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Synthesis, structural characterization and some properties of a germanic analogue of phillipsite
Mat. Res. Bull. Vol. Ii, pp. 813-8Z0, 1976. P e r g a m o n Press, Inc. Printed in the United States.
SYNTHESIS,
STRUCTURAL C H A R A C T E R I Z A T I O N AND SOME PROPERTIES GERMANIC ANALOGUE OF PHILLIPSITE
OF A
G. Poncelet, k4. L. Dubru and T. Lux Laboratoire de Physico-Chimie Min~rale Universit~ Catholique de Louvain Place Croix du Sud 1 B-1348 Louvain-la-Neuve (Belgium)
(Received May 17, 1976; C o m m u n i c a t e d by S. Arnelinckx)
ABSTRACT G~rmanic phillipsite, with the chemical formula K~O.AI203.2GeO2.xH20, has been synthesized at 90°C from K ~ containing gels. The parameters of its p{imitive (tetra@onal) unit c e l l are : a = b = 14.515 A and c = 9.733 A. IR spectroscopy shows that all the absorption bands are shifted towards longer wavelengths. The structural stability towards ion-exchange has been followed by X-ray diffraction. Adsorption isotherms of N 2 and H20 have been measured. The pore opening of K-germanic phillipsite is approximately 3 ~.
Introduction Synthetic zeolites with partial or total substitution of structural aluminium and/or silicon atoms have been described in the literature and recently reviewed by Breck (i). Gallium and germanium have been often used to substitute, partially or totally, the lattice aluminium and silicon atoms, respectively. Barrer et al. (2) are among the first authors who have studied the crystallization of zeolites from gallium and g e r m a n i u m containing gels. Gallium analogues of the X and Y zeolites were reported by Selbin and Mason (3), and Argauer (4). A germanic near faujasite zeolite was synthesized by Lerot et al. (5). These authors showed that the cubic unit cell parameter of this zeolite was slightly higher (25,59 A) than in the silicic X-zeolite. Some surface and catalytic properties of this Gefaujasite were further reported (6,7). Recently, Poncelet et al. (8) described the results of low temperature syntheses (90-220°C) carried out in the system K20-AI203-GeO2-H20.
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Vol. II, No. 7
The present study aims to provide additional data on the synthesis and some properties of a germanic phillipsite. Experimental Reagents Ge02, at the electronic purity level (from M~tallurgie Hoboken s.a.) was used as source of germanium. A l u m i n i u m was supplied either as metallic powder or from aluminium foils dissolved in potassium hydroxide (p.a. Merck). Procedure Given amounts of germanium oxide and potassium aluminate were dissolved in adequate volumes of distilled water, or in potassium hydroxide solutions. The dissolution was carried out directly in teflon containers w h i c h were hermetically closed and heated in an oven at 90°C. After 72 hours of reaction, the mixture was centrifuged and washed several times with distilled water, and oven-dried at I10°C before examination. The use of teflon or any other silica free reaction vessel is a critical requirement to avoid contamination by silica. Indeed, at high pH values, silica would readily dissolve from the walls and compete with germanium oxide and crystallize into silicic zeolites. Product examination The solid phase was X-rayed on a Philips unit using Nifiltered K~ radiation of copper anticathode fed at 40 kV and 20 mA. IR spectra were recorded with a Perkin-Elmer 180 grating instrument. The samples were prepared as KBr pellets. Chemical analyses of the synthetic phillipsite were carried out using the procedure described elsewhere (5). Results Synthesis of germanic phillipsite A few compositions of the starting gel mixtures expressed in molar percentages of the anhydrous oxides, are indicated in Table i. All the starting gels were prepared with a water/solid weight ratio of 2. The initial compositions are spotted in the triangular projection shown in Fig. i, where the points within the dashed zone correspond to the gels which crystallized into a very good germanic phillipsite. The yields of crystalline material, indicated in Table i, have been appreciated from the intensity of the X-ray diffraction peaks. Very good yields mean 80-100% germanic phillipsite; good: 40-80% and mean : 20-40%. As far as yields and crystallinity are concerned, the best results were obtained from gels having the following initial molar composition: Ge02: 35-40%; A1203: 20%; K20: 45-40%. The syntheses were generally carried out at 90°C for 72 hours. However, a few experiments have been performed at shorter times with gels having the following molar composition GeO2: 35; A1203: 20; K20: 45. The X-ray diffraction diagrams showed that very well crystallized phillipsite was synthesized after only
Vol. ll, No. 7
GERMANIC
ANALOGUE
TABLE
OF PHILLIPSITE
815
1
Molar C o m p o s i t i o n of the Initial Gel Mixtures and Yields Phillipsite, E s t i m a t e d from the X-ray Peak Heights.
