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Fourier Transform Far Infrared Spectroscopy of Silver Atoms and Silver Clusters Entrapped in Sodium Y Zeolite.

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M. Di Vaira, C.A. Ghilardi, S, Midollini. L. Sacconi.
/I/
J. Am. Chem. SOC.
( 1 9 7 8 ) 2 5 5 0 ; P. Dapporto, S . Mxdol-
lini, L. Sacconi, Anqew. Chem.
Int. Ed. Engl.
2
9'
( 1 9 7 9 ) 510; Angew. Chem.
( 1 9 7 9 ) 4 6 9 ; F. Cecconi, C.A.
Ghilardi,
S. Mldollini. A. Orlandini, 3 . Chem. SOC. Chem. Commun.
__
1982,
2 2 9 ; F. Cecconi, C.A. Ghilardi, S. Midollini. A.
95
Orlandini, Anqew. Chem.
( 1 9 8 3 ) 5 5 4 ; Angew. Chem. Int.
Ed. Engl. 22 ( 1 9 8 3 ) 5 5 4 ; Angew. Chem. Suppl.
1983, 7 1 8 .
/2/
A. W. Cordes, R . D. Joyner, R . D. Shores, E. D. Dill,
/3/
M. Di Vaira. M. Peruzzinl, P. Stoppioni, J. Chem. soc.
Inorg. Chem.
11
Chem. Commun.
/4/
894.
/5/ Y.
6
widely used in large scale industrial processes.
Silver
zeolites have been extensively studied in this COnneCtiOn
/12/, and have recently been the focus of considerable
structural and spectroscopic attention/l3-16/.
The crys-
tallographic data on silver zeolites has made them an
the metal atoms and clusters are in a well defined setting
as found for metal clusters entrapped in rare gas
matrices.
(19671 1 9 7 .
c. Leung.
J. waser, S. Van Houten, A. vos, G. A .
Wiegers, E. H. Wiebenga. Acta Crystallogr.
lo
(1957) 574.
-
/ 6 / G. J. Penney, G. M. Sheldrick, J. Chem. SOC. (A) 1 9 7 1 ,
The desire to understand the size, structure and support dependence of the chemical reactions that occur via
supported metal cluster catalysts has spurred a flurry of
activity in studyingthe physicochemical properties
1100.
/7/
These mater-
ials are of clear catalytic importance /5-11/ and are
/17/
P. W . R. Corfield, R . 3. Doedens. J. A. Ibers, %.
Chem.
entrapped within the zeolite cages / 1 - 4 1 .
attractive system for detailed spectroscopic study, since
(1974) 132.
1982,
In recent years there has been a renewed interest
in the spectroscopy of zeolites, and of metal clusters
R. M. Tuggle, D. L. Weaver, Inorg. Chem.
(1972) 2237.
Of
these
materials. However, as yet there is a lack of good infrared
data on the "metal core" of these catalysts /18-20/ which
would give clues as to how their geometry and electronic
structure 1s affected by the reacting molecules or by the
Received June 6 , 1 9 8 3
/Z
4 0 9 S/
immobilizing support.
In this preliminary communication, we wish to report
the far infrared spectra of silver atoms and clusters en-
- 1074 -
1076 -
-
trapped within the cages of zeolite Y.
Dieses Manuskript ist
zu zitieren als
Angew. Chem. Suppl.
7983.1075- I 087
'
This manuscript is
to be cited as
Angew. Chem. Suppl.
rapid
19a3.1075-1087
micron mylar heamsplitter and a triglycine sulphate detector
B V s r l q Ulsmis GmbH. 06940Weinhim. 1983
Spectra were recorded with a Nicolet 2 0 0 S X high vacuum,
ID*
i
scanning FT-IR spectrometer equipped with a 6 . 2 5
LO9 cm. Hz watt).
The spectra shown are the result
07214227/83/1010-107802 5010
of fourier transformation of 1000 coadded interferograms
Fourier Transform Far Infrared Spectroscopy of Silver Atoms
and Silver clusters Entrapped in Sodium Y Zeolite
encompassing a measurement time of about 1 hour, and are
not smoothed in any way.
