)

c o n t a i n e d i n the reactant

compositions

d e s c r i b e d here. T h e shifts a n d changes i n i n f r a r e d s p e c t r a for the p h o s p h a t e zeolites c o m p a r e d w i t h t h e i r r e l a t e d p h o s p h o r u s - f r e e analogues are i n agreement w i t h the a b o v e p r o p o s e d s u b s t i t u t i o n m e c h a n i s m s . I n c o n c l u s i o n , w e p r o p o s e that the p r o p e r t i e s a n d characteristics of the p h o s p h a t e

zeolites p r e s e n t e d , i n c l u d i n g s i n g l e - c r y s t a l m i c r o p r o b e

analysis, i n f r a r e d spectra, zeolite f r a m e w o r k s t o i c h i o m e t r y , a n d u n i t c e l l d a t a , establishes b e y o n d d o u b t the s u b s t i t u t i o n of p h o s p h o r u s i n z e o l i t e frameworks.


98

MOLECULAR SIEVE ZEOLITES

1

Acknowledgment The authors thank J. V. Smith, Univ. of Chicago, for the electron microprobe analyses and for many helpful discussions on structural as pects. The expert assistance of Barbara A. Bierl in the infrared deter minations and interpretation, L. G. Dowell in the x-ray studies, and R. G. Pankhurst in chemical analyses is gratefully acknowledged. We thank D. W. Breck for his encouragement, support, and helpful advice during the course of these studies and in the preparation of the manuscript.


Literature Cited (1) Barrer, R. M., Baynham, J. W., Bultitude, F. W., Meier, W. M.,J.Chem. Soc. 1959, 195. (2) Barrer, R. M., Marshall, D. J.,J.Chem. Soc. 1965, 6616. (3) Birle, J. D., Knowles, C. R., Smith, J. V., Dowell, L. G., in preparation. (4) Breck, D. W., Flanigen, Ε. M., "Conference on Molecular Sieves," p. 47, Society of the Chemical Industry, London, 1968. (5) Flanigen, Ε. M., Szymanski, Η. Α., Khatami, H., ADVAN. CHEM. SER. 1971, 101, 201. (6) Frondel, C., "Dana's System of Mineralogy," 7th ed., Vol. III, p. 5, Wiley, New York, 1962. (7) Kühl, G. H., "Conference on Molecular Sieves," p. 85, Society of the Chemical Industry, London, 1968. (8) Kühl, G. H., U. S. Patent 3,355,246 (1967). (9) McConnell, D., Am. Mineralogist 1937, 22, 977. (10) Ibid., 1952, 37, 609. (11) McConnell, D., Mineral. Mag. 1964, 33, 799. (12) McConnell, D., Verhoek, F. H.,J.Chem. Educ. 1963, 40, 512. (13) Sadanaga, R., Marumo, F., Takeuchi, Y., Acta. Cryst. 1961, 14, 1153-63. (14) Steinfink, H., Acta. Cryst. 1962, 15, 644. ( 15) Taylor, A. M., Roy, R., Am. Mineralogist 1964, 49, 656. RECEIVED March 4, 1970. Discussion W . M. Meier ( Eidgenossische Technische Hochschule, Zurich ) : Work done by Liebau and coworkers on silicon phosphates (Z. Anorg. Allgem. Chem. 1968, 359, 113) should perhaps be mentioned here. At least five different crystalline phases of composition S i P 0 have been synthesized by these investigators using reaction mixtures containing silica gel and phosphoric acid at temperatures ranging from 250°C upwards and autogenous pressures. The crystalline products thus obtained are quite remarkable since the silicon was shown to be octahedrally coordinated (Acta Cryst. 1970, 26, 233). H . Villiger (Martinswerk GmbH, West Germany): 1) The cell constant of P - A is given in Table V as a = 12.24 Â (pseudo cell). Are 2

7


6.

FLANIGEN

AND

GROSE

Phosphorus

99

Substitution

there a n y extra lines v i s i b l e w h i c h w o u l d i n d i c a t e the presence

of

a

l a r g e r cell? T a b l e I I I does n o t c o n t a i n s u c h lines. I w o u l d l i k e to k n o w i n p a r t i c u l a r w h e t h e r the l i n e 531 (d

«

4.05 Â, a »

24.5 Â )

is c l e a r l y

absent, a state of affairs w h i c h m i g h t p o i n t to a d i s o r d e r e d d i s t r i b u t i o n of S i a n d A l c a u s e d b y p h o s p h o r u s s u b s t i t u t i o n . 2)

T h e u n i t c e l l d i m e n s i o n of

P-L

w i t h t h e h i g h a l u m i n a content observed.

(α-direction)

is

compatible

H o w e v e r , there is a d r a s t i c d r o p

i n a d s o r p t i o n c a p a c i t y w h i c h I b e l i e v e is o w i n g to o c c l u s i o n of p h o s p h a t e . D o y o u t h i n k t h a t the larger n u m b e r of cations explains the l o w e r s o r p t i o n capacity?