Molar GeO 2 i0 I0 I0 I0 15 20 20 20 20 20 22 27 28 30 30 30 30
composition AI203 i0 20 30 40 40 i0 20 25 30 40 33 50 5 10 15 20 25
(%1
Yields
K20 80 70 60 50 45 70 60 55 50 40 45 23 67 60 55 50 45
GeO 2 mean good good mean good good good good good good mean mean mean mean mean V good V good
30 minutes. The kinetics of the crystallization has not been studied in detail, but, considering that it was completed after 72 hrs, then after 30 min, 82 % of crystalline p h i l l i p s i t e was formed; after 1.5 hour, 84%; after "18 hrs, 98%. Germanic phillipsite is thus readily synthesized when the composition of the starting gel is suitable. Determination parameters
Molar
30 30 35 40 40 40 40 40 42 45 45 46 48 50 50 50 50
composition
(%)
AI203
K20
30 40 20 5 i0 20 30 40 21 15 i0 24 16 i0 19 22 30
40 30 45 55 50 40 30 20 37 40 15 30 36 40 31 28 20
in Ge-
Yields
V good good V good mean good V good mean mean mean V good mean mean mean mean mean mean mean
G,o2
of the unit cell
The unit cell parameters of G e - p h i l l i p s i t e were e s t a b l i s h e d according to the method for powder diagram indexing developed by T a u p i n (9) and Jamard et al. (I0). The observed and calculated d values and the corresponding hkl's are compiled in Table 2. The parameters of the primitive (tetragonal) un~to cell are : a = ~ = 14.5155 A and c = 9.7331 A. These values
50
FIG.
AI203
I
Triangular projection of the system K20-AI203-GeO 2 . Dashed zone: very well crystallized phillipsite.
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TABLE 2 Experimental and Calculated d Values and Miller Indices.
2 Oexp. 12 52 17 32 18 24 19 33 21 37 21 96 24 50 25 28 25 90 26 85 27.51 27.70 28.83 30.73 32.77 33.22 33.81 34.80 35.90 36.90
37.15 38.21 39.10 39.56 39.82 41.02 41.60 42.18 43.65 45.10 45.85 46.03 46.65 47.44 47.66 48.50 48.71 49.09 50.87 51.61 51.79 52.55 52.70 53.35 53,80 53.92
dexp.
dcal.
7 5 4 4 4 4 3 3
0699 1199 8636 5918 1578 0474 6333 5229
7.0626 5.1320 4.8666 4.5902 4.1517
3 3 3 3 3
4400 3204 2422 2181 0967
2 9094 2 7328 2 6968 2 6511 2 5779 2 4980 2 4359 2 4201 3 3553 2 3037 2 2780 2.2637 2.1984 2.1691 2.1406 2.0718 2.0085 1.9791
56.84
1.9701 1.9453 1.9164 1.9081 1.8754 1.8678 1.8558 1.7934 1.7709 1.7652 1.7414 1.7354 1.7158 1.7039 1.7004 1.6908 1.6698 1.6570 1.6184
57.21 58.28 59.39 59.92 60.34 62.64 64,79 65.29 65.96 66.16 66.92 67.15 67.34
1.6102 1.5818 1.5549 1.5424 1.5339 1.4818 1.4377 1.4279 1.4162 1.4124 1.3982 1.3940 1.3905
54.20 54.94
95.40
4.0420
3.6289 3.5205 3.4312 3.3106
3.2444 3.2277 3.0935 2.9091 2.7323 2.6955 2.6494 (2.5660) 2.4932 2.4333 2.4193 2.3542 2.3071 2.2785 2.2669 2.1987 2.1663 2.1426 2.0733 2.0086 1.9772 1.9712 1 9469 1 9125 1 9060 1 8737 1 649 1 583 1 921 1 7704 1 7656 1 7401
1 7347 1 7156 1 7037 1 7001
1 6919 1 6696 1 6587 1 6170
1.6069 1.5817 1.5542 1.5422
1.5335 1.4810 1.4371 1.4287 1.4161 1.4125 1.3993 1.3929 1.3903
hkl 111 220 OO2 310, 311, 202, 400, 410, 302,
130 131 022 040 140 032
411, 141 O03 331 113 402, 042 511, 151 520, 313,
250, 133
303,033
342,
502,052
(440) 432, 004
600, 060, 403,043 333 204, 214,
024 124
450, 540 224 602, 612, 523, 551, 632, 641, 424, 115 730, 623, 434, 543, 315 ,
741, 444 534, 553, 604, 614, 802, 335 624 544 364 505 515 911 761 724 535
062 162 253, 700,070 171, 711 362 461 244, 005 370 263 344, 453 135
504,054
471, 811,181 354 713, 173 064, 405,045 164, 415,145 082 264, 454 634, 055 155 191 671, 274 355
425,245 345,435
921,291
406
046
913 1011 506 555 465 834
193 1101 056, 436,346 715, 175 645 384, 725,275 1 0 3 0 , 3100
007
7
Vol. II, No. 7
GERMANIC
ANALOGUE
OF PHILLIPSITE
817
are s i g n i f i c a n t l y d i f f e r e n t from th~se of the silicic h o m o l o g u e where a = c = 14.25 ~ and b = 9.96 A (ii). These d i f f e r e n c e s are due to the lattice g e r m a n i u m atoms w h i c h are bigger than the o silicon atoms (ionic radii of Ge 4+ and Si 4+ are 0.53 ~ and 0.41 A, r e s p e c t i v e l y (12)). Empirical
formula
The empirical formula of germanic phillipsite, c a l c u l a t e d from the chemical analysis data, is: K20.AI203.2GeO2.2H20. Variations of the c o e f f i c i e n t s not higher than 5% were observed. Thus, in Ge-phillipsite, there is one g e r m a n i u m atom for each a l u m i n i u m atom. This i:i ratio is a p p r e c i a b l y lower than the 1.7:1 to 2.4:1 Si/AI values g e n e r a l l y found in silicic p h i l l i p s i t e (ii). IR S p e c t r o s c o p y The IR spectra of germanic p h i l l i p s i t e and of a silicic K-M zeolite s y n t h e s i z e d by Bosmans et al (13), scanned in the 1200-300 cm -I region, are shown in Fig. 2. The spectrum of K-M is m u c h similar to the one of W zeolite obtained by F l a n i g e n et al.
