mapo-43 molecular sieve: synthesis, characterization and thermal stability

Microporous Materials, 2 (1994) 137-144 Elsevier Science B.V., Amsterdam

137

MAPO-43 molecular sieve: synthesis, characterization and thermal stability

D.B. Akolekar and S. Kaliaguine*

Dkpartement de Ginnie Chimique et CERPIC, Universitt Laval. Q&bee GlK 7P4, Canada

(Received 7 April 1993; accepted 25 August 1993)

Abstract

A small-pore magnesium-containing aluminophosphate molecular sieve of type 43 (MAPO-43) with three-dimensional structure and monoclinic symmetry [unit cell composition: (AI,,,Mg,,,)P,O,,.2.4NC,H,,.0.83H,O] was synthesized. MAPO- 43 has gismondine topology. The synthesis was performed by hydrothermal crystallization from a gel of composition 2.35 di- n-propylamine.0.30 MgO.0.85 A1,Os.l.O P,O,*50 H,O at 423 K for 240 h. The crystallization product was characterized by XRD, SEM, TG/DTG/DTA, IR and XPS techniques. Effects of thermal treatment on the structural stability and physical properties (viz. siz.e and morphology of crystals, surface concentrations and binding energies of Mg,,, Al,, and P2J of MAPO- 43 have been investigated. MAPO-43 shows a low thermal stability. The crystal structure collapse starts above 653 K and is complete above 823 K. At the higher thermal treatment temperature of 923 K, transformation of MAPO-43 phase into tridymite is observed. The surface analysis of MAPO-43 by XPS indicates that the concentration of magnesium is higher in the bulk than on the surface, and a modification of the surface composition occurs upon thermal treatment. The XPS analysis indicates that magnesium is tetrahedrally coordinated into the aluminophosphate framework, as the observed binding energy of Mgl,, which is 50.3 eV, corresponds to that of tetrahedrally coordinated magnesium. Changes in the binding energies of Mg*,, Alzp, P,, and O,, are observed with the calcination temperature.

Keywords: MAPO-43; GIS topology; synthesis; XPS; thermal stability.

Introduction

The aluminophosphate-based molecular sieves are an important new class of catalyst and adsorbent materials which includes the AlP04-n, SAPO- n, MeAPO-n and MeAPSO-n families [l-5]. The structures of AlPO,-n consist of alternating tetrahedra of aluminium and phosphorus, and various elements can be incorporated into the aluminophosphate framework. The incorporation of metal cations (Mg2+, Co’+ Fe’+, Fe3+, Zn2+, Mn2+) into the aluminophosbhate have been reported by Flanigen et al. [l]. The incorporation of a divalent cation (Me’+) in the hypothetical aluminium (A13’) site develops a negative charge on the aluminophosphate framework, and, subsequently,

* Corresponding author.

0927-6513/94/%7.00 0 1994 - Elsevier Science B.V. All rights reserved. SSDI 0927-6513(93)E0045-I

Brarnsted acidity or ion-exchange capacity is gener- ated [6].

MAPO-43 is a small-pore magnesium- containing aluminophosphate molecular sieve with pore opening of 0.43 nm. Pluth et al. [7] reported the crystal structure of the as-synthesized MAPO- 43 determined by single-crystal X-ray diffraction. It has a unique three-dimensional structure with monoclinic symmetry (cell constants: a = 10.2 192 A, b= 10.2198 A, and c= 10.0126 A; a=90”, /?= 90” and y=90.987”) [7]. The 4-connected framework, with PO4 tetrahedra alternating with (Al, Mg)O, tetrahedra, has the gismondine topology (GIS) embracing a three-dimensional channel system bounded by eight oxygen rings. The tetrahedral ordering reduces the symmetry from tetra- gonal to monoclinic. The MAPO-43 framework is negatively charged due to the incorporation of

138 D.B. Akoiekar and S. Kaliaguine / Microporous Mater. 2 (1994) 137-144

Mg2 + into the A13+ tetrahedral site in the AlPO, framework. It is interesting to investigate the properties of the small-pore MAPO-43 molecular sieve so that it can be used as an adsorbent/catalyst. So far very few information is available on MAPO- 43 [1,7,8]. Therefore, the present study deals with the synthesis, characterization and thermal stability of pure MAPO-43 phase.

