Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії
The mechanism of binding of Cr(acac)3 molecules at active sites of the surface of silica and alumina supports has been studied by temperature programmed desorption mass spectrometry (TPD-MS), UV-vis and IR spectroscopy. It has been found out that surface hydroxyl groups are responsible for binding o...
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Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2010
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Surface| _version_ | 1869291531752439808 |
|---|---|
| author | Davydenko, L. Mischanchuk, B. Pokrovskiy, V. Babich, I. Plyuto, Yu. |
| author_facet | Davydenko, L. Mischanchuk, B. Pokrovskiy, V. Babich, I. Plyuto, Yu. |
| author_institution_txt_mv | [
{
"author": "L. Davydenko",
"institution": "Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України"
},
{
"author": "B. Mischanchuk",
"institution": "Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України"
},
{
"author": "V. Pokrovskiy",
"institution": "Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України"
},
{
"author": "I. Babich",
"institution": "Університет Твенте"
},
{
"author": "Yu. Plyuto",
"institution": "Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України"
}
] |
| author_sort | Davydenko, L. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:39:14Z |
| description | The mechanism of binding of Cr(acac)3 molecules at active sites of the surface of silica and alumina supports has been studied by temperature programmed desorption mass spectrometry (TPD-MS), UV-vis and IR spectroscopy. It has been found out that surface hydroxyl groups are responsible for binding of Cr(acac)3 molecules only in the case of silica support due to hydrogen bonding with acetylacetonate ligand. In contrast, the binding of Cr(acac)3 molecules at the alumina surface can be due to donor-acceptor interaction of π-electrons of acetylacetonate ligands with Al3+ sites. |
| first_indexed | 2025-07-22T19:32:49Z |
| format | Article |
| fulltext |
Поверхность. 2010. Вып. 2(17). С. 119–128 119
UDC: 544.723.23
TPD-MS AND SPECTROSCOPIC STUDIES OF Cr(acac)3
BINDING AT SILICA AND ALUMINA SURFACE
L. Davydenko*1, B. Mischanchuk1, V. Pokrovskiy1, I. Babich2, Yu. Plyuto1
1Chuiko Institute of Surface Chemistry, National Academy of Sciences of Ukraine,
17 General Naumov Str. Kyiv, 03164, Ukraine
2University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
The mechanism of binding of Cr(acac)3 molecules at active sites of the surface of silica and
alumina supports has been studied by temperature programmed desorption mass spectrometry (TPD-MS),
UV-vis and IR spectroscopy. It has been found out that surface hydroxyl groups are responsible for binding
of Cr(acac)3 molecules only in the case of silica support due to hydrogen bonding with acetylacetonate
ligand. In contrast, the binding of Cr(acac)3 molecules at the alumina surface can be due to donor-acceptor
interaction of π-electrons of acetylacetonate ligands with Al3+ sites.
Introduction
The binding of chromium acetylacetonate Cr(acac)3 with the surface of silica [1-6],
alumina [3, 7–9] and silica-alumina [6, 10, 11] was widely discussed in connection with the
synthesis of supported heterogeneous catalysts. Two mechanisms of binding of Cr(acac)3 at
surface active sites of the supports are contradictory. Molecular Cr(acac)3 may bind to the surface
due to the formation of hydrogen bonds with hydroxyl groups [3–6, 8, 10, 11] or donor-acceptor
interaction with coordinatively unsaturated Al3+ sites [8, 10]. The chemical interaction of Cr(acac)3
molecules with surface active sites may also result in the formation of Cr(acac)x (x<3) species at
the support surface [2, 3, 5–7, 9, 11]. Therefore, the binding of Cr(acac)3 molecules at the support
surface should be reasonably considered as the first step of the formation of Cr(acac)x species.
Although IR spectroscopy was widely used to study the binding of Cr(acac)3 molecules at
the surface of oxide supports [2–6, 8, 10, 11] the details of interaction of acetylacetonate ligands
with surface active sites are not clear yet. This concerns, first of all, the supports which differ in
the nature and chemistry of surface sites.
The possibility of hydrogen bonding of Cr(acac)3 molecules with hydroxyl groups of
alumina surface was supposed earlier [8] but was not proved experimentally unlike the case of
silica surface.
The ligand substitution reaction between the hydrogen bonded Cr(acac)3 molecules and
hydroxyl groups of silica surface that occurs upon thermal activation was reported [2, 5]. It
resulted in covalent bonding of chromium acetylacetonate species ≡SiO–Cr(acac)2. The release of
acetylacetone molecules was assumed by Haukka et al. [2] and later confirmed by Hakuli et al. [5].
