9
Synthesis and Crystal Structure of Zeolite R h o — A New Zeolite Related to Linde Type A
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H A R R Y E . ROBSON Esso Research Laboratories, Baton Rouge, La. 70821 D A V I D P. S H O E M A K E R Oregon State University, Corvallis, Ore. 97331 R O B E R T A A. OGILVIE" and PHILIP C.
b
MANOR
Massachusetts Institute of Technology, Cambridge, Mass. 02139
A new synthetic zeolite was prepared using the faujasite syn thesis modified by substitution of C OH for 10% of the NaOH. The typical product composition (dry basis) is 0.78Na O· 0.24Cs2O·Al2·5.8SiO2. The x-ray powder diagram (body– centered cubic, a = 15.02 A) suggested the hypothetical structure proposed earlier by Meier, containing type-Α cages linked by joining eight-membered rings by oxygen bridges. Structure refinement on the calcined hydrogen form (a = 15.0 A) with an Im3m model gave R = 0.12 (unweighted, 93 reflections incor porated in 50 powder lines) and reasonable interatomic distances. A further significant drop to R = 0.077 was obtained with space group I-43m, but unreasonable (Si, Al)-O distances (1.50-1.72 A) were indicated. A distortion of this model to FdSc with a = 30.0 is proposed. 8
2
0
0
0
T n t h e course of e x p e r i m e n t a t i o n w i t h f o r m u l a t i o n s of s i l i c a , a l u m i n a , a n d v a r i o u s a l k a l i m e t a l oxides i n a t t e m p t s t o prepare n e w s y n t h e t i c zeolites, a f o r m u l a t i o n c o n t a i n i n g c e s i u m r e p l a c i n g some of t h e s o d i u m i n a t y p i c a l faujasite p r e p a r a t i o n y i e l d e d a n e w c r y s t a l l i n e z e o l i t i c p r o d u c t w h i c h s h o w e d a t y p i c a l l y c u b i c p o w d e r d i a g r a m h a v i n g a b o d y - c e n t e r e d p a t t e r n of A
a
Present address: University of Nebraska, Lincoln, Neb. 68508. Present address : Max-Planck-Institut fur experimentelle Medizin, 34, Gôttingen, B.R.D. 6
106 In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
9.
ROBSON E T A L .
Zeolite Rho
107
s y s t e m a t i c e x t i n c t i o n s a n d a l a t t i c e c o n s t a n t ( u n i t c e l l edge) of a b o u t 15 A . S i n c e t h i s exceeds t h e l a t t i c e c o n s t a n t of zeolite A b y a b o u t 3 A , i t seemed t h a t t h e n e w zeolite m i g h t h a v e a s t r u c t u r e c o m p o s e d of separated t y p e - A cages b r i d g e d b y o x y g e n l i n k a g e s at the 8-rings,
T h e cages are i n t e r -
c o n n e c t e d b y 8 - 8 double r i n g s r a t h e r t h a n b y single 8-rings as i n zeolite A , m u c h as t h e sodalite cages i n zeolite A are i n t e r c o n n e c t e d w i t h 4 - 4 d o u b l e r i n g s , w h i l e i n sodalite itself t h e y are c o n n e c t e d b y single 4-rings (./), or as A cages i n zeolite Z K - 5 are i n t e r c o n n e c t e d b y 6 - 6 double r i n g s (2).
Thus,
for a c u b i c u n i t c e l l w i t h A cages centered a t t h e corners, for t h e n e w zeolite, t h e cage centered at t h e b o d y center of the cube is a n o t h e r A cage ( t h e r e b y a c c o u n t i n g for t h e b o d y - c e n t e r e d Downloaded by COLUMBIA UNIV on June 23, 2013 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0121.ch009
i t is a sodalite u n i t .
e x t i n c t i o n s ) w h i l e for z e o l i t e A i t s e l f
T h i s s t r u c t u r e was discussed b y M e i e r (3) as a h y p o -
t h e t i c a l zeolite s t r u c t u r e w i t h n o t h e n - k n o w n e x i s t i n g examples ( F i g u r e 1). T h i s s t r u c t u r a l a r r a n g e m e n t was presented as e a r l y as 1907 i n a m a t h e m a t i c a l p a p e r b y A n d r e i n i (4).
