Catalytic properties of RhSe2/Ga/H-ZSM-5 system in the reaction of glycerol dehydration in the gas phase

Article abstract of DOI:10.1134/S1070427216020117

Catalytic properties of the RhSe₂/Ga/H-ZSM-5 system formed upon thermal treatment of a mechanical mixture of rhodium selenochloride Rh₂Se₉Cl₆ and a gallium-containing zeolite Ga/H-ZSM-5 at 300–340°C in a flow of nitrogen were studied in the course of glycerol dehydration in the gas phase. It was shown that the promotion of Ga/H-ZSM-5 with rhodium selenide RhSe₂ makes higher the yield of the target product acrolein.

Full text of DOI:10.1134/S1070427216020117

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2016, Vol. 89, No. 2, pp. 233−237. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © S.V. Volkov, L.B. Khar’kova, S.A. Baranets, O.G. Yanko, P.E. Strizhak, G.R. Kosmambetova, V.I. Gritsenko, 2016, published in Zhurnal
Prikladnoi Khimii, 2016, Vol. 89, No. 2, pp. 224−229.
CATALYSIS
Catalytic Properties of RhSe /Ga/H-ZSM-5 System
2
in the Reaction of Glycerol Dehydration in the Gas Phase
a
a
a
a
b
S. V. Volkov , L. B. Khar’kova , S. A. Baranets , O. G. Yanko , P. E. Strizhak ,
b
b
G. R. Kosmambetova , and V. I. Gritsenko
a
Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. Akademika Palladina 32/34, Kyiv, 03142 Ukraine
b
Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine,
pr. Nauki 31, Kyiv, 03028 Ukraine
e-mail: svyatium@mail.ru
Received August 17, 2015
Abstract—Catalytic properties of the RhSe /Ga/H-ZSM-5 system formed upon thermal treatment of a mechani-
2
cal mixture of rhodium selenochloride Rh Se Cl and a gallium-containing zeolite Ga/H-ZSM-5 at 300–340°C
2
9
6
in a flow of nitrogen were studied in the course of glycerol dehydration in the gas phase. It was shown that the
promotion of Ga/H-ZSM-5 with rhodium selenide RhSe makes higher the yield of the target product acrolein.
2
DOI: 10.1134/S1070427216020117
Rhodium and its compounds are effective catalysts for
purification of technological and exhaust gases, hydroge-
nation of organic compounds, oxidation of ammonia to
nitric acid, etc. This is due to its high chemical stability
in corrosive media and ability to form complex coordi-
nation compounds, which makes it possible to create a
prescribed structure of the active center of a catalyst. The
specific structural features of the complex compounds in
which active metals are surrounded by ligands provide a
high selectivity of the catalysts synthesized on their basis
in processes of partial conversion of organic compounds
wider the range of their practical applicability in catalysis
2–
[4]. It can be assumed that the presence of the ligands S ,
2
–
–
Se , and Cl in the coordination compounds of this kind
provides the formation of acid centers and promotes the
activation of complex organic compounds.
About ten chalcogen-halide complexes of rhodium are
known, but the catalytic properties have been studied only
for some of its selenochlorides (Rh Se Cl , Rh Se Cl ,
4
19 11
2
8
5
Rh Se Cl , Rh Se Cl, Rh Se Cl) and products of their
2
9
5
3
5
3
3
thermal decomposition on silica gel and carbon supports
in the reaction of oxidative carbonylation of methane
into C –C oxygenates (methanol, methyl acetate, acetic
[1]. The high selectivity is exhibited in this case not only
1
3
by the starting complex compounds, but also by products
of their thermal decomposition, in which the initial coor-
dination of the active metal is preserved [2].
acid) [4–6].
The need to utilize glycerol is due to the large volumes
of its formation as a by-product in manufacture of bio-
diesel via transesterification of fats with low-molecular
alcohols [7]. The following compounds may be formed
in the course of dehydration: allyl alcohol as a product
of splitting-off of a water molecule, acrolein as a product
of splitting-off of two molecules of water, and products
of glycerol decomposition. The most valuable among the
above-mentioned oxygen-containing products is acrolein
used in production of solid plastics, esters, and medicinal
preparations.
As objects promising as organic synthesis catalysts
may serve chalcogenide and chalcogen-halide rhodium
compounds synthesized in nonaqueous inorganic media
without use of expensive templates, as well as the prod-
ucts of their thermal decomposition [3]. In contrast to
thermally unstable organic complexes, the above inor-
ganic coordination compounds of rhodium are thermally
stable up to 300–350°C, and products of their thermal
decomposition, up to 900°C, which makes substantially
2
33