Experimental

Preparation of n-Pr,NH-MAPO-43

n-Pr,NH-MAPO-43 was prepared by crystallizing the magnesium-containing aluminophosphate reactive gel and di-n-propylamine (n-Pr,NH) hydrothermally. A modified procedure was used to synthesize pure MAPO-43 crystals since the reported procedure [7] yielded co-phases of MAPO-43 and MAPO-46. Pure n-Pr,NH- MAPO-43 was obtained by crystallization from a gel of composition 2.35 n-Pr,NH*0.30 MgO.0.85 A1203* 1.0 P205*50 Hz0 in a PTFE-coated auto- clave (ca. 200 cm3) at 423 K for 240 h at autogenous pressure. The sources of A1203, P,O, and MgO were pseudo-boehmite (courtesy: Vista Chemical Company, USA), orthophosphoric acid (85%, Aldrich) and magnesium sulfate hepta- hydrate (puriss, Fluka), respectively. The crystals of magnesium aluminophosphate were washed thoroughly with deionized, distilled water, filtered, and dried in an air oven at 358 K for 16 h.

Characterization

The X-ray powder diffraction spectrum was obtained using a Holland Philips PW/1730 X-ray generator with a N&filtered CuKa radiation source and a scintillation counter.

Atomic absorption spectroscopy (using a Perkin Elmer 1lOOB spectrometer), gravimetric and C,H,N analysis were used for the determination of composition of the synthesized material. XPS measure- ments were conducted for determining the surface concentration and binding energy (BE) of C(ls), N(ls), O(ls), Mg(2p), Al(2p) and P(2p). A VG Scientific Escalab Mark II system with a hemi-

spherical analyzer operated in the constant pass energy mode (20 eV) was employed. An MgKa X-ray source (hu= 1253.6 eV) was operated at 20 mA and 15 kV. The intensity of XPS bands was determined using linear background subtraction and integration of peak areas. The accuracy of the BE determined was within k 0.10-0.15 eV.

The water sorption capacity of MAPO-43 was determined gravimetrically [9]. The size and morphology of the crystals of MAPO-43 were studied using a JEOL JSM-840A scanning electron micro- scope. The IR spectrum was recorded for a self- supporting wafer prepared by pressing 1.5 mg of the MAPO-43 sample in 100 mg of KBr. The spectra were recorded in the range 4000-400 cm- ’ with 2 cm- ’ resolution using a Digilab FTS-60 spectrometer.

Thermal analysis the n-Pr,NH-MAPO-43 dried at 358 K in air for 16 h was performed. Thermal analysis (TG/DTG/DTA) data of the n- Pr,NH-MAPO-43 were obtained under inert and oxidizing atmospheres, using a fully automated and computer-assisted TG/DTA 220 system (Seiko Instruments, Japan) under the following conditions: sample size, 20 mg; reference compound, a alumina; sample holder, platinum crucible; temperature range, 301-1211 K; heating rate, 10 deg min-‘; atmosphere, flowing air or nitrogen (flow rate, 100 cm3 min-‘).

