New cluster-type rhodium selenochlorides in oxidative carbonylation of methane

Article abstract of DOI:10.1134/S107042720702005X

New rhodium selenochlorides Rh₄Se₁₆Cl₁₀ and Rh₄Se₁₈Cl₁₀ whose structure is based on the cluster "cubane" [Rh₄(μ₃-Se)₄] and products of their thermal transfo

Full text of DOI:10.1134/S107042720702005X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 2, pp. 193 200.
Original Russian Text S.V. Volkov, L.B. Khar’kova, Z.A. Fokina, O.G. Yanko, P.E. Strizhak, G.R. Kosmambetova, V.I. Gritsenko, A.M. Korduban,
007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 2, pp. 195 201.
Pleiades Publishing, Ltd., 2007.
2
INORGANIC SYNTHESIS
AND INDUSTRIAL INORGANIC CHEMISTRY
New Cluster-Type Rhodium Selenochlorides in Oxidative
Carbonylation of Methane
S. V. Volkov, L. B. Khar’kova, Z. A. Fokina, O. G. Yanko, P. E. Strizhak,
G. R. Kosmambetova, V. I. Gritsenko, and A. M. Korduban
Vernadskii Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
Kiev, Ukraine
Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, Kiev, Ukraine
Kurdyumov Institute of Metal-Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine
Received March 30, 2006; in final form, October 2006
Abstract New rhodium selenochlorides Rh Se Cl
and Rh Se Cl
whose structure is based on
4
16 10
4
18 10
the cluster cubane [Rh4( 3-Se) ] and products of their thermal transformations were obtained. The catalytic
4
properties of the compounds on various carbon and silica supports in oxidative carbonylation of methane in
the gas phase and their dependence on the catalyst preparation technique, type of support, and size of its
nanopores were analyzed.
DOI: 10.1134/S107042720702005X
The ability to coordinate in the inner coordina-
phase under elevated pressure [4], but carrying out
the reaction in a heterogeneous catalytic system under
atmospheric pressure is a simpler and more attractive
method [5 8]. In this case, no aggressive and toxic
solvents are used and liquid reaction products are
easily removed from the reaction mixture.
tion sphere both organic and inorganic ligands creates
a wide variety of complex compounds of rhodium,
with the resulting opportunity to use these systems to
develop catalytic systems with controllable functional
properties. Possibly promising objects as catalysts
for organic synthesis are chalcogenide and chalco-
halide compounds of rhodium, synthesized in non-
aqueous organic media without use of expensive tem-
plates [1, 2], and products of thermal destruction of
these compounds. In systems of this kind, activation
and conversion of reagents may occur not only at
the central metal atoms, but also at chalcogenide sites.
As a result, rhodium chalcohalides may be of par-
ticular interest for direct synthesis of complex sub-
stances from simple molecules. Single-stage synthesis
of alcohols, aldehydes, acids, and esters from
methane, carbon monoxide, and oxygen is a possible
alternative to the multistage and energy-intensive
processing of natural gas, which includes stages of
In this study, catalysts prepared by deposition of
new cluster-type rhodium selenochlorides onto silica
and porous carbon materials in the reaction of ox-
idative carbonylation of methane to give oxygen-con-
taining compounds were examined.
EXPERIMENTAL
Rhodium selenochlorides were synthesized in
the medium of Se Cl , with rhodium(III) chloride
2
2
RhCl3 4H O used as a reaction form. In this medi-
2
um, selenium can be present in various states and ox-
idation levels: as neutral molecules Se Cl , anions,
2
2
2
2
0
n
Se , chain anions Sen or molecules Se , selenium
steam reforming of methane into a mixture of H and
2
dioxide SeO , and selenyl dichloride SeOCl . For
2
2
CO (3 : 1), high-temperature conversion of a mixture
this reason, the first stage of synthesis was performed
of H and CO (2 : 1) into methanol, and subsequent
2
at 80 90 C in the course of 120 h (RhCl3 4H O :
2
synthesis of aromatic oxygen-containing compounds
from methanol [3].
