T. B. REEDAND D. W. BRECK
5972 [CONTRIBUTION FROM
THE
VOl. 78
RESEARCH LABORATORY ow THE LINDEAIR PRODUCTS COMPANY, A DIVISIONOF UNION CARBIDE AND CARBON CORPORATION]
Crystalline Zeolites. 11. Crystal Structure of Synthetic Zeolite, Type A Bv T. B. REEDAND D. W. BRECK RECEIVED APRIL23, 1956
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of 24(Si,A1)-0, tetrahedra which are joined to form 8-membered oxygen ;in& i n ~ t h efaces and distorted 6-membered rings on the 3-fold axes. A large cavity 11.4 A. in diameter occupies the center of the cell and smaller 6.6 A. cavities are located on the 3-fold axes. Probable positions of the cations in the lithium, sodium, thallium and calcium forms are indicated, and correlation of the structure with the adsorptive and ion-exchange properties of the Type A zeolite is discussed.
Introduction
Experimental
A new synthetic crystalline zeolite, not known to exist in nature, has been reported recently and its properties described.' The novel adsorptive properties of certain zeolites after dehydration have been the subject of many investigations and are intimately related to their open crystal structure and pores of uniform dimensions.z.' In order to
The composition of the Type A zeolite is expressed by the structural formula Mem/n[(AIO1).(SiO~)al.NH~Owhere Me represents exchangeable cations of charge n. The aluminosilicate framework, [(A102),2(SiO~)l~], will be designated by [A]. The largest crystals of the Type A zeolite that have been prepared are about 25 p in diameter, so that most of the structural work was done from X-ray powder diffraction data obtained on a geiger-counter spectrometer as previously
Fig. la, 1b.-Assembly
more completely understand the properties of the new zeolite, Type A, an X-ray structural analysis was undertaken and the results are reported here. Only a few zeolite structures have been studied in detail. A n a l ~ i t e , ~habazite,~,' ~.~ certain fibrous zeolites such as natrolite,* and the related felspathoids such as sodalitegJOhave been the subject of structural investigations. Generally, these structures are based on the filling of space by Si(Al)O1 tetrahedra as discussed by Wells." ( 1 ) D. W. Breck, W. 0.Eversole. R. M . Milton. T. B. Reed and T. L. Thomas. Tais J o u a w r ~78, . 5863 (1956). (2) R. M . Barrer. Ann. Rcp. Probr. Chcm., Chcn. Soc. London. 11, 31 (19441: Quo?:. Rcu. (Londoi), 8 . No. 4293 (1849). (3) G. L. Kington and W. Laiog. Trnns. Porodoy Soc.. El, 287 (1855). (4) W . H. Taylor, 2. K&l., 71. 1 (1930). ( 5 ) I. R. Beattie. Acln CvysI., 7 . 357 (1954). ( 6 ) J. Wyart, Bull. Sor. Min. PI.. E6, 81 (1933). (7) 1. R. Beattie, N o l w e , 171, 999 (1953). (8) L. Pading, 2. K ~ < s I .74, , 213 (1930). ( 8 ) 1.Pading, ibid.. 71, 213 (1930). (10) W. L. Rragg. "Atomic Structure of Minerals." Coroell University Press, Ithace, N. Y.,1937. p. 255.
of eight tetmlmlm. described.' Peak intensities (with no correction for Lorenz and polarization effects) for the fully hydrated and dehydrated Lit, Na+, Cat+, Ag+ and TI+ exchanged A zeolite are presented in Table I. Resolution of some of the ambiguous reflections of the sodium form was possible from single crystal photographs of a hydrated 25-p crystal taken on a n oscillation camera with helium shielding. Exposures of about 48 hr. produced easily visible darkening for the stronger reflections. Visual estimates of intensities from these oscillation photographs appear in Table I. Chemical composition, unit cell dimensions, densities and adsorption volumes for water and oxygen are shown in Table 11.
Structure Determination No systematic extinctions are observed and the data are consistent with the space group O&Pm3m. An attempt to obtain phase information by heavy ion substitution failed. Although the silicate framework is unaltered by cation exchange, apparently the cations do not occupy the same sites. From reflections obtained with the lithium form, it was felt that the alumina-silicate framework could be (11) A. F. Wells. Arln Ciyrl., 7 , 545 (1954).
5973
CRYSTAL STRUCTURE OF A SYNTHETIC ZEOLITE
Dee. 5, 1956
TABLE I POWDER DIFFRACTION DATA-A ZEOLITES Hydrated sodium form oscillation -LiaNalAl-pictures I , rel. Hydrated
------
hkl
100 110 111 200 210 211 220 221 300 310 311 222 320 321 400 410 322 411 330 331 420 42 1 332 422 430 500 43 1 510 511 333 520 432 521 440 441 522 530 433 531 600 442 620 622 444 640
VS
vs vs
N.O.
S N.O. M S
}
N.0:
vs
180 130 53 6 67
17
21
3 47 .... 13 21
")
...
}
45
29
7
14
5
6
7 13 2 10 13 2
..
..
..
...
11 12 14 1
15 14 9 1 9
17 2.5 7.5 21.5
14 1.5 2 21
....
2 9 5 0 10 1
*.
...
15.5
15
....
46 ...
39
14 40
4 17
....
..
7
..
47
26
17
22
7.5
8
4
5
8
5
4
3
2.5
4
....
...
....
..
..
62 22 13 4.5 6 2.5 2 19
5
4 3 17
3.5
10 4 19 4
5 4 18 2.5
1 11 0 11 6
3 2 2 23 2
2.5
4
7
3
12
..
