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Growth of large crystals of silicoaluminophosphate molecular sieve SAPO-5
Growth of large crystals of silicoaluminophosphate molecular sieve SAPO-5 G. Finger CentralInstitute of Physical Chemistry, Academy of Sciences of the German Democratic Republic, Berlin, GDR and J. Kornatowski Institute of Chemistry, Nicolaus Copernicus University, Toru~, Poland In a systematic experimental study of the system AI203-P2Os-SiO2-TEA-H20, large crystals of SAPO-5 up to 580 i~m were obtained and the yield was within the range of 60-80%. The morphology of the crystals is strongly dependent on both the composition and the preparation of the gel.
Keywords: Synthesis; molecular sieve, silicoaluminophosphate; SAPO-5; large crystals; morphology
INTRODUCTION Numerous patents have been filed and papers published since the first synthesis of microporous aluminophosphates (ALPOs) in 19821'2 and, in particular, of silicoaluminophosphate molecular sieves (SAPOs) in 1984. 3"4 These phases were synthesized mostly in the form of fine powders composed of small crystals or growth aggregates. Considering the growth of large crystals, some first efforts were published for the AFI structure only. Electron micrographs of ALPO4-5 hexagonal rods up to about 150 ~tm were published in Ref. 5. Applying some factorial design, Miiller and Unger and Mfiller et al. obtained A1PO4-5 crystals up to 600 and 500 ~tm, respectively, but in very low yield. 6'7 Finger et al. synthesized hexagonal SAPO-5 crystals up to 100 ~tm long, showing the influence of silicon content in the gels on silicon incorporation and crystal morphology, s We performed systematic examinations of the SAPO-5 system with the aim of growing large crystals and to obtain them in a good yield. Detailed studies on this system will be published separately. 9
ratios of the fundamental components in the gels are given in Table 1 as well. The substances used for forming the gel were 85% orthophosphoric acid (H3PO4), an aluminium oxide hydrate sol (containing 2.345% in weight of A1203), a silica sol (containing 30% in weight of SiO2), triethylamine (TEA), and bidistilled water. The gels were formed as follows: By mixing together, both sols were reacted forming mixture A. Then, solution B composed of H3PO4, water, and TEA mixed together was dropped under vigorous stirring into mixture A. If necessary, strong acid was added to keep the pH value at 3.5 _+ 0.2. Then, the gel was filled into autoclaves and placed in an air-heated oven for appropriate periods. After the completion of crystallization, the autoclaves were cooled down, samples filtered, and the SAPO-5 crystals separated from byproduct if necessary, then washed, dried, and calcined at about 925 K. The products were examined with X-ray technique, light and scanning electron microscopy, and 29Si MAS n.m.r, technique.
EXPERIMENTAL The hydrothermal synthesis of SAPO-5 crystals was performed in PTFE-lined stainless-steel autoclaves under autogeneous pressure within the temperature range of 453-473 K for periods given in Table I. The Address reprint requests to Dr. Finger at the Central Institute of Physical Chemistry, Academy of Sciences of the German Democratic Republic, Rudower Chaussee 5, DDR-1199 Berlin, GDR. Received 10 August 1989; accepted 2 November 1989
© 1990 Butterworth-Heinemann
Table I Ratios of components in the gels forming large crystals of SAPO-5 and periods of crystallization Group of samples
PzOs AI203
TEA P2Os
H20 TEA
SiO2 AI203
Crystallization period (d)
A
1.0ol.05
B
1.0-1.05
C
1.0-1.05
1.5 1.5 3-5
~>400 300-400 />300
~<0.3 ~<0.3 ~<0.3
~< 10 ~< 7 ~< 5
ZEOLITES, 1990, Vol 10, July/August 615
Growth of large crystals of SAPO-5: G. Finger and J. Kornatowski