Se Cl = 1 : 10) in an open reactor to enable release of
2
2
the gaseous products, H Se and HCl. In the second
2
The reaction of oxidative carbonylation of methane
to give acetic acid was first performed in the liquid
stage, the reactor was sealed and the heating was con-
tinued at 100 C in two different temperature modes:
193

194
VOLKOV et al.
The thermal decomposition products, Rh Se Cl
3
3
and Rh Se Cl, were obtained in 40 h at 345 and
3
5
320 C in accordance with the reactions
3
45 C
3
Rh Se Cl
4Rh Se Cl + 13Se Cl + 10Se,
3 3 2 2
4
16 10
3
20 C
3
Rh Se Cl
4Rh Se Cl + 13Se Cl + 8Se.
3 5 2 2
4
18 10
Rhodium selenochlorides were studied using a set
of mutually complementary physicochemical tech-
niques: vibrational and X-ray photoelectron (XPS)
spectroscopies; X-ray phase, thermal, and elemental
chemical analyses. It was found that the complexes
2
2
2
2
contain the structural fragments -Se , -Se , -Se ,
3
Clterm, and Clbridge, as well as coordinated Se Cl
2
2
molecules.
A thermographic study was performed on an MOM
Q-1500 instrument (Hungary) in the temperature
1
range 20 1000 C (sample heating rate 5 deg min ,
sensitivity 250 V, sample weight 0.5 1 g) in special
cuvettes under a constant lowered pressure, with
gaseous decomposition products condensed in liquid
nitrogen. To isolate solid thermolysis products,
the starting compounds were kept at the temperatures
of the effects recorded in the thermograms (345 and
320 C) for 40 h to constant weight of the solid re-
sidue.
For all the compounds formed both by direct syn-
thesis and by thermal destruction, a chemical ele-
mental analysis was made. The content of the metal
was determined gravimetrically upon reduction of
weighed portions of the compounds in a flow of hy-
drogen at 20 1000 C; that of chlorine, by argentom-
etry in alkaline solutions through which gases evolved
in reduction by hydrogen were passed; and that of
selenium, from the difference.
Fig. 1. IR spectra: (a) Rh Se Cl , Rh Se Cl and
18 10
IR spectra of the compounds suspended in Nujol
were recorded on Nicolet Magna-IR 750 and Spe-
cord M-80 spectrometers, and Raman spectra, on
a DFS-24 spectrometer with a He Ne laser excitation
source (632.8 nm).
4
16 10
4
(
b) Rh Se Cl, Rh Se Cl; (c) variation of the relative in-
3 3 3 5
tensities of lines of the Raman spectrum of Rh Se Cl
1
4
18 10
in the course of 2 h. (A) Absorption and ( ) wave number.
with cyclic heating cooling (60 80 h) and with con-
tinuous heating (180 h). The forming solid products,
Rh Se Cl (1) and Rh Se Cl (2), were yielded by
XPS spectra were measured with a modified ES-
402 electron spectrometer. An X-ray gun with
2
4
16 10
4
18 10
a magnetic anode (EMg K = 1253.6 eV, P = 300 W)
served as excitation source.
the following reactions
4
4
RhCl3 4H O + 12H O + 15Se Cl = Rh Se Cl
16 10
The catalytic properties of the samples were
studied by passing a gas mixture with component ratio
2
2
2
2
4
+
32HCl + 6Se + 8SeO2,
RhCl3 4H O +12H O + 23Se Cl = Rh Se Cl
18 10
1
The authors are grateful to B.V. Lokshin and Z.S. Klemen-
2
2
2
2
4
kova, staff members of INESS (Moscow), for assistance in
IR spectral measurements.