Results and discussion

Highly crystalline n-Pr,NH-MAPO-43 was obtained by crystallization of the gel at 423 K for 240 h. The pH of the final gel (7.4) was high due to the presence of a large amount of organic template. The product (mother liquor) pH (>8.9) was found to be higher than in the case of A1P04- 5 and MAPO-36 [9,10]. The somewhat low yield of the product obtained may be attributed to the high pH of the product mother liquor. In our earlier studies it has been reported that the structure and other properties of aluminophosphate type 5 are very sensitive to acid-base treatment, and dissolution of the aluminophosphate occurs in acidic and basic media. Moreover, it has been mentioned [12] that a high crystallization pH can

D.B. Akolekar and S. Kaliaguine / Microporous Mater. 2 (1994) 137-144 139

r

1 10

h --T

Fig. 1. X-Ray powder diffractogram of the Pr,NH-MAPO-43.

be problematic because the product tends to become more soluble at higher pH.

Fig. 1 shows the powder XRD spectrum of the as-synthesized MAPO-43, which is very similar to that reported earlier for n-Pr,NH-MAPO-43 [13]. The powder XRD analysis showed that the new synthesis procedure yields a product free of any MAPO-46 impurity.

The elemental analysis of as-synthesized MAPO-43 is reported in Table 1. This analysis shows that Mg substitutes for some of Al in the aluminophosphate framework, The framework charge calculated from the chemical composition of the material is - 0.112 electron/T atom which is in the range reported [ 141 for MeAPO-n. Carbon analysis on the as-synthesized MAPO-43 indicated a di-n-propylamine content of 15.6 wt%, while hydrogen analysis indicated that water molecules are also present in the channels of MAPO-43 along with the di-n-propylamine molecules. The unit cell composition of as-synthesized MAPO-43 (determined from elemental and C,H,N analysis and total weight loss on ignition) is (Als.2Mg,.,)P,032*2.4 N&H,,*0.83 H,O (molecular mass = 1229.7).

Fig. 2 shows scanning electron microphoto-

Fig. 2. Scanning electron micrograph of (a) n-Pr,NH-MAPO- 43 and (b) MAP043 calcined at 823 K for 24 h.

graphs of (a) n-Pr,NH-MAPO-43 and (b) MAPO- 43 calcined at 823 K for 24 h in the presence of air. SEM investigations (Table 1) reveal that the MAPO-43 crystals are large (crystal size 60 x 90 urn), octahedral in shape and uniform. The IR spectrum of n-Pr,NH-MAPO-43 in the lattice vibration range is provided in Fig. 3.

The removal of the organic template from MAPO-43 is a very important task. Because of the small pore opening, large crystal size and lower thermal stability of the material and also due to the large critical molecular diameter of the organic

TABLE I

Properties of MAPO-43 (A) calcined in vacuum (lo-’ Torr) at 653 K for 30 h

Product molar composition Water sorption capacity at 293 K (cm3 g-‘) Crystal shape Crystal size

(0.112 Mg.0.388 A1.0.500 P)O, 0.285 Octahedral 60x90 urn

D.B. Akolekar and S. Kaliaguine / Microporous Mater. 2 (1994) 137-144

L w,, , ,

1200 1000 800 600 coo

WAVENUMBER, cm-’

Fig. 3. IR spectrum of n-Pr,NH-MAPO-43.

I2

‘9

4

h22

2

template which is inside the channels of MAPO- 43, it was difficult to remove the template under normal calcination conditions. The as-synthesized MAPO-43 was subjected to different calcination conditions (Table 2) in order to investigate the removal of the occluded template from the channels. Changes in the crystallinity and crystalline phase(s) of the material subjected to different calcination treatments are presented in Table 2. The crystallinities of MAPO-43 (B-F) samples were determined by taking into consideration the height (intensity) of their XRD peaks with respect to those of MAPO-43 (A). Calcination of the material in vacuum (lo-’ Torr) at 653 K (heating rate 2 K min- ‘) for 30 h was found to yield good crystallinity and pure crystalline phase. The water

sorption capacity of MAPO-43 calcined under these conditions (Table 1) is 0.285 cm3 g-’ which is nearly identical to the reported value [l]. The water sorption capacity of MAPO-43 is higher than that of aluminophosphates of type 5 [SJS], 11, 31, 41 and 39 [8].

