Catalytic conversions of chloroolefins over iron oxide nanoparticles 2. Isomerization of dichlorobutenes over iron oxide nanoparticles stabilized on the surface of ultradispersed poly(tetrafluoroethylene)

Article abstract of DOI:10.1007/s11172-005-0422-1

Nanosized iron oxides stabilized on the surface of ultradispersed poly(tetrafluoroethylene) (UPTFE) granules were synthesized by the thermal destruction of iron formate in boiling bed of UPTFE on the surface of heated mineral oil. The particle size of nanoparticles (～6 nm) containing 5, 10, and 16 wt.% Fe depends weakly on the temperature of synthesis and iron to polymer ratio. The metal state is determined by the synthesis conditions. The nanoparticles synthesized at 280°C consist mainly of the Fe ₃O₄ and Fe₂O₃ phases. The samples obtained at 320°C also contain iron(II) oxide. The catalytic properties of the obtained samples were tested in dichlorobutene isomerization. Unlike isomerization on the iron oxide nanoparticles supported on silica gel, reaction over the UPTFE supports proceeds without an induction period. The sample with 10 wt.% Fe containing magnetically ordered γ-Fe₂O₃ nanoparticles possesses the highest catalytic activity. Fast electron exchange between the iron ions in different oxidation states and high defectiveness of the nanoparticles contribute, most likely, to the catalytic activity.

Full text of DOI:10.1007/s11172-005-0422-1

Russian Chemical Bulletin, International Edition, Vol. 54, No. 6, pp. 1425—1432, June, 2005
1425
Catalytic conversions of chloroolefins over iron oxide nanoparticles
2
.* Isomerization of dichlorobutenes over iron oxide nanoparticles stabilized
on the surface of ultradispersed poly(tetrafluoroethylene)
T. N. Rostovshchikova, M. S. Korobov, D. A. Pankratov, G. Yu. Yurkov, and S. P. Gubinb
a
b
a
bꢀ
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1
Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (095) 932 8846. Еꢀmail: rtn@kinet.chem.msu.ru
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
b
3
1 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 954 1279. Eꢀmail: gubin@igic.ras.ru; gy_yurkov@mail.ru
Nanosized iron oxides stabilized on the surface of ultradispersed poly(tetrafluoroethylene)
UPTFE) granules were synthesized by the thermal destruction of iron formate in boiling bed
(
of UPTFE on the surface of heated mineral oil. The particle size of nanoparticles (~6 nm)
containing 5, 10, and 16 wt.% Fe depends weakly on the temperature of synthesis and iron to
polymer ratio. The metal state is determined by the synthesis conditions. The nanoparticles
synthesized at 280 °C consist mainly of the Fe O and Fe O phases. The samples obtained at
3
4
2
3
3
20 °C also contain iron(II) oxide. The catalytic properties of the obtained samples were tested
in dichlorobutene isomerization. Unlike isomerization on the iron oxide nanoparticles supꢀ
ported on silica gel, reaction over the UPTFE supports proceeds without an induction period.
The sample with 10 wt.% Fe containing magnetically ordered γꢀFe O nanoparticles possesses
2
3
the highest catalytic activity. Fast electron exchange between the iron ions in different oxidaꢀ
tion states and high defectiveness of the nanoparticles contribute, most likely, to the catalytic
activity.
Key words: nanosized iron oxide, ultradispersed poly(tetrafluoroethylene), catalysis,
nanoparticles, nanosized supports, dichlorobutene isomerization, catalysis by nanoparticles.
Nanosized iron oxides stabilized on silicas or in the
volume of polymer matrix serve as active and selective
catalysts of halogenolefin conversions.1 The key factors
determining specific features of nanoparticles are their
size and simultaneous presence of iron species in two
charge states in the active phase of the catalyst. Iron oxide
nanoparticles supported by silicas are characterized by a
strong dependence of the catalyst composition on the
iron to support ratio, silica structure, particle size, and
specific features of their distribution on the support. Polyꢀ
meric matrices are successfully used to stabilize metallic
the well developed surface, mechanical strength, and reꢀ
sistance of UPTFE and related nanocomposites to agꢀ
gressive media. Metalꢀcontaining nanoparticles are stabiꢀ
lized not inside but on the surface of matrix and easily
accessible to reactants. Accordingly, the material seems
to be a promising support for the preparation of nanosized
catalysts, especially for their use in fluid bed.
,2
Experimental
Composite materials consisting of metalꢀcontaining nanoꢀ
particles stabilized on the surface of UPTFE were synthesized
by the thermal destruction of the metalꢀcontaining compound
in a dispersion system UPTFE—mineral oil.6 Iron(III) formate
3
—5
and metal oxide nanoparticles rather uniform in size.