+
32HCl + 16Se + 8SeOCl2 + 4SeO2.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

NEW CLUSTER-TYPE RHODIUM SELENOCHLORIDES
195
CH : CO : O = 10 : 4 : 1 through a quartz reactor Table 1. Rh3d5/2 XPS spectra of rhodium selenochlorides
4
2
with an inner diameter of 10 mm. The catalyst volume
was 1.0 cm . The experiments were performed under
3
I of com-
ponent a
I of com-
ponent b
I of com-
ponent c
atmospheric pressure in the temperature range 400
Se3d
FWHM =
1.5 eV
1
6
00 C at a volumetric flow rate of 6000 h . The spe-
cific surface area of the samples, SBET, was found by
the method of thermal desorption of nitrogen. The start-
ing substances and gaseous reaction products (CH4,
CO, O , CO ) were analyzed with an LKhM-80 gas
at Eb, eV
3
06.4
308.3
309.6
1.0
2
2
Rh Se Cl
16 10
chromatograph equipped with a heat-conductivity de-
tector. Liquid reaction products were frozen-out in
a trap at a temperature of 70 C and then analyzed on
a Khrom-5 chromatograph with a flame-ionization de-
tector and a column packed with Separon-BD sorbent.
4
Rh Se Cl
4
18 10
Rh Se Cl
1.0
0.8
3
3
Rh Se Cl
3
5
Rh Se Cl/F1
0.2
3
5
The vibrational spectra of Rh Se Cl
and
4
16 10
Rh Se Cl are identical. The spectra contain a com-
4
18 10
and Se Se bonds, which indicates that selenide bridges
plex set of frequencies repeated in the IR and Raman
Se and perselenide fragments -Se2 appear in
2
-
1
2
spectra (Figs. 1a, 1c). The broad band at 360 350 cm
(
the structure.
1
IR), and the strong band at 350 cm (Raman) are
The Rh3d5/2 XPS spectra of the compounds
associated with stretching vibrations of the Se Cl
bond in the Se Cl molecule. The frequencies 334,
Rh Se Cl
and Rh Se Cl , Rh Se Cl and
4
16 10
4 18 10 3 3
2
2
15, 307 cm 1 (IR) and 331, 319, 310 cm (Raman)
1
Rh Se Cl, and of Rh Se Cl on a carbon support are
3
3
5
3
5
presented in Table 1 and Fig. 2. The spectra were
analyzed by decomposition into components by
the Gauss Newton method. The Rh3d5/2 XPS spec-
tra of the compounds Rh Se Cl and Rh Se Cl
can be attributed to stretching vibrations of the Rh Cl
2
and Rh
and 239 cm (IR) and the lines at 269, 255, and
40 cm 1 (Raman) lie in the range of vibrations of
Se bonds. The weak bands at 274, 251,
3
1
2
4
16 10
4
18 10
(
Fig. 2a) have a single component (c) with Rh3d5/2
the Se Se bond in chain and annular Se molecules.
n
Eb = 309.6 eV, which indicates that rhodium is pres-
From the whole set of frequencies of deformation
1
ent in the oxidation state +3. The spectra of the ther-
vibrations, which lie below 200 cm , the following
1
mal decomposition products Rh Se Cl and Rh Se Cl
frequencies can be distinguished: 146, 138 cm (IR)
3
3
3
5
1
(
Fig. 2b) contain a single component (b) with Rh3d5/2
and 149, 138 cm (Raman). These frequencies corre-
spond to deformation vibrations of the SeSeCl bonds
1
in the individual Se Cl molecule (149 and 135 cm ).
2
2
Particular attention is attracted by the strong band
at 215 cm 1 (IR) and the line at 209 cm (Raman).
The intensity of this line in the Raman spectrum
sharply decreases under the action of laser light,
whereas the intensities of the other lines remain un-
changed (Fig. 1c). This frequency can be attributed
1
0
to vibrations of the (Se Se) group coordinatively
bound to rhodium. This group lies as a kind of dumb-
bell over faces of the cubane core. Relatively weakly
bound -Se fragments can be split-off under the ac-
2
tion of laser light, with the cubane structure preserved.
