|
CHA |
SAPO-34 |
Al(47), P(32), Si(21) |
Contributed
by A. M.
Prakash
Verified by J. López Nieto and by N. Tusar
Type Material mR[Al17P12Si7O12] (R = morpholine)
Method A. M. Prakash, S. Unnikrishnan [1]
Batch Composition Al2O3 : 1.06 P2O5 : 1.08 SiO2 : 2.09 R : 66 H2O a,b
Source Materials
distilled water
phosphoric acid (Merck, 85%)
pseudoboehmite (Vista Catapal-B, 70% Al2O3)
fumed silica (Degussa Aerosil-200 99+% SiO2)
morpholine (Aldrich, 99% C4H9O)
Batch Preparation(for 20 g product) c
(1) [18.0 g water + 15.37 g phosphoric acid], mix
(2) [(1) + 9.20 g pseudoboehmite], add slowly (2 hours) with stirring
(3) [(2) + 10 g water], stir thoroughly for 7 hours
(4) [4.09 g fumed silica + 11.62 g morpholine + 15 g water], mix thoroughly
(5) [(3) + (4)], add (4) dropwise to (3) while stirring
(6) [(5) + 24 g water], stir thoroughly for 7 hours; pH of gel = 6.4 to 7.5
Crystallization
Vessel: 150 mL Teflon-lined autoclave
Incubation: 24 hours at 380C without agitation d
Temperature: 2000C
Time: 24 hours
Agitation: none
Product Recovery
(1) Decant the mother liquor
(2) Dilute with distilled water and filter
(3) Wash 3 to 4 times with distilled water
(4) Dry at 1000C for 6 hours
(5) Yield: 98% based on alumina
Product Characterization
XRD: SAPO-34 (CHA) [1], a0 = 13.78 Å, c0 = 14.85 Å; competing phase: AlPO4 (crystobalite) when silica and/or template concentration is low
Elemental Analysis: 1.0 Al2O3 : 0.68 P2O5 : 0.87 SiO2 : 0.59 R : 1.07H2O
Crystal size and habit: 5 to 20 um crystals with cubic-like rhombohedral morphology [1]
Click here to view XRD pattern
Reference
[1] A. M. Prakash, S. Unnikrishnan, J. Chem. Soc. Faraday Trans. 90 (1994) 2291
Notes
a. H2O includes water from phosphoric acid, pseudoboehmite and added water.
b. Concentration of SiO2 and organic template can vary over a range without affecting the phase purity. At low concentration of silica (SiO2/Al2O3 £ 0.3) or template (R/Al2O3 £ 1.5), however, dense phase AlPO4-crystobalite co-crystallizes with SAPO-34.
c. Use Teflon or stainless steel equipment throughout.
d. Although SAPO-34 crystallizes without aging, the crystallinity of the resulting product can be improved by aging.