The data in Table 2 indicate that an increase in the calcination temperature of MAPO-43 from 698 to 923 K results in a significant decrease in its crystallinity as indicated by the decrease in the height (intensity) of the XRD peaks. Also, at and above 723 K, a tridymite phase appears (in major amounts), the concentration of which increases with increasing temperature. Complete transformation of the MAPO-43 phase to tridymite is observed at or above 923 K. A comparison of the scanning electron micrograph of MAPO-43 calcined at 823 K for 24 h (Fig. 2b) with that of n- Pr,NH-MAPO-43 (Fig. 2a) indicates that the calcination temperature has no significant effect on the size and morphology of the crystals of MAPO- 43. The results (Table 2) lead to the conclusion that, unlike zeolites and aluminophosphate of type 5, MAPO-43 has a low thermal stability. Its crystal structure remains intact up to 653 K under vacuum calcination. One of the reasons for the lower thermal stability may be the high concentration of magnesium present in the AlPOd- framework, as already observed in the case of MAPO-36 [ 161 and SAPO-5 [17], in which the thermal stability was found to decrease with an increase in the

TABLE 2

Changes in the crystallinity and crystalline phase(s) of MAPO-43 due to the different calcination conditions

Sample Calcination conditions Crystallinity Crystalline as MAPO-43 phase(s)

Temperature Period Atmosphere W) (K) (h)

MAPO-43 (A) 653 30 lo-‘Torr 100 MAPO-43 (B) 653 30 Static air 10 MAPO-43 (C) 123 24 Static air 2 MAPO-43 (D) 823 24 low5 Torr 1

MAPO-43 (E) 823 24 Static air 0.5

MAPO-43 (F) 923 24 Static air _

43 43 43 T (major) 43 (minor) T (major) 43 (minor) T (major) MgO (minor)

“43 = MAPO-43; T = tridymite; heating rate = 2 K min - ‘.


concentration of magnesium and silicon, respectively, in the AlP04 framework.

Figs. 4 and 5 show the TG, DTG and DTA curves for the decomposition of n-Pr,NH-MAPO- 43 in nitrogen and air, respectively. From the TG and DTG data it follows that there are three distinct steps of weight loss from MAPO-43 containing di-n-propylamine in inert and oxidizing atmospheres,

The result of TG/DTG/DTA indicates that in an inert atmosphere most of the processes occurring in the removal of occluded materials from the metal aluminophosphate are endothermic. The

I I 1

273 523 773 1023 1273

TEMPERATURE (K)

Fig. 4. TG, DTG and DTA curves for the decomposition of n- Pr,NH-MAPO-43 in nitrogen.

TEMPERATURE (K)

Fig. 5. TG, DTG and DTA curves for the decomposition of n- Pr,NH-MAPO-43 in air.

total weight loss at 1225 K amounts to 16.5 wt.% in inert atmosphere. In the first stage, the weight loss is 1.3 wt.% at 301-653 K which is due to the desorption of physisorbed water and possibly di- n-propylamine from the metal aluminophosphate. The major weight loss (15.4 wt.%) occurs in the second stage at 653-893 K. The second stage corresponds to the desorption of di-n-propylamine and possibly to cracking of the occluded di-n- propylamine molecules to smaller hydrocarbons and ammonia. In the third stage, the weight loss of 1.1 wt.% occurs at 893-1225 K. This weight loss is due to the very slow desorption of ammonia and/or small hydrocarbon fragments adsorbed strongly on MAPO-43. Also a fraction of the weight loss (cu. 0.4 wt%) is exothermic in nature, which is likely due to the release of trapped gaseous products after complete collapse of the structure [lS]. In the present study it was observed that the complete collapse of the MAPO-43 structure occurs above 823 K. The total weight loss in the decomposition is 16.50%. Since the concentration of di-n-propylamine in the metal aluminophosphate (estimated from carbon and nitrogen analysis) is 15.6%, the concentration of water in the metal aluminophosphate is expected to be 0.9% which is very low compared to Pr,N-AlPO,-5 [lo] for which the water content is 4.4%.