Ε. M . Flanigen: 1) W e d i d n o t observe a n y extra lines i n P—A zeolite c o m p a r e d w i t h N a A zeolite. T h e m a j o r difference i n x - r a y is the decrease i n u n i t c e l l d i m e n s i o n w i t h i n c r e a s i n g p h o s p h o r u s content i n P - A . [531]

The

s u p e r s t r u c t u r e reflection is o b s e r v e d as a w e a k s h o u l d e r i n P - A

zeolites a n d i n N a A z e o l i t e (d «

4.13 Â, n o t l i s t e d i n T a b l e I I I ) .

2 ) O n e of the m a i n p r o b l e m s here is the simultaneous s u b s t i t u t i o n of A l w i t h P . I t is difficult to separate the changes i n p r o p e r t i e s e x p e c t e d w i t h i n c r e a s e d A l content f r o m those o w i n g to p h o s p h o r u s s u b s t i t u t i o n . T h e establishment of p r o o f of f r a m e w o r k s u b s t i t u t i o n is v e r y difficult a n d cannot be b a s e d o n one single p r o p e r t y s u c h as a d s o r p t i o n . t r i e d to c o n s i d e r c a r e f u l l y a l l of t h e i n t e r r e l a t e d c o m p l e x

We

have

effects a n d

properties a n d c h a r a c t e r i z e the p h o s p h a t e zeolites b y as m a n y t e c h n i q u e s as possible before p r o p o s i n g p h o s p h o r u s

framework substitution.

We

are c o n v i n c e d that t h e o n l y e x p l a n a t i o n for a l l of the o b s e r v e d p r o p e r t i e s a n d characteristics is f r a m e w o r k i n c o r p o r a t i o n of p h o s p h o r u s .

The re-

d u c e d a d s o r p t i o n c a p a c i t y a n d p o r e size of the P - L zeolite m a y be r e l a t e d to c a t i o n content since w e r e p o r t t h a t c a t i o n exchange alters the a d s o r p t i o n properties. W i t h respect to t h e structure of P - L , J . M . B e n n e t t has d o n e some i n i t i a l electron d i f f r a c t i o n w o r k f r o m w h i c h t h e u n i t c e l l d a t a g i v e n i n the p a p e r w e r e t a k e n . J . M . Bennett

( U n i o n C a r b i d e C o r p . , T a r r y t o w n , Ν. Y .

10591):

T h e r e are differences b e t w e e n the space g r o u p of L a n d P - L . I n P - L , the c d i m e n s i o n is d o u b l e d b y e l e c t r o n d i f f r a c t i o n , a n d systematic a b sences s h o w the presence of t w o c g l i d e planes. G . H . Kiihl ( M o b i l Research and Development

Corp., Paulsboro,

N . J . 0 8 0 6 6 ) : Y o u postulate O H " a l o n g w i t h N a . I n w h a t w a y is this +

different f r o m o c c l u d e d N a O H ? Ε. M . Flanigen: If b y o c c l u d e d N a O H , y o u m e a n N a O H

molecules

w h i c h are extraneous to the z e o l i t e structure, w e p r o p o s e t h a t the N a i o n is not d i r e c t l y associated w i t h the h y d r o x y l i o n , b u t t h a t e a c h serves as a framework charge-compensating

m o i e t y , the N a

for A 1 0 " t e t r a h e d r a , a n d the O H " for P 0 2

2

+

+

charge

compensating

tetrahedra.


100

M O L E C U L A R

SIEVE

ZEOLITES

1

R. M . Barrer ( I m p e r i a l C o l l e g e , L o n d o n S W 7 , E n g l a n d ) : 1) B a r r e r and Marshall

(/.

Chem.

Soc.

1965,

6616), w o r k i n g under apparently

s i m i l a r c o n d i t i o n s of t e m p e r a t u r e , o b t a i n e d a l u m i n o p h o s p h a t e s a n d a l u minosilicates from

the

system

B a s e - A l 0 - P 0 - S i 0 - H 0 , often 2

3

2

5

2

as

2

co-precipitates of crystals. C a n y o u c l a r i f y the differences i n t h e c r y s t a l l i zations

and/or

the experimental conditions

which could

yield

these

different results? 2 ) O n the q u e s t i o n h o w m u c h of the p h o s p h a t e w a s i n t h e f r a m e w o r k a n d h o w m u c h w a s m e r e l y i n t e r c a l a t e d , it is to b e o b s e r v e d that i n t h e t i g h t a n a l c i t e f r a m e w o r k , there is n o r o o m f o r i n t e r c a l a t i o n . H o w


ever, a n a l c i t e is a l r e a d y k n o w n to h a v e a m o d i f i c a t i o n w i t h

(presumably)

f r a m e w o r k p h o s p h o r u s , w h i c h is viseite. T h e r e f o r e , h a v e y o u m a d e a n y o t h e r t i g h t n e t w o r k zeolite

(possibly

n a t r o l i t e ) w h i c h contains

phos

p h o r u s ? T h i s c o u l d s h e d c o n s i d e r a b l e l i g h t o n t h e site of the p h o s p h o r u s . Ε. M . Flanigen: 1) W e c a n o n l y a t t r i b u t e differences i n the results of B a r r e r a n d M a r s h a l l a n d those r e p o r t e d h e r e to v a r i a t i o n i n t h e m e t h o d of p r e p a r i n g t h e g e l n e t w o r k , a n d i n s o m e cases p e r h a p s to c r y s t a l l i z a t i o n temperatures.

different

W e b e l i e v e the c r i t i c a l p o i n t i n a c h i e v i n g

f r a m e w o r k s u b s t i t u t i o n is i n c o r p o r a t i o n of a l l of the p h o s p h a t e i n the insoluble gel network, rather than i n a soluble phosphate form.

