Catalytic conversions of chloroolefines over iron oxide nanoparticles 3. Electronic and magnetic properties of γ-Fe2O3 nanoparticles immobilized on different silicas

Article abstract of DOI:10.1007/s11172-006-0485-7

Catalytic properties of superparamagnetic γ-ferric oxide nanoclusters, which are uniform in terms of size and magnetic properties were studied. The catalysts were supported on the activated silica gel matrix (AGM) prepared from the KSK-2 silica gel of globular structure and on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher that of usual supported catalysts based on α-ferric oxide. Analysis of the Moessbauer spectra of the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at T = 3-300 K shows that during the reaction some Fe^III ions arranged in ～2-3-nm γ-Fe₂O₃ nanoclusters magnetically ordered at 6 K are reduced to form a high-spin Fe^II complex in the paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at T = 2 K demonstrates a linear field dependence of the magnetization passing through the coordinate origin. Analysis of the Moessbauer spectra and magnetic properties suggests that during the catalytic reaction the Fe ^III ions in the γ-Fe₂O₃ nanoclusters interact with chloroolefin with the allylic structure to be partially reduced to the Fe^II ions that are bound in a complex containing chloride ions and O^II ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic activity of γ-Fe₂O₃ nanoparticles.

Full text of DOI:10.1007/s11172-006-0485-7

1
768
Russian Chemical Bulletin, International Edition, Vol. 55, No. 10, pp. 1768—1774, October, 2006
Catalytic conversions of chloroolefines over iron oxide nanoparticles
3
.* Electronic and magnetic properties of γꢀFe O nanoparticles
2
3
immobilized on different silicas
T. N. Rostovshchikova,aꢀ O. I. Kiseleva, V. V. Smirnov, Yu. V. Maksimov, I. P. Suzdalev,
a
a
b
b
b
c
d
V. E. Prusakov, M. V. Tsodikov, and V. N. Ikorskii
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119992 Moscow, Russian Federation.
1
Fax: +7 (495) 932 8846. Еꢀmail: rtn@kinet.chem.msu.ru
N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences,
b
4
ul. Kosygina, 119991 Moscow, Russian Federation.
Fax: +7 (495) 137 8318. Eꢀmail: maksimov@chph.ras.ru
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences,
c
2
9 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 230 2224. Eꢀmail: tsodikov@ips.ac.ru
d
International Tomography Center, Siberian Branch of the Russian Academy of Sciences,
3
a ul. Institutskaya, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383 2) 33 1399. Eꢀmail: ikor@tomo.nsk.ru
Catalytic properties of superparamagnetic γꢀferric oxide nanoclusters, which are uniform
in terms of size and magnetic properties were studied. The catalysts were supported on the
activated silica gel matrix (AGM) prepared from the KSKꢀ2 silica gel of globular structure and
on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters
are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and
alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher
that of usual suppоrted catalysts based on αꢀferric oxide. Analysis of the Mössbauer spectra of
the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at Т =
III
3
—300 К shows that during the reaction some Fe ions arranged in ∼ 2—3ꢀnm γꢀFe O
2
3
II
nanoclusters magnetically ordered at 6 K are reduced to form a highꢀspin Fe complex in the
paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial
clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward
magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at Т = 2 К demonstrates
a linear field dependence of the magnetization passing through the coordinate origin. Analysis
of the Mössbauer spectra and magnetic properties suggests that during the catalytic reaction the
III
Fe ions in the γꢀFe O nanoclusters interact with chloroolefin with the allylic structure to be
partially reduced to the Fe ions that are bound in a complex containing chloride ions and
2
3
II
II
O
ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic
activity of γꢀFe O nanoparticles.
2
3
Key words: chloroolefins, isomerization, alkylation, γꢀferric oxide nanoclusters, silicas,
iron(II) oxychloride, Mössbauer spectroscopy, magnetic properties, hysteresis loop.
Supported nanosized iron oxide clusters with superꢀ
chloroolefins. This was assumed to relate to the formation
paramagnetic properties are of interest as catalysts of a
new generation. We have previously1 found that superꢀ
paramagnetic nonstoichiometric nanoclusters γꢀFe O
of mixedꢀvalence iron oxides favored by specific condiꢀ
—4
1—3
tions or by the action of chloroolefins.