(14). As it may be expected, the heavier lattice Ge atoms produce a shift of the absorption bands towards longer wavelengths. A s s u m i n g isolated Ge-O and Si-O harmonic oscillators, like in Ge- and Si-based tetrahedra, a simple c a l c u l a t i o n indicates that the b a t h o c h r o m a tic effect would displace the c o r r e s p o n d i n g a b s o r p t i o n bands o B by a factor 1.13. The o b s e r v e d values range b e t w e e n 1.09 and 1.20, d e p e n d i n g upon the absorption band. Such v a r i a t i o n s from the theoretical value are easily I ~1 i i I J J J 1100 1 0 0 0 900 800 700 600 500 4 0 0 cm "~ understandable. Indeed, because of the low value of the Ge/AI ratio, pure isolated harmonic Ge-O o s c i l l a t o r s are rather FIG. 2 imporbable. The slight d i f f e r e n IR spectra of G e - p h i l l i p s i t e ces in the unit cell p a r a m e t e r s (A) and K-M (B) of the two zeolites might also influence the v i b r a t i o n modes and in any case, the stretching modes should be more sensitive to the b a t h o c h r o m a t i c effect than the d e f o r m a t i o n modes. o
Cation
exchange
Samples of germanic K r p h i l l i p s i t e have been e x c h a n a e d _ w i t h the following cations: Na t , NH~, Mg +2, Ca +2, Ni +2, Cu +~, Co +2 and Zn +2. The exchanges were c a r r i e d out using 0.5 N solutions under static and stirring conditions. After exchange, the samples were washed several times with d i s t i l l e d water and o v e n - d r i e d at 60°C. C a t i o n uptakes were e s t a b l i s h e d from the atomic absorption data. NH~ c o n t e n t was d e t e r m i n e d by m i c r o k j e l d h a l d i s t i l l a t i o n followed by back-titration.
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Vol. II, No. 7
Dried samples were X-rayed in order to estimate the loss in crystallinity resulting from the exchange operation.This was done by measuring the intensities of ~he diffraction peaks at 21.3 o 28 (4.17 A) and 30.7 ° 28 (2.91 A) and comparing them to those of unexchanged samples. Table 3 indicates the nature of the exchanging salts, the exchange percentages achieved under static and stirring conditions, and the relative intensities of the diffraction peaks. The exchange percentages were calculated on the basis of 5.4 meq/g, w h i c h corresponds to the K + (or AI) content (total C.E.C.). TABLE 3 Nature of the Exchanging Salt, Exchange Percentages and Relative Intensities of Two Diffraction Lines at 21.3 ° 28 and 30.7 ° 28 of Ge-Phillipsite Exchanged under Static and Stirring Conditions.
Exchanging salt
NaCl NH4Cl Ca-acetate MgSO 4 Zn-acetate CuCI 2 CoCI 2 NiCI 2
Exchange percentages stat. stir.
Relative
I00 20 19 14 32 49 32 22
I00 41 97 64 35 31 45 60
i00 34 74 22 64 77 37 60
intensities of the peaks at 21.3°28 30.7028 star. stir. stat. stir. i00 46 96 60 22 24 24 -
I00 38 90 67 35 33 50 55
I00 45 90 65 17 22 25 -
Higher percentages were reached when the exchange operation was carried out under stirring conditions. K + was completely exchanged by Na + under static conditions. Ca +2 and Cu +2, and Zn +2 and Ni +z u~takes represented nearly 75% and 60% of the total exchange capacity. N ~ , Mg +2 and Co 2+ did not exchange with K + to a great extent, at least under the experimental procedure used. With exchange cations belonging to the metal group, the X-ray diffraction diagrams showed that stirring the system also resulted in smaller intensities of the peaks, and accordingly, in deeper lattice breakdown. A similar observation has been reported in the case of a germanic near faujasite zeolite (5).No significative structural damage was noticed when Ge phillipsite was exchanged with Ca 2+ and Na +. Sorption
properties
Water and nitrogen adsorption isotherms were m e a s u r e d 20.5°C and at liquid nitrogen temperature, respectively, in a conventional BET apparatus, on a Ca-exchanged sample outgassed 350°C. The isotherms are illustrated in Fig. 3.
