6 Crystal Structure of Tetrapropylammonium Hydroxide-Aluminum Phosphate Number 5
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J. M. BENNETT, J. P. COHEN, and EDITH M. FLANIGEN Union Carbide Corporation, Tarrytown Technical Center, Tarrytown, NY 10591 J. J. PLUTH and J. V. SMITH The University of Chicago, Department of Geophysical Sciences, Chicago, IL 60637
A new family of aluminophosphate molecular sieves with zeolite-like properties has potential as adsorbents, catalysts, and catalyst supports. Number 5 of the family (hexagonal, a 13.726, c 8.484Å, P6cc) contains alternating A l and Ρ atoms on the tetrahedral nodes of hypothetical framework #81. Non-connecting parallel channels spanned by 12-rings i n the as-synthesized material contain tetrapropylammonium hydroxide species in a tripod-shaped conformation, which possibly acted as polar templates during crystallization. Removal of the TPA(OH) by calcination yields a one-dimensional channel theoretically capable of polar diffusion. Framework oxygens i n the as-synthesized material show strong displacements analogous to those i n high-cristobalite and high-tridymite: mean distances respectively uncorrected and corrected for displacement of oxygen from i t s centroid of electron density are: P-O 1.49 and 1.53Å; A l - O 1.71 and 1.74Å. Uncorrected P-O-Al angles of 148 to 178° become more equal when adjusted for oxygen displacements.
0097-6156/83/0218-0109$06.00/0 © 1983 American Chemical Society In Intrazeolite Chemistry; Stucky, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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INTRAZEOLITE
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A new family of crystalline molecular sieves(1, 2) having aluminophosphate frameworks was synthesized. Strict alternation of A l and P on the tetrahedral nodes yields neutral oxygens i n contrast to the aluminosilicate zeolites, and non-framework cations are not needed for charge balance. Whereas a microporous s i l i c a ( s i l i c a l i t e , 3) with neutral oxygens i s hydrophobic, the aluminophosphate sieves are moderatley hydrophilic. The precursor to the AlPO^ #5 molecular sieve crystallizes at 150 C from a hydrothermal system containing an aluminophosphate gel and tetrapropylammonium hydroxide. Its ideal chemical composition i s TPAOH• 12AlP0i . Removal of the TPAOH by calcination at 400-600 C produces a molecular sieve for which absorption studies are consistent with unconnected pores bounded by 12-rings. The AlPOi* #5 sieve i s thermally stable to 1000°C above which i t transforms to the AlPO^ analog of tridymite.
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f
Experimental The f i r s t synthetic crystals were very small hexagonal prisms. Electron diffraction patterns showed hexagonal symmetry with a ML3.7, £ ^8.5&. Sections t i l t e d around a* indicated a c. glide plane, but the systematic absences around ja were not determined. The X-ray powder pattern (Figure la) was completely indexed with the hexagonal c e l l (Table I). Later results have shown that the c e l l dimensions of an uncalcined AlPOi^ #5 sample vary slightly depending on the organic phase used i n the synthesis. A later batch of large crystals range i n size from hexagonal barrels to smaller hexagonal prisms. The i n i t i a l crystal structure analysis on a hexagonal barrel was complicated by much greater broadness of (00£) than (hkO) diffractions, as also was observed i n X-ray patterns of several powders. Transmission electron micrographs of crushed fragments by G.D. Price of Cambridge University revealed no structural inhomogeneities, and i t i s concluded that each large barrel consists of a stack of hexagonal plates. Single-crystal photographs yielded systematic absences consistent with P6/mcc or P6cc, and the latter was chosen because of the expected alternation of A l and P over tetrahedral nodes. A data set with 2°
H
w
H H
m
w w
OS
In Intrazeolite Chemistry; Stucky, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Figure l b .
C a l c u l a t e d powder d i f f r a c t o m e t e r
patterns
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H
S)
g
w
S
W
Η
Ε
Ο
w
Η
I—*
to
6.
BENNETT
ET AL.
Zeolite Crystal Structure
113
Table I Observed and C a l c u l a t e d d-spacings f o r d , obs
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26 7.457 12.917 14.917 19.775 21.090
11.844 6.847 5.933 4.486 4.209
22.434
3.959
24.803 25.968
3.587 3.428
29.053 30.071 33.655
3.071 2.969 2.660
34.572 37.020 37.734 47.768
2.592 2.426 2.382 1.903
C e l l dimensions:
A1P0I+
#5
cal
index
11.876 6.857 5.938 4.489 4.213 3.971 3.962 3.959 3.590 3.428 3.294 3.072 3.068 2.969 2.659 2.592 2.592 2.427 2.381 1.903
100 110 200 210 002 102 211 300 112 220 310 212 311 400 222 321 410 402 213 512
a « 13.713 c * 8.427 y - 120°
These data were c o l l e c t e d on a Siemens D500 d i f f r a c t o m e t e r , using monochromatic CuKa r a d i a t i o n , 6 seconds count time and a 0.01° 28 step s i z e . The r e c e i v i n g s l i t was 0.05° and the apertures were 0.3°. The data were processed using programs w r i t t e n a t Union Carbide Corporation.
F i g u r e 2. S t e r e o p l o t showing branches l i n k i n g t e t r a h e d r a l nodes o f framework #81.
In Intrazeolite Chemistry; Stucky, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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INTRAZEOLITE
CHEMISTRY
After careful search, a small hexagonal prism 30 urn across and 180 ym long with a sharp p a r a l l e l extinction was found to give sharp diffractions throughout reciprocal space. It was attached to a glass fiber and sprayed with polyurethane to control the humidity. Diffraction intensities were collected with graphite-monochromatized CuKa radiation on a Picker diffractometer. Centering of 20 diffractions (56°