The role of
II
structures including two charge states of iron ions (Fe
2
3–х
III
(
0 < x < 1/3) with d ≈ 2—3 nm prepared from iron(III)
and Fe ) was also found in the Fischer—Tropsch reacꢀ
tion and some other catalytic processes.5
,6
acetylacetonate and stabilized on activated mesoporous
silica gel (AGM) or on the activated layered silica matrix
The purpose of the present work is to compare the
(
ASM) exhibit high activity in catalytic conversions of
catalytic activity of γꢀFe O
nanoparticles prepared by
2
3–х
the impregnation of the AGM and ASM with iron(III)
acetylacetonate (2.5 wt.%) followed by thermolysis. The
*
For Part 2, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1705—1711, October, 2006.
066ꢀ5285/06/5510ꢀ1768 © 2006 Springer Science+Business Media, Inc.
1

Catalysis over γꢀFe O nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1769
2
3
isomerization of 3,4ꢀdichlorobutꢀ1ꢀene (3,4ꢀDCB) and
benzene alkylation with allyl chloride were chosen as
model reactions. In addition, it was of interest to reveal
the nature of mixedꢀvalence iron complexes formed on
the supported catalysts upon the interaction with chloroꢀ
olefin of allylic structure. Changes in the electronic and
magnetic properties of the catalysts during the reactions
were examined by Mössbauer spectroscopy in the temꢀ
perature interval 3—80 K and using measurements of macꢀ
roscopic magnetization (SQUID) in the range 2—300 K.
oxidation including aldehydes and ketones of complicated
structure. In the IR spectrum of allyl chloride (recorded
on an In Fralum FT 801 FTꢀIR spectrophotometer in the
1
4
00—4000 cm– range) heated with the 2.5% Fe/ASM catalyst
in a decane solution at 110 °C, the intensity of the absorption
–
1
band of the С=С bond stretching vibration (1640 cm ) weakꢀ
ens and new absorption bands appear (1740, 1737, 1793, and
–1
1
797 cm ) that are characteristic of stretching vibrations of the
carbonyl groups.8
Mössbauer spectra were obtained on a Wissel electrodyꢀ
namic spectrometer with a source of 57Co (Rh) γꢀradiation (acꢀ
tivity 10—20 mCi) in the temperature interval 3—80 K. Isoꢀ
meric shifts were calculated relative to the center of magnetic
HFS lines of αꢀFe. The spectra were processed using standard
leastꢀsquare programs for the Mössbauer transition 3/2 → 1/2.
Magnetic properties of ironꢀcontaining samples were studꢀ
ied in the temperature interval 2—300 K on an SQUID magneꢀ
tometer of the International Tomography Center (Siberian
Branch of the Russian Academy of Sciences, Novosibirsk). To
measure the static magnetic susceptibility, a sample was cooled
in the zero magnetic field down to T = 1 K, then the meaꢀ
surements were conducted in the field with H = 5000 Oe with a
temperature increment of 10—50 K in the interval from 2
to 300 K.
Experimental
Silica gel KSKꢀ2 of usual globular structure and layered
silica prepared from natural vermiculite2 were used for supꢀ
porting γꢀferric oxide. The initial crystalline vermiculite conꢀ
tained ~14 wt.% Al, 1 wt.% Ca, 2 wt.% Mg, and 1 wt.% Fe, as
well as trace amounts of other metals. Vermiculite was subjected
to twoꢀstep acid leaching in a mixture of hydrochloric and sulfuꢀ
,3
5
ric acids followed by washing. All metal ions were almost comꢀ
pletely removed by the acid treatment, which was confirmed by
elemental analysis. Activation resulted in substantial changes in
the properties of layered silica: amorphization of the material,
Xꢀray diffraction analysis of the ironꢀcontaining phases was
carried out on a DRONꢀ3M diffractometer using filtered
СuꢀКα radiation.
2
–1
an increase in the specific surface area to 350 m g , and an
increase in the micropore fraction.7 Iron (2.5 wt.%) was supꢀ
ported on the ASM samples obtained after activation. For this
purpose, the activated matrix was impregnated with a solution
Results and Discussion
of Fe(acac) with a specified concentration followed by drying
3
in air, evacuation, and heating at 400 °C. Temperatureꢀproꢀ
grammed heating was carried out with a rate of 10 deg min–
1
.
Catalytic properties of γꢀferric oxide nanoparticles
Then the sample was stored for 2 h at 400 °C. The obtained
catalyst 2.5 wt.% Fe/ASM (hereinafter 2.5% Fe/ASM) is amorꢀ
phous to Xꢀrays.