The purpose of this work is to compare the catalytic propꢀ
erties of the ironꢀcontaining nanoparticles stabilized on
the surface of ultradispersed poly(tetrafluoroethylene)
,7
(
Fe(HCOO) ) was used as the main metalꢀcontaining precurꢀ
3
sor. In addition, samples were obtained by the thermolysis of
(
UPTFE) with those of the earlier studied catalysts based
iron pentacarbonyl Fe(CO) . The metalꢀcontaining precursor
1
5
on iron oxides and stabilized on silicas or in the polyethꢀ
ylene volume. UPTFE was chosen as a polymeric stabiꢀ
was decomposed in an inert atmosphere at 280—320 °С. The
flow rate of the inert gas (argon) used for nanoparticle synthesis
was controlled in a way to ensure the fast and complete removal
of volatile decomposition products of the precursor and solvent
from the reactor. Due to a small size (150—500 nm), UPTFE
nanogranules form a "fluid" bed above the surface of heated
mineral oil.6 This regime provides a uniform distribution of
2
lizing matrix, because its surface can uniformly be covꢀ
ered with metalꢀcontaining nanoparticles by the thermolyꢀ
sis of metalꢀcontaining compounds.6 This material shows
,7
,7
*
For Part 1, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1383—1390, June, 2005.
066ꢀ5285/05/5406ꢀ1425 © 2005 Springer Science+Business Media, Inc.
1

1426
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
Rostovshchikova et al.
forming metalꢀcontaining nanoparticles over the nanogranule
surface. With an increase in the number of the metalꢀcontaining
nanoparticles on the UPTFE surface, the weight of the nanoꢀ
granules increases and they leave the zone of nanoparticle forꢀ
mation in the fluid bed and enter the oil. The oil from a formed
dark precipitate was washed off with benzene in a Soxhlett apꢀ
paratus, and solvent residues were removed in vacuo. The samples
were stored in air. The produced materials were finely dispersed
powders, whose color turned from gray to black, depending on
the metalꢀcontaining phase concentration.
Results and Discussion
Particle size. Under electron beam UPTFE nanoꢀ
granules look like almost planar spheres with diffuse
boundaries (Fig. 1). When ironꢀcontaining particles were
dispersed on a support, the sample contains poly(tetraꢀ
fluoroethylene) granules of approximately the same sizes
as in the UPTFE powder with the only distinction that
dark spherical aggregates (metalꢀcontaining nanoparticles)
are observed on their surface.
The iron concentration in the polymer was varied from 4 to
1
6 wt.%, and its content in the prepared samples was deterꢀ
The average diameter of the metallic particles (d) deꢀ
pends slightly on the conditions of synthesis, and the
mined by elemental analysis.
The particle size was determined by transmission electron
microscopy (TEM) on a JEMꢀ100B setup (JEOL). For this
examination, the material under study was ultrasonicated in an
aqueousꢀalcohol solution, and a droplet of the resulting suspenꢀ
sion was introduced on a copper support covered with carbon.
The compositions of the starting catalysts were determined
by Mössbauer spectroscopy. Absorption Mössbauer spectra were
recorded on an MS1101E electrodynamicꢀtype spectrometer
a
(
MNPP "MosTek") at room temperature. Isotope 57Со in
the metallic rhodium matrix with an activity of 1 mCi
ZAO "Tsiklotron") was used as a γꢀradiation source. Isomeric
(
shifts were determined relatively to αꢀFe. Spectra were proꢀ
cessed by the standard leastꢀsquares method assuming the
Lorentz lineshape and using the UNIVEM v.4.50 program.
3
,4ꢀDichlorobutꢀ1ꢀene (3,4ꢀDCB) was isomerized in
sealed glass ampules with stirring in a temperature interval of
1
7
(
0—100 °С in the presence of oxygen. 3,4ꢀDCB (0.1—0.2 mL,
–
3
–5
1—2)•10 mol) and catalyst (0.005—0.01 g, (0.5—3)•10
moles of iron) were used. The composition of the reaction mixꢀ
ture was determined on an LKhMꢀ3700 chromatograph with
the SEꢀ30 stationary phase at 100 °С. The main product
of 3,4ꢀDCB isomerization is transꢀ1,4ꢀdichlorobutꢀ2ꢀene
6
0 nm
(
transꢀ1,4ꢀDCB). The yield of the cisꢀisomer and byꢀproducts
N
did not exceed 2—3%.