T h i s is

c o n t r o l l e d b y the exact m e t h o d of c o p r e c i p i t a t i o n a n d gelation. 2 ) N o , w e h a v e not. D . E . W . Vaughan ( W . R . G r a c e a n d C o . , C l a r k s v i l l e , M d . 2 1 0 2 9 ) : A l t h o u g h the d a t a c o n v i n c i n g l y demonstrate Ρ s u b s t i t u t i o n i n the zeolite f r a m e w o r k s , s u b s t a n t i a l o c c l u s i o n of p h o s p h a t e is also e v i d e n t o n the basis of t h e s t o i c h i o m e t r y p r e s e n t e d i n t h e tables (i.e., A 1 0 - P 0 2

Na 0).

3

2

5

T h e s o r p t i o n d a t a for A w o u l d seem to i n d i c a t e s u c h o c c l u s i o n

2

reflected i n r e d u c e d s o r p t i o n c a p a c i t y , c o m p a r e d w i t h z e o l i t e W

where

the e x p e c t e d e n h a n c e d c a p a c i t y is o b s e r v e d , reflecting l o w e r c a t i o n c o n tent of the zeolite. Ε. M . Flanigen: S i n c e different m e c h a n i s m s h a v e b e e n p r o p o s e d

for

p h o s p h o r u s s u b s t i t u t i o n , t h e s t o i c h i o m e t r y of s u b s t i t u t i o n cannot b e g e n e r a l i z e d b u t w o u l d h a v e to b e

discussed for e a c h p h o s p h a t e

zeolite

species. H o w e v e r , i t is n o t correct to assume t h a t f r a m e w o r k s u b s t i t u t i o n imposes a s t o i c h i o m e t r i c r e q u i r e m e n t of A 1 0 - P 0 2

3

2

5

=

N a 0 . In addi 2

t i o n , the p r o p o s e d p h o s p h o r u s s u b s t i t u t i o n is b a s e d not o n l y o n s t o i c h i o m e t r y b u t o n a c o m b i n a t i o n of at least several other characteristics. I n t h e case of p h o s p h a t e zeolites c o n t a i n i n g 15 to 23 w t % P 0 , c o n s i d e r i n g 2

5

y o u r suggestion t h a t a s u b s t a n t i a l p o r t i o n of that is o c c l u d e d , t h e changes expected

i n the p r o p e r t i e s i n m a n y cases w o u l d b e greater t h a n a n y

changes o b s e r v e d o r r e p o r t e d . I n the case of P—A zeolite, a l t h o u g h some r e d u c t i o n i n a d s o r p t i o n c a p a c i t y is o b s e r v e d i n the case of some c a t i o n forms of P - A a n d w i t h


6.

FLANIGEN

AND

GROSE

Phosphorus

101

Substitution

some adsorbates, i n the case of C a - e x c h a n g e d P - A , n o r e d u c t i o n w a s observed.

It does not seem l i k e l y t h a t C a - e x c h a n g e s h o u l d r e m o v e

c l u d e d m a t e r i a l , a n d i n d e e d , c h e m i c a l analysis s h o w e d

no change

oc in

f r a m e w o r k c o m p o s i t i o n before a n d after exchange. L.

Moscou

(Ketjen

N.V., Amsterdam,

Netherlands):

I

wonder

w h e t h e r the a c c u r a c y of the m i c r o p r o b e analysis y o u m e n t i o n e d is g o o d e n o u g h to b e a b l e to s t u d y h o m o g e n e i t y

i n composition over

separate

crystals. Ε. M . Flanigen: S i n c e t h e e l e c t r o n m i c r o p r o b e analyses w e r e c a r r i e d out b y J. V . S m i t h a n d C . R . K n o w l e s , I w o n d e r i f Professor S m i t h w o u l d


comment. J . V . Smith ( U n i v e r s i t y of C h i c a g o , C h i c a g o , 111. 6 0 6 3 7 ) : T h e r e p r o d u c i b i l i t y of the i n s t r u m e n t is 1 or 2 % , b u t because it is a zeolite, y o u h a v e to use s o m e t h i n g l i k e a 10- to 20-μ b e a m , w i t h crystals of the o r d e r of 50 to 100 μ; therefore, y o u c a n n o t take m a n y p o i n t s across a c r y s t a l . A l t h o u g h t h e a n a l y t i c a l r e p r o d u c i b i l i t y c i t e d a p p l i e s to a n y c r y s t a l a n d between

crystals, y o u cannot p r o v e to a l-μ

variation i n phosphorus

l e v e l t h a t there is not a

content.


Phosphorus Substitution in Zeolite Frameworks

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