Iron was supported on mesoporous silica gel KSKꢀ2 after
preliminary activation of the silica gel by the single treatment
with hydrochloric acid followed by washing. Iron (2.5 wt. %)
was supported on the obtained AGM sample by impregnation
immobilized on silicas
Isomerization of 3,4ꢀDCB. Isomerization of 3,4ꢀDCB
occurs quantitatively in the presence of γꢀferric oxide
nanoparticles supported on silicas of the both types withꢀ
out an induction period at rather low temperatures
(>70 °C). The catalytic activities of the two catalysts on
the AGM and ASM supports are compared in Fig. 1. It is
seen that at 70 and 80 °С the AGMꢀbased catalyst excels
in activity the ASMꢀbased catalysts. However, their acꢀ
with a solution of Fe(acac) . The AGM surface area was
3
2
–1
3
2
40 m g . The 2.5 wt.% Fe/AGM sample (hereinafter
.5% Fe/AGM) is also amorphous to Xꢀrays.
Isomerization of 3,4ꢀDCB and alkylation of benzene with
allyl chloride were conducted in sealed glass ampules with stirꢀ
ring in the temperature interval 70—110 °C in the presence of
oxygen. Procedures of catalytic experiments, analysis of the comꢀ
position of reaction mixtures by chromatography and GCꢀMS,
A/mole of products (mole of Fe)–1 h–1
2
4
3
000
2
,3
and calculation of the catalytic activity have previously been
presented in detail. The major products of 3,4ꢀDCB isomerizaꢀ
tion is transꢀ1,4ꢀdichlorobutꢀ2ꢀene. The yield of the cisꢀisomer
does not exceed 2%. The reaction of benzene with allyl chloride
affords mainly allylbenzene and 1ꢀphenylꢀ2ꢀchloropropane.
Their ratio depends on the process conditions. Allylbenzene
prevails at low conversions and then its ratio in the reaction
mixture decreases, while that of 1ꢀphenylꢀ2ꢀchloropropane inꢀ
creases.3 Particular experiments showed that 1ꢀphenylꢀ2ꢀ
chloropropane can be formed due to the catalytic hydroꢀ
chlorination of allylbenzene. In both cases, at high conversions
the reaction products contain up to several percentage of byꢀ
products, such as chloroprene, products of chloroolefin oligoꢀ
merization and benzene translalkylation, and products of their
1
1
2
000
1
2000
000
1
1
2
2
7
0
80
90
100
T/°C
Fig. 1. Comparison of the catalytic activity of γꢀFe O (A) on
the AGM (1) and ASM (2) in the isomerization of 3,4ꢀDCB at
different temperatures.
2
3

1
770
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Rostovshchikova et al.
tivities become comparable with the temperature increase
lytic activities calculated from the initial rates were 144
–
1
–1
to 90 °C, whereas at 100 °C the γꢀFe O nanoparticles on
and 117 moles of products (mole of Fe)
h
for the
2
3
the ASM are more active than those on the AGM. The
maximum activity of the 2.5% Fe/ASM catalyst at 100 °C
is more than an order of magnitude as high as the activity
achieved for the most active catalyst based on αꢀFe O
AGM and ASM, respectively. However, the catalyst based
on the AGM rapidly loses activity and the allyl chloride
consumption ceases with time, whereas the ASMꢀbased
catalysts retain activity and can be used repeatedly
(see Fig. 2).
2
3
2
with a high (15%) Fe content. The apparent activation
energies calculated from the temperature plots of the rate
constants of the forward and backward reactions were 65
Both the isomerization of 3,4ꢀDCB 2 and alkylation
of benzene on the supported γꢀferric oxide nanoparticles
occur without a noticeable induction period. These cataꢀ
lysts are almost 20 times as active as the most active anaꢀ
logs based on the αꢀFe O nanoparticles: for the latꢀ
–
1
and 78 kJ mol for the AGM catalyst and 128 and
40 kJ mol–1 for the ASMꢀbased samples. These values
1
are higher than those found previously for larger iron
oxide particles in similar catalytic systems.1,2 The high
apparent activation energies and a lower catalytic activity
at moderate temperatures for the ASM are caused, probꢀ
ably, by the fact that at relatively low temperatures small
γꢀFe O clusters immobilized on the layered silica matrix
2
3
ter the activity did not exceed 5—6 moles of allyl
–
1
–1
chloride (mole of Fe)
tent (12%).
h
even at a high iron conꢀ
3
Mössbauer spectra and magnetic measurements
2
3
are less accessible to the reactants that larger particles.