at at
The surface areas, calculated according to the "B point" method (15), are 260 m2g -I and 10 m2g -I for water and nitrogen, respectively. This clearly means that the value obtained from the N 2 adsorption isotherm corresponds to the external surface area
Vol. 1 I, No. 7
GERMANIC
of the particles, whereas the internal surface is accessible only to H20 molecules. A c c o r d i n g l y the pore opening should lie between 2.6 A and 3.6 A, w h i c h are the kinetic diameters of H20 and N 2. Under saturated humidity atmosphere, Na-exchanged germanic phillipsite was found to adsorb 16 weight percent of H20, which is very close to 17% observed for silicic phillipsite (16). Discussion
ANALOGUE
OF PHILLIPSITE
819
03
6
~4
°i
c !oi
2
o o
I Q1
I Q2
I Q3
I 04
PIpo
Germanic phillipsite readily crystallized at 90°C from p o t a s s i u m containing FIG. 3 gels. It has been shown, in Water and nitrogen adsorption a previous study (8), that the isotherms m e a s u r e d at 20.5°C initial liquid/solid ratio had and -180°C on a Ca-Ge philliplittle effect, if any, on the crystallization, provided the site. initial molar composition of the gel was suitable. Such compositions would fall within the dashed zone of Fig. i. It was also reported that increasing replacement of K + by Na + in the starting gel resulted in the progressive development of the germanic analogue of hydroxy-sodalite. Pure Na + gels never crystallized into Na-phillipsite. Total substitution of Ge for Si atoms in the framework results in slight changes in the unit cell parameters, due to the size of Ge atoms. IR absorption bands are shifted towards smaller wave number by a factor of approximately 1.13, as can be expected from the bathochromatic effect. The fact that the main Ge-O stretching vibration is shifted near 860 cm -I clears up the spectral region near 1100-1000 cm -I, which, in the silicic homologues, is not accessible to the IR investigation of adsorbed molecules. In the case of Ge near faujasite, this feature was illustrated by an IR study of the dehydration of isopropanol (6). An important difference between the germanic phillipsite and the silicic analogues appears in the Ge/AI ratio vis. the Si/AI ratio. A ratio of 1 was also found in the germanic near faujasite, and attempts to increase the Ge content, i.e. to synthesize the germanic analogues of the X and Y molecular sieves, always failed. With the K-gels, increasing the Ge/AI ratios in the starting mixture resulted in the progressive d e v e l o p m e n t of acidic p o t a s s i u m germanate, KH3Ge206, at the expenses of K-phillipsite. Those were the phases synthesized at 90°C (8). As for the germanic near faujasite, the formation of phillipsite seems to occur only when one GeO 4 tetrahedron is sandwiched between two AIO~ tetrahedra. Excess g e r m a n i u m is demixted and crystallizes into a potassium germanate.
8Z0
G. P O N C E L E T ,
et al
Vol. ii. No. 7
The polanizing field of the exchange cations has been advocated to account for the structural damage occuring when X and Y silicic sieves are exchanged with metal cations (17). It is also known that the Y sieve, with a higher Si/AI ratio, is more stable than the X sieve. It is expected that if the Si/AI ratio still decreases, the structural stability of the framework would also decrease. This was observed for the Ge near faujasite where the Ge/AI ratio is i:i. Ge-philllpsite with a Ge/AI ratio i:i behaves similarly. Another factor which also contributes to weaken the framework is that, because of its ionic radius, Ge is at the limit of stability of the four-fold to the six-fold coordination. A k n o w l e d @ e m e n t : The authors acknowledge Prof. H. Bosmans and E. Tambuyzer of the L a b o r a t o r i u m voor Minerale Scheikunde,Katholieke Universiteit Leuven,for the determination of the unit cell parameters. Bibliography I. D.W. Breck, Zeolite Molecular Sieves, p. 320, J. Wiley and Sons, New York (1974). 2. R.M. Barrer, J.W. Baynham, F.W. Bultitude and W.M. Meier, J. Chem. Soc. 195 (1959). 3. J. Selbin anf R.B. Mason, J. Inorg. Nucl. Chem. 20, 222 (1961). 4. R.J. Argauer, U.S. Pat. 3.431.219 (1969). 5. L. Lerot, G. Poncelet and J.J. Fripiat, Mat. Res. Bull. 9, 979 (1974). 6. L. Lerot, G. Poncelet, M.L. Dubru and J.J. Fripiat, J. Catal. 37, 396 (1975). 7. L. Lerot, G. Poncelet and J.J. Fripiat, J. Solid State Chem. 12, 283 (1975). 8. G. Poncelet and M. Lauriers, Mat. Res. Bull. 10, 1205 (1975). 9. D. Taupin, J. Appl. Cryst. 178, 17 (1968). I0. C. Jamard, D. Taupin et A. Guinier, Bull. Soc. Franq. Min~r. Cristal. 89, 312 (1966). Ii. D.W. Breck, same ref. as i, p. 170. 12. L. Pauling, The Nature of the Chemical Bond, Cornell Univ. Press p. 514 (1960). 13. H. Bosmans, E. Tambuyzer, J. Paenhuys, L. Yhen and J. Vanchuysen. Molecular Sieves, Adv. Chem. Series 121, Am. Chem. Soc. Washington D.C., p. 179 (1973). 14. E.M. Flanigen, H. Khatami and H.A. Szymanski, "Molecular Sieve Zeolites" Advan. Chem. Ser. i01, Amer. Chem. Soc. Washington D.C., p. 201 (1971). 15. P.N. Emmett and S. Brunauer, J. Am. Chem. Soc. 59, 1553 (1937). 16. D.W. Breck, same ref. as i, p. 626. 17. M. von Selenina, Zeitschr. Anorg. Allg. Chem. 2, 179 (1972).