Specific catalytic activity and isomerization rate constants
were used as measures of catalytic activity. The specific catalytic
1
00
b
activity (A ) was calculated from the initial isomerization rate
sp
as a ratio of the molar amount of transꢀ1,4ꢀDCB formed within
1
h to the iron content in the sample. The isomerization rate
8
0
constants of the first order with respect to 3,4ꢀDCB were deterꢀ
mined by the linearization of kinetic curves of transꢀ1,4ꢀDCB
accumulation in the coordinates of the firstꢀorder reversible
reaction ln[A /(A∞ – A)]—t, where A∞ is the equilibrium conꢀ
centration of transꢀ1,4ꢀDCB, and А is its current concentraꢀ
60
40
∞
1
tion. Based on the found rate constants of the forward (k ) and
1
backward (k–1) isomerization reactions of the first order with
respect to 3,4ꢀDCB, apparent rate constants of the second order
with respect to the reactant and catalyst were calculated
2
0
k = k /[Fe].
2
1
4
6
8
10
d/nm
The obtained values were independent of the iron concentration
in the reaction mixtures.
Apparent activation energies of isomerization were deterꢀ
mined from the temperature dependence of the rate constants of
Fig. 1. TEM microphotograph of the ironꢀcontaining nanoꢀ
particles (6.5±1.5 nm) stabilized on the UPTFE surface (a) and
the size distribution diagram (b) for sample 4 with an iron conꢀ
tent of 10.3 wt.% (N is the number of particles, and d is their
diameter).
the forward and backward reactions (k and k–2, respectively) in
2
the 70—100 °С range.

Catalysis over iron oxide nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
1427
Table 1. Results of mathematical processing of the TEM microphotographs and Mössbauer spectra of
samples 1—4 with different iron contents (see Figs 1 and 2)
Sample [Fe]
d
Subꢀ
δ
∆
Bhf
/kOe
Γexp
/mm s–1
S
(%)
(
wt.%)
/nm spectrum
mm s–1
Temperature of synthesis 280 °С
1
2
4.7
5.0
5.0
5.0
5.0
5.0
6.5
6.5
6.5
6.5
6.5
6.5
6.0
6.0
6.0
6.0
6.0
6.0
1
2
3
4
5
1
2
3
4
5
6
1
2
3
4
5
6
0.37±0.02
0.56±0.03
0.34±0.02
1.23±0.01
1.38±0.01
0.31±0.01
0.63±0.01
0.62±0.01
0.70±0.20
0.30±0.01
1.40±0.01
0.38±0.01
0.32±0.01
0.58±0.01
0.63±0.02
1.29±0.01
1.35±0.01
–0.02±0.04
–0.02±0.05
0.85±0.03
1.65±0.03
2.76±0.01
–0.01±0.01
0.01±0.01
0.07±0.03
0.08±0.04
0.99±0.02
2.85±0.01
–0.22±0.01
–0.09±0.01
–0.01±0.01
0.00±0.01
2.42±0.02
2.80±0.01
480.6±1.5
434.7±2.8
—
0.64±0.08
1.13±0.12
0.55±0.04
0.70±0.05
0.21±0.01
0.38±0.01
0.59±0.02
0.63±0.08
0.54±0.10
0.54±0.03
0.29±0.01
0.34±0.01
0.52±0.02
0.85±0.04
1.10±0.08
1.44±0.03
0.25±0.01
19
32
15
21
13
23
39
12
6
4
4
4
4
.7
.7
.7
.7
—
—
10.1
504.4±0.2
472.6±0.5
442.7±1.8
404.3±2.0
—
1
1
1
1
1
0.1
0.1
0.1
0.1
0.1
6
—
14
11
16
24
11
20
18
3
4
16.3
510.4±0.4
485.0±0.6
450.9±0.8
396.7±2.8
—
1
1
1
1
1
6.3
6.3
6.3
6.3
6.3
—
Temperature of synthesis 320 °С
10.3
6.5
6.5
6.5
6.5
6.5
1
2
3
4
5
0.29±0.01
0.56±0.01
0.64±0.02
0.42±0.02
1.11±0.02
–0.01±0.01
0.01±0.01
–0.03±0.04
0.89±0.03
2.36±0.04
480.7±0.3
446.7±0.5
391.4±2.7
—
0.39±0.02
0.76±0.03
1.26±0.12
0.74±0.02
0.94±0.02
13
30
15
19
23
1
1
1
1
0.3
0.3
0.3
0.3
—
Note. d is the average particle diameter, δ is the isomeric shift, ∆ is the quadrupole shift, Bhf is the magnetic
field, Γexp is the linewidth, and S is the relative subspectrum surface area.
mean size deviation does not exceed 30%. The results of
calculation of the average particle deviation for the samples
studied are presented in Table 1. It has previously been
shown that the particle size is also ∼ 6 nm when iron carꢀ
bonyl is used as a precursor.
(Γexp) of these sextets, it can be noted that crystallites
formed in samples 1 and 3 are evidently less defect than
those in sample 2 synthesized under the same conditions.
