Synthesis and Characterization of an Aluminophosphate Material With A1PO-15 Framework Type Structure

J. Weitkamp, H.G. Karge, H. Pfeifer and W. Hfilderich (Eds.)

Zeolites and Related Microporous M a m i a l s : Slate of [he Art 1994 Studies in Surface Science and Caralysis, Vol. 83 0 1994 Elscvicr Science B.V. All rights rcservcd.

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SYNTHESIS AND CHARACTERIZATION OF AN ALUMINOPHOSPHATE MATERIAL WITH APO-15 FRAMEWORK TYPE STRUCTURE N.Bilba' ,A. Azzouzz, N. Naum' ,D. Nibou' I

Faculty of Chemistry , "Al.I.Cuza" University ,6600 ,Jassy ,Romania

' Organic Synthesis Laboratory ,CDM , 2 , B4Frantz Fanon ,Alger , 1600 ,Algeria ABSTRACT Synthesis of the crystalline aluminophosphate with AlPO- I5 framework type structure from the aqueous system with a various Et,N-NH40H-Al,0,-P20,-H20molar compodtion has been investigated. The products have been characterized by powder X-ray diffraction (XRD) , infrared spectroscopy (IR) ,scanning electron microscopy (SEM) ,chemical analysis, thermal gravimetric analysis and aluminum NMR. Our experiments show that crystallization of N O - 15 depends strongly on ammonia presence. INTRODUCTION The first framework oxide molecular sieves synthesised without silica are the microporous crystalline aluminophosphates which were denominated by their inventors with the acronym AP0,-n [ 1,2 1. Similar to zeolites ,the APO,-n molecular sieves are composed of AlO, and PO, tetrahedra which may form different three-dimensional neutral framework structures. The hydrothermal synthesis of aluminophosphates in the presence of various alkali inorganic cations or organic structure-directing molecules ,which can include an organic amine and a quaternary ammonium salt , conducted to a large number of framework structure types which include the microporous phases ,the dense phases and the hydrate phases ,with four-, five- or six-co-ordinate aluminum. Wilson et al.[ 3 ] have stated that in the absence of organic template molecules no microporous aluminophosphates can be synthesized and, that to overcome the tendency of Al to be octahedrally co-ordinated in acid media, high synthesis temperatures are necessary [ 4 1. There are some exceptions from this statements. According to Parise [ 5 ] there are three types of aluminophosphate framework structures which differ from one another by state of aluminum coordination : - the framework containing only six-co-ordinated aluminum, Al"' (octahedrally) , and four-co-ordinated phosphorus , like in variscite and metavariscite , corresponding to formula AlP0,.2€40 [ 6,7 ] and in APO-15 [ 8 1; - the framework containing only four-co-ordinated aluminum, AIN (tetrahedrally) , and phosphorus ,like in microporous aluminophosphates [ 1,2 1;

606

- the framework containing five-co-ordinated aluminum, Alv (trigonal pyramid), four-co-ordinated aluminum and four-co-ordinated phosphorus ,like in AlPO, -12en [ 9,l I ] , AlP04-21py [ 5,12 ] , AlPO,-EN, [ 5,11 3 ,AlP0,-P, [ 13 ] ,EA-6 [ 14 ] In addition ,there is another type of framework containing six-co-ordinated aluminum and four-co-ordinated aluminum in different ratio and four-co-ordinated phosphorus , like in AlPO,-H,[ 15,161,MCM-I [ 1 7 ] , V P I J [ 18,19],AlP0,-H1[ 15,191. Similar structures were found in gallophosphates : Ga$,O,,OHNEt, [ 20 3 , GaPO,-14 [11,21] ,GaPO, No. 1 and No. 6 [ 21 3 and cloverite [ 22 ] . The inorganic and organic agents appear to play a critical structure-directing role , controlling the geometry of structures , serving to pH adjustement of the reaction mixtures , thus avoiding the formation of dense phases [ 23 ] The template is entrapped , occluded or clathrated in the structural void during the crystal1 growing. For a neutral or acid pH ,which is proper to AlPO.,-n synthesis , the amines are protonated and they electrostatically react with Alt3(H20),species . In our studies , the aluminophosphate synthesis was performed in presence of Et,N, a molecule that organizes the structure of water as water "icebergs" and, NH; , a voluminous inorganic cation, which "breaks" the structure of water. The addition of Et,N to ammonia mixtures has no inductive effect over microporous AlP0,-n structures . ,