The ASM support is a sorbent with the labile layered
structure in which the distance between the layers and,
hence, a possibility of insertion into the interlayer space
for molecules of organic reactants enhances with the temꢀ
perature increase. Another possible explanation is associꢀ
ated with the strong interaction of the catalyst active phase
with the layered silica matrix. It is most likely that
the temperature increase facilitates transportation of a
Catalyst evolution under the action of chloroolefins
was studied in detail for 3,4ꢀDCB isomerization, because
the low boiling point of allyl chloride impeded exꢀ
periments. At the qualitative level the changes in the
Mössbauer spectra of the γꢀFe O nanoparticles after heatꢀ
9
2
3
ing with 3,4ꢀDCB or with an allyl chloride—benzene
mixture are close. The Mössbauer spectra of the
2.5% Fe/AGM catalyst before and after the catalytic
isomerization of 3,4ꢀDCB are shown in Fig. 3. The
parameters of the spectra of the 2.5% Fe/AGM and
2.5% Fe/ASM samples obtained at 78 and 3 K are summaꢀ
rized in Table 1. The spectrum of the initial 2.5% Fe/AGM
catalyst at 78 K contains only a "paramagnetic" doublet
3
,4ꢀDCB molecule to the active sites of the catalyst or
weakens the interaction of the small iron oxide particles
with the support. The catalysts retain high activity upon
multiple (up to five cycles) utilization in catalysis.
Alkylation of benzene with allyl chloride. The catalytic
properties of the γꢀferric oxide nanoparticles on the AGM
and ASM in benzene alkylation with allyl chloride are
comparable. Figure 2 shows the kinetic curves of allyl
chloride consumption in the reaction with benzene to
III
from the highꢀspin Fe complex in the octahedral enviꢀ
II
ronment of the O ions. The parameters of the spectrum
of the complex differ substantially from those of the relaxꢀ
3
ation spectrum of Fe(acac) used for iron supporting.
3
form two products, namely, allylbenzene and 1ꢀphenylꢀ
The spectrum at 6 K (see Fig. 3, a) is characterized by the
magnetic HFS lines with Hin = 45.0 T and a "paramagꢀ
netic" doublet with a relative content of 22%. The obꢀ
served transformation of the spectrum with the temperaꢀ
ture change from 78 to 6 K is typical of the superꢀ
paramagnetic system of γꢀferric oxide with the particle
3
2
ꢀchloropropane, at 110 °C for the catalysts under disꢀ
cussion. It can be seen that the initial reaction rate in the
presence of the AGMꢀbased catalyst slightly exceeds the
process rate for the catalyst based on the ASM. The cataꢀ
3
C (%)
size d ≈ 2—3 nm.
2
5
4
3
2
1
0
0
0
0
0
The magnetic properties of the initial catalysts before
3
,7
testing in the reactions are rather close. For the both
samples, the runs of the magnetic susceptibility curves
χ(T ) are similar and the absolute χ curves almost coinꢀ
cide, which indicates magnetic homogeneity of the
samples. The extrapolation of the rectilinear (highꢀtemꢀ
perature) regions of the curves to the lowꢀtemperature
1
–
1
region showed that the χ —T plots for the two catalysts
obey the Curie—Weiss law with the negative values of the
Weiss constants. This is typical of the superparamagnetic
iron oxide clusters with the antiferromagnetic type of magꢀ
0
4
0
80
120
160
t/min
Fig. 2. Kinetic curves of accumulation of the products (C) of
–
1
–1
benzene (9.7 mol L ) alkylation with allyl chloride (2.5 mol L
)
at 110 °C ([Fe] = 0.01 mol L–1) in the presence of γꢀFe O on
–1
netic ordering. The χ —T plot for the 2.5% Fe/ASM
2
3
the AGM (1) and ASM (2).
sample was characterized by a sharp decrease in the reꢀ

Catalysis over γꢀFe O nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1771
2
3
A (rel. units)
Table 1. Parameters of the Mössbauer spectra for the
.5% Fe/AGM catalysts before and after catalysis and for the
2
1
0
0
.000
.995
.990
2.5% Fe/ASM catalyst after catalysis (δ is the isomeric shift
relative to αꢀFe, ∆ is the quadrupole splitting or quadrupole
shift, Hin is the internal field on the 57Fe nucleus, and А is the
relative content)
T
Component
δ±0.03
mm s–1
.5% Fe/AGM (before entry)3
∆±0.03 H ±0.5 А±5
in
a
/
К
/T
(%)
2
3
+
v/mm s–1
78
6
Fe (paramagn.)
0.33
0.32
0.29
0.93
0.76
0.00
—
—
100
22
–
6
0
6
3
+
Fe (paramagn.)