This follows from the fact that the valent state of the iron
atoms in the Fe O sublattices cannot be distinguished in
7
3
4
Nanoparticle composition. According to the data of
Mössbauer spectroscopy, the tested composites syntheꢀ
sized by the thermal destruction of iron(III) formate conꢀ
tain iron in several different states, as the most part of
the spectrum of sample 2. As a rule, Mössbauer spectra of
Fe O with the structure of inverse spinel are described by
3
4
the superposition of three subspectra as sextets: one sextet
–
1
with an isomeric shift of 0.28—0.34 mm s correspondꢀ
ing to the iron(III) atoms in the tetrahedral environment
(magnetic field at 300 K Bhf = 485—495 kOe)8 and
two subspectra with isomeric shifts in an interval of
3
—5
similar materials.
When UPTFE is used as a stabilizing
matrix, the formation of fluoroꢀsubstituted iron derivaꢀ
tives can be expected along with oxygen compounds.6
Taking into account a possible presence of mixed iron
fluorooxo compounds, similar parameters of the
Mössbauer spectra, and relaxation effects for nanosized
objects, we cannot interpret unambiguously some specꢀ
tral components, and the interpretation given should be
considered only as the most probable one.
,7
–
1
II
III
0.60—0.68 mm s corresponding to the Fe and Fe
ions (Bhf = 450—460 kOe), which are located in octaꢀ
hedral gaps involving in fast electron exchange. However,
in sample 2, unlike samples 1, 3, and 4, no subspectrum
–
1
with an isomeric shift of 0.28—0.34 mm s is detected.
Evidently, the tetrahedral gaps in the Fe O nanoparticles
3
4
The Mössbauer spectra of samples 1—4 and the correꢀ
sponding parameters are presented in Fig. 2 and Table 1.
The property common for all samples is the presence of
of sample 2 remained unfilled because of defect nature of
particles, which results in the disappearance of the corꢀ
responding magnetic sublattice. In addition, the specꢀ
trum of sample 2 distinctly shows subspectrum 1 characꢀ
magnetically ordered Fe O4 (subspectra 1 and 2 for
3
8
samples 1 and 4, subspectrum 2 for sample 2, and
subspectra 2 and 3 for sample 3). Despite a large linewidth
teristic of more oxidized iron oxide (γꢀFe O ) with the
2
3
spinel superstructure. In the latter, the tetrahedral subꢀ

1428
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
Rostovshchikova et al.
A (%)
A (%)
1
1
2
2
3
4
3
4
5
5
6
0
0
.5
.0
.5
.0
.5
.0
.5
.0
0
1
1
2
2
3
3
4
1
2
3
4
5
a
c
–
8
–4
0
4
8
v/mm s–1
–8
–4
0
4
8
v/mm s–1
A (%)
A (%)
1
2
1
2
3
4
3
4
5
6
5
0
0
2
4
6
8
0
0
0
1
1
.4
.8
.2
.6
b
d
1
–
8
–4
0
4
8
v/mm s–1
–8
–4
0
4
8
v/mm s–1
Fig. 2. Mössbauer spectra of the ironꢀcontaining nanoparticles supported in the UPTFE surface by the thermal destruction of iron
formate at 320 (a) and 280 °С (b—d); iron content 10.3 (sample 4) (a), 4.7 (sample 1) (b), 10.1 (sample 2) (c), and 16.3 wt.%
(
sample 3) (d); v is the rate of the γꢀradiation source.
lattice is filled completely, 4/3 positions of the octahedral
sublattice are filled with iron(III) ions, and 8/3 positions
are vacant. That is why, probably, nanosized particles
have a complex spinelꢀbased structure including γꢀFe O
superparamagnetic Fe O is not virtually detected in the
2 3
spectra of samples 3 and 4.
Broad doublet lines with δ = 1.34—1.40 mm s or δ =
–
1
–
1
1.23—1.29 mm s , which are observed in the spectra of
samples 1—3 (see Fig. 2, b—d), are attributed, most likely,
to iron(II) fluoroꢀsubstituted derivatives, for example,
2
3
and Fe O and are highly defective.
3
4
The spectrum of sample 3 with the maximum iron
–
1
9
content has rather narrow (Γexp = 0.34 mm s ) magnetiꢀ
cally split lines (see Fig. 2, d and Table 1, subspectrum 1,
FeF , or to crystal hydrates of iron(II) fluoride, respecꢀ
2
tively.