W e h a v e d e s i g n a t e d t h i s zeolite as " z e o l i t e
r h o " since i t also appears as a p a r t of a f a m i l y of zeolite s t r u c t u r e s , r e a l a n d h y p o t h e t i c a l , w h i c h are convenient t o d i s t i n g u i s h b y G r e e k letters (5). H e r e we describe the synthesis of t h i s zeolite a n d the v e r i f i c a t i o n of t h e proposed sihca-alumina framework b y x-ray powder diffraction work on the dehydrated hydrogen form. Synthesis Zeolite r h o was p r e p a r e d f r o m a l u m i n o s i l i c a t e h y d r o g e l s c o n t a i n i n g s o d i u m a n d c e s i u m cations. T h e procedure is e n t i r e l y c o m p a r a b l e w i t h t h e synthesis of faujasite except for s u b s t i t u t i o n of C s O H for a b o u t 1 0 % of t h e N a O H i n t h e faujasite synthesis gel. A l u m i n a t r i h y d r a t e ( A l c o a C - 3 3 grade) was d i s s o l v e d i n 5 0 % N a O H s o l u t i o n a t 100°. A f t e r c o o l i n g to a m b i e n t t e m p e r a t u r e , the r e q u i r e d a m o u n t of C s O H s o l u t i o n was a d d e d , a n d the r e s u l t i n g l i q u o r was b l e n d e d i n t o 3 0 % silica sol ( d u P o n t L u d o x L S - 3 0 ) w i t h v i g o r o u s m i x i n g . A f t e r 3-7 d a y s i n c u b a t i o n at 2 5 ° , t h e s y n thesis gel was h e l d at constant t e m p e r a t u r e , 80, 90, or 100°, u n t i l c r y s t a l s f o r m e d ; m a x i m u m c r y s t a l l i n i t y was u s u a l l y a c h i e v e d i n 2 - 4 d a y s . T h e c o m p o s i t i o n of a t y p i c a l synthesis gel is g i v e n b y t h e f o r m u l a 3 N a 0 • 0 . 4 C s O • A 1 0 • 1 0 S i O • 1 1 0 H O . Z e o l i t e r h o was c r y s t a l l i z e d f r o m gels w i t h C s / ( N a + C s ) of 0.06 t o 0.15 w i t h 0.12 preferred. T o o l i t t l e C s O H r e s u l t e d i n t h e appearance of f a u j a s i t e i n t h e p r o d u c t ; t o o m u c h gave c h a b a z i t e or p o l l u c i t e . T h e c o m b i n a t i o n N a O H - C s O H appears t o be a u n i q u e r e q u i r e m e n t for p r e p a r i n g zeolite r h o . N o other c o m b i n a t i o n of alkali hydroxides a n d / o r quaternary a m m o n i u m hydroxides produced i t ; f u r t h e r , a t h i r d a l k a l i c o m p o n e n t s u c h as K O H or R b O H , w h e n a d d e d t o t h e N a O H - C s O H s y s t e m , p r e v e n t e d c r y s t a l l i z a t i o n of zeolite r h o . 2
2
2
3
2
2
T h e c o m p o s i t i o n of the c r y s t a l l i n e p r o d u c t i s : 0 . 7 8 N a O • Q . 2 4 C s 0 • A 1 0 - 5 . 8 S i 0 ( d r y basis). A b o u t 8 0 % of t h e C s + c o n t e n t of t h e synthesis gel was i n c o r p o r a t e d i n t o t h e c r y s t a l l i n e p r o d u c t c o m p a r e d w i t h 2 6 % of t h e 2
2
3
2
In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
2
108
MOLECULAR SIEVES
Na+. Exchange w i t h N H r e m o v e s s u b s t a n t i a l l y a l l C s a n d over 9 0 % of t h e N a + c o n t e n t of the c r y s t a l l i n e p r o d u c t . T h i s is consistent w i t h t h e p r o posed s t r u c t u r e w h i c h shows n o " m i n o r cages" s u c h as t h e sodalite u n i t w h i c h c o u l d act as c a t i o n t r a p s . T a b l e I gives x - r a y d i f f r a c t i o n d a t a for the ( N a , C s ) f o r m ( c r y s t a l l i z e d a n d d r i e d a t 120°) a n d t h e H f o r m ( N H N 0 exchanged a n d c a l c i n e d at 5 4 0 ° ) . T h e l a t t i c e c o n s t a n t s for these t w o p a r t i c u l a r specimens were 14.60 a n d 14.99 A , r e s p e c t i v e l y . I n several cases, the synthesis p r o d u c t seemed t o c o n t a i n b o t h t h e phase described a b o v e a n d a s m a l l a m o u n t of a n u n i d e n t i f i e d phase. C r y s t a l l o g r a p h i c w o r k was l i m i t e d t o m a t e r i a l s h o w i n g o n l y the lines c o r r e s p o n d i n g t o a = 15.0 A . 4
+
+
4
3
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0
Figure 1. Crystal structure of zeolite rho in full symmetry ImSm. Vertices correspond to (Si, Al) atoms. Oxygen atoms are now shown, but are near the midpoints of the line segments. Top: arrangement of A cages. Dashed lines indicate the cage centered at the unit-cell body center, sharing 6-rings with the cages centered at the corners, and 8-8 rings connecting it to other body-center cages. Bottom: stereo drawing prepared with ORTEP (18) on the CALCOMP plotter.
In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
9.
Table I. ,
£
2 +
2
+ I
X - R a y Diffraction Data for Zeolite Rho
(Na, Cs) form
H form
d,A
I/h
d, A
2 4 6 8 10 12 14 16 18 20 22 24 26
10 .33 7..25 5 .95 5 .14 4 .61 4..20 3 90 3 .64 3 .44 3 .26 3 .11 2 .979 2..862
100 3 30 1 2 13 16 1 51 52 24 32 8
10.53 7.44 6.09 5.28 4.72 4.31 4.00 3.74 3.52 3.35 3.19 3.05 2.936
100 3 41 8 16 3 6 6 26 17 2 6 13
zo 30 32 34 36 38 40 42 44 46
2 .667 2 .578 2 501 2. 433 2 .368 2 .309 2 .254 2 .201 2..154
22 1 4 4 2 7 3 9 2
2.730 2.648 2.567 2.495 2.430
8 2 1 7 1
2 .067 2..025 1..987 1..951 1..918
6 3 2 4 2
2.120
1.855 1.824 1.798 1.771 1.746 1.722 1.698 1.675 1.653 1.633 1.613 1.594 1.575 1.556 1.540
3 3 4 5 0.5 4 6 0.5 2