In the oxidizing atmosphere, TG/DTG/DTA results indicate that the decomposition is an exothermic process which occurs in three distinct stages with a total weight loss of 15.8 wt.%. In the first stage, the desorption of physisorbed water and di-n-propylamine from the n-Pr*NH-MAPO-43 occurs at lower temperatures (301-659 K) and the weight loss is 1.4 wt.%. In the second stage, a major weight loss occurs at 659-836 K. In this stage, the removal of di-n-propylamine is expected to be mostly due to its oxidative decomposition which is an exothermic process. The third weight loss (1.1 wt%) occurs at 836-1216 K.

The oxidative decomposition is thought to involve the thermal cracking of the occluded di-n- propylamine, followed by oxidation of the cracking products in the intra- and intercrystalline spaces. The maximum weight loss occurs in the narrow temperature range of 75 1-812 K. As indicated by our XRD study (see Table 2) the structural collapse

142 D.B. Akolekar and S. Kaliaguine / Microporous Mater. 2 (1994) 137-144

of the material should have occurred and hence most of the template is removed over this narrow temperature range.

Bulk and surface composition of n- Pr,NH-MAPO-43 and MAPO-43 samples calcined under different conditions are presented in Table 3. The estimation of surface atomic ratios is obtained from the ratios of Mg,,, Alzp, P,,, CIS, and N1, XPS band intensities as reported elsewhere [19]. In all the samples, the Al/P ratio on the surface is higher than in the bulk which indicates that the concentration of aluminium is somewhat higher on the surface. Comparisons of bulk and surface Mg/Al ratios for n-Pr,NH-MAPO-43 and MAPO-43 (A) indicate that the surface concentration of Mg is lower than the bulk. In the case of MAPO-43 (D-F) samples, however, the Mg/Al ratio on the surface increases with the treatment temperature. It is also observed that the overall (Mg+ Al)/P ratio is cu. 10% higher on the surface. The concentration of carbon from the organic template present on the surface decreases as the calcination temperature increases.

Examination of the bulk and surface composition results (Table 3) of the metal aluminophosphate indicates that the concentration of magnesium is initially higher in the bulk and a modification in the surface occurs due to thermal treatment. The difference between the surface Mg/Al ratio of n-Pr,NH-MAPO-43 and MAPO- 43 (A) (in both cases the structure is intact) may be associated with the non-uniform spatial distri- bution of Mg and Al in the crystals occurring due to the changes in Al and Mg concentration in the

TABLE 3

solution during crystallization. The surface Mg/Al ratio increases with calcination temperature (Table 3) [MAPO-43 (A, D-F) samples]. It can be seen from Table 3 that the Mg/Al ratio is increased by 7.6, 11.5 and 30.7%, respectively, in MAPO-43 (D, E and F) compared with MAPO-43 (A). It seems thus that the structural collapse associated with increasingly higher calcination temperature is accompanied by Mg extraction from the AlP04 framework and Mg migration to the external surface of the crystals.

The XPS binding energy data for n- Pr,NH-MAPO-43 and other MAPO-43 samples are given in Table 4. The main carbon signals observed on MAPO-43 samples did not result from the adventitious contamination but from the organic template (di-n-propylamine) in the case of n-Pr2NH-MAPO-43 and from decomposition products of di-n-propylamine in the case of MAPO-43 (A, D-F) samples. The binding energy measured for Mg,, in n-Pr,NH-MAPO-43 and MAPO-43 (A) is 50.3 eV. This value is identical with the one reported for tetrahedrally coordinated Mg in the spine1 structure MgA1204 [20,21]. It is, therefore, concluded that the observed Mg,, line in MAPO-43 is for the tetrahedrally coordinated Mg in this lattice. Changes in the binding energies of Mg,,, Alzp, Pzp and Oi, are observed in MAPO- 43 samples following different thermal treatments. In the case of Mg,,, the binding energy increases with calcination temperature while the binding energies for Al,, and Pzp decrease. The binding energy of 50.8 eV observed at the higher calcination