SYNTHESIS,
STRUCTURAL C H A R A C T E R I Z A T I O N AND SOME PROPERTIES GERMANIC ANALOGUE OF PHILLIPSITE
OF A
G. Poncelet, k4. L. Dubru and T. Lux Laboratoire de Physico-Chimie Min~rale Universit~ Catholique de Louvain Place Croix du Sud 1 B-1348 Louvain-la-Neuve (Belgium)
(Received May 17, 1976; C o m m u n i c a t e d by S. Arnelinckx)
ABSTRACT G~rmanic phillipsite, with the chemical formula K~O.AI203.2GeO2.xH20, has been synthesized at 90°C from K ~ containing gels. The parameters of its p{imitive (tetra@onal) unit c e l l are : a = b = 14.515 A and c = 9.733 A. IR spectroscopy shows that all the absorption bands are shifted towards longer wavelengths. The structural stability towards ion-exchange has been followed by X-ray diffraction. Adsorption isotherms of N 2 and H20 have been measured. The pore opening of K-germanic phillipsite is approximately 3 ~.
Introduction Synthetic zeolites with partial or total substitution of structural aluminium and/or silicon atoms have been described in the literature and recently reviewed by Breck (i). Gallium and germanium have been often used to substitute, partially or totally, the lattice aluminium and silicon atoms, respectively. Barrer et al. (2) are among the first authors who have studied the crystallization of zeolites from gallium and g e r m a n i u m containing gels. Gallium analogues of the X and Y zeolites were reported by Selbin and Mason (3), and Argauer (4). A germanic near faujasite zeolite was synthesized by Lerot et al. (5). These authors showed that the cubic unit cell parameter of this zeolite was slightly higher (25,59 A) than in the silicic X-zeolite. Some surface and catalytic properties of this Gefaujasite were further reported (6,7). Recently, Poncelet et al. (8) described the results of low temperature syntheses (90-220°C) carried out in the system K20-AI203-GeO2-H20.
813
814
G. P O N C E L E T ,
et al
Vol. II, No. 7
The present study aims to provide additional data on the synthesis and some properties of a germanic phillipsite. Experimental Reagents Ge02, at the electronic purity level (from M~tallurgie Hoboken s.a.) was used as source of germanium. A l u m i n i u m was supplied either as metallic powder or from aluminium foils dissolved in potassium hydroxide (p.a. Merck). Procedure Given amounts of germanium oxide and potassium aluminate were dissolved in adequate volumes of distilled water, or in potassium hydroxide solutions. The dissolution was carried out directly in teflon containers w h i c h were hermetically closed and heated in an oven at 90°C. After 72 hours of reaction, the mixture was centrifuged and washed several times with distilled water, and oven-dried at I10°C before examination. The use of teflon or any other silica free reaction vessel is a critical requirement to avoid contamination by silica. Indeed, at high pH values, silica would readily dissolve from the walls and compete with germanium oxide and crystallize into silicic zeolites. Product examination The solid phase was X-rayed on a Philips unit using Nifiltered K~ radiation of copper anticathode fed at 40 kV and 20 mA. IR spectra were recorded with a Perkin-Elmer 180 grating instrument. The samples were prepared as KBr pellets. Chemical analyses of the synthetic phillipsite were carried out using the procedure described elsewhere (5). Results Synthesis of germanic phillipsite A few compositions of the starting gel mixtures expressed in molar percentages of the anhydrous oxides, are indicated in Table i. All the starting gels were prepared with a water/solid weight ratio of 2. The initial compositions are spotted in the triangular projection shown in Fig. i, where the points within the dashed zone correspond to the gels which crystallized into a very good germanic phillipsite. The yields of crystalline material, indicated in Table i, have been appreciated from the intensity of the X-ray diffraction peaks. Very good yields mean 80-100% germanic phillipsite; good: 40-80% and mean : 20-40%. As far as yields and crystallinity are concerned, the best results were obtained from gels having the following initial molar composition: Ge02: 35-40%; A1203: 20%; K20: 45-40%. The syntheses were generally carried out at 90°C for 72 hours. However, a few experiments have been performed at shorter times with gels having the following molar composition GeO2: 35; A1203: 20; K20: 45. The X-ray diffraction diagrams showed that very well crystallized phillipsite was synthesized after only
Vol. ll, No. 7
GERMANIC
ANALOGUE
TABLE
OF PHILLIPSITE
815
1
Molar C o m p o s i t i o n of the Initial Gel Mixtures and Yields Phillipsite, E s t i m a t e d from the X-ray Peak Heights.