,

EXPERIMENTAL Materials The commercial aluminum sulphate , Al,( SO,),. 18H20 or aluminum chloride, AlC1,.6H20 as alumina source , phosphoric acid (Loba Chemie , 89 wt YO), ammonium hydroxide (27 wt %) ,triethylamine (Et,N) and distilled water have been used in our syntheses. A typical procedure is given below . To 92 g of phosphoric acid (0.418 mole P20,) , 250 ml of distilled water is added to constitute solution A . 226 g of aluminum sulphate (0.339 mole Al,O,) is dissolved in 100 ml of water at 50 "C and then is added 147 g ammonium hydroxide (1.17 mole (NH,),O) under stirring , and 100 g Et,N (0.495 mole (Et,N),O) to constitute solution B. Solution A is finally added to mixture B with constant vigourous stirring for 2 hours . A solid aluminophosphate gel is formed , its pH being 4.5-5.0 . The final mixture having the molar composition 1.46(Et,N),O. 3.45(NH4),0. Al,O,. 1.23P20,. 88.5H20 was then transferred to a 1 liter stainless steel autoclave and heated at 190 O C for 48 hours under autogenous pressure and intermittent stirring . The solid product is filtered , washed with hot distilled water till the filtrate is sulphate ions fiee and dried in air at 1 10 O C for 6 hours. Characterization of solid product The identity and crystallinity of the solid products were checked by X-ray diffraction. X-ray powder diffraction patterns were recorded on a Philips PW 1800 X-ray difiactometer with monochromatic CUK, radiation (generator settings , 50 kV ,35 mA , step size 0.020 deg , count time 1 .OO sec) . Crystal morphology of products was determined using a scanning electron microscopy (XL 30) . Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out simultaneously on a Stanton thermoanalysis system at heating rate of SO/minin air . IR measurements were performed with an UR-20 Karl-Zeiss Jena instrument and lattice vibration spectra were obtained using the KBr technique . Solid state "A-NMR spectra were carried out using MAS at a fiequency of 78.17 MHz with a Briiker MSL300HP spectrometer.

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The concentration of aluminum and phosphorus was determined by AA spectroscopy and photometry.

RESULTS AND DISCUSSION A series of aluminophosphate materials with AIPO- 15 framework structure were prepared according to the conventional procedure [ 1,2 ] . Details about the most representative synthesis are reported in Table 1. Table 1. Aluminophosphate synthesis mixtures and products obtained . Sample Reactant composition (AI,O,=I) Al Crystallization Products, no. source conditions crystallinity (EtJ), “HJzO PzO, HzO time, temp. pH 0

7 8 9 10

1.46 1.46 1.46 1.46

3.45 3.45 3.45 3.45

1.23 1.23 1.23 1.23

88.5 88.5 88.5 88.5

a.s. a.s. as. as.

h

O C

24 48 72 24

190 190 190 220

4.5-5 AlPO-15 ; 97% 4.5-5 AlPO-15 ; 100% 4.5-5 AIPO-15 ; 100% 4.5-5 Crystallineno AlPO- 15 4.5-5 APO-15 ; 100%

11 1.11 2.76 0.89 60 a.ch. 144 190 a.s - aluminum sulphate ; a.ch. - aluminum chloride . The X-ray powder diffraction patterns for sample no.9 as-synthesized are shown in fig.1. 1.80 -