The experiments were successful in obtaining large SAPO-5 crystals in good yield. Choosing appropriate gel compositions, differently sized crystals can be synthesized ranging from about 30 ~tm up to about 580 Ixm long accompanied by various amounts of byproducts. In Table 2, some examples for the larger-sized crystals have been compiled. All show the euhedral form of hexagonal needles, differing in morphology. Twins or larger agglomerates occur very rarely (Figures 1-3). The XRD pattern of the
crystals obtained corresponds exactly to that of the AFI structure. From the more dilute gels (group A), the largest crystals form and, most are slightly spindle-like shaped (Figure 1). T h e more concentrated gels (groups B and C) yield shorter but almost or even completely regular hexagonal rods (Figures 2 and 3). SAPO-5 crystals of similar length along the c-axis but more stout, i.e., of lower aspect ratio length/width, can be grown from the gels with higher TEA content (Figures 2 and 3). The yield of the SAPO-5 phase exceeds 60% in mass (Table 2). The resting solid material is composed of spherulitic agglomerates of dimensions up to 30 ~tm (Figure 4) and occasionally some very small remnants of unreacted gel. These byproducts can be easily separated from the SAPO-5 crystals by simple decantation. The spherulitic particles d-spacings that are given in Table 3 could not be identified on the basis of the Powder Diffraction File (International Centre of Diffraction Data), Index 1987. Note that the diffraction lines obtained may belong to more than one phase. For all SAPO-5 samples listed above, 298i MAS
Figure I duct
SAPO-5 crystals of group A after separation of bypro-
Figure 3 SAPO-5 crystals of group C after separation of byproduct
Figure 2 SAPO-5 crystals of group B after separation of byproduct
Figure 4 Byproduct of SAPO-5 synthesis containing some SAPO-5 crystals
Table 2 Characteristics of SAPO-5 crystal charges obtained Yield of Group of samples
Range of Length of
crystals (mass %)
largest crystal a
Whole (p.m)
Most (l~m)
length/
60-70 60-80 60-70
580 280 260
120-580 100-280 80-260
300-500 150-220 150-200
10-14
A
B C
crystal length a
Aspect ratio
SAPO-5
width 6- 9 3- 6
According to light microscope observation
RESULTS
616
ZEOLITES, 1990, Vol 10, July/August
Growth of large crystals of SAPO-5: G. Finger and d. Kornatowski Table 3 X-ray Guinier data (CUK(~ radiation) for the spherulitic
byproduct particles d-spacings (A) 12.30' 8.04 5.83 5.09 4.45
Intensity m/s vw
w/m vs vvw
4.40 4.35 4.16 3.82 3.57 3.08 3.03 2.91 2.53 2.47 2.12 2.09 2.05
w vvw s w/m m m/s vw w vw vvw
1.91
vw
vw
vw vw
.
.
.
-60
vvw: very very weak; vw: very weak; w: weak; m: medium; s: strong; vs: very strong
n.m.r, spectra show the sharp signal at about - 9 5 p p m , p r o v i n g the i n c o r p o r a t i o n o f silicon on phosphorus-T-sites of the structure i0 [Figure 5, curve (a)], whereas the spherulitic particles do not contain silicon [Figure 5, curve (b)]. By 27A1 MAS n.m.r. measurement, these particles were characterized as aluminophosphate.
CONCLUSIONS W h e n growing large crystals of SAPO-5, one has to make a compromise between the crystal sizes and the phase purity. T h e latter seems to be limited to about 80% in mass.
ACKNOWLEDGEMENTS T h e authors are indebted to Prof. Dr. sc. M. Billow for initiating and supporting this work. Furthermore, they thank B. Zibrowius for the MAS n.m.r, measurem e n t and J. Richter-Mendau and Dr. E. Schierhorn for the scanning electron micrographs, and Dr. H.
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-80
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-100 PPM
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, . . . .
= .