The amount of the evolved acetylacetone is proportional to the hydrogen bonded Cr(acac)3
molecules whose loading depends on the reaction temperature.
The combination of UV-vis and IR spectroscopy and temperature programmed desorption
mass spectrometry can be used to clarify the details of interaction of Cr(acac)3 with surface active
sites on the molecular level. First, the energy of electron transitions of Cr(acac)3 and the
frequencies of the vibrations in acetylacetonate ligands are sensitive to their involvement into
molecular interactions. Second, the release of acetylacetone upon the thermal activation of
Cr(acac)3 at the support surface can help to detect the hydrogen bonded molecules.
The aim of this work was to study the mechanism of the interaction of Cr(acac)3 molecules
120
with active sites of silica and alumina surface.
Experimental
Decoration of the surface of fumed silica (Aerosil 200, Evonik Degussa AG, particle size
12 nm, 200 m2/g) and alumina (Aeroxide Alu C, Evonik Degussa AG, particle size 13 nm, 100
m2/g) nanoparticles with Cr(acac)3 (Aldrich, 97%) was performed according to the procedure
described by Babich et al. [4, 8]. The supports were compacted by pressing, crushed and sieved
(the fraction of particle size of 0.25-0.50 mm was used). The supports were calcined at 673 K for 2
h prior decoration procedure. The loading of chromium in silica and alumina samples decorated
with Cr(acac)3, denoted hereinafter as Cr(acac)3/SiO2 and Cr(acac)3/Al2O3, was 0.69 and
0.78 at/nm2, respectively. The acac/Cr molar ratio of 3 indicated the binding of the intact Cr(acac)3
molecules at the surface of both supports [4, 8].
The reference samples with chromium loading of 0.69 Cr/nm2 and 0.78 at/nm2, denoted
hereinafter as Cr(acac)3 ~ SiO2 and Cr(acac)3 ~ Al2O3, were prepared by dry blending of Cr(acac)3
with the preliminary calcined silica and alumina, respectively.
The encapsulation of Cr(acac)3 into silica matrix was performed by sol-gel technique. First,
tetraethylorthosilicate (TEOS) (Aldrich, 98%) was pre-hydrolysed for 2 h at room temperature to
form the primary siloxane species terminated with hydroxyl groups (the reactant molar ratio was
1.0 TEOS : 0.05 HCl : 3.82 H2O). Then the resulting composition was diluted with 0.037 M
ethanol solution of Cr(acac)3 in the proportion 1:3 per volume. To complete gelation, the
composition was left in the closed vessel at room temperature for 6 months and dried in air at
room temperature for 1 week. The synthesised silica gel with encapsulated Cr(acac)3 is denoted
hereinafter as Cr(acac)3-SiO2.
UV-vis diffuse reflectance spectra were recorded within 190 - 1100 nm with resolution of
1 nm by means of a Lambda 35 UV-vis spectrometer (Perkin-Elmer) equipped with a Labsphere
RSA-PE-20 diffuse reflectance and transmittance accessory. The background correction was
performed using certified reflectance standard Spectralon (Labsphere) supplied with the
spectrometer. Kubelka-Munk function for infinitely thick samples was used to convert the
reflectance measurements into equivalent absorbance spectra. The conversion was performed
using UV Winlab Advanced Spectroscopy Software supplied with the spectrometer.
IR reflectance spectra of the powdered samples were recorded within 400 - 4000 cm-1 with
resolution of 4 cm-1 by means of a Nexus Nicolet Fourier Transform Infrared spectrometer
(Thermo Scientific) equipped with a Smart Collector reflectance accessory. The background
correction was performed using KBr (Merck, for IR spectroscopy) as a diffuse reflectance
standard. The samples were diluted with KBr in the proportion 1:10 per weight before IR spectrum
recording. The bulk Cr(acac)3 and Al(acac)3 (Aldrich, 99%) were diluted in the proportion 1:25
per weight.
The temperature programmed desorption mass spectrometric (TPD-MS) study was
performed under vacuum (10-6 Pa) in the temperature range of 303 – 1073 K with a heating rate of
10 K/min. The release of acetylacetone upon thermal activation of Cr(acac)3 at silica and alumina
supports was controlled by means of quadrupole mass spectrometer МХ 7304А (Selmi, Ukraine).
Electron ionisation mass spectra of volatile products in the range of m/z 12 – 200 were recorded
continuously upon the increase of temperature.