The IR spectra of the products of thermal de-
composition, Rh Se Cl and Rh Se Cl, are identical
3
3
3
5
(
Fig. 1b), but strongly differ from the IR spectra of
the starting rhodium selenochlorides, Rh Se Cl and
4
16 10
Rh Se Cl , which points to profound changes in
4
18 10
the original molecular structure. The doublet at 318
Fig. 2. Rh3d
XPS spectra of rhodium selenochlorides:
1
5/2
and 311 cm corresponds to vibrations of Rh Cl and
(
a) Rh Se Cl , Rh Se Cl ; (b) Rh Se Cl, Rh Se Cl;
4 16 10 4 18 10 3 3 3 5
2
Rh -Se . The broad absorption band peaked at
2
and (c) Rh Se Cl on a carbon support (fullerene black F1).
3
3 5
70 cm is associated with vibrations of the Rh Se2
1
(I) Intensity and (E) energy.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

1
96
VOLKOV et al.
structure [Rh ( -Se) ] is due to a specific electronic
Table 2. Cl2p3/2 XPS spectra of rhodium selenochlorides
4
3
4
structure of the selenium atom, which has free, com-
paratively low-lying d-orbitals capable of additional
bonding [11]. Therefore, analysis of the vibrational
and XPS spectra suggests that the structure of the com-
pounds obtained is Rh ( -Se) ( -Se ) Cl (Se Cl )
Cl2p3/2
FWHM = 1.2 eV
I of a component at E , eV
b
Rh Se Cl
0.64/197.8 0.36/198.1
4
16 10
4
3
4
2 3
4
2
2 3
Rh Se Cl
and Rh ( -Se) ( -Se ) Cl (Se Cl ) . The intensity ra-
4
18 10
4 3 4 2 4 4 2 2 3
Rh Se Cl
0.42/197.2 0.53/198.0 0.05/200.5
3
3
tio of the lines in the Se3d spectrum, 0.23 : 0.53 : 0.24,
approximately corresponds to the selenium distribu-
tion among the fragments.
Rh Se Cl
3
5
The Se3d spectra of the thermal decomposition
Table 3. Se3d XPS spectra of rhodium selenochlorides
Se3d
products, Rh Se Cl and Rh Se Cl, have two compo-
3
3
3
5
nents with Se3d E = 54.6 and 55.3 eV. The binding
b
FWHM =
.5 eV
I of a component at E , eV
energy of 54.6 eV is typical of metal selenides. This
means that the charge on selenium is close to 2e
and confirms the conclusion furnished by vibrational
spectroscopy, according to which the molecules of
the starting selenochlorides undergo a deep transfor-
mation in thermal decomposition to give selenide
b
1
Rh Se Cl
0.24/55.9 0.53/56.5 0.23/57.0
4
16 10
Rh Se Cl
4
18 10
Rh Se Cl
0.38/54.6 0.62/55.3
3
3
2
2
Rh Se Cl
3
5
fragments -Se and -Se . The value of 55.3 eV
2
2
can be attributed to the 3-Se fragment.
On heating rhodium selenochlorides, Se Cl
2
Eb = 308.3 eV, which may be due both to a significant
decrease in the number of chlorine atoms substituted
by selenium and to a lowering of the oxidation state
of rhodium.
2
molecules and Se2 dumbbells are eliminated and
the remaining molecular structure is constituted by
the 3-Se fragment linking three rhodium atoms, be-
tween which the fragments -Se and -Se are situated.
2
The Cl2p3/2 spectra of the starting rhodium seleno-
chlorides (Table 2) contain two components with
Cl2p3/2 Eb 197 and 198 eV, which can be attributed,
according to published data [9], to a bridging chloride
atom in the polymeric structure of rhodium seleno-
chlorides. The Se3d spectra of rhodium selenochlo-
rides (Table 3) have three components, which points
to three different energy states of selenium in these
The structure of the compounds can be represented as
Rh ( -Se)( -Se) Cl and Rh ( -Se)( -Se) ( -Se )Cl.
