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Dehydroxylation of Hydrogen Zeolites Conditions for the Preparation of Thermally Stable Catalysts.

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ml) at room temperature. 20 ml of 50% NaOH was added
dropwise to the vigorously stirred solution; after a further 5
min the solution turned yellowish-brown. The solution was
treated with 11 mmol of methyl iodide, stirred for 10 min,
and then poured into an ether/ice mixture (150 m1/50 g).
The aqueous phase was separated off and extracted with ether. The combined organic extracts were dried over MgS04,
treated with activated charcoal, filtered, and the solvent removed in a vacuum. A yellowish oily residue crystallized on
cooling. Recrystallization from ether/n-hexane furnished (4)
in 90% yield as colorless crystals of m. p. 73-75 "C.
(2): 1 g (2.98 mmol) of (4) was completely decomposed (ca.
4-6 h) by Tschugaeff pyroly~is'~]
(170-180 "C/12 torr). Column chromatographic separation (ethylacetate/n-hexane
1 :3) afforded (5) (64%) as colorless oil and its 4,5-didehydro
isomer (5%) together with some (3) (6%).-A solution of (5)
(0.5 g, 2.2 mmol) in 15 ml HzO/dioxane (1 : 1) was hydrolyzed (2 hours) with 5 ml of 50% NaOH. The solvent was removed in a vacuum and the crude product recrystallized
from ether/n-hexane; yield 0.328 g (2), m.p. 92-95°C;
[ a ] g =-249.8 (c=1.04 in MeOH)"'.
tion of HX and HY zeolites showed that elimination of water
in vacuo or under shallow bed conditions[31proceeds in two
steps with formation of Lewis acid centers having different
properties.
The first step affords partially dehydroxylated zeolites
whose properties are compatible with the presence of tricoordinated silicon and aluminum in the crystal lattice.
In the second step framework aluminum atoms migrate
into the intracrystalline pore system. This can give rise to a
variety of products having differing crystallinity and ion exchange capacity, including products resembling deep bedcalcined Y zeolites in their thermal properties.
T
900
800
700
600
Received April 10, 1980 [ Z 564 I€]
German version. Angew. Chem. 92, 761 (1980)
Ill A. M . Felix, Ch. Wang, A. A. Liebman, Ch. M. Delaney, T. Mowles, B. A .
Burghardt, A. M. Charnecki, J. Meienhofer, Int. J. Pept. Protein Res. 10, 299
(1977).
12) Ch. R. Botos, C. W. Smith, Y:L. Chan, R. Walter, J. Med. Chem. 22, 926
(1979).
[3] G. H. Fisher, W. Ryan, FEBS Lett. 107, 273 (1979).
141 S. Natarajan, M. E. Condon, M. S. Cohen, J Reid, D W. Cushman, B. Rubin.
M. A. Ondettrt 6th American Peptide Symposium. June 17-22, Abstract E3,
62 (1979).
151 S. S. Kerwar, A M. Felix, R. J. Marcel, I Tsay, R. A . Sahador, J. 8101.
Chem. 251. 503 (1976).
[6] A. Corbella, P. Gariboldi, G. Jommi. F Mauri, Chem Ind. (London) 1969,
583.
-791-0.5 (c=1.03 in MeOH) i s obtainable from
171 13). m.p. 97-98°C. [a]:'=
Bachem Feinchemikalien AG, CH-4416 Bubendorf, Switzerland.
[8] P. Dicesare. B. Gross, Synthesis, in press.
191 C. H. De Puy, R. W. King, Chem. Rev. 60, 431 (1960); H. R. Nace, Org.
React 12. 57 (1962).
Dehydroxylation of Hydrogen Zeolites:
Conditions for the Preparation of
Thermally Stable Catalysts
By Laszlo MarosiI']
Dedicated to Professor Matthias Seefelder on the occasion
of his 60th birthdav
Hydrogen zeolites of Y type are finding increasing use as
industrial catalysts for transformations of hydrocarbons; they
are produced by thermal decomposition of the ammonium
form[']. However, catalytically inactive products may also
arise. One possible reason for the loss of activity might be the
elimination of the catalytically active hydroxyl groups (as
water) together with ammonia on heating. The mechanism
of this scientifically and industrially important dehydroxylation process is still a matter of controversy. In particular, it is
unclear whether elimination of water in a shallow bed involves formation of tricoordinated (Si Al) sites or of oxoaluminum cations"]. Our studies on the thermal dehydroxyla+
[*I
Dr. L. Maros!
Ammoniaklaboratorium der BASF A G
D-6700 Ludwigshafen (Germany)
Angew. Chem. Int. Ed. Engl. 19 (1980) No. 9
500
LOO
300
200
100
.
.
fmg
Fig. 1. Thermogravimetric diagram for the thermal decomposition of NH4Y
zeolite (Si/AI= 2.0).