B = 510.4 kOe), which are attributed to a highly crystalꢀ
The most striking distinctive feature of sample 4 (see
Fig. 2, a) synthesized at 320 °С is the absence of a narrow
doublet component with the isomeric shift value correꢀ
sponding to iron(II) fluoride compounds. Unlike other
samples, a broad doublet with δ = 1.11 mm s– is obꢀ
served (subspectrum 5), which can be assigned to the
iron(II) atoms in the octahedral oxygen environment, for
example, to a nanosized oxide similar to FeO. The other
spectral components of this sample can be assigned to the
nanosized Fe O particles. The most part of them is deꢀ
hf
8
line αꢀFe O . The other magnetically split subspectra in
2
3
all samples are assigned to the iron ions on the nanoparticle
surface or in nanoparticles of a smaller size.
1
The spectrum of sample 1 with a low iron content
exhibits a resonance signal as a doublet (subspectrum 3)
–
1
with δ = 0.34 mm s . A similar doublet, although less
intense, is observed for the spectrum of sample 2 (subꢀ
spectrum 5). This indicates that samples 1 and 2 contain
iron(III) oxide in the superparamagnetic state, while
3
4

Catalysis over iron oxide nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
1429
scribed by subspectra 1 and 2 with somewhat lower magꢀ
netic fields on the atoms, which is characteristic of
nanoparticles. Subspectrum 3 has a considerable linewidth
and a small relative surface area and characterizes, eviꢀ
dently, the atoms on the surface of Fe O particle. The
doublet of subspectrum 4 corresponding to smaller crysꢀ
tallites can be ascribed to the same substance but in the
superparamagnetic state. Taking into account the probꢀ
ability of fluoride formation during the synthesis, we canꢀ
not exclude that this component is attributed to an iron(III)
oxofluoroꢀsubstituted derivative in the octahedral enviꢀ
ronment.10
Catalytic properties of iron oxides stabilized on the
UPTFE surface. The specific catalytic activity of different
ironꢀcontaining polymeric UPTFEꢀbased nanocompoꢀ
sites in 3,4ꢀDCB isomerization to transꢀ1,4ꢀDCB at
100 °С (Table 2) was compared with the data for nanoꢀ
composites obtained with lowꢀdensity polyethylene
3
4
2
(LDPE) as a stabilizing matrix. It is seen that ironꢀconꢀ
taining salts of carboxylic acids are the best precursors for
synthesis of catalytically active nanoparticles. A lower acꢀ
tivity of the samples prepared from iron carbonyls is due
to the presence of the catalytically inert iron carbide
2
phase. The use of the UPTFE matrix for nanoparticle
Thus, the method proposed for the synthesis of iron
oxide nanoparticles by iron formate thermolysis in the
presence of UPTFE makes it possible to stabilize nanoꢀ
particles with similar sizes but containing iron atoms in
different environments on the polymer surface. In all
cases, the main phase of nanoparticles is Fe O . An inꢀ
stabilization provides more active catalysts, which can be
due to both easier accessibility of nanoparticles located
on the surface rather than in the bulk support and differꢀ
ences in the size and composition of the particles. In the
earlier described nanocomposites, the average particle
size in the LDPE matrix corresponded to 15 nm, and
5
3
4
crease in the temperature of formation decomposition
produces samples with a higher degree of reduction conꢀ
taining iron(II) oxides. Nanoparticles synthesized at a
lower temperature are oxidized to a higher extent and in
addition contain iron(III) oxides, whose state changes from
superparamagnetic to magnetically ordered γꢀFe O or
γꢀFe O was the main ironꢀcontaining phase. The isomerꢀ
ization rate on these catalysts at temperatures below 100 °С
was low.
2
3
The particles stabilized on UPTFE are comparable in
activity with the iron oxide particles immobilized on siliꢀ
1
cas. However, the induction period for transꢀ1,4ꢀDCB
2
3
αꢀFe O with an increase in the metal content in the
polymer.
Another substantial feature of the nanoparticles synꢀ
formation, which is characteristic of iron oxide nanoꢀ
particles immobilized on the silica gel surface, is not obꢀ
served in the presence of the ironꢀcontaining particles on
UPTFE. As in the case of iron oxides supported on the
2
3
thesized at lower temperatures is the appearance of the
iron fluoride phase in the composition of nanoparticles,
which has previously been observed for nanocomposites
obtained in a similar way using UPTFE and iron pentaꢀ
carbonyl as a metalꢀcontaining precursor. In this case,
the nanoparticles contained iron carbides and αꢀFe in
1
oxide supports, the isomerization can formally be deꢀ
scribed by a kinetic equation of the reversible reaction of
the first order with respect to 3,4ꢀDCB. This is indicated
by the kinetic curves linearized in the corresponding coꢀ
ordinates (Figs 3 and 4). The kinetic data in Fig. 3 conꢀ
cern samples 1—3 prepared under the same conditions at
a destruction temperature of 280 °С. As can be seen from
a comparison of curves 3 and 3´ (see Fig. 3), the linear
character of the dependence is retained when the amount
of the catalyst used decreases. The kinetic data obtained
at 70 and 80 °C for sample 4, synthesized at higher temꢀ
7
addition to the oxide and fluoride phases. According to
7
the known model, the nanoparticles are multilayer solids,
a fraction of their surface contacting with polymeric supꢀ
port is covered with an iron fluoride layer, whereas surꢀ
face areas not interacting with the polymer are covered
with oxide.