3
3
2
3
3
2
2
The compositions of these compounds might in-
dicate that rhodium is in the oxidation state +1 and
-
SE and -Se fragments have zero charges. How-
2
ever, the IR and XPS spectra more likely correspond
to selenide fragments -Se2 and -Se2 . In this case,
2
2
molecules. To the 3-Se group is attributed the peak
rhodium retains the oxidation state +3.
at Se3d E = 55.9 eV. This energy somewhat exceeds
b
the corresponding value for selenides MSe with Se3d
Eb = 53.3 54.5 eV [9] and is caused by a decrease
in the amount of negative charge on the selenium
atom bonded to three, rather than one, metal atoms.
A decomposition of the Rh3d5/2 XPS spectrum
of a sample synthesized in Se Cl in the presence of
2
2
a carbon support gave two lines indicating that there
exist two different states of rhodium (Fig. 2c, Table 1).
Presumably, the line Rh3d5/2 Eb = 308.3 eV with
the highest intensity (b) belongs to rhodium which
is possibly in the oxidation state Rh2 in a ligand en-
vironment of selenium and chlorine, and the low-
The component Se3d E = 56.5 eV is attributed to
b
Se Se chain fragments with zero charge and is
larger than that in elementary selenium, in which Se3d
Eb = 55.5 eV because of the complexation. The high-
+
er-lying line Se3d E = 57.0 eV must be associated
b
lying weak line Rh3d5 Eb = 306.4 eV is associated
/2
0
with the Se Cl molecule, in which the strong elec-
2
2
with Rh (a), i.e., with metallic rhodium. The second
trophile, chlorine, makes greater the positive charge
on selenium atoms, with the complexation acting in
the same direction.
line lies at somewhat lower energies, compared with
Rh3d5/2 Eb = 307.2 eV for pure metallic rhodium,
which may be due to interaction of adsorbed rhodium
with the carbon of the substrate. The presence of three
lines in the spectrum indicates that the thermal de-
composition of Rh Se Cl in the presence of carbon
Selenium derivatives are characterized by formation
of multinuclear complexes whose structure is based on
a cubane-like core [Rh ( -Se) ] [10]. The cubane
4
3
4
4
18 10
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

NEW CLUSTER-TYPE RHODIUM SELENOCHLORIDES
197
Table 4. Catalytic properties of rhodium selenochlorides on carbon supports in oxidative carbonylation of methane
1
[
reaction mixture (MPa): CH4 0.066, CO 0.027, O2 0.007; volumetric flow rate of the process 6000 h ]
Output capacity, mol g 1 h 1
cat
Type of
support
Preparation
method
T,
C
CH OH
C H OH
CH COOH
C H COOH
3
2
5
3
2
5
S1
S1
S1
S2
F1
F2
II
400
50
4
5
5
00
50
0.0412
0.018
0.026
0.009
III
IV
IV
IV
IV
400
4
5
5
50
00
50
0.077
0.006
400
0.047
0.971
0.090
0.125
450
500
550
0.103
400
450
500
550
0.040
0.04
1.391
0.001
0.050
0.015
0.014
0.04
0.04
400
450
500
550
0.022
0.08
400
0.038
0.028
0.056
4
5
5
50
00
50
0.031
0.019
supports yields three potentially possible catalytically
active centers.
was synthesized on the surface of carbon supports and
then subjected to thermal destruction (method III). Fi-
nally, the fourth procedure included mechanical mix-
ing of the thermal decomposition product Rh Se Cl
Tests with various catalyst supports (SiO , Al O ,
2
2
3
3
5
ZrO , TiO , MgO) in synthesis of rhodium seleno-
2
2
with carbon supports (method IV).
chlorides demonstrated that only carbon materials
are stable in Se Cl .
The thermal decomposition of samples prepared
using methods II and III was carried out at 320 C for
2
2
Catalysts containing rhodium compounds on car-
40 h.