Up to about 320 "C, physically bound water and ammonia
are liberated, affording the hydrogen zeolite. Only a slow
loss of weight is observed in the first dehydroxylation step
from 320 to 550 " C .No changes are seen in the X-ray diffraction pattern. Nevertheless, precise evaluation of the thermogravimetric diagram (Fig. 1) shows that 40% of the hydroxy
groups are eliminated in this step.
The second dehydroxylation step is characterized by a fast
elimination of water at 550 to 6:O0C. The lattice constant
decreases from 24.70 to about 24 A. Moreover, lattice distortions occur, leading to complete disruption of the crystal lattice on further increasing the temperature.
For detailed studies NaX and NaY zeolites with different
Si/AI ratios were prepared by known method~[~I,
transformed into the ammonium form, and calcined under shallow-bed conditions at a temperature below that of lattice destruction (Fig. 2).
The residual content of hydroxy groups (a)decreases with
increasing aluminum content, and the lattice constant remains unchanged. The ion exchange capacity after partial
dehydroxylation, determined by fourfold exchange with a
0.1 M solution of AgN03, always corresponds to the sum of
the sodium content and the residual proton content.
The resulting Lewis acid centers do not possess ion exchange properties. The contribution of this step to the overall
dehydroxylation can be estimated from a simple scheme: the
faujasite structure consists of cuboctahedra made up of six
four-membered rings of tetrahedra. At a molar ratio of Si/
A1 = 3, i. e. the composition of the silicon-richest Y zeolite,
each of the four-membered rings contains an aluminum
0 Verlag Chemie, GmbH, 6940 Weinheim, 1980
0S70-0U33/U0/0909-0743
$02.50/0
743
atom. Replacement of further silicon atoms leads to neighboring pairs of aluminum atoms in opposite corners of the
four-membered rings whose contribution increases with increasing aluminum content. It can be deduced from the experimental results shown in Figure 2 that for HX and HY
21.70
2 L.6 0
24.50
l-7
100
1
5
m"
Si/Al
24.40
21.30
2.0
2L.20
60
1.0
: 2.00
io1
0.8
0.6
0
0.2
0.1
Equiv. Na+
Fig. 3. Lattice constant ug of NaHY zeolite (Si/A1=2.43) ( 0 )and the corresponding completely dehydroxylated products ( x ) and the increase in ion exchange capacity (0).
The sample was heated to 750°C for dehydroxylation.
Hatched: ion exchange capacity.
20
1.18
0 1
0.8
I
I
I
i
a6
0.1
0.2
0
Equiv. N d
Fig. 2. Decrease in content of hydroxy groups (a)on heating of sodium-containingNH4zeolite:60hat470"C(0); 15 h t o 4 7 0 " C ( x ) : 8 h t o 4 7 0 " C ( + ) ; 4 h t o
530°C (0).
zeolites the number of eliminated water molecules in the first
dehydroxylation step is in agreement with the number of
pairs of aluminum atoms for a given Si/A1 ratio (Table 1).
change capacity. Their lattice constant lies between 24.30
and 24.50 A.
Since the migration of the framework aluminum atoms
into the intracrystalline pore system also takes place in uucuo
it cannot be interpreted as a result of hydrolysis. It appears
more likely that the AlO(0H) skeletal units swing out in the
course of their thermal motion and under subsequent cationization according to the following scheme. (The vacancy at
r---i
A~O~OH
H
H
I
t
Table 1. Relationships between the calculated amount of neighboring aluminum
atoms and the experimentally determined extent of dehydroxylation for HX and
HY zeolites having various Si/AI molar ratios.
Si/AI
3.0
2.43
2.0
1.67
1.18
Neighboring
Dehydrox ylation
A1 atoms
1x1
0
28.50
50
66
91
30
50
63
90
A10@
It must therefore be assumed that in the first dehydroxylation step water is eliminated from those hydroxy groups
which are coordinated to neighboring framework aluminum
atoms. Remarkably, the same number of hydroxy groups
prove to be non-acidic on amine titrationl'l.
The second step of dehydroxylation always involves migration of framework aluminum atoms into the intracrystalline pore system. This leads to products having an ion exchange capacity considerably greater than their respective
sodium content; this suggests formation of AIO ions during
the elimination of water (see Fig. 3).
The elimination of water becomes increasingly slower with
increasing sodium content; even after complete dehydroxylation the samples are still crystalline. The influence of the dehydroxylation rate on the crystallinity can also be demonstrated for Si-rich HY zeolites. For instance, if the sample is
heated at a rate of 0.1 "C/min between 500 and 600°C then
the crystal structure is retained to over 1000 "C. Samples of
this kind obtained by controlled dehydroxylation resemble
deep-bed calcined Y zeolites in their propertiesl31. They possess a high thermal stability and-as demonstrated by the
hatched region in Figure 3-exhibit a considerable ion ex+
144
0 Veriag Chemie, GmbH. 6940 Weinherm, 1980
the AlO(0H) is occupied by silica, e.g. from peripheral regions.)