Table 2. Specific catalytic activity (A /mole of transꢀ1,4ꢀDCB (mol Fe)– h–1) of the ironꢀcontaining polymeric
1
sp
composites in 3,4ꢀDCB isomerization
Catalyst
support
Precursor
Weight of
catalyst/g
Volume of
3,4ꢀDCB/mL
t
Yield of
1,4ꢀDCB (%)
Аsp
/
/min
4
1
1
1
5
5
4
1
5
.7 wt.% Fe/UPTFE
0.1 wt.% Fe/UPTFE
6.3 wt.% Fe/UPTFE
0.3 wt.% Fe/UPTFE
wt.% Fe/LDPE
Fe(HCOO)3
Fe(HCOO)3
Fe(HCOO)3
Fe(HCOO)3
Fe(HCOO)3
Fe(AcO)3
Fe(CO)5
Fe(CO)5
Fe(CO)5
0.005
0.005
0.005
0.005
0.010
0.006
0.010
0.010
0.010
0.1
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.1
30
30
30
30
30
60
30
30
60
60
61
67
63
58
65
43
44
10
260
250
170
130
113
112
110
030
452
2
2
wt.% Fe/LDPE
.1 wt.% Fe/UPTFE
4 wt.% Fe/UPTFE
wt.% Fe/LDPE

1430
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
Rostovshchikova et al.
lny
different iron contents in different experiments, we asꢀ
sumed that the reaction rate and observed rate constants
of the first order with respect to reactant are linear funcꢀ
tions of the iron concentration. The apparent rate conꢀ
2
2.0
1.5
1.0
0.5
1
stants of the second order (k and k–2) calculated assumꢀ
3
2
ing a linear dependence of the isomerization rate on the
iron concentration are also given in Table 3. It is seen that
these values are almost independent of the iron content.
This confirms the assumption that the reaction rate is
described satisfactorily by a kinetic equation of the secꢀ
ond order and depends linearly on the concentrations of
3
´
3
,4ꢀDCB and iron. Based on the temperature plot of the
average rate constants of the secondꢀorder reaction k2
and k–2 (Fig. 5), we estimated the apparent activation
energies of the forward (E ) and backward (E–2) reactions
2
logk + 4
2
0
1
0
30
50 t/min
a
Fig. 3. Kinetic curves of transꢀ1,4ꢀDCB accumulation in the
presence of samples 1—3 (80 °С, [3,4ꢀDCB] = 9.2 mol L– ) in
the coordinates lny—t (y = A /(A – A)): [Fe] = 0.089 (1, 2),
1
2.0
∞
∞
0
.13 (3), and 0.08 mol L–1 (3´). Numbers of curves correspond
to the numbers of samples.
2
1
1
.5
lny
2
3
1
1
0
.5
.0
.5
0
1.0
4
3
–1
2
.6
2.8
T –1•10 /K
logk–2 + 4
1
1
1
0
.5
b
1
0
30
t/min
.0
.5
Fig. 4. Kinetic curves of transꢀ1,4ꢀDCB accumulation in the
presence of sample 4 ([3,4ꢀDCB] = 9.2 mol L , [Fe] =
.18 mol L ) in the coordinates lny—t (y = A /(A – A)) at
0 (1) and 80 °С (2).
2
–
1
1
–
1
0
7
∞ ∞
3
perature (320 °С) than samples 1—3 are shown in Fig. 4.
It is seen that the dependence is linear in this case as well.
The observed rate constants of the forward and backward
4
3
–1
2
.6
2.8
T –1•10 /K
reactions (k and k–1, respectively) determined under difꢀ
1
ferent conditions are collected in Table 3.
Fig. 5. Rate constants of the forward (a) and backward (b)
It is seen that the constants depend on both the comꢀ
position and method of preparation of the catalyst and the
iron content in reaction mixtures. To take into account
secondꢀorder reactions (k and k–2, respectively) for samples 1—4
in the Arrhenius coordinates. Numbers of curves correspond to
the numbers of samples.