A (rel. units)
3+
Fe (magn.)
45.0
78
2
.5% Fe/AGM (after entry)*
3
+
3
7
3
00 Fe (paramagn.)
0.32
1.15
0.37
1.24
0.38
1.28
0.62
2.13
0.63
3.02
0.73
3.22
—
—
—
—
—
—
78
22
68
32
62
38
1
0
0
.00
.99
.98
2
+
Fe (paramagn.)
Fe (paramagn.)
Fe (paramagn.)
Fe (paramagn.)
3
+
8
2
+
3
+
2+
Fe (paramagn.)
b
2
.5% Fe/ASM (after entry)*
3
+
3
7
00 Fe (paramagn.)
0.35
1.14
0.37
1.17
0.61
2.11
0.47
2.91
—
—
—
—
59
41
69
31
2
+
Fe (paramagn.)
Fe (paramagn.)
Fe (paramagn.)
3
+
8
2
+
–
5
0
5
v/mm s–1
*
Data of the present work.
Fig. 3. Mössbauer 57Fe spectra of the initial catalyst
.5% Fe/AGM at 6 K (a) and the same catalyst after 3,4ꢀDCB
isomerization at 3 K (b) (v is the rate of γꢀradiation source).
2
plex of Fe3+ with a relative content of 68 and 62%, reꢀ
spectively.
The spectrum of the 2.5% Fe/ASM sample after caꢀ
talysis obtained at 78 K resembles the corresponding specꢀ
trum of the 2.5% Fe/AGM catalyst. The spectrum conꢀ
tains lines only of the highꢀspin complexes of triꢀ and
bivalent iron, whose parameters are given in Table 1. The
macroscopic susceptibility data for the 2.5% Fe/ASM
catalyst before and after 3,4ꢀDCB isomerization are shown
in Figs 4 and 5. It is seen that after the reaction the
magnetization curve becomes smoother (see Fig. 4, b)
and no hysteresis loop is observed contrary to the initial
catalyst (see Fig. 4, a). This is especially noticeable in
inset (see Fig. 4, b), where the linear magnetization isoꢀ
therm at 2 K is presented.
gion ≤10 K, unlike the smooth decrease at ≤50 K for the
2
χ
.5% Fe/AGM system. The sharper decrease in the
–
1
values at T ≤ 10 K indicates that for the ASM the
cluster size distribution is more narrow than that for
the AGM. The presence of the small γꢀferric oxide magꢀ
netic clusters in the 2.5% Fe/AGM and 2.5% Fe/ASM
samples is confirmed by hysteresis loops in the curves
of forward and backward magnetization of the
7
samples at 2 K.
The lowꢀtemperature Mössbauer spectra of the
2
3
.5% Fe/AGM and 2.5% Fe/ASM catalysts after
,4ꢀDCB isomerization differ sharply from the lowꢀtemꢀ
perature spectra of the initial samples. The spectrum of
the 2.5% Fe/AGM sample recorded at 3 K after the reacꢀ
tion is presented in Fig. 3, b, and the spectral parameters
of the same sample at 300 and 78 K (which are omitted in
the figure) and at 3 K are given in Table 1. Note that the
lines of magnetic HFS characterizing the magnetically
ordered γꢀFe O clusters, which were present in the sample
The curves of the temperature dependence of the inꢀ
verse magnetic susceptibility (1/χ) of the 2.5% Fe/ASM
catalyst (see Fig. 5, a, b) show that the plot of 1/χ vs. T is
linear for neither the initial sample nor the sample over
which 3,4ꢀDCB was isomerized. In the both cases, the
extrapolation of the curves in the highꢀtemperature reꢀ
gion to low temperatures gives the intersection point at
negative temperatures. As already observed above, this
2
3
before catalysis, disappear in samples used in catalysis. In
addition, lines of the doublet from the octahedrally coorꢀ
–
1
χ
—T dependence is characteristic of superparamagnetic
II
dinated highꢀspin Fe complex with a relative content of
clusters with the antiferromagnetic type of magnetic orꢀ
dering.
Evidently, the structure of the γꢀferric oxide nanoꢀ
clusters (d ≈ 2—3 nm), which are present in the initial
3
2
2 and 38%, respectively, appear in the spectra of the
.5% Fe/AGM sample at 78 and 3 K along with the "paraꢀ
magnetic" doublet from the octahedral highꢀspin comꢀ

1
772
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Rostovshchikova et al.