Results and discussion
The colour of Cr(acac)3/SiO2 and Cr(acac)3/Al2O3 samples was found to be green while bulk
Cr(acac)3, Cr(acac)3 ~ SiO2 and Cr(acac)3 ~ Al2O3 are magenta. Since the initial magenta colour of
121
bulk Cr(acac)3 turned green upon decoration of the supports, this indicates the interaction of
Cr(acac)3 molecules with silica and alumina surface.
UV-vis spectra of Cr(acac)3~SiO2, Cr(acac)3/SiO2, Cr(acac)3 ~ Al2O3 and Cr(acac)3/Al2O3 are
shown in Figure 1. The positions of the absorbance bands in the spectra of Cr(acac)3 ~ SiO2 and
Cr(acac)3 ~ Al2O3 correlate with the reported data for ethanol solution and gaseous Cr(acac)3 [12]
and makes it possible their assignment (Table 1).
200 300 400 500 600 700 800
2
1
K
ub
el
ka
-M
un
k
ab
so
rb
an
ce
l, nm
200 300 400 500 600 700 800
2
1K
ub
el
ka
-M
un
k
ab
so
rb
an
ce
l, nm
a b
Fig. 1. UV-vis spectra of a) Cr(acac)3 ~ SiO2 (1) and Cr(acac)3/SiO2 (2), b) Cr(acac)3 ~ Al2O3 (1)
and Cr(acac)3/Al2O3 (2) samples.
Table 1. Band positions and assignments in UV-vis spectra of Cr(acac)3~SiO2, Cr(acac)3/SiO2,
Cr(acac)3 ~ Al2O3 and Cr(acac)3/Al2O3 samples
Cr(acac)3 ~ SiO2 Cr(acac)3 / SiO2 Cr(acac)3 ~ Al2O3 Cr(acac)3 / Al2O3 assignment [12]
220 220 219 211 p3(e) à p4(a1)
* 267 * 301 p3(e) à p4(e);
p3(a2) à p4(a1)
330 330 327 326 d (et) à p4(a1);
d(et) à p4(e)
392 398 391 370 S à T
560 573 563 589 4A2 à 4A2 + 4E
The Cr(acac)3 ~ SiO2 sample exhibits the absorbance bands which correspond to different
electron transitions in Cr(acac)3 molecule at 220, 330, 392, and 560 nm. The Cr(acac)3 / SiO2
exhibits a similar UV-vis spectrum with absorbance bands located at 220, 267, 330, 398 and 568 nm.
This can mean only minor changes of Cr(acac)3 molecules during their binding at silica surface.
The Cr(acac)3 ~ Al2O3 sample exhibits the absorbance bands which correspond to the
electron transitions in Cr(acac)3 molecule at 219, 327, 391, and 563 nm. The Cr(acac)3 / Al2O3
exhibits a UV-vis spectrum with absorbance bands located at 211, 301, 326, 370 and 589 nm. One can
122
conclude stronger influence of alumina surface on Cr(acac)3 molecules that is reflected in more
substantial shift of the band positions as well as in variation of relative intensity of bands.
The red shift of bands of S ® T and 4A2 ® 4A2 + 4E electron transitions in Cr(acac)3
molecule was observed upon silica decoration. While in the case of alumina support the red shift
of band of 4A2 ® 4A2 + 4E transition and substantial blue shift of bands of p3(e) ® p4(a1) and
S ® T electron transitions in Cr(acac)3 molecule was observed. This indicates to the difference in
the mechanism of binding of Cr(acac)3 molecules at silica and alumina supports and to the distinct
influence of alumina on acetylacetonate ligands of Cr(acac)3 if compared with silica support. The
observed change of magenta colour of bulk Cr(acac)3 to green upon decoration of silica and
alumina surface may be explained by the red shift of the band of d ® d electron transition in UV-
vis spectra by 13 and 26 nm, respectively.
IR spectroscopic study was performed to clarify the changes of Cr(acac)3 molecules during
their binding at silica and alumina surface.
IR spectra of bulk Cr(acac)3, Cr(acac)3/SiO2 and Cr(acac)3-SiO2 samples in the region of
1250–1650 cm−1 characteristic for the vibrations of acetylacetonate ligand are shown in Figure 2.
The position of the observed bands and their assignment [13-15] are summarised in Table 2. The
bands of n (C – C) + n (C – O),
n (C = C ) + n (C – C) and n (C = O) vibrations
of acetylacetonate ligand are taken for the
detailed consideration.
The bulk Cr(acac)3 exhibits the bands at
1278, 1522 and 1577 cm−1 (Fig. 2, curve 1).