2

Catalysis over iron oxide nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
1431
Table 3. Rate constants of the forward and backward reactions of the first and second orders of
3
,4ꢀDCB isomerization to transꢀ1,4ꢀDCB (k , k , k , and k–2, respectively) for samples 1—4
1 –1 2
Sample*
Т/°С
[Fe]**
mol L–1
(k + k )•104
k •104
k–1•104
k2
k–2
1
–1
1
/
s–1
L mol–1 s–1
1
(4.7)
100
0.045
0.022
0.045
0.089
0.022
0.045
0.089
0.045
0.045
0.089
0.045
0.089
0.07
0.08
0.07
0.13
0.27
0.07
0.13
0.09
0.09
8.4
1.6
3.8
6.5
1.1
2.7
4.5
8.7
5.7
8.3
2.5
4.2
9.9
12.6
3.6
4.9
11.1
1.3
4.1
9.5
2.4
8.0
0.8
2.5
6.5
1.3
3.0
5.3
0.9
2.2
3.8
6.7
4.6
6.7
2.1
3.5
7.3
9.7
2.9
4.0
9.0
1.1
3.4
7.3
1.9
6.5
0.66
2.1
1.9
0.3
0.8
1.2
0.2
0.5
0.7
2.0
1.1
1.6
0.4
0.7
2.3
2.9
0.7
0.9
2.1
0.2
0.7
2.2
0.5
1.5
0.13
0.4
0.014
0.006
0.007
0.006
0.004
0.005
0.004
0.015
0.010
0.008
0.005
0.004
0.010
0.012
0.004
0.003
0.003
0.0016
0.0026
0.008
0.002
0.004
0.0013
0.0012
0.004
8
8
8
7
7
7
0
0
0
0
0
0
0.0014
0.0018
0.0013
0.0009
0.0011
0.0008
0.0044
0.0024
0.0018
0.0009
0.0008
0.0032
0.0036
0.001
0.0007
0.0008
0.0003
0.0005
0.0024
0.0006
0.0008
0.0003
0.0002
2
3
(10.1)
(16.3)
100
8
8
7
7
0
0
0
0
100
00
1
8
8
8
7
7
0
0
0
0
0
4
(10.3)
100
8
8
7
7
0
0
0
0
0.18
0.05
0.18
*
*
The iron content in the catalyst (wt.%) is given in parentheses.
* Iron content in reaction mixtures.
for the samples tested. The results obtained are given
below.
The specific catalytic activities of the ironꢀcontaining
nanoparticles calculated from the initial reaction rates at
8
0 °С are presented below. When the iron content inꢀ
Sample
1
2
3
4
creases from 4.7 to 16.3 wt.% in samples 1—3 obtained
under the same conditions, the specific catalytic activity
passes through a maximum for the 10% metal content and
further decreases. Sample 4 is less active.
–
1
Е /kJ mol
44±4
57±4
44±4
57±4
64±6
77±7
68±6
82±8
2
–
1
Е–2/kJ mol
It follows from the data in Table 3 that samples 1 and 2
with the iron content up to 10.1 wt.% show the highest
catalytic activity. The rate constants decrease with an
increase in the iron content to 16.3 wt.%. Sample 4 obꢀ
tained at a higher temperature is less catalytically active
than sample 2 with the same iron content (∼ 10 wt.%) but
prepared at a lower decomposition temperature. The most
active catalysts (samples 1 and 2) are characterized by
lower apparent activation energies: 44 and 57 kJ mol for
the forward and backward isomerization reactions, reꢀ
spectively, which are rather low for the tested reaction.
For the iron oxides of optimum composition supported
Sample
[Fe]
wt.%)
Asp
/mole of product (mol Fe) h–1
–1
(
1
2
3
4
04.7
10.1
16.3
10.3
140
170
80
80
–
1
It is most likely that the differences in catalytic activꢀ
ity caused by an increase in the metal content in the
sample and a change in the preparation conditions are
related to specific features of the nanoparticle composiꢀ
tion. The data presented in Table 1 show that the particle
size changes insignificantly; however, the compositions
of samples 1—4 differ substantially. It seems rather probꢀ
able that the high catalytic activity of samples 1 and 2 is
due to the Fe O and γꢀFe O oxides, whose structure is
on silica gel, these values are higher, being 53 and
9 kJ mol–1, respectively. For less active catalysts, the
1
6
apparent activation energies increase and become equal
–
1
–1
to 64 and 77 kJ mol (sample 3) and 68 and 82 kJ mol
sample 4).
(
3
4
2
3

1432
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
Rostovshchikova et al.
close to spinel and which are present in the composition
of the surface layers. These oxides include catalytically
active mixedꢀcharge states of metal11 and can participate
in electron transfer in the key step of isomerization, as it
has been proposed earlier.1 The high activity and the
absence of the induction period on accumulating the
isomerization products indicate that the catalytically acꢀ
tive sites of the iron oxides stabilized on the UPTFE
surface are accessible to reactants. Somewhat higher speꢀ
cific activity of sample 2 compared to sample 1 can be
related, in particular, to a higher imperfectness of the
particles.