..
3
2
5
...
....
2
0
..
..
..
...
5
3
3
2
7
..
..
1
3
....
1
2.6
1
3
3
3
1
...
5
2.6 6
2.5 3
0 5
0 0
..
..
..
...
....
8
8
4
3
3.5
8.6
2.6
5
8
..
..
2
2.5
2.5
3.5
2.6
3
2
7
..
3.5
1.5
...
....
3.5
3
1
5
..
.. ..
2
1.0
15
8
5
2
3
5
6
2.5
4.0
3.5 5 1.5
6 7.5 3 4
N.O. N.O. W M N.O.1
N.O. iV.0.
39
....
28
3 14 20 4
3.5 12 24 5
M
28 9 3 22 2.5
29
...
N.O. S W S
55 5 5
21 4 5 19 2
21 2 5
...
....
122 13 20 2 12
59 20 0 7 43 0 7
173 100 28
..
Cas[A]-Dehydrated
Hydrated
36 10 0 10 14 I 12
86 59 30
31
37
3 41
...
W
W W
....
24 31
)
Hydrated
...
44
W
S S N.O. S
Dehydrated
98 63 35 4 23
...
Intensity, arbitrary scale--Aglr[AI--Tls.sNan.r[AlDeHyDeDedrated hydrated Hydrated hydrated hydrated
_ I _ _
--Nair[A]-
. .
...
...
13
....
20
.. 4.5 18
2 TABLE I1 CHEMICAL COMPOSITION A N D PHYSICAL DATA Adsomtion vol. A.I/;nit cell H~O oi
Zeolite compn./unit cell
Density, g./cc.
LLNad[A] . 2 4 H ~ 0 Nalz[A] .27&0 Agiz[A].24Hz0 Tlp.eNaz.4[A].20H10 Caa[A].30HzO a X-Ray density, [A]
1.91 12.04 735 1.99 12.32 833 12.38 733 2.76" 3.36" 12.33 584 2.05 12.26 883 = [(AlO&(SiOt)t~l.
an,
A.
0 610 0 0 700
determined independently since the lithium ions would contribute little to the structure factors.
27
.. 3 25
1.5 4 1.5 12.5 2.5
1 2 2.5 12.5 0.5
Aluminosilicate Framework.-Known zeolite structures are often described as frameworks of A104 and Si04 tetrahedra linked at their corners (Fig la). On this basis, the analysis of the A zeohte structure reduced to the problem of joining 24 tetrahedra to form a structure consistent with the possible space groups, and a 12.3 A. unit cell which gives the accepted oxygen-oxygen distance, do-0, of 2.70 A. Since the calcium form will adsorb molecules with critical dimensions up to about 5 A., any proposed structure should also provide an opening of about this size. The zeolite chabazite, with enlarged 6-membered
3974
T. B. REEDAND D. W. BRECK
oxygen rings of 3.1-3.3 A. diameter will not admit hydrocarbon molecules that are readily adsorbed by calcium A, which suggests that a t least an 8membered oxygen ring is req~ired.1.~Placing 8 tetrahedra in each face of a cube to form an 8membered oxygen ring accounts for 24 tetrahedra in a unit cell of the right size, satisfies the space group, and gives a pore opening of sufficient diameter. Figure IC shows a model of the structure thus formed. Figures l a and l b show the assembly of 8 tetrahcdra which is characteristic of the structure. These are located a t the centers of the edges of the cell. Table I11 lists the positions of the atoms in the aluminosilicate framework which are fixed by the oxygen packing. The (0-0) distance is determined by this rigid structure and is given by the relation
Vol. 78
And the average silicon or aluminun-oxygen distance, ~ ( S I . A I ) - O is given by dm.*t,-o
=
3d3 16(1
''
+ 4)= 0.134doo = 1.66
Smith has correlated ( A I S - 0 distances in aluminosilicate structures with the Al/Si ratio. For AI/Si = 1, the sveragc (A1,Si-0) distance was found to be 1.69 ,&.Iz To test the validity of this structure, structure factors were computed for the model described using the Hartree scattering factors for light atoms and ions. These were compared (Table IV) with unambiguous observed reflections of the lithium form. A reliability factor, R = Z / F o - F&F0 of 0.246 was obtained for 10 (hkO) rcflections and 0.267 for 17 (hkl) reflections. All observed and calculated structure factors and structural interpretations are for the dehydrated zeolites. This 3ao agreement, with no adjustable atomic positions, - 0.439200= 2.70 A. = Z 4 ( l + 42) and ignoring contributions of 4 residual sodium ions, suggested that this structure was basically correct. TABLE I11 ATOMICPOSITIONS IN THE ALUMINOSILICATE FRAMEWORK A Fourier projection using (hkO) data for the No. Atom POSitiOl3 sodium form (Fig. 2a) shows the large, 8-membered oxygen ring and a 6-fold ring on .the 3-fold 24 Or (0.110, ,110, ,345) Adjacent to6-fold ring axis. The corresponding positions of the atoms is 12 On (0 , ,220. ,500) Adjacent to %fold rina shown in Fig. 2b while Fig. 3 illustrates a (110) sec12 0 1 1 1 (0 259. 289, 0 i Bridge oxygen 21 Si, AI (n 3717, 1x3, n ) (12) J. V. Smith, A r l n Cryst, 1. 4 (In.54).
Dec. 5 , 1956
CRYSTAL STRUCTURE OF A SYNTIIETIC ZEOLITE
5975
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