1.404-

’31.00c al

c

C

0.60 -

0.20-

2 Theta-CuK,

Fig. 1. X-ray diffraction powder pattern of as-synthesised AIPO- 15 (sample no. 9) The powder diffraction in fig. 1 shows that the product is very crystalline . The observed interplanar spacings for this sample are almost identical to the AlPO-15 as in the literature data [ 8,24 ] . An approximate estimation of the percentage crystallinity can be made from the X-ray diffraction peaks height at 20 = 14.9475 deg., d= 5.9220 A and 20 = 13.2425 deg., d= 6.6803 A , respectivelly ,the planes (101) and (1 10).

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Chemical analysis of the product showed the incorporation of Et,N and NH4 'and, thermal analysis proved this by endo and ex0 weight losses when the sample is heated in air (the exo effect does not occur when heating in argon). The relative thermal stability of framework structure was obtained by XRD of samples heated in air or argon at 200 O C (6 hours) , 250 O C (1 hour) and 540 O C (6 hours). At temperature between 200-540 O C the solid phase transforms finally into NO,-tridymit (see fig. 2-4.).

1.801.40-

2

'f 1.00-

+ 01

- 0.60C

0.20-

Fig.2.The XRD pattern for APO-I 5 (no.9) heated in air or argon at 200 "C (6 hours).

tcH

2 Theta-CuK,

*

t .lo

E

01 t

C

10

14

18

22

26

30

34

2 Theta -CuKe

38

Fig.3. The XRD pattern for &PO-15 (no.9) heated in air at 250°C (1 hour).

The size and morphology of the AIPO- 15 crystals is illustrated by the scanning electron micrographs presented in fig. 5 . The image of APO - 15 ( no . 9 ) shows aggregates, intergrowths and hexagonal leaf-shapes. The TGA and DTA curves for AlPO-15 (dried at 110 O C) are given in fig. 6. There can be distinguished three weight losses in the TGA and five effects in the DTA. The first three of them are endothermic ones, with maxima at 160 , 235 , 265 O C, for loss of water, ammonia, water from dehydroxylation and Et,N, respectively. The fourth exothermic effect at 300 O C corresponds to the combustion of amine (in air) and the fifth exothermic effect with maxima at 520 O C corresponds to the recrystallization with tridymit formation . After heating of the sample at 250 O C, the first two weight losses desappear and, a structural change occurs (in agreement with XRD ,fig.3) .

,103~ 2.001.62 1.28c 0.98

-

.-

0.72-

f 0.50-

- 0.320.120.080.02-

0.0 10.0 20.0 30.0 40.0 50.0 60.0 ~

Fig.4. Observed powder XRD pattern for AIPO- 1 5 (no.9) heated in air at 540°C (6 hours).

2 Theta-CuK,

Fig.5. SEM image of AIPO- 15 as-synthesized (110.9).

2350 I

I

I

100 200 300 400 500 6 10 Temperature, O C

Fig.6.Thermaldecomposition pattern of AlPO-15 (no.9) (TGA, DTA and TG) dried at 1 10" C 0 and, only TGA at 250" C 0 .

610

A typical analysis gave AI,O, 32 wt% , P,O, 45.6 wt% , N 5.4 wt% and a weight loss of 22.3 wt% from the TGA curve. The atomic AIP ratio is 0.98. These results are in good agreement with AIPO-15 formula NH,A12(OH)(H,0)(P0,)2.~0[ 8 3 . IR spectroscopy of the lattice vibrations and hydroxyl groups of AlPO-15 (no.9) synthesized with Et,N and ammonium hydroxide are shown in fig.7 (a, b, c). These structure sensitive and structure insensitive vibrations are in the range of 400-1400 ern-'. . The infrared absorption at -1445 cm" indicates the presence of Et,N (partial protonated) and NHications.