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-120
Figure 5 29Si MAS n.m.r, spectra of products of synthesis: (a) SAPO-5 crystals; (b) spherulitic byproduct containing some SAPO-5 crystals (see Figure 4)
Fichtner for the X-ray Guinier data. The work was partially supported by VEB Leuna-Werke 'Walter Ulbricht,' the fund of the President of the Academy of Sciences of GDR, and the Polish Ministry of National Education within the Project CPBP 01.06. REFERENCES 1 2 3 4 5 6 7 8 9 10
Wilson, S.T., etal. J. Am. Chem. Soc. 1982, 104, 1146 Wilson, S.T., et al. US Pat. 4 310 440 (1982) Lok, B.M., etal. J. Am. Chem. Soc. 1984, 106, 6092 Lok, B.M., et al. US Pat. 4 440 871 (1984) Wilson, S.T., et al. ACS Symp. Ser. 218, Am. Chem. Soc., Washington, DC, 1983, p. 79 Mfiller, U. and Unger, K.K.Z. Kristallogr. 1988, 182, 190 MLiller, U., et al., in Advances in Zeolite Synthesis (Ed. M.L. Occelli) ACS Symp. Ser., Am. Chem. Soc., Washington, DC, 1989 Finger, G., et al. Bull. Soc. Chim. Belg. 1989, 98, 291 Kornatowski, J. and Finger, G. To be published Appleyard, J.P., Harris, R.K. and Fitch, F.R. Chem. Lett. 1985, 1747
ZEOLITES, 1990, Vol 10, July/August
617
Keywords: Synthesis; molecular sieve, silicoaluminophosphate; SAPO-5; large crystals; morphology
INTRODUCTION Numerous patents have been filed and papers published since the first synthesis of microporous aluminophosphates (ALPOs) in 19821'2 and, in particular, of silicoaluminophosphate molecular sieves (SAPOs) in 1984. 3"4 These phases were synthesized mostly in the form of fine powders composed of small crystals or growth aggregates. Considering the growth of large crystals, some first efforts were published for the AFI structure only. Electron micrographs of ALPO4-5 hexagonal rods up to about 150 ~tm were published in Ref. 5. Applying some factorial design, Miiller and Unger and Mfiller et al. obtained A1PO4-5 crystals up to 600 and 500 ~tm, respectively, but in very low yield. 6'7 Finger et al. synthesized hexagonal SAPO-5 crystals up to 100 ~tm long, showing the influence of silicon content in the gels on silicon incorporation and crystal morphology, s We performed systematic examinations of the SAPO-5 system with the aim of growing large crystals and to obtain them in a good yield. Detailed studies on this system will be published separately. 9
ratios of the fundamental components in the gels are given in Table 1 as well. The substances used for forming the gel were 85% orthophosphoric acid (H3PO4), an aluminium oxide hydrate sol (containing 2.345% in weight of A1203), a silica sol (containing 30% in weight of SiO2), triethylamine (TEA), and bidistilled water. The gels were formed as follows: By mixing together, both sols were reacted forming mixture A. Then, solution B composed of H3PO4, water, and TEA mixed together was dropped under vigorous stirring into mixture A. If necessary, strong acid was added to keep the pH value at 3.5 _+ 0.2. Then, the gel was filled into autoclaves and placed in an air-heated oven for appropriate periods. After the completion of crystallization, the autoclaves were cooled down, samples filtered, and the SAPO-5 crystals separated from byproduct if necessary, then washed, dried, and calcined at about 925 K. The products were examined with X-ray technique, light and scanning electron microscopy, and 29Si MAS n.m.r, technique.
EXPERIMENTAL The hydrothermal synthesis of SAPO-5 crystals was performed in PTFE-lined stainless-steel autoclaves under autogeneous pressure within the temperature range of 453-473 K for periods given in Table I. The Address reprint requests to Dr. Finger at the Central Institute of Physical Chemistry, Academy of Sciences of the German Democratic Republic, Rudower Chaussee 5, DDR-1199 Berlin, GDR. Received 10 August 1989; accepted 2 November 1989
© 1990 Butterworth-Heinemann
Table I Ratios of components in the gels forming large crystals of SAPO-5 and periods of crystallization Group of samples
PzOs AI203
TEA P2Os
H20 TEA
SiO2 AI203
Crystallization period (d)
A
1.0ol.05
B
1.0-1.05
C
1.0-1.05
1.5 1.5 3-5
~>400 300-400 />300
~<0.3 ~<0.3 ~<0.3
~< 10 ~< 7 ~< 5
ZEOLITES, 1990, Vol 10, July/August 615
Growth of large crystals of SAPO-5: G. Finger and J. Kornatowski