The corresponding bands in the spectrum of
Cr(acac)3/SiO2 (Fig. 2, curve 2) are slightly
different and located at 1282, 1526 and
1573 cm−1, respectively. The difference in the
position of the bands in IR spectra of bulk
Cr(acac)3 and Cr(acac)3/SiO2 is within the
spectrometer resolution and can hardly be used
to attribute it to the particular interaction of
Cr(acac)3 with surface active sites.
IR spectrum of Cr(acac)3-SiO2 is shown
in Figure 2 (curve 3). The positions of the
considered bands at 1284, 1527 and 1562 cm−1
differ from those in the spectrum of bulk
Cr(acac)3 (Table 2). A substantial difference in
the position of n (C = O) vibration band in IR
spectra of bulk and encapsulated Cr(acac)3 at
1577 and 1562 cm−1, respectively, can indicate
the involvement of C = O groups in interaction with silica network.
The IR spectra of bulk Cr(acac)3, Cr(acac)3/Al2O3 and bulk Al(acac)3 in the region of
1250–1650 cm−1 are shown in Figure 3. In contrast to bulk Cr(acac)3 for which the bands at 1278,
1522 and 1577 cm−1 are typical (Fig. 3, curve 1), Cr(acac)3/Al2O3 exhibits the bands at 1286, 1527
and 1582 cm−1 (Fig. 3, curve 2) that indicates the involvement of acetylacetonate ligands into
interaction with alumina surface sites. The position of the observed bands and their assignment are
summarised in Table 2.
1800 1700 1600 1500 1400 1300 1200
3
2
1
Re
fle
ct
an
ce
, a
rb
. u
ni
ts
Wavenumber, cm-1
Fig. 2. IR spectra of bulk Cr(acac)3 (1),
Cr(acac)3/SiO2 (2) and Cr(acac)3-SiO2 (3).
123
Table 2. Band positions and assignments in IR spectra of bulk Cr(acac)3, Cr(acac)3/SiO2,
Cr(acac)3-SiO2, Cr(acac)3/Al2O3 and bulk Al(acac)3
Band position, cm-1
Band assignment
Cr(acac)3 Cr(acac)3/SiO2 Cr(acac)3-SiO2 Cr(acac)3/Al2O3 Al(acac)3
n (C – C) + n (C – O) 1278 1282 1284 1286 1289
d (C – H) 1320-1470 1320-1470 1320-1470 1320-1470 1320-1470
n (C = C) + n (C – C) 1522 1526 1527 1527 1535
n (C = O) 1577 1573 1562 1582 1593
The positions of the bands in IR spectrum of bulk Al(acac)3 at 1289, 1535 and 1593 cm-1
are very close to those in Cr(acac)3/Al2O3. Therefore it is not possible to detect correctly the
surface Al(acac)x species which can be formed from acetylacetone evolved upon covalent bonding
of Cr(acac)3 at the alumina surface.
One should consider in detail the
position of the band which correspond to
n (C = O) vibration of acetylacetonate ligand
in different surrounding. In IR spectra of bulk
Cr(acac)3 this band is located at 1577 cm−1.
For Cr(acac)3/SiO2 this band is shifted to 1573
cm−1. For Cr(acac)3-SiO2 further shift to
1562 cm−1 is observed. Such behaviour of
vibration of C = O group can be explained by
its interaction with active sites either on silica
surface or inside silica matrix. In the latter
case, somewhat stronger interaction should be
observed for steric reasons that results in more
substantial band shift. In contrast, for
Cr(acac)3/Al2O3 the opposite band shift to
1582 cm−1 is observed. Therefore, it
reasonable to assume the difference in the
mechanism of the binding of Cr(acac)3
molecules at silica and alumina supports that
agrees with the results of UV-vis
spectroscopic study.
To discuss the molecular binding of
metal acetylacetonates M(acac)n at the support surface (silica, alumina, titania etc), one should
consider two alternative ligand structures. First, the ligand can be postulated mostly as the system
with delocalised p-electrons [16] responsible for interaction (scheme 1, a). Second, the irregular
distribution of the electron density in acetylacetonate cycle may be supposed (scheme 1, b) and
binding is expected to realise via definite group rather then a whole p-electron system.
Furthermore, the acetylacetonate ligand possesses C = O and C – H groups which differ in
chemical properties [17] and the ability to be involved in interaction with surface sites.
1800 1700 1600 1500 1400 1300 1200
3
2
1
Re
fle
ct
an
ce
, a
rb
. u
ni
ts
Wavenumber, cm-1
Fig. 3. IR spectra of bulk Cr(acac)3 (1),
Cr(acac)3/Al2O3 (2) and bulk Al(acac)3 (3).