32597), the International Scientific Technical Center
(Grant 1991), the Russian Science Support Foundation,
and the Division of Chemistry and Materials Science of
the Russian Academy of Sciences (fundamental research
programs "Fundamental Problems of Physics and Chemꢀ
istry of Nanodimensional Systems and Materials" and
"Directed Synthesis of Inorganic Substances with Speciꢀ
fied Properties and Creation of Related Functional Maꢀ
terials").
,2
References
The main reason for decreasing catalyst activity of the
sample with a higher iron content (sample 3) can be the
1
. 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
[Russ. Chem. Bull., Int. Ed., 2005, 1418].
absence of γꢀFe O in its composition. It follows from the
2
3
1
known data that αꢀFe O is less catalytically active. The
2
3
synthesis at a higher temperature (sample 4) also provides
a less active catalyst due to the formation of iron(II) oxide
reduced to a higher extent and showing lower catalytic
2. 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. Mosk. Gos.
Univ., Ser. 2. Khim., 2001, 42, 318 [Vestn. Mosk. Univ., Ser.
Khim., 2001 (Engl. Transl.)].
1
activity. Another possible reason for a low activity of
sample 4 is the absence of the iron fluoride phases. It has
3
. I. D. Kosobudskii and S. P. Gubin, Vysokomol. Soedin.,
985, 27, 689 [Polym. Sci. USSR, 1985, 27 (Engl. Transl.)].
2
previously been shown that the highest catalytic activity
1
is characteristic of composites based on nanoparticles of
iron(III) oxide and iron(II) chloride synthesized from
iron(III) chloride. Probably, similar combination of iron
oxides and fluoride in the same nanoparticle also favors
catalysis.
4
. S. P. Gubin, Yu. I. Spichkin, G. Yu. Yurkov, and A. M.
Tishin, Zh. Neorg. Khim., 2002, 47, 32 [Russ. J. Inorg. Chem.,
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5. G. Yu. Yurkov, S. P. Gubin, D. A. Pankratov, Yu. A.
Koksharov, A. V. Kozinkin, Yu. I. Spichkin, T. I.
Nedoseikina, I. V. Pirog, and V. G. Vlasenko, Neorg. Mater.,
Thus, the method proposed for the synthesis of iron
oxide nanoparticles by the thermolysis of iron formate on
the surface of the UPTFE stabilizing matrix provides the
nanocomposites active in catalysis of chloroolefins.
Multiphase nanoparticles, which are formed during the
2
002, 38, 186 [Inorg. Mater., 2002, 38 (Engl. Transl.)].
6
7
. S. P. Gubin, M. S. Korobov, G. Yu. Yurkov, A. K.
Tsvetnikov, and V. M. Buznik, Dokl. Akad. Nauk, 2003,
3
88, 493 [Dokl. Chem., 2003 (Engl. Transl.)].
. M. S. Korobov, G. Yu. Yurkov, A. V. Kozinkin, Yu. A.
Koksharov, I. V. Pirog, S. V. Zubkov, V. V. Kitaev, D. A.
Sarychev, V. M. Buznik, A. K. Tsvetnikov, and S. P. Gubin,
Neorg. Mater., 2004, 40, 31 [Inorg. Mater., 2004, 40 (Engl.
Transl.)].
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act., 1998, 112, 59.
. F. Menil, J. Phys. Chem. Sol., 1985, 46, 763.
III
II
synthesis and in which some Fe ions are reduced to Fe ,
require no additional "activation" by reactants and perꢀ
form isomerization without an induction period inherent
in other catalytic systems based on iron oxides. Similarly
to the iron oxides localized on the silica surface, the highꢀ
est activity is characteristic of the highly defective samples
including the γꢀFe O phase. Their activity more than
8
9
2
3
1
1
0. E. G. Walton, D. B. Brown, H. Wong, and W. M. Reiff,
Inorg. Chem., 1977, 16, 2425.
1. O. S. Morozova, Yu. V. Maksimov, D. P. Shashkin, P. A.
Shirjaev, V. A. Zhorin, and O. V. Krylov, Appl. Catal., 1991,
78, 227.
twofold exceeds that of the nanocomposites containing
nanoparticles similar in size and composition but stabiꢀ
lized in the volume rather than on the surface of the
polymeric polyethylene matrix.2
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 05ꢀ03ꢀ32083,
Received September 12, 2004;
in revised form April 6, 2005
0
3ꢀ03ꢀ33104, 04ꢀ03ꢀ32090, 04ꢀ03ꢀ32311, and 04ꢀ03ꢀ