The experiments were successful in obtaining large SAPO-5 crystals in good yield. Choosing appropriate gel compositions, differently sized crystals can be synthesized ranging from about 30 ~tm up to about 580 Ixm long accompanied by various amounts of byproducts. In Table 2, some examples for the larger-sized crystals have been compiled. All show the euhedral form of hexagonal needles, differing in morphology. Twins or larger agglomerates occur very rarely (Figures 1-3). The XRD pattern of the
crystals obtained corresponds exactly to that of the AFI structure. From the more dilute gels (group A), the largest crystals form and, most are slightly spindle-like shaped (Figure 1). T h e more concentrated gels (groups B and C) yield shorter but almost or even completely regular hexagonal rods (Figures 2 and 3). SAPO-5 crystals of similar length along the c-axis but more stout, i.e., of lower aspect ratio length/width, can be grown from the gels with higher TEA content (Figures 2 and 3). The yield of the SAPO-5 phase exceeds 60% in mass (Table 2). The resting solid material is composed of spherulitic agglomerates of dimensions up to 30 ~tm (Figure 4) and occasionally some very small remnants of unreacted gel. These byproducts can be easily separated from the SAPO-5 crystals by simple decantation. The spherulitic particles d-spacings that are given in Table 3 could not be identified on the basis of the Powder Diffraction File (International Centre of Diffraction Data), Index 1987. Note that the diffraction lines obtained may belong to more than one phase. For all SAPO-5 samples listed above, 298i MAS
Figure I duct
SAPO-5 crystals of group A after separation of bypro-
Figure 3 SAPO-5 crystals of group C after separation of byproduct
Figure 2 SAPO-5 crystals of group B after separation of byproduct
Figure 4 Byproduct of SAPO-5 synthesis containing some SAPO-5 crystals
Table 2 Characteristics of SAPO-5 crystal charges obtained Yield of Group of samples
Range of Length of
crystals (mass %)
largest crystal a
Whole (p.m)
Most (l~m)
length/
60-70 60-80 60-70
580 280 260
120-580 100-280 80-260
300-500 150-220 150-200
10-14
A
B C
crystal length a
Aspect ratio
SAPO-5
width 6- 9 3- 6
According to light microscope observation
RESULTS
616
ZEOLITES, 1990, Vol 10, July/August
Growth of large crystals of SAPO-5: G. Finger and d. Kornatowski Table 3 X-ray Guinier data (CUK(~ radiation) for the spherulitic
byproduct particles d-spacings (A) 12.30' 8.04 5.83 5.09 4.45
Intensity m/s vw
w/m vs vvw
4.40 4.35 4.16 3.82 3.57 3.08 3.03 2.91 2.53 2.47 2.12 2.09 2.05
w vvw s w/m m m/s vw w vw vvw
1.91
vw
vw
vw vw
.
.
.
-60
vvw: very very weak; vw: very weak; w: weak; m: medium; s: strong; vs: very strong
n.m.r, spectra show the sharp signal at about - 9 5 p p m , p r o v i n g the i n c o r p o r a t i o n o f silicon on phosphorus-T-sites of the structure i0 [Figure 5, curve (a)], whereas the spherulitic particles do not contain silicon [Figure 5, curve (b)]. By 27A1 MAS n.m.r. measurement, these particles were characterized as aluminophosphate.
CONCLUSIONS W h e n growing large crystals of SAPO-5, one has to make a compromise between the crystal sizes and the phase purity. T h e latter seems to be limited to about 80% in mass.
ACKNOWLEDGEMENTS T h e authors are indebted to Prof. Dr. sc. M. Billow for initiating and supporting this work. Furthermore, they thank B. Zibrowius for the MAS n.m.r, measurem e n t and J. Richter-Mendau and Dr. E. Schierhorn for the scanning electron micrographs, and Dr. H.
.
.
.
.
.
.
.
.
.
.
.
.
.
-80
.
.
.
.
.
.
.
.
.
.
.
.
.
.
-100 PPM
.
, . . . .
= .
.
.
.
.
.
-120
Figure 5 29Si MAS n.m.r, spectra of products of synthesis: (a) SAPO-5 crystals; (b) spherulitic byproduct containing some SAPO-5 crystals (see Figure 4)
Fichtner for the X-ray Guinier data. The work was partially supported by VEB Leuna-Werke 'Walter Ulbricht,' the fund of the President of the Academy of Sciences of GDR, and the Polish Ministry of National Education within the Project CPBP 01.06. REFERENCES 1 2 3 4 5 6 7 8 9 10
Wilson, S.T., etal. J. Am. Chem. Soc. 1982, 104, 1146 Wilson, S.T., et al. US Pat. 4 310 440 (1982) Lok, B.M., etal. J. Am. Chem. Soc. 1984, 106, 6092 Lok, B.M., et al. US Pat. 4 440 871 (1984) Wilson, S.T., et al. ACS Symp. Ser. 218, Am. Chem. Soc., Washington, DC, 1983, p. 79 Mfiller, U. and Unger, K.K.Z. Kristallogr. 1988, 182, 190 MLiller, U., et al., in Advances in Zeolite Synthesis (Ed. M.L. Occelli) ACS Symp. Ser., Am. Chem. Soc., Washington, DC, 1989 Finger, G., et al. Bull. Soc. Chim. Belg. 1989, 98, 291 Kornatowski, J. and Finger, G. To be published Appleyard, J.P., Harris, R.K. and Fitch, F.R. Chem. Lett. 1985, 1747
ZEOLITES, 1990, Vol 10, July/August
617