2
1
bon supports (SKT-1 carbon: S1, Ssp = 700 m g ;
2
1
The data on the catalytic activity of the samples
spherical enterosorbent: S2, Ssp = 1400 m g ; and
2
1
are listed in Table 4. The first set of catalysts was
prepared by ordinary impregnation of carbon supports
with an aqueous solution of rhodium chloride (meth-
od I). Tests of impregnated samples in oxidative car-
two fractions of fullerene black: F1, S = 20 m g
sp
2
1
and F2, 65 m g , produced by pyrolysis of styrene
and a copolymer of divinylbenzene) were prepared
by the following four methods. The first included
impregnation of carbon supports with an aqueous so-
bonylation of methane revealed that CO is the only
2
reaction product.
lution of RhCl and subsequent thermal decomposi-
3
tion at 120 C for 5 h and 320 C for 40 h (method I).
The second was based on thermal decomposition of
a mechanical mixture of a preliminarily synthesized
Rh Se Cl and carbon supports (method II). In the
It was found in a study of catalysts containing
rhodium selenochlorides that methanol and acetic and
propionic acids are formed in addition to the main
reaction product, CO (Table 4). A comparison of
4
18 10
2
third technique, rhodium selenochloride Rh Se Cl
the data in Table 4 demonstrated that the activity and
4
18 10
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

198
VOLKOV et al.
ygenates are formed on the samples synthesized by
methods II and IV, but the quantitative composition
of the products depends on the catalyst preparation
method. A higher output capacity for acetic acid
1
cat
1
(
0.971 mol g h ) is observed in the case when
the support is mixed with the thermal destruction
product (method IV), compared with the starting
selenochloride (method II). Only ethanol is found in
liquid reaction products formed on a sample syn-
thesized by introducing a support into the starting re-
action mixture RhCl3 4H O : Se Cl = 1 : 10 (meth-
2
2
2
od III). A test in the reaction of samples prepared by
method IV on other carbon supports demonstrated that
acetic acid and alcohols are formed on all the cata-
lysts, but the output capacity of the process depends
on the nature of a carbon support.
The data obtained show that the widest variety
of reaction products (methanol, ethanol, acetic and
propionic acids) is observed when the catalyst is pre-
pared by mechanical mixing of the thermal destruction
product Rh Se Cl with carbon support S2, spherical
3
5
enterosorbent.
The next series of experiments was devoted to cat-
alytic properties of rhodium selenochlorides on silica
supports, synthesized by their mechanical mixing with
Rh Se Cl, which is a product of thermal destruction
3
3
of a cluster selenochloride Rh Se Cl , and of
4
16 10
samples prepared by impregnation of the KSS-5 sup-
port with rhodium trichloride and its mixture with
ammonium metavanadate. As supports for rhodium
selenochlorides served the following silicas: KSS-5,
KSS-4, KSS-3, ShSM, and KSK, which differ in spe-
cific surface area, volume, and average pore size
(Table 5).
Fig. 3. Output capacity of Rh Se Cl/SiO catalysts for
3
3
2
(
a) methanol, (b) ethanol, and (c) acetic acid in relation
to the process temperature T and support pore size.
A) Output capacity and (r) pore radius.
It has been shown previously that pure silica sup-
ports are inactive in oxidative carbonylation of meth-
ane carbonylation and insignificant amounts of methyl
(
selectivity of rhodium selenochlorides on carbon sup-
ports largely depends on the catalyst preparation tech-
nique. This result can be illustrated by the example of
a catalyst deposited on an S1 support by three differ-
1
cat
1
acetate (0.05 0.5 mol g h ) are formed on sam-
ples prepared by introduction of ammonium meta-
vanadate in template synthesis of MCM-41 meso-
porous silica [8]. Only gaseous products, carbon ox-
ides, were formed on catalysts prepared by impregna-
tion of the supports KSS-5, KSS-4, KSS-3, ShSM,
and KSK supports with a rhodium trichloride solution.