Whether, and to what extent, the AlO(0H) groups are cationized depends upon the relative rate of swinging and cationization. Too fast a heat-up rate between 500 and 600°C
causes most of the aluminum atoms to leave the crystal
framework. The lattice then collapses. Depending upon the
rate of dehydroxylation a variety of products can arise which
differ in their crystallinity and ion exchange capacity and
also contain defect sites. By a suitable choice of calcination
conditions it is possible to balance these two processes such
that the products have a particularly high thermal stability.
This mechanism of water elimination in the second dehydroxylation step can also be applied to shallow-bed and
deep-bed dehydroxylation and thus permits a coherent view
of the processes occurring under different dehydroxylation
conditions.
Received: January 2, 1980;
revised: June 16, 1980 [ Z 565 IE]
German version: Angew. Chem. 92, 759 (1980)
CAS Registry numbers:
N o compounds indexed
0570-0833/80/0909-0744
B 02.50/0
Angew. Chem. Int. Ed. Engl. 19 (1980) No. 9
[I1 H . A. Szymanski. C. N . Slamires, G. R. Lynch, J . Opt. SOC.Am. 50, 1323
( 1960).
12) J. B. Uyfferhoeuen,L. C. Chrismer, W. K . Hall, J . Phys. Chem. 69, 2117
(1965): C H . Kuhl in J. B. Uyfterhoeuen: Molecular Sieves. Leuven Universty Press, Leuven 1973. p. 227; D. W. Breck, G. W. Skeeis, ACS Symp. Ser.
40, 271 (1977); P. A. Jacobs. H. K. Beyer, J . Phys. Chem 83, 1174 (1979): J.
V Smirh. Adv. Chem. Ser. 101, 183 (1971).
I31 G. T. Kerr, J . Catal. 15. 200 (1969).
[4] R. M. Millon, US-Pat. 2882244 (1959); D. W Breck, US-Pat. 3130007
(1964).
[ S ] R. Beoumonr, D. Barfhomeuf; Y. Trambonze, Adv. Chem. Ser. 102, 327
(1971).
Amorphous Zeolites
By John M . Thomas and Leslie A . Bursill"]
Crystalline zeolites possess a wide range of properties that
make them industrially important. It is less widely known
that imperfectly-ordered (quasi-crystalline or semiamorphous) zeolites also exist, and that these, too, possess potentially attractive properties. There is, however, some difficulty
in characterizing these amorphous variants; and it is rather
puzzling that a material which lacks long-range order can
nevertheless exhibit marked cation-exchange capacity and
catalytic activity, which in the case of the crystalline varieties, arise because of the unit-cell level porosity of the aluminosilicate. Our communication focuses on these two points;
and, in particular, describes how high resolution electron microscopy (h.r.e.m.) helps rationalize these problems.
We have recently shown"] that it is possible, notwithstanding their beam-sensitivity, :t record direct structural images,
at a resolution close to 3 A, of crystalline zeolites such as
Na-A, Na-X, Na-Y and ZSM 5. During the course of
examination the zeolites gradually become amorphous; but
advantage may be taken of this fact since both the course of
the process of amorphization as well as the various degrees of
quasicrystallinity may be analyzed by direct (real-space)
imaging. (The reliability of the images taken by h. r. e. m.,
both for crystalline and amorphous materials, is known from
computer simulation procedures that are described fully else~here[~.~I.)
Considerable insight is gained from the study of amorphous zeolites in this way. This is illustrated with reference
to Fig. 1 which is a high-resolution image of a dehydrated
crystal of Na-A (idealized formula Na12AI12Sii2048)
that has
been appreciably converted to an amorphous condition141.
There are several noteworthy features:
(i) A 'raft' (ca. lo4 A' in projected area) of crystalline material consisting of an ordered array of so-called supercaged'l-ca.
lo2 in all-is surrounded by essentially
amorphous a1uminosilicate.(ii) A smaller 'raft' (ca. 3 x lo3A' in area), less well-ordered
than the other and not in registry with it, consisting of
some 30 supercages, is also surrounded by amorphous
material.
(iii) Several isolated supercages, one of which is arrowed,
may be identified in the amorphized background.
Fig. 1. High resolution electron micrograph of a thin film ( ~ 4 A0 thick) of quasi-crystalline zeolite A, showing the supercages as white dots. For details see text
Prof. Dr. J . M Thomas, Dr. L. A. Bursill [**I
Department of Physical Chemistry, University of Cambridge
Lensfield Road, Cambridae. CB2 IEP (Enelandl
[**I On leave from Department of Physics, University of Melbourne (Australia)
['I
.
Angew. Chem. Inr. Ed. Engl. I9 (1980) No. 9
L
I
We may now appreciate how amorphous zeolites can retain
much of their cation-exchange capacity: even though clusters
of sodalite cages (which circumscribe the supercage-see inset) are detached from the parent crystal, thereby generating
0 Verlag Chemre, GmbH, 6940 Weinheim, 1980
0570-0833/80/0909-0745
$ 02.50/0
745
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