124
n
Mn+
O O
n
Mn+
O O
a b
Scheme 1. Alternative structures of acetylacetonate ligand in metal acetylacetonates M(acac)n.
Köhler et al. [3] proposed the mechanism of bonding of Pt(acac)2 molecules with hydroxyl
groups of silica surface. The possibility of the formation of hydrogen bonds with participation of
both delocalised p-electrons of acetylacetonate ligands and oxygen free electron pairs was
assumed.
The observed behaviour of acetylacetonate ligand vibrations for Cr(acac)3/Al2O3 can be
explained by interaction of its π-electrons with alumina surface active sites.
It is also necessary to take into account the dependence of the loading of the deposited
Cr(acac)3 on the concentration of surface hydroxyl groups of silica [4]. This indicates the
involvement of C = O groups in hydrogen bonding with hydroxyl groups of silica network. This
conclusion agrees with earlier reported results on quantum chemical simulation of interaction of
Cr(acac)3 with silanol groups ≡Si–OH [18]. The formation of hydrogen bonds via the oxygen atom
of acetylacetonate ligand and the hydrogen atom of ≡Si–OH was found out to be most
energetically favourable. The binding of Cr(acac)3 molecules at Al3+ sites of alumina surface was
supposed since the concentration of surface hydroxyl groups on the alumina surface did not
influence the Cr(acac)3 loading [8].
The scheme 2 illustrates the possible mechanism of binding of Cr(acac)3 molecules at
active sites of silica and alumina surface.
Cr
O
O
O O
O
O
Si
O
H
Cr
O
O
O O
O
O
Al3+
Al
O
H
silica alumina
Scheme 2. Binding of Cr(acac)3 molecule at active sites of silica and alumina surface.
The proposed mechanism of binding of Cr(acac)3 molecules at the active sites of silica and
alumina surface was proved by TPD-MS technique. The desorption of acetylacetone could be
controlled by its molecular ion (m/z 100). The fragment ions [H3CCOCH2CO]+ and [H3CCO]+
with m/z 85 and 43 (scheme 3) are also characteristic for acetylacetone [19, 20].
125
The mass spectra of the volatile products desorbed from Cr(acac)3/SiO2 and
Cr(acac)3/Al2O3 at 435 K are shown in Figure 4. The peak at m/z 18 corresponds to water
desorbing from the surface of both samples. The acetylacetone related peaks at m/z 43, 85 and 100
dominate in the case of Cr(acac)3/SiO2 (Fig. 4, a). In the case of Cr(acac)3/Al2O3 (Fig. 4, b), the
molecular ion (m/z 100) as well as fragment [H3CCOCH2CO]+ (m/z 85) are not detected.
Fig. 4. Mass spectra of the products desorbed from Cr(acac)3/SiO2 (a) and Cr(acac)3/Al2O3 (b)
at 435 K
TPD-MS patterns of m/z 43, 85 and 100 for Cr(acac)3/SiO2 and Cr(acac)3/Al2O3 are shown
in Figure 5.
300 400 500 600 700 800 900 1000
a
43
85
100
I,
ar
b.
u
ni
ts
T, K
300 400 500 600 700 800 900 1000
b43
85
100
I,
ar
b.
u
ni
ts
T, K
Fig. 5. TPD-MS patterns of m/z 43, 85 and 100 for Cr(acac)3/SiO2 and Cr(acac)3/Al2O3
TPD-MS of Cr(acac)3/SiO2 (Fig. 5, a) exhibits the pattern of the molecular ion (m/z 100) in
[ ] [ ] [ ]+-··+-·+ ¾¾¾¾ ®¾¾¾ ¾¬ CCOHCOCHCCOCHHCOCCOCHH 332323
323 COCHCHCH
m/z 85 m/z 100 m/z 43
Scheme 3. Fragmentation of cation-radical of acetylacetone.
126
the region of 400-600 K. This means the release of acetylacetone molecules which can originate
from Cr(acac)3 molecules hydrogen bonded to surface hydroxyl groups. Upon thermal activation, a
substitution of acetylacetonate ligands with surface hydroxyl groups occurs that results in the
formation of the covalently bonded chromium acetylacetonate species (scheme 4).
HacacacacCrOacacCrOH +--¾®¾+- 23 )()(
Scheme 4. Substitution of acetylacetonate ligand of Cr(acac)3 with surface hydroxyl group.