Bulk and surface composition of the n-Pr,NH-MAPO-43 and MAPO-43 samples calcined under different calcination conditions

Sample Atomic ratio

Al/P MB/Al C(Mg + W/PI c/p C/N

Bulk Surface Bulk Surface Bulk Surface Bulk Surface Bulk Surface

n-PraNH-MAPO-43 0.776 0.88 0.289 0.234 1.00 1.08 0.70 0.73 5.14 6.18 MAPO-43 (Ay 0.776 0.89 0.289 0.260 1.00 1.12 0.38 MAPO-43 (D) 0.776 0.88 0.289 0.280 1.00 1.12 0.22 MAPO-43 (E) 0.776 0.85 0.289 0.290 1 .oo 1.10 0.20 MAPO-43 (F) 0.776 0.81 0.289 0.340 1.00 1.09 0.12

*See Table 2 for definition of treatments A-F.


TABLE 4

XPS data for the n-Pr,NH-MAPO-43 and MAP043 samples calcined under different calcination conditions

Sample Binding energy (eV)

M&p Al,, P ZP Or, N1,

n-Pr,NH-MAPO-43 50.3 74.8 134 531.8 400.4 MAPO-43 (A)b 50.3 74.9 134.1 532.0 MAPO-43 (D) 50.5 74.6 133.7 531.6 MAPO-43 (E) 50.7 74.4 133.5 531.4 MAP043 (F) 50.8 74.4 133.4 531.3

“Reference Cr, =285.0 eV. %e Table 2 for definition of treatments A-F.

temperature of 923 K [sample MAPO-43 (F)] is the value reported for magnesium oxide [22].

The change in the binding energies of Mg,,, Alzp, PZp and 01, when calcination is performed in different conditions is in good agreement with the conclusion of Mg being extracted from the tetrahedral environment in MAPO-43 lattice to yield extra-lattice magnesium oxide. This oxide is in higher concentration at the external surface of the particles after thermal degradation at 923 K as indicated by the higher Mg/Al value observed in MAPO-43 (F) (see Table 3). Changes in the binding energy of Alzp and PZp are also observed. The binding energy of Alzp and PZp decreases with an increase of calcination temperature. The XPS results suggest that magnesium aluminophosphate may be transformed into magnesium oxide and aluminophosphate products in the course of the thermal treatment. The formation of MgO is evi- denced in the X-ray powder pattern of MAPO-43 (F) calcined at 923 K.

Conclusions

Pure MAPO-43 can be obtained by hydrothermally crystallizing a gel of composition 2.35 n- Pr,NH*0.30 MgO-0.85 AlzO,*l.O P,05*50 Hz0 at 423 K and autogenous pressure for 240 h. This modified procedure provides a sample free of MAPO-46 phase. MAPO-43 crystals are octahedral, large in size (60 x 90 pm) and possess a water sorption capacity of 0.285 cm3 g- ‘.

MAPO-43 has a low thermal stability. The

collapse of the crystal structure starts above 653 K and is complete above 823 K. However, the crystal- lite size and morphology are not affected by the thermal treatment at high temperature. Above 923 K, MAPO-43 transforms into tridymite.

Thermal analysis (TG/DTG/DTA) results indicate that most of the removal of the occluded di- n-propylamine from the metal aluminophosphate in the inert and oxidizing atmospheres occurs over a narrow range of temperature above 653 K.

The results of the bulk and surface composition of the as-prepared MAPO-43 indicate that the concentration of magnesium is higher in the bulk than on the surface. Modifications of the surface composition occur upon thermal treatment. The concentration of magnesium increases on the surface as the calcination temperature is increased. This is probably associated with the magnesium being removed from the framework prior to the collapse of the crystal structure at high temperature.