The resolution is 4 cm-l.
The
samples were prepared by standard ion exchange techniques
/21/ performed in the absence of light due to the extreme
BY
Geoffrey A. Ozin',
Mark D. Baker, and Jonathan M. Parnis
photosensitivity of silver zeolites. Three samples were
used in this study: a "blank" unexchanged NaY zeolite, a
partially exchanged Ag Na
6
49
Y and a fully exchanged Ag
55y.
The raw hydrated zeolite was purchased from Union Carbide.
The samples were pressed into self-supporting, 2 0 mm diameter wafers weighing about 50 mg., with an applied pressure
of 2 tOnS per square inch.
Spectroscopic measurements
were made in a vacuum cell which allowed for in situ thermal
treatment of the samples.
The optical train through the
IR cell amounted to two 3 mm thick polyethylene windows plus
*Professor A. Ozin, Dr. M.D. Baker and Xr. J.M. Parnis
Lash Miller Chemistry Department, University of Toronto,
80 St. George Street, Toronto, Ontario, Canada M5S IAl.
the zeolite wafer resulting in a total transmission of about
10%.
In the spectra shown in Figures 1 and 2 , zeolite framework,
silver cluster.silver atom and cationic vibrational modes were
observed in the region 4 0 0 to 30 cm-l.
-
1075 -
-
1077 -
Figure 1 shows how
we were able to track the dehydration of unexchanged N ~ Y
from room temperature to 600°C.
at room temperature.
All spectra were recorded
There are clear changes in the spec-
trum between 300 and 400 cm-',
this region being linked
with the vibrations of the pore openings /22/.
Changes
also occurred in the 2 5 0 to 300 cm-I region, and bands in
this region are thought to be due to vibrations of polyhedral building units (18-24 tetrahedra,
SA
this assignment has not been substantiated.
across) but
The spectrum
recorded after dehydration at 600°C is very simllar to that
of Peuker
/19/.
All the bands below 200 cm-l have
been assigned to vibrations of sodium ions in different
sites in the zeolite lattice.
The strong doublet at 190
and 150 cm-l has been assigned to cationic occupancy of
site I1 and site I respectively and the 100 cm-l band to a
site I' sodium ion.
The feature at 90 cm-I 1 s to our know-
ledge unassigned
I n Figure 2 , we show the far infrared spectra of the
three samples
The growth of new features below 170 cm-'
for the ion exchanged zeolites is striking, and we can immediately assign these to vibrational modes ,nvolving silver
+bo
/la/ for Na, K, Rb and C s exchanged
The work of Brodski
3bo
2bo
ibo
? O
WFWENUMBER
zeolites has shown that the vibrational frequency of cationic
modes (in the same sites) i s proportional to m-tR-3'2
Figure 1: PT far IS absorption spectra of sodiun zeolite Y, showing
the spectral chancres induced by 60 min. vacua: thermal
dehyZratlon at 25, 300, 5 0 0 and 600'C and subsequently
recorded at room temperature.
-
1078
m
IS
the cation mass and R is the cationic radius.
where
We have
applied this empirical formula to the case of a silver ion
1080 -
-
-
located in sites I and 11.
The sodium Ions sitting in
these sites give rise to bands at 190 and 156 cm-',
and
would therefore shift to 70 cm-l and below for a silver
ion in the same site.
bands at 6 0 and 30 cm-'
We therefore tentatively assign the
in the AgS5Y spectrum to vibrational
modes of Ag+ in sites I and I1 respectively.
This then
allows us to assign the bands above 60 cm-I to either silver
atom vibrations or to silver cluster modes.
It has been conclusively shown /23/ that the thermal
treatment of silver exchanged Y zeolites in vacua induces
autoreduction and clustering processes giving rise to the
charged silver clusters Ag;(slte
1,I'I ,and Ag:+(n=5-131
(%-cage)
as well as A$ [Site 11. In tne case of Ag6Ma49Y,the ma~ority
, whereas with the fully exchanged
species are
Ago
AgS5Y, Ag:
is also present.
and Agl
and Ag;+
The locations of these Ago
species in the hexagonal prism site of the zeolite
framework is shown in Figure 3 .