Molar GeO 2 i0 I0 I0 I0 15 20 20 20 20 20 22 27 28 30 30 30 30
composition AI203 i0 20 30 40 40 i0 20 25 30 40 33 50 5 10 15 20 25
(%1
Yields
K20 80 70 60 50 45 70 60 55 50 40 45 23 67 60 55 50 45
GeO 2 mean good good mean good good good good good good mean mean mean mean mean V good V good
30 minutes. The kinetics of the crystallization has not been studied in detail, but, considering that it was completed after 72 hrs, then after 30 min, 82 % of crystalline p h i l l i p s i t e was formed; after 1.5 hour, 84%; after "18 hrs, 98%. Germanic phillipsite is thus readily synthesized when the composition of the starting gel is suitable. Determination parameters
Molar
30 30 35 40 40 40 40 40 42 45 45 46 48 50 50 50 50
composition
(%)
AI203
K20
30 40 20 5 i0 20 30 40 21 15 i0 24 16 i0 19 22 30
40 30 45 55 50 40 30 20 37 40 15 30 36 40 31 28 20
in Ge-
Yields
V good good V good mean good V good mean mean mean V good mean mean mean mean mean mean mean
G,o2
of the unit cell
The unit cell parameters of G e - p h i l l i p s i t e were e s t a b l i s h e d according to the method for powder diagram indexing developed by T a u p i n (9) and Jamard et al. (I0). The observed and calculated d values and the corresponding hkl's are compiled in Table 2. The parameters of the primitive (tetragonal) un~to cell are : a = ~ = 14.5155 A and c = 9.7331 A. These values
50
FIG.
AI203
I
Triangular projection of the system K20-AI203-GeO 2 . Dashed zone: very well crystallized phillipsite.
816
G.
PONCELET,
el: al
Vol.
Ii, N o .
TABLE 2 Experimental and Calculated d Values and Miller Indices.
2 Oexp. 12 52 17 32 18 24 19 33 21 37 21 96 24 50 25 28 25 90 26 85 27.51 27.70 28.83 30.73 32.77 33.22 33.81 34.80 35.90 36.90
37.15 38.21 39.10 39.56 39.82 41.02 41.60 42.18 43.65 45.10 45.85 46.03 46.65 47.44 47.66 48.50 48.71 49.09 50.87 51.61 51.79 52.55 52.70 53.35 53,80 53.92
dexp.
dcal.
7 5 4 4 4 4 3 3
0699 1199 8636 5918 1578 0474 6333 5229
7.0626 5.1320 4.8666 4.5902 4.1517
3 3 3 3 3
4400 3204 2422 2181 0967
2 9094 2 7328 2 6968 2 6511 2 5779 2 4980 2 4359 2 4201 3 3553 2 3037 2 2780 2.2637 2.1984 2.1691 2.1406 2.0718 2.0085 1.9791
56.84
1.9701 1.9453 1.9164 1.9081 1.8754 1.8678 1.8558 1.7934 1.7709 1.7652 1.7414 1.7354 1.7158 1.7039 1.7004 1.6908 1.6698 1.6570 1.6184
57.21 58.28 59.39 59.92 60.34 62.64 64,79 65.29 65.96 66.16 66.92 67.15 67.34
1.6102 1.5818 1.5549 1.5424 1.5339 1.4818 1.4377 1.4279 1.4162 1.4124 1.3982 1.3940 1.3905
54.20 54.94
95.40
4.0420
3.6289 3.5205 3.4312 3.3106
3.2444 3.2277 3.0935 2.9091 2.7323 2.6955 2.6494 (2.5660) 2.4932 2.4333 2.4193 2.3542 2.3071 2.2785 2.2669 2.1987 2.1663 2.1426 2.0733 2.0086 1.9772 1.9712 1 9469 1 9125 1 9060 1 8737 1 649 1 583 1 921 1 7704 1 7656 1 7401
1 7347 1 7156 1 7037 1 7001
1 6919 1 6696 1 6587 1 6170
1.6069 1.5817 1.5542 1.5422
1.5335 1.4810 1.4371 1.4287 1.4161 1.4125 1.3993 1.3929 1.3903
hkl 111 220 OO2 310, 311, 202, 400, 410, 302,
130 131 022 040 140 032
411, 141 O03 331 113 402, 042 511, 151 520, 313,
250, 133
303,033
342,
502,052
(440) 432, 004
600, 060, 403,043 333 204, 214,
024 124
450, 540 224 602, 612, 523, 551, 632, 641, 424, 115 730, 623, 434, 543, 315 ,
741, 444 534, 553, 604, 614, 802, 335 624 544 364 505 515 911 761 724 535
062 162 253, 700,070 171, 711 362 461 244, 005 370 263 344, 453 135
504,054
471, 811,181 354 713, 173 064, 405,045 164, 415,145 082 264, 454 634, 055 155 191 671, 274 355
425,245 345,435
921,291
406
046
913 1011 506 555 465 834
193 1101 056, 436,346 715, 175 645 384, 725,275 1 0 3 0 , 3100
007
7
Vol. II, No. 7
GERMANIC
ANALOGUE
OF PHILLIPSITE
817
are s i g n i f i c a n t l y d i f f e r e n t from th~se of the silicic h o m o l o g u e where a = c = 14.25 ~ and b = 9.96 A (ii). These d i f f e r e n c e s are due to the lattice g e r m a n i u m atoms w h i c h are bigger than the o silicon atoms (ionic radii of Ge 4+ and Si 4+ are 0.53 ~ and 0.41 A, r e s p e c t i v e l y (12)). Empirical
formula
The empirical formula of germanic phillipsite, c a l c u l a t e d from the chemical analysis data, is: K20.AI203.2GeO2.2H20. Variations of the c o e f f i c i e n t s not higher than 5% were observed. Thus, in Ge-phillipsite, there is one g e r m a n i u m atom for each a l u m i n i u m atom. This i:i ratio is a p p r e c i a b l y lower than the 1.7:1 to 2.4:1 Si/AI values g e n e r a l l y found in silicic p h i l l i p s i t e (ii). IR S p e c t r o s c o p y The IR spectra of germanic p h i l l i p s i t e and of a silicic K-M zeolite s y n t h e s i z e d by Bosmans et al (13), scanned in the 1200-300 cm -I region, are shown in Fig. 2. The spectrum of K-M is m u c h similar to the one of W zeolite obtained by F l a n i g e n et al.