χ–1•10–3/(g of Fe) cm–3
3
–1
3
3
–1
J/G cm (g of Fe)
χ•10 /cm (g of Fe)
2
.5
a
3.0
2
0
0
0
2
2
2
.5
.0
a
2.0
1.5
1
3
–1
J/G cm (g of Fe)
8
4
0
4
1.5
1.0
0.5
1
0
.0
.5
–
10
20
–
1
–
–
1.0 –0.5 0
5
H•10–3/Oe
H•10–3/Oe
5
0
100
150
200
250
T/K
–
10
–5
0
3
3
–1
χ–1•10–3/(g of Fe) cm–3
χ•10 /cm (g of Fe)
3
–1
J/G cm (g of Fe)
4
3
.0
.5
2
.5
b
4
0
0
2.0
1.5
2
3.0
.5
b
2
3
–1
J/G cm (g of Fe)
2.0
1.5
1.0
0.5
8
0
8
1
0
.0
.5
–
–
40
80
1
–
–1.0 –0.5 0 H•10–3/Oe
H•10–3/Oe
50
100
150
200
250
T/K
–
8
–4
0
4
Fig. 5. Temperature plots of the magnetic susceptibility χ (1)
and parameter 1/χ (2) for the 2.5% Fe/ASM sample before (а)
and after catalysis (b) (H = 5000 Oe).
Fig. 4. Magnetization (J ) isotherms of the 2.5% Fe/ASM sample
before (a) and after catalysis (b) at 2 K. An expanded fragment
of the J isotherm in the region –1000 Oe ≤ H ≤ 1000 Oe is shown
in insets.
be oriented along the easyꢀmagnetization axis) and the
magnetization energy of the magnetized sample in the
magnetic field due to which J tends to be oriented along
the H field. In the considered model, the hysteresis loop is
transformed into a straight line at ϕ = 90°. In this case,
magnetization in the positive and negative fields occurs
through the reversible gradual rotation of J.
state of the catalyst, undergo the substantial rearrangeꢀ
ment under the action of chloroolefins. According to the
Mössbauer spectroscopic data, some Fe ions are reꢀ
duced to Fe , and the reduced ions exist in the paramagꢀ
netic state. The other Fe ions are not isolated and still
III
II
III
participate in exchange interactions within the nanoꢀ
clusters with sizes smaller than 2—3 nm. The absence of a
hysteresis loop and the linear dependence of the curves of
forward and backward magnetization (see Fig. 4, b) can
be explained as follows. The cluster exists in the singleꢀ
domain state until the cluster sizes achieve some critical
value.10 In the absence of domain boundaries, transꢀ
magnetization can occur through uniform (coherent) or
nonuniform rotation of the spontaneous magnetization
vector J.11 According to the model of uniform rotation of
the spontaneous magnetization vector in a magnetically
uniaxial nanocrystal, the ϕ angle between the direction of
the external magnetic field H and easyꢀmagnetization axis
is the parameter determining hysteresis.1 The equilibꢀ
rium orientation of J is determined by the ratio of the
magnetic anisotropy energy (because of which J tends to
Let us consider the Mössbauer parameters of the
FeII ion formed upon the interaction with chloroolefin.
The parameters of the highꢀspin octahedral Fe complex
II
formed in the reaction are analogous to the parameters of
similar FeCl complexes. The isomeric shifts (δ) of the
2
2
+
Fe complex obtained in the present work at 3—300 K
range within ~1.13—1.30 mm s , which corresponds to
–1
the data for compounds of the following series: FeCl2,
FeCl •H O, FeCl •2H O, and FeCl •4H O (δ ≈ 1.1
2
2
2
2
2
2
–1
12
(300 K)—1.4 (5 K) mm s ). More definite conclusions
about the composition and electronic structure of the
FeCl complex formed in the reaction follow from analyꢀ
2
sis of the quadrupole splitting values (∆). The ∆ values for
1
anhydrous FeCl and three its crystal hydrates at different
2
temperatures are compared in Fig. 6. Solid lines show the
1
2—14
linear anamorphoses of the ∆ values measured earlier

Catalysis over γꢀFe O nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1773
2
3
∆
/mm s–1
Scheme 1
6
5
4
3
2
1
1
2
through the step of electron transfer from the catalyst to
the reactant with the formation of the chloride anion.
3
1—4,15
The chloride anion is inserted into the structure of a comꢀ
plicated active site including iron ions in two oxidation
states, as well as anionic and cationic vacancies and labile
0
5
0
100
150
200
250
T/K
Fig. 6. Experimental (points) and literature data (lines) on quaꢀ
drupole splitting of the Fe ion (∆) in the temperature interval
—300 K for the 2.5% Fe/AGM (1) and 2.5% Fe/ASM cataꢀ
lysts (2) after the reaction and for FeCl (3), FeCl •H O (4),
2
,3
lattice oxygen,
and is involved in further steps of
II
chloroolefin conversion.