3b that in the case of Ag+
parent
Ago
It is evident from Figure
the vibratronal spectrum of the
in site I will be perturbed
the annroach of
5x3
a silver ion in site 1'. Coupled with the frequency and breadth
of the absorption Dand centred around 130
the sharp multicomponent 80 cm-'
A
2 0
WCIVENUMBER
Figure 2 :
band to
1079 -
we have assigned
and
the 130 cm-l band to the larger cluster in the
2
Agi
and
cage.
Annealing of the A g 5..<Y sample from 300 to 400°C removed the
splitting of the 80 cm-l band and sharpened the peak. This
Far Infrared absorbance spectra of NaS5Y, A96Ma49Y
and AgS5Y zeolites.
-
err-',
Ago
-
1081 -
indicates that the band splittings are probably not due to site
effects associated with the Si/A1 distribution around site I, I'
and did not arise from 107Ag/109Ag isotopes. A more plausible
explanation is to ascribe the multiplet structure to a perturcage vlbrational modes by a or 6-cage
bation of the AgD or AqZ
residual intrazeolitic water, the latter being present at 300°C
SITE
I
Ago
and absent at 40OOC.
In summary, this study demonstrates that it is viable
to study the infrared vibrational spectra of metal atoms
and clusters immobilized in zeolite supports.
This will
provide a direct and highly sensitive spectroscopic probe
of metal ator-cage and metal cluster core modes and hence
a new insight into the nature of their interaction with
the surroundings (metal-support effects].
We plan to con-
tinue this study in parallel with reflectance,fluorescence,
A
Figure 3A:
esr, and laser Raman spectroscopies
The location of Ago in the hexagonal prism
(site I) of the zeolite lattice.
-
1082 -
-
1084 -
KKNOWLEDGEMENTS
The generous financial assistance of the Natural
Sciences and Engineering Council of Canada's Oaerating,
Halor Equipment and Strategic Energy Programmes and the
Connaught Fund of the University of Toronto is gratefully
acknowledged.
JMP expresses his gratitude for an NSERC
graduate scholarship.
The assistance of Mr. K. Molnar
and Mr. T. H l g S O n i n the designing of the in situ far IR
zeolite cell was invaluable.
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Angew. Chem. Suppl.
7983,1088- 1 105
Angew. Chem. Suppl
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lxefert a l s MeBgroOen
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_
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_
_
~
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1086 -
-
1088
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Grenzen von Aufldsung und Empfindlichkeit. Doppeiresonani-Verfahren
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reduzieren durch rusPtzlithe Auswahlregeln die erlaubten Uberqange,
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2N
N
.
1
and Risen, W.M.,
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ESR-MUltiplettS von Gruppen \Xquivalenter
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Kerne mit dem Kernspin IN
gehen jewerlr in ein ENDOR-Llnlenpaar Gber and fiihren so zu betrkht-
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lichem Aufl6sungsqewrnn. Gegendber NMR-Doppelresonanz-Methoden 121
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ist der experimentelle Aufwand allerdings erh6ht.und daher wezden
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E,5 6 ,
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AbSChhtzunq der ENDOR-MeBbedinqungen
Die Theorie der ENDDR-Spektroskopre
Weise
die Signale
131
zeigt, ~n welch komplexer
von d e n S p l n / G i t t e r - R e l a x a r l o n s r a t e n w
~ r nunter-
suchten System abhangen, und d d 0 sie s i c h durch gezielte veranderung
Received June 6 , revised August 9, 1983 /z 408
S/
der MeBbedrngunqeil optimreren lassen. Ausganqspunkt sind die magnetrschen Eigenschaften der betreffenden Kerne, z . 8.
Kern N
lH
' 3c
1087 -
YN
IN
'N
TrA:
1/2
2.67510
1.108
1/2
0.61263
3.52
1
0.19324
1.01
13709
2.18
44991
99.63
29S1
4.70
100
1/2
-0.53141
1/2
-
1.08290
1089
14.00
..
-
99.985
14N
31P
-
8 N
49467
5.67 494214
-
(1)
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