The observed XPS binding energy of Mg,, (50.3 eV) in MAPO-43 suggests that the magnesium is tetrahedrally coordinated into the aluminophosphate framework. The binding energies of

Mg,,, Alzp, Pzp and 01, are affected by thermal treatments. On the basis of the XPS results it can be concluded that the magnesium aluminophosphate breaks, due to high temperature treatment, into magnesium oxide and an aluminophosphate phase.

MAPO-43 can be successfully employed as an adsorbent or a catalyst. For example it might be useful in water separation processes because of its small pore size and good water sorption capacity.

144 D.B. Akolekar and S. Kaliaguine / Microporous Mater. 2 (1994) 137-144

Acknowledgement

D.B.A. is thankful to the Natural Sciences and Engineering Research Council of Canada (Ottawa, Canada) for the award of an international post- doctoral fellowship.

References

1 E.M. Flanigen, B.M. Lok, R.L. Patton and S.T. Wilson, Pure Appl. Chem., 58 (1986) 1351.

2 S.T. Wilson, B.M. Lok and E.M. Flanigen, U.S. Pat., 4 310 440 (1982).

3 ST. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan and E.M. Flanigen, .J. Am. Chem. Sot., 104 (1982) 1146.

4 B.M. Lok, C.A. Messina, R.L. Patton, R.T. Gajek, T.R. Cannan and E.M. Flanigen, U.S. Pat., 4440 871 (1984).

5 S.T. Wilson and E.M. Flanigen, U.S. Pat., 4 567029 (1986). 6 E.M. Flanigen, B.M. Lok, R.L. Patton and S.T. Wilson, in

Y. Murakami, A. Iijima and J.W. Ward @Is.), Proceedings of the 7th International Zeolite Conference, Tokyo, 1986, Kodansha, Tokyo, 1986, p. 103.

7 J.J. Pluth, J.V. Smith and J.M. Bennett, J. Am. Chem. Sot., 111 (1989) 1692.

8 S.T. Wilson and E.M. Flanigen, ACS Symp. Ser., 398 (1989) 329.

9 D.B. Akolekar, J. Catal., in press. 10 D.B. Akolekar, Ph.D. Thesis, University of Poona, Poona,

1987. 11 V.R. Choudhary, D.B. Akolekar, A.P. Singh and

S.D. Sansare, J. Catal., 111 (1988) 254. 12 S.T. Wilson, Stud. Surf. Sci. Catal., 58 (1991) 137. 13 R. von Ballmoos and J.B. Higgins (Eds.), Collection of

Simulated XRD Powder Patterns for Zeolites, Butterworth- Heinemann, London, 2nd revised ed., 1990, p. 4085.

14 E.M. Flanigen, R.L. Patton and S.T. Wilson, Stud. Surf. Sci. Catal., 37 (1988) 13.

15 V.R. Choudhary, D.B. Akolekar, A.P. Singh and S.D. Sansare, J. Catal., 111 (1988) 23.

16 D.B. Akolekar, J. Catal., 143 (1993) 227. 17 D.B. Akolekar, J. Chem. SOL, Faraday Trans., in press. 18 S. Ernst, L. Puppe and J. Weitkamp, Stud. Surf. Sci. Catal.,

49 (1989) 447. 19 M. Huang, A. Adnot and S. Kaliaguine, J. Catal., 137

(1992) 322. 20 J.A. Tossell, J. Am. Chem. Sot., 97 (1975) 4840. 21 D.E. Haycock, C.J. Nicholls, D.S. Urch, M.J. Webber and

G. Wiech, J. Chem. Sot. Dalton, (1978) 1785. 22 Y. Inoue and I. Yasumori, Bull. Chem. Sot. Jpn., 54 (1981)

1505.

mapo-43 molecular sieve: synthesis, characterization and thermal stability

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