From Figure 5, a one can see that above 600 K the intensity of signal of the molecular ion
(m/z 100) is negligible while the fragment ion [H3CCO]+ (m/z 43) demonstrates the intense peak at
610 K. The predominant release of the fragment ion [H3CCO]+ in the absence of the molecular ion
indicates the thermal decomposition of those acetylacetonate ligands in Cr(acac)3 molecule which
are not in hydrogen bonding with the silica surface.
The obtained results are in agreement with the observations of Hakuli et al. [5] who
reported the reaction of Cr(acac)3 with hydroxyl groups of silica surface within 433-473 K and the
formation of ≡SiO–Cr(acac)2 surface species at 473 K. The partial decomposition of
acetylacetonate ligands in surface chromium acetylacetonate species was observed within 493-
513 K.
The TPD-MS patterns of m/z 43, 85 and 100 for Cr(acac)3/Al2O3 are shown in Figure 5, b.
In contrast to TPD-MS of Cr(acac)3/SiO2 (Fig. 5, a), the TPD-MS of Cr(acac)3/Al2O3 exhibits only
negligible intensity of the molecular ion (m/z 100) in the region of 400-600 K while the intense
signal of the fragment ion [H3CCO]+ (m/z 43) is observed within 400-750 K. Since the molecules
of acetylacetone are not released it is reasonable to suppose the thermal decomposition of
acetylacetonate ligands which are not in hydrogen bonding with the alumina surface.
Conclusions
The TPD-MS of Cr(acac)3/SiO2 sample exhibits the pattern of the molecular ion (m/z 100)
in the region of 400-600 K. This means the release of acetylacetone molecules which can originate
from Cr(acac)3 molecules hydrogen bonded to surface hydroxyl groups.
The TPD-MS of Cr(acac)3/Al2O3 sample exhibits only negligible intensity of the molecular
ion (m/z 100) in the region of 400-600 K while the intense signal of the fragment ion [H3CCO]+
(m/z 43) is observed within 400-750 K. Since the molecules of acetylacetone are not released, the
thermal decomposition of acetylacetonate ligands which are not in hydrogen bonding with the
alumina surface predominates.
The surface hydroxyl groups are responsible for binding of Cr(acac)3 molecules only in the
case of silica support due to hydrogen bonding with C = O group in acetylacetonate ligand. In
contrast, the binding of Cr(acac)3 molecules at the alumina surface can be due to donor-acceptor
interaction of π-electrons of acetylacetonate ligands with Al3+ sites.
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4th ed. – Wiley–Interscience, 1986.
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Chemistry. R. A. Meyers (Ed.). – Chichester: Wiley, 2000. – 10815 p.
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with trivalent transition metal ions // J. Inorg. Nucl. Chem. – 1961. – V. 21. – P. 221–237.
17. Mehrotra R. C. Chemistry of metal b–diketonates // Pure Appl. Chem. – 1988. – V. 60. –
P. 1349–1356.
18. Davydenko L. A., Grebenyuk A. G., Plyuto Yu. V. The state of chromium acetylacetonate on
the fumed silica surface // Chem. Phys. Technol. Surf. – 2004. – V. 10. – P. 40–45.
19. NIST Chemistry WebBook, NIST Standard Reference Database Number 69,
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20. Spectral Database for Organic Compounds, SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/
(National Institute of Advanced Industrial Science and Technology, 26 Sept. 2009).
128
ИССЛЕДОВАНИЕ Cr(acac)3 НА ПОВЕРХНОСТИ ОКСИДОВ
КРЕМНИЯ И АЛЮМИНИЯ МЕТОДАМИ ТПД–МС, УФ И ИК
СПЕКТРОСКОПИИ
Л. А. Давиденко1, Б. Г. Мисчанчук 1, В. А. Покровский1, И. В. Бабич2,
Ю. В. Плюто1
1Институт химии поверхности им. А.А. Чуйко Национальной академии наук Украины,
ул. Генерала Наумова, 17, Киев, 03164, Украина
e–mail: l.davydenko@yahoo.com
2Университет Твенте, а/я 217, 7500 АЕ Энсхеде, Нидерланды
Методами температурно–программируемой десорбционной масс–спектрометрии (ТПД–
МС), УФ и ИК спектроскопии исследован механизм взаимодействия молекул Cr(acac)3 с активными
центрами поверхности оксидов кремния и алюминия. Установлено, что в случае оксида кремния
поверхностные гидроксильные группы взаимодействуют с Cr(acac)3 с образованием водородных
связей с ацетилацетонатными лигандами. В случае оксида алюминия реализуется донорно–
акцепторное взаимодействие π–электронов ацетилацетонатных лигандов молекул Cr(acac)3 с
координационно–ненасыщенными центрами Al3+ поверхности.