(14). As it may be expected, the heavier lattice Ge atoms produce a shift of the absorption bands towards longer wavelengths. A s s u m i n g isolated Ge-O and Si-O harmonic oscillators, like in Ge- and Si-based tetrahedra, a simple c a l c u l a t i o n indicates that the b a t h o c h r o m a tic effect would displace the c o r r e s p o n d i n g a b s o r p t i o n bands o B by a factor 1.13. The o b s e r v e d values range b e t w e e n 1.09 and 1.20, d e p e n d i n g upon the absorption band. Such v a r i a t i o n s from the theoretical value are easily I ~1 i i I J J J 1100 1 0 0 0 900 800 700 600 500 4 0 0 cm "~ understandable. Indeed, because of the low value of the Ge/AI ratio, pure isolated harmonic Ge-O o s c i l l a t o r s are rather FIG. 2 imporbable. The slight d i f f e r e n IR spectra of G e - p h i l l i p s i t e ces in the unit cell p a r a m e t e r s (A) and K-M (B) of the two zeolites might also influence the v i b r a t i o n modes and in any case, the stretching modes should be more sensitive to the b a t h o c h r o m a t i c effect than the d e f o r m a t i o n modes. o
Cation
exchange
Samples of germanic K r p h i l l i p s i t e have been e x c h a n a e d _ w i t h the following cations: Na t , NH~, Mg +2, Ca +2, Ni +2, Cu +~, Co +2 and Zn +2. The exchanges were c a r r i e d out using 0.5 N solutions under static and stirring conditions. After exchange, the samples were washed several times with d i s t i l l e d water and o v e n - d r i e d at 60°C. C a t i o n uptakes were e s t a b l i s h e d from the atomic absorption data. NH~ c o n t e n t was d e t e r m i n e d by m i c r o k j e l d h a l d i s t i l l a t i o n followed by back-titration.
818
G. P O N C E L E T ,
et al
Vol. II, No. 7
Dried samples were X-rayed in order to estimate the loss in crystallinity resulting from the exchange operation.This was done by measuring the intensities of ~he diffraction peaks at 21.3 o 28 (4.17 A) and 30.7 ° 28 (2.91 A) and comparing them to those of unexchanged samples. Table 3 indicates the nature of the exchanging salts, the exchange percentages achieved under static and stirring conditions, and the relative intensities of the diffraction peaks. The exchange percentages were calculated on the basis of 5.4 meq/g, w h i c h corresponds to the K + (or AI) content (total C.E.C.). TABLE 3 Nature of the Exchanging Salt, Exchange Percentages and Relative Intensities of Two Diffraction Lines at 21.3 ° 28 and 30.7 ° 28 of Ge-Phillipsite Exchanged under Static and Stirring Conditions.
Exchanging salt
NaCl NH4Cl Ca-acetate MgSO 4 Zn-acetate CuCI 2 CoCI 2 NiCI 2
Exchange percentages stat. stir.
Relative
I00 20 19 14 32 49 32 22
I00 41 97 64 35 31 45 60
i00 34 74 22 64 77 37 60
intensities of the peaks at 21.3°28 30.7028 star. stir. stat. stir. i00 46 96 60 22 24 24 -
I00 38 90 67 35 33 50 55
I00 45 90 65 17 22 25 -
Higher percentages were reached when the exchange operation was carried out under stirring conditions. K + was completely exchanged by Na + under static conditions. Ca +2 and Cu +2, and Zn +2 and Ni +z u~takes represented nearly 75% and 60% of the total exchange capacity. N ~ , Mg +2 and Co 2+ did not exchange with K + to a great extent, at least under the experimental procedure used. With exchange cations belonging to the metal group, the X-ray diffraction diagrams showed that stirring the system also resulted in smaller intensities of the peaks, and accordingly, in deeper lattice breakdown. A similar observation has been reported in the case of a germanic near faujasite zeolite (5).No significative structural damage was noticed when Ge phillipsite was exchanged with Ca 2+ and Na +. Sorption
properties
Water and nitrogen adsorption isotherms were m e a s u r e d 20.5°C and at liquid nitrogen temperature, respectively, in a conventional BET apparatus, on a Ca-exchanged sample outgassed 350°C. The isotherms are illustrated in Fig. 3.