ent methods. It can be seen from Table 4 that C -ox-
2
Table 5. Texture characteristics of silica supports
1
cat
1
Pore volume, Pore diameter,
Trace amounts of acetic acid (0.02 mol g h )
2
1
Support
S, m g
3
1
cm g
nm
were found on a catalyst synthesized by joint depo-
sition of rhodium trichloride and ammonium meta-
vanadate onto a KSS-5 silica, with the catalyst strong-
ly carbonized in the course of the reaction. Meth-
anol, ethanol, and acetic acid were formed in ox-
idative carbonylation of methane on samples pre-
pared by mixing Rh Se Cl with silicas. Figure 3
KSK
270
520
650
500
720
0.76 0.93
0.920
0.76
0.71
0.40
12 15
KSS-3
KSS-4
KSS-5
ShSM
7
5
3
1.1 1.2
3
3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

NEW CLUSTER-TYPE RHODIUM SELENOCHLORIDES
199
shows how the output capacity of the catalysts for
methanol, ethanol, and acetic acid depends on
the process temperature and support pore size. As
can be seen in Fig. 3a, the highest output capacity
on its texture characteristics. This makes it possible
to regard nanovoids in porous silicas and carbon ma-
terials as nanoreactors whose size affects the selec-
tivity of oxidative carbonylation of methane on rho-
dium selenochlorides [13]. It should be noted that
none of the catalyst samples containing rhodium sele-
no-chlorides was carbonized in the tests, in contrast
to the catalyst prepared by impregnation with rhodium
trichloride and ammonium metavanadate.
1
1
for methanol (1.5 mol g h ) is observed on the
cat
Rh Se Cl/KSS-3 sample with a support pore size of
3
3
3
nm. Acetic acid is mostly formed on Rh Se Cl/KSS-4
3 3
and Rh Se Cl/KSS-5 samples with a pore size of 7
3
3
8
nm. As the support pore size increases to 12 nm,
ethanol becomes the main liquid product of the pro-
cess.
CONCLUSIONS
It was shown in [12] that single-stage synthesis
from methane and carbon monoxide yields methanol
in the presence of nitrogen(II) oxide as oxidizing
agent and iron(III) phosphate as catalyst, and methyl
acetate upon addition of highly dispersed Rh O to
(
1) New cluster-type cubane-like rhodium seleno-
chlorides Rh Se Cl and Rh Se Cl were syn-
4
16 10
4
18 10
thesized and products of their thermal transformations,
Rh Se Cl and Rh Se Cl, were obtained. An analysis
3
3
3
5
2
3
of the vibrational (IR, Raman) and Rh3d , Se3d,
5
/2
the catalyst. A conclusion was made on the basis of
these data that presence of a single active center
and Cl2p3/2 XPS spectra of these compounds sug-
gested the following structure of the rhodium seleno-
chlorides obtained: Rh ( -Se) ( -Se ) Cl (Se Cl )
and Rh ( -Se) ( -Se ) Cl (Se Cl ) , based on the
cubane core [Rh ( -Se) ].
(
FePO ) on the catalyst surface leads to activation of
4
4
3
4
2 3
4
2
2 3
methane to give a methyl radical and, subsequently,
4
3
4
2 4
4
2
2 3
C -oxygenate. Presence of a second closely lying
1
4
3
4
active center (Rh O ) enables carbonylation and
2
3
makes it possible to obtain longer-chain C C -oxy-
(2) The catalytic properties of Rh Se Cl and
4 18 10
2
3
genates.
a product of its thermal destruction, Rh Se Cl, depos-
3 5
ited on various carbon supports were studied in the re-
action of oxidative carbonylation of methane. It was
shown that, in contrast to samples prepared by im-
pregnation of supports with rhodium trichloride, rho-
dium selenochlorides exhibit catalytic activity in car-
bonylation of methane. The output capacity of the pro-
cess for methanol, ethanol, and acetic acid depends on
the method of catalyst preparation and type of a car-
bon support.