3
From the data of the present work it is difficult to
conclude about the amount and role of oxygen ions in the
2
2
2
FeCl •2H O (5), and FeCl •4H O (6).
2
2
2
2
II
nearest environment of the Fe ion. When assuming that
in a wide temperature interval (0.15—300 K). It is seen
that the quadrupole splitting values obtained in the present
oxygen of the support lattice can be one of the polydentate
ligands in the structure of the local Fe polyhedron, then
II
work correspond to hydrated FeCl rather than anhydrous
the mechanism of strong cluster—support interaction is
operative.
2
iron chloride. The increase in the ∆ values on going from
anhydrous FeCl to the hydrated forms FeCl •nH O is
Note that FeCl possesses no catalytic activity in conꢀ
2
2
2
2
4
related to the fact that in the structure of the local polyꢀ
versions of chloroolefins. However, the process is faꢀ
II
hedron (octahedron) of Fe one, two, or four bridged
vored if the catalytically active site contains simultaneously
III
II
chlorine ions are substituted for the corresponding numꢀ
the Fe and Fe ions and at least two types of ligands,
viz., chloride anion and oxygenꢀcontaining groups.
Since changes in the oxidation state of the iron ions
and their ligand environment during the interaction with
the reactants appear feasible, the absence of induction
periods in chloroolefin conversions over the γꢀferric oxide
nanoparticles of nonstoichiometric composition and their
high activity can readily be understood.
1
2
ber of oxygen ions from the water molecules. Nonꢀ
equivalence of the ligands results in an increase in crystalꢀ
line field nonuniformity and an increase in quadrupole
splitting.
The analysis performed agrees with the assumption on
the formation of bivalent oxychloride upon the interacꢀ
tion of the catalyst with chloroolefin. The ability of iron
oxides to perform dehydrochlorination of chlorohydroꢀ
carbons is well known.15 In particular, the presence of a
low amount of chloroprene in the products of 3,4ꢀDCB
isomerization is caused, most likely, by the dehydrochloꢀ
rination of 3,4ꢀDCB. In benzene alkylation with allyl
chloride, the formation of allylbenzene is accompanied
by the release of hydrogen chloride. The latter can also
interact with the catalyst, for instance, replacing its hydrꢀ
oxyl groups by the chloride anion with water formation.
In turn, chloroolefins undergo the whole series of transꢀ
formations in the presence of iron oxides. Such a seꢀ
Thus, analysis of the Mössbauer spectra of the two ironꢀ
containing catalysts (2.5% Fe/AGM and 2.5% Fe/ASM)
measured at temperatures from 3 to 300 K before and
after 3,4ꢀDCB isomerization shows that during the reacꢀ
III
tion some Fe ions in the γꢀFe O nanoclusters magnetiꢀ
2
3
cally ordered at 6 K and ~2—3 nm in size are reduced to
II
the highꢀspin Fe complex in the paramagnetic state.
According to the macroscopic magnetization data
(SQUID), the initial clusters, on the one hand, demonꢀ
strate curves with hysteresis in the plots of forward and
backward magnetization at 2 K. On the other hand, after
the reaction completion this plot obtained at 2 K for the
2.5% Fe/ASM catalyst exhibits the linear field depenꢀ
dence of the magnetization passing through the coordiꢀ
nate origin. Analysis of the Mössbauer spectra and magꢀ
netic properties suggests that during the reaction the
III
quence of processes is possible when Fe is partially
II
reduced to Fe by the oxidation of chloroolefin molꢀ
ecules (Scheme 1).
Olefin oxidation over the oxide catalysts is known to be
1
6
promoted by chlorineꢀcontaining organic compounds.
III
Absorption bands of carbonyl groups were observed by
IR spectroscopy in the spectra of allyl chloride after heatꢀ
ing with the catalyst.
Fe ions in the γꢀferric oxide nanoclusters are partially
II
reduced by the reaction medium to form the Fe comꢀ
II
plexes in which the chloride anions and O ion(s) of the
II
The appearance of Fe ions in the catalyst structure
silicate matrix serve as ligands. The formation of mixedꢀ
valence states of iron and insertion of the chloride anion
facilitates the C—Cl bond cleavage that occurs, probably,

1
774
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Rostovshchikova et al.
into the catalyst active phase cause, probably, the high
activity of the γꢀferric oxide nanoparticles of nonstoichioꢀ
metric composition in conversions of chloroolefins.