I

800 [ a)

I

I

I

I

700 600 500 400 Wavenumber Icm-')

Fig.7.IR spectrum ofAlPO-I5 (no.9) : 1) as-synthesized and dried at 110 O C ; 2) aAer heating at 250 O C ; 3) after heating at 600 O C

I

I

I

I

3800 3600 3400 3200 3000

I

.

.

Wavenumber lcm 1

[cl

The i.r. spectra of hydroxyl groups are shown in fig.7 c in the region of stretching vibrations of OH bonds (3400-3700 cm" ). The i.r. spectra of AIPO-15 (no.9) after heating at 250' C (curve 2) and 600' C (curve 3) are different as a result of the structural transformations, these beeing proved by XRD and thermal analysis also. Fig.8 illustrates the solid state "Al NMR spectra of AIPO-15 (no.9). A sharp 27AI line is observed at -10 ppm and additional signals at 1 1 1 , 15 and -102 ppm. No 27AI lines between 42-29 ppm which are ascribed to tetrahedrally co-ordinated aluminum (A") [ 251 The 27AI line observed at cca -10 ppm is attributed to octahedrally co-ordinated aluminum 4"' [ 17,26 ] and suggests the presence of a octahedral Al complex containing two water molecules in its coordination shell.

-

61 1

-10.343

I

I

I

I

150 100 50

I

I

I

I

0 -50 -100-150 PPm

Fig.8,"Al MAS NMR spectra of AlPO-l5(no.9)

CONCLUSIONS The AlPO- 15 can be synthesized hydrothermally from different reaction mixtures in the presence of ammonium hydroxide and Et,N. The AIPO-I 5 is a hybrid between the microporous aluminophosphate molecular sieves containing Al"' and the dense aluminum phosphate hydrates containing Al'"'' . The AlPO- 15 framework structure is thermally unstable. A change of initial structure takes place at cca. 250 O C and hrther at 540 O C becomes AlP0,-tridymit. XRD spectra , thermal analysis and IR spectra proved this structure instability. REFERENCES I . S.T. Wilson, B.M. Lok and E.M. Flanigen, U.S. Patent 4,310,440 (1982). 2. S.T. Wilson , B.M. Lok , C.A.Messina , T.R. Cannan and E.M. Flanigen , J.Am.Chem.Soc. , 104 (1982) , 1146-1 147. 3. S.T. Wilson , B.M. Lok , C.A.Messina , T.R. Cannan and E.M. Flanigen , In Intrazeolite Chemistry, Stucky G.D. Dwyer F.G. ,(Eds). , ACS Symp.Ser. 218 , 1983, 79. 4. S.T. Wilson , B.M. Lok ,C.A.Messina ,and E.M. Flanigen , in Proceed. 6" 1nt.Zeolite C o d . , Olson, D . , Bisio,A., (Eds). Butterworths, 1984,97. 5.J.B. Parise , in Zeolites , Drzaj B. , Hoeevar S. and Pejovnik S. , (Eds). Elsevier Sci. Pub]., 1985,271-278. 6. R. Kniep ,D. Mootz ,Acta Crystallog. ,B29, (1973) ,2292-2294. 7. R. Kniep ,D. Mootz ,A. Vegas ,Acta Crystallog. ,B33 ,(1977), 263-265. 8. J.J. Pluth ,J.V. Smith ,J.M. Bennett and J.P. Cohen , Acta Crystallog. ,Sect. C Cryst. Struct. Common ,(1984) ,C,( 12) ,2008-20 11 , 9. J.B. Parise, J. Chem. SOC.Chem. Comm., 21, (1984), 1449-1450. 10. J.B. Parise, Inorg. Chem. , 2 4 , (1985),4312-4316. 11. J.M. Bennett , N.J. Dytrych ,J.J. Pluth ,J.H. Richardson , J.V. Smith , Zeolites , 6 , (1986) ,349-360. 12. J.B. Parise, C.S. Day,ActaCrystallog. (1985), C,, ,515-520

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