ДОЛІДЖЕННЯ Cr(acac)3 НА ПОВЕРХНІ ОКСИДІВ КРЕМНІЮ ТА
АЛЮМІНІЮ МЕТОДАМИ ТПД–МС, УФ ТА ІЧ СПЕКТРОСКОПІЇ
Л. О. Давиденко1, Б. Г. Місчанчук 1, В. О. Покровський1, І. В. Бабич2,
Ю. В. Плюто1
1Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України,
вул. Генерала Наумова, 17, Київ, 03164, Україна
e–mail: l.davydenko@yahoo.com
2Університет Твенте, а/я 217, 7500 АЕ Енсхеде, Нідерланди
Методами температурно–програмованої десорбційної мас–спектрометрії (ТПД–МС), УФ
та ІЧ спектроскопії досліджено механізм взаємодії молекул Cr(acac)3 з активними центрами
поверхні оксидів кремнію та алюмінію. Встановлено, що у випадку оксиду кремнію поверхневі
гідроксильні групи взаємодіють з Cr(acac)3 з утворенням водневих зв’язків з ацетилацетонатними
лігандами. У випадку оксиду алюмінію реалізується донорно–акцепторна взаємодія π–електронів
ацетилацетонатних лігандів молекул Cr(acac)3 з координаційно–ненасиченими центрами Al3+
поверхні.
Introduction
Fig. 4. Mass spectra of the products desorbed from Cr(acac)3/SiO2 (a) and Cr(acac)3/Al2O3 (b) at 435 K
Fig. 5. TPD-MS patterns of m/z 43, 85 and 100 for Cr(acac)3/SiO2 and Cr(acac)3/Al2O3
TPD-MS of Cr(acac)3/SiO2 (Fig. 5, a) exhibits the pattern of the molecular ion (m/z 100) in the region of 400-600 K. This means the release of acetylacetone molecules which can originate from Cr(acac)3 molecules hydrogen bonded to surface hydroxyl groups. Upon thermal activation, a substitution of acetylacetonate ligands with surface hydroxyl groups occurs that results in the formation of the covalently bonded chromium acetylacetonate species (scheme 4).
From Figure 5, a one can see that above 600 K the intensity of signal of the molecular ion (m/z 100) is negligible while the fragment ion [H3CCO]+ (m/z 43) demonstrates the intense peak at 610 K. The predominant release of the fragment ion [H3CCO]+ in the absence of the molecular ion indicates the thermal decomposition of those acetylacetonate ligands in Cr(acac)3 molecule which are not in hydrogen bonding with the silica surface.
The obtained results are in agreement with the observations of Hakuli et al. [5] who reported the reaction of Cr(acac)3 with hydroxyl groups of silica surface within 433-473 K and the formation of ≡SiO–Cr(acac)2 surface species at 473 K. The partial decomposition of acetylacetonate ligands in surface chromium acetylacetonate species was observed within 493-513 K.
The TPD-MS patterns of m/z 43, 85 and 100 for Cr(acac)3/Al2O3 are shown in Figure 5, b. In contrast to TPD-MS of Cr(acac)3/SiO2 (Fig. 5, a), the TPD-MS of Cr(acac)3/Al2O3 exhibits only negligible intensity of the molecular ion (m/z 100) in the region of 400-600 K while the intense signal of the fragment ion [H3CCO]+ (m/z 43) is observed within 400-750 K. Since the molecules of acetylacetone are not released it is reasonable to suppose the thermal decomposition of acetylacetonate ligands which are not in hydrogen bonding with the alumina surface.
Conclusions
The TPD-MS of Cr(acac)3/Al2O3 sample exhibits only negligible intensity of the molecular ion (m/z 100) in the region of 400-600 K while the intense signal of the fragment ion [H3CCO]+ (m/z 43) is observed within 400-750 K. Since the molecules of acetylacetone are not released, the thermal decomposition of acetylacetonate ligands which are not in hydrogen bonding with the alumina surface predominates.
The TPD-MS of Cr(acac)3/Al2O3 sample exhibits only negligible intensity of the molecular ion (m/z 100) in the region of 400-600 K while the intense signal of the fragment ion [H3CCO]+ (m/z 43) is observed within 400-750 K. Since the molecules of acetylacetone are not released, the thermal decomposition of acetylacetonate ligands which are not in hydrogen bonding with the alumina surface predominates.