6. Yu. V. Maksimov, M. V. Tsodikov, M. A. Perederii, I. P.
Suzdalev, A. I. Nekhaev, V. T. Popov, and O. V. Bukhtenko,
Izv. Akad. Nauk, Ser. Khim., 1997, 86 [Russ. Chem. Bull.,
1
997, 46, 81 (Engl. Transl.)].
7
8
9
. Yu. V. Maksimov, I. P. Suzdalev, V. N. Ikorskii, O. G.
Ellert, V. M. Novotortsev, M. V. Tsodikov, and Kh. A. Navio,
Neorg. Mater., 2006, 42, 1 [Inorg. Mater., 2006, 42 (Engl.
Transl.)].
. L. A. Kazitsina and N. B. Kupletskaya, Primenenie UFꢀ,
IKꢀ i YaMRꢀspektroskopii v organicheskoi khimii [The Use of
UV, IR, and NMR Spectroscopy in Organic Chemistry],
Vysshaya Shkola, Moscow, 1971, 236 (in Russian).
. B. V. Kuznetsov, S. N. Lanin, T. A. Rakhmanova, V. V.
Smirnov, M. V. Tsodikov, and D. V. Tarasova, Zh. Fiz. Khim.,
The authors are grateful to A. O. Chizhov for GCꢀMS
analysis.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 06ꢀ03ꢀ
3
2006).
References
. T. N. Rostovshchikova, M. S. Korobov, D. A. Pankratov,
1
2
007, 81, No. 5 [Russ. J. Phys. Chem., 2007, 81 (Engl.
Transl.)].
0. S. V. Vonsovskii, Magnetizm [Magnetism], Nauka, Moscow,
984, 112 (in Russian).
G. Yu. Yurkov, and S. P. Gubin, Izv. Akad. Nauk, Ser.
Khim., 2005, 1383 [Russ. Chem. Bull., Int. Ed., 2005,
1
1
5
4, 1425].
1
2
. T. N. Rostovshchikova, V. V. Smirnov, M. V. Tsodikov,
O. V. Bukhtenko, Yu. V. Maksimov, O. I. Kiseleva, and
D. A. Pankratov, Izv. Akad. Nauk, Ser. Khim., 2005, 1376
1. G. S. Kandaurova and L. T. Onoprienko, Domennaya
struktura magnetikov. Osnovnye voprosy mikromagnetiki
[
Domain Structure of Magnetics. The Main Problems of
[
Russ. Chem. Bull., Int. Ed., 2005, 54, 1418].
Micromagnetics], Izdꢀvo UrGU, 1986, 106 (in Russian).
2. N. N. Greenwood and T. C. Gibb, Mössbauer Spectroscopy,
Chapman and Hall, London, 1971, 117.
3. E. Pfletschinger, Z. Physik., 1968, 200, 119.
4. S. Chandra and G. R. Hoy, Phys. Lett., 1966, 22, 254.
5. F. Alonso, I. P. Beletskaya, and M. Yus, Chem. Rev., 2002,
3
4
. M. V. Tsodikov, T. N. Rostovshchikova, V. V. Smirnov,
O. I. Kiseleva, Yu. V. Maksimov, I. P. Suzdalev, and V. N.
Ikorskii, Catal. Today, 2005, 105, 634.
. T. N. Rostovshchikova, O. I. Kiseleva, G. Yu. Yurkov, S. P.
Gubin, D. A. Pankratov, Yu. D. Perfil´ev, V. V. Smirnov,
P. A. Chernavskii, and G. V. Pankina, Vestn. MGU, Ser. 2.
Khim., 2001, 42, 318 [Vestn. Mosk. Univ., Ser. Khim., 2001,
1
1
1
1
1
02, 4009.
1
6. O. V. Krylov, Geterogennyi kataliz [Heterogeneous Catalysis],
42 (Engl. Transl.)].
Akademkniga, Moscow, 2004, 337 (in Russian).
5
. M. V. Tsodikov, Ya. R. Katsobashvili, E. V. Slivinskii, Yu. V.
Maksimov, V. V. Matveev, I. P. Suzdalev, O. G. Ellert, and
G. F. Ivanova, Izv. Akad. Nauk SSSR, Ser. Khim., 1986,
2
666 [Bull. Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 2443
Received May 18, 2006;
(
Engl. Transl.)].
in revised form September 13, 2006