It was experimentally demonstrated that oxygen-
containing products are formed in oxidative carbon-
ylation of methane either on a rhodium selenochloride
or in the joint presence of rhodium and vanadium
oxides. The formation of acetic acid on the rhodi-
um-vanadium catalyst can be attributed, by analogy
with [12], to presence of two active centers respon-
sible for activation of methane and its subsequent
carbonylation into acetic acid. Use of rhodium seleno-
chloride instead of rhodium and vanadium oxides can
improve the output capacity for acetic acid by more
than an order of magnitude. In addition, the reaction
of oxidative carbonylation of methane yields ethanol
and ethanol.
(3) A study of the catalytic properties of a mech-
anical mixture of rhodium selenochloride Rh Se Cl
3
3
and silicas with various texture characteristics dem-
onstrated that support nanopores can be regarded as
nanoreactors whose size affects the output capacity
and selectivity of oxidative carbonylation of meth-
ane.
A detailed study of the structure of active centers
of the reaction of oxidative carbonylation of methane
on rhodium selenochlorides is beyond the scope of this
study. The suggested structure of both the starting rho-
dium selenochlorides, Rh ( -Se) ( -Se ) Cl (Se Cl )
REFERENCES
1. Kosmambetova, G.R., Gritsenko, V.I., Strizhak, P.E.,
et al. The Eur. Catalysis Forum EuropaCat-VI ,
31.08 4.09, 2003, Austria, Innsbruck, CD: Abstracts,
2003, Poster 1546.
4
3
4
2 3
4
2
2 3
and Rh ( -Se) ( -Se ) Cl (Se Cl ) , and products of
4
3
4
2 4
4
2
2 3
their thermal transformations, Rh ( -Se)( -Se) Cl
3
3
2
and Rh ( -Se)( -Se) ( -Se )Cl, leads to a conclusion
3
3
2
2
that the starting reagents are activated not only on
rhodium atoms, but on selenium as well. The sub-
sequent transformations of the activated complex and
the qualitative composition of the reaction products
strongly depend both on the nature of a support and
2. Kosmambetova, G.R., Gritsenko, V.I., Strizhak, P.E.,
et al., Ukr. Khim. Zh., 2004, vol. 70, no. 2, pp. 75 80.
3. Sheldon, R.A., Chemicals from Synthesis Gas: Cata-
lytic Reactions of CO and H , Dordrecht: Reidel,
2
1983.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

200
VOLKOV et al.
4
5
6
7
8
9
. Lin, M. and Sen, F., Nature, 1994, vol. 368, khimicheskikh soedinenii (X-ray Photoelectron Spec-
pp. 613 615.
. Wilcox, E.M., Roberts, G.W., and Sprivey, J.J.,
troscopy of Chemical Compounds), Moscow: Khi-
miya, 1984.
Catal. Today, 2003, vol. 88, pp. 83 90.
10. Pekhn’o, V.I., Stepanenko, I.N., Fokina, Z.A., et al.,
. Wang, Y., Katagiri, M., and Otsuka, K., Chem.
Commun., 1997, pp. 1187 1188.
. Otsuka, K. and Wang, Y., Appl. Catal., Ser. A, 2001,
Zh. Neorg. Khim., 2004, vol. 49, no. 5, pp. 813 816.
11. Schulz, S., Andruh, M., and Pape, T., Organometal-
lics, 1994, vol. 13, pp. 4005 4007.
vol. 222, pp. 145 161.
1
2. Yuan, Q., Zhang, Q., and Wang, Y., J. Catal., 2005,
. Pavlenko, N.V., Kosmambetova, G.R., Gritsenko, V.I.,
vol. 233, pp. 221 233.
et al., Ukr. Khim. Zh., 2003, vol. 69, no. 11, pp. 27 32.
1
3. Buchachenko, A.L., Usp. Khim., 2003, vol. 72, no. 5,
. Nefedov, V.I., Rentgenoelektronnaya spektroskopiya
pp. 420 437.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007