The TPD-MS of Cr(acac)3/Al2O3 sample exhibits only negligible intensity of the molecular ion (m/z 100) in the region of 400-600 K while the intense signal of the fragment ion [H3CCO]+ (m/z 43) is observed within 400-750 K. Since the molecules of acetylacetone are not released, the thermal decomposition of acetylacetonate ligands which are not in hydrogen bonding with the alumina surface predominates.
The TPD-MS of Cr(acac)3/Al2O3 sample exhibits only negligible intensity of the molecular ion (m/z 100) in the region of 400-600 K while the intense signal of the fragment ion [H3CCO]+ (m/z 43) is observed within 400-750 K. Since the molecules of acetylacetone are not released, the thermal decomposition of acetylacetonate ligands which are not in hydrogen bonding with the alumina surface predominates.
References
16.Barnum D. W. Electronic absorption spectra of acetylacetonato complexes – I. Complexes with trivalent transition metal ions // J. Inorg. Nucl. Chem. – 1961. – V. 21. – P. 221–237.
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| id | oai:ojs.pkp.sfu.ca:article-405 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-03-12T17:11:26Z |
| publishDate | 2010 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/63/3025f9ee8d5d5da120a7bfa14da95363.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-4052018-11-27T09:39:14Z TPD-MS and spectroscopic studies of Cr(acac)3 binding at silica and alumina surface Исследование Cr(acac)3 на поверхности оксидов кремния и алюминия методами ТПД–МС, УФ и ИК спектроскопии Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії Davydenko, L. Mischanchuk, B. Pokrovskiy, V. Babich, I. Plyuto, Yu. The mechanism of binding of Cr(acac)3 molecules at active sites of the surface of silica and alumina supports has been studied by temperature programmed desorption mass spectrometry (TPD-MS), UV-vis and IR spectroscopy. It has been found out that surface hydroxyl groups are responsible for binding of Cr(acac)3 molecules only in the case of silica support due to hydrogen bonding with acetylacetonate ligand. In contrast, the binding of Cr(acac)3 molecules at the alumina surface can be due to donor-acceptor interaction of π-electrons of acetylacetonate ligands with Al3+ sites. Методами температурно–программируемой десорбционной масс–спектрометрии (ТПД–МС), УФ и ИК спектроскопии исследован механизм взаимодействия молекул Cr(acac)3 с активными центрами поверхности оксидов кремния и алюминия. Установлено, что в случае оксида кремния поверхностные гидроксильные группы взаимодействуют с Cr(acac)3 с образованием водородных связей с ацетилацетонатными лигандами. В случае оксида алюминия реализуется донорно–акцепторное взаимодействие π–электронов ацетилацетонатных лигандов молекул Cr(acac)3 с координационно–ненасыщенными центрами Al3+ поверхности. Методами температурно–програмованої десорбційної мас–спектрометрії (ТПД–МС), УФ та ІЧ спектроскопії досліджено механізм взаємодії молекул Cr(acac)3 з активними центрами поверхні оксидів кремнію та алюмінію. Встановлено, що у випадку оксиду кремнію поверхневі гідроксильні групи взаємодіють з Cr(acac)3 з утворенням водневих зв’язків з ацетилацетонатними лігандами. У випадку оксиду алюмінію реалізується донорно–акцепторна взаємодія π–електронів ацетилацетонатних лігандів молекул Cr(acac)3 з координаційно–ненасиченими центрами Al3+ поверхні. Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2010-08-28 Article Article application/pdf https://surfacezbir.com.ua/index.php/surface/article/view/405 Surface; No. 2(17) (2010): Surface; 119-128 Поверхность; № 2(17) (2010): Поверхность; 119-128 Поверхня; № 2(17) (2010): Поверхня; 119-128 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/405/403 Авторське право (c) 2010 L. Davydenko, B. Mischanchuk, V. Pokrovskiy, I. Babich, Yu. Plyuto |
| spellingShingle | Davydenko, L. Mischanchuk, B. Pokrovskiy, V. Babich, I. Plyuto, Yu. Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії |
| title | Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії |
| title_alt | TPD-MS and spectroscopic studies of Cr(acac)3 binding at silica and alumina surface Исследование Cr(acac)3 на поверхности оксидов кремния и алюминия методами ТПД–МС, УФ и ИК спектроскопии |
| title_full | Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії |
| title_fullStr | Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії |
| title_full_unstemmed | Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії |
| title_short | Долідження Cr(acac)3 на поверхні оксидів кремнію та алюмінію методами ТПД–МС, УФ та ІЧ спектроскопії |
| title_sort | долідження cr(acac)3 на поверхні оксидів кремнію та алюмінію методами тпд–мс, уф та іч спектроскопії |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/405 |
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