at at
The surface areas, calculated according to the "B point" method (15), are 260 m2g -I and 10 m2g -I for water and nitrogen, respectively. This clearly means that the value obtained from the N 2 adsorption isotherm corresponds to the external surface area
Vol. 1 I, No. 7
GERMANIC
of the particles, whereas the internal surface is accessible only to H20 molecules. A c c o r d i n g l y the pore opening should lie between 2.6 A and 3.6 A, w h i c h are the kinetic diameters of H20 and N 2. Under saturated humidity atmosphere, Na-exchanged germanic phillipsite was found to adsorb 16 weight percent of H20, which is very close to 17% observed for silicic phillipsite (16). Discussion
ANALOGUE
OF PHILLIPSITE
819
03
6
~4
°i
c !oi
2
o o
I Q1
I Q2
I Q3
I 04
PIpo
Germanic phillipsite readily crystallized at 90°C from p o t a s s i u m containing FIG. 3 gels. It has been shown, in Water and nitrogen adsorption a previous study (8), that the isotherms m e a s u r e d at 20.5°C initial liquid/solid ratio had and -180°C on a Ca-Ge philliplittle effect, if any, on the crystallization, provided the site. initial molar composition of the gel was suitable. Such compositions would fall within the dashed zone of Fig. i. It was also reported that increasing replacement of K + by Na + in the starting gel resulted in the progressive development of the germanic analogue of hydroxy-sodalite. Pure Na + gels never crystallized into Na-phillipsite. Total substitution of Ge for Si atoms in the framework results in slight changes in the unit cell parameters, due to the size of Ge atoms. IR absorption bands are shifted towards smaller wave number by a factor of approximately 1.13, as can be expected from the bathochromatic effect. The fact that the main Ge-O stretching vibration is shifted near 860 cm -I clears up the spectral region near 1100-1000 cm -I, which, in the silicic homologues, is not accessible to the IR investigation of adsorbed molecules. In the case of Ge near faujasite, this feature was illustrated by an IR study of the dehydration of isopropanol (6). An important difference between the germanic phillipsite and the silicic analogues appears in the Ge/AI ratio vis. the Si/AI ratio. A ratio of 1 was also found in the germanic near faujasite, and attempts to increase the Ge content, i.e. to synthesize the germanic analogues of the X and Y molecular sieves, always failed. With the K-gels, increasing the Ge/AI ratios in the starting mixture resulted in the progressive d e v e l o p m e n t of acidic p o t a s s i u m germanate, KH3Ge206, at the expenses of K-phillipsite. Those were the phases synthesized at 90°C (8). As for the germanic near faujasite, the formation of phillipsite seems to occur only when one GeO 4 tetrahedron is sandwiched between two AIO~ tetrahedra. Excess g e r m a n i u m is demixted and crystallizes into a potassium germanate.
8Z0
G. P O N C E L E T ,
et al
Vol. ii. No. 7
The polanizing field of the exchange cations has been advocated to account for the structural damage occuring when X and Y silicic sieves are exchanged with metal cations (17). It is also known that the Y sieve, with a higher Si/AI ratio, is more stable than the X sieve. It is expected that if the Si/AI ratio still decreases, the structural stability of the framework would also decrease. This was observed for the Ge near faujasite where the Ge/AI ratio is i:i. Ge-philllpsite with a Ge/AI ratio i:i behaves similarly. Another factor which also contributes to weaken the framework is that, because of its ionic radius, Ge is at the limit of stability of the four-fold to the six-fold coordination. A k n o w l e d @ e m e n t : The authors acknowledge Prof. H. Bosmans and E. Tambuyzer of the L a b o r a t o r i u m voor Minerale Scheikunde,Katholieke Universiteit Leuven,for the determination of the unit cell parameters. Bibliography I. D.W. Breck, Zeolite Molecular Sieves, p. 320, J. Wiley and Sons, New York (1974). 2. R.M. Barrer, J.W. Baynham, F.W. Bultitude and W.M. Meier, J. Chem. Soc. 195 (1959). 3. J. Selbin anf R.B. Mason, J. Inorg. Nucl. Chem. 20, 222 (1961). 4. R.J. Argauer, U.S. Pat. 3.431.219 (1969). 5. L. Lerot, G. Poncelet and J.J. Fripiat, Mat. Res. Bull. 9, 979 (1974). 6. L. Lerot, G. Poncelet, M.L. Dubru and J.J. Fripiat, J. Catal. 37, 396 (1975). 7. L. Lerot, G. Poncelet and J.J. Fripiat, J. Solid State Chem. 12, 283 (1975). 8. G. Poncelet and M. Lauriers, Mat. Res. Bull. 10, 1205 (1975). 9. D. Taupin, J. Appl. Cryst. 178, 17 (1968). I0. C. Jamard, D. Taupin et A. Guinier, Bull. Soc. Franq. Min~r. Cristal. 89, 312 (1966). Ii. D.W. Breck, same ref. as i, p. 170. 12. L. Pauling, The Nature of the Chemical Bond, Cornell Univ. Press p. 514 (1960). 13. H. Bosmans, E. Tambuyzer, J. Paenhuys, L. Yhen and J. Vanchuysen. Molecular Sieves, Adv. Chem. Series 121, Am. Chem. Soc. Washington D.C., p. 179 (1973). 14. E.M. Flanigen, H. Khatami and H.A. Szymanski, "Molecular Sieve Zeolites" Advan. Chem. Ser. i01, Amer. Chem. Soc. Washington D.C., p. 201 (1971). 15. P.N. Emmett and S. Brunauer, J. Am. Chem. Soc. 59, 1553 (1937). 16. D.W. Breck, same ref. as i, p. 626. 17. M. von Selenina, Zeitschr. Anorg. Allg. Chem. 2, 179 (1972).