234
VOLKOV et al.
As catalysts for dehydration of glycerol in the gas
carried out on an MOM Q-1500 instrument (Hungary)
in the temperature range 20–1000°C (sample heating
phase serve oxide systems: modified, natural, and syn-
thetic zeolites, aluminosilicate and silicate mesoporous
materials, and systems based on solid heteropolyacids
having acid surface properties, which is due to the spe-
cific features of glycerol activation [8]. The high catalytic
activity of zeolites of the type of ZSM-5 and its hydrogen
forms H–ZSM-5 in the course of glycerol dehydration is
due to the specific features of their structure and, in par-
ticular, to the 3D system of open channels and separation
of cations at a large Si/Al ratio, and also to the presence
of acid centers [9]. One of ways to raise the activity of
systems of the H–ZSM-5 type is by modification with
gallium additives for making higher the concentration of
acid centers and improving the catalytic properties of the
material in the reactions of the acid-base type, including
the dehydration of glycerol to acrolein [10–12].
–
1
rate 5 deg min , sensitivity 250 μV, weighed portion
0.5–1 g) in special cuvettes under reduced pressure, with
condensation of gaseous decomposition products in a trap
submerged in liquid nitrogen. To isolate solid thermolysis
products, the starting compound was kept at temperatures
fixed in the thermogram of the effects for 16–24 h until a
constant mass of the solid residue was reached.
An elemental composition of the Rh Se Cl complex
2
9
6
and products of its thermal transformations was made
with an ElvaX Light X-ray fluorescence spectrometer.
IR spectra of the compounds in the form of suspensions
in Nujol were recorded with Nicolet Magna-IR 750
spectrometer. Diffraction patterns were obtained on an
STOE STADI P diffractometer with a linear position-
precision detector.
There have been several reports that metal-modified
bifunctional catalysts also having redox properties are
promising for application in glycerol transformation
processes [13, 14]. It was noted that a specific feature of
bifunctional systems is the certain structure of an active
center, which is an active metal surrounded by ligands.
The acid properties of the surface of the samples were
determined by the method of temperature-programmed
desorption of ammonia (TPDA). Preliminarily, the
samples were heated in a flow of helium at 400°C for 1 h
and then cooled to 100°C and saturated with ammonia for
1 h. The thermal desorption of ammonia was examined
in the temperature range 100–700°C at a heating rate of
Previously, it has been found in a study of the catalytic
properties of rhodium chalcogen-halides in the course of
oxidative carbonylation of methane that the active centers
of catalysts of this kind have the form of metallic rhodium
–
1
1
0 deg min .
The catalysts were prepared by mechanical mixing
of rhodium selenochloride Rh Se Cl (10 wt %, which
2
9
6
3+
and Rh in the coordination environment of Cl and Se,
which can serve as catalytic centers [3].
corresponds to 1.8% Rh in terms of the metal) and high-
silica gallium-containing zeolite Ga/H–ZSM-5 (90 wt %).
The Si/Al ratio in Ga/H–ZSM-5 was 40/1, and the total
The specific features of the chemical composition and
structure of metal chalcogen-halides and products of their
thermal decomposition suggest that systems of this kind
may possess not only redox, but also acid properties,
thereby exhibiting bifunctionality. It is noteworthy that
the acid properties of rhodium chalcogen-halides and
products of their thermal decomposition have not been
studied previously.
concentration of acid centers, 2.341 mM NH /g.
3
The catalytic properties of Ga/H–ZSM-5 and a sample
containing rhodium selenochloride Rh Se Cl were
2
9
6
studied in a flow-through kinetic installation at various
experimental temperatures of 300, 320, and 340°C.A0.5-
3
cm weighed portion of the catalyst (1–2-mm fraction)
3
was placed between layers (0.5 cm each) of quartz with
grain size of 2–3 mm. Three samples were examined at
each temperature, with averaged data used in calculations.
Preliminarily, a sample was treated in a flow of nitrogen at
the experimental temperature, and, therefore, the final for-
The goal of our study was to examine the catalytic
properties of the RhSe /Ga/H–ZSM-5 system formed as
2
a result of a thermal treatment of a mechanical mixture
of Rh2Se9Cl6 and a gallium-containing zeolite Ga/H–
ZSM-5 in the course of glycerol dehydration to acrolein
in the gas phase.
mation of the catalyst and the decomposition of Rh Se Cl
2
9
6
to rhodium selenide RhSe occurred in the course of its
2
thermal treatment in the atmosphere of nitrogen.
EXPERIMENTAL
The reactor had the form of a quartz tube with inner
diameter of 10 mm. A water–glycerol mixture (10 vol %
glycerol, which corresponds to 12.6 wt %) was delivered
Rhodium selenochloride of composition Rh Se Cl
6
2
9
–1
was produced by the procedure dscribed in [15]. A at a rate of 0.033 mLmin into the mixer heated to 200°C,
–1
thermographic study of rhodium selenochloride was
with nitrogen gas fed therein at a rate of 30 mL min . The
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CATALYTIC PROPERTIES OF RhSe /Ga/H-ZSM-5 SYSTEM
235
2
A
(a)
(b)
Fig. 1. Thermogram of Rh Se Cl decomposition.
2
9
6
content of glycerol and liquid reaction products (acrolein,
allyl alcohol, and acetaldehyde) was monitored with a
Khrom-5 chromatograph equipped with a flame-ionization
detector on a column packed with Carbopac (B). The gas-
eous products (CO, CO ) were analyzed on an LKhM-80
2
chromatograph with a heat-conductivity detector.
ν, cm–1
Fig. 2. IR spectra of (a) Rh Se Cl and (b) RhSe . (A)Absorption
2
9
6
2
RESULTS AND DISCUSSION
and (ν) wave number.
The structure of the starting rhodium selenochloride can
be represented as packing of structural units of Rh Se Cl
Se 42.97 at a composition calculated for RhSe (%): Rh
2
9
6
5
6.58 and Se 43.42.
composition. The metal atoms are in the deformed octahe-
dral environment [RhCl Se ] characteristic of Rh(III). Two
Thus, the thermal transformations of rhodium seleno-
3
3
chloride Rh Se Cl occur by the scheme
[
RhCl Se ] octahedral are connected at faces of selenium
2
9
6
3
3
atoms bound into an annular crown-like Se structure. The
9
μ -Se and μ -Rh fragments form a structure with a cubane-
3
3
like structure: D -trishomocubane [15, 16].
3
The IR spectrum of the decomposition product RhSe2
Fig. 2) is markedly different from that of the starting
When Rh Se Cl is heated to 160°C, evolution of
2
9
6
(
Se Cl vapor is observed. A dip of the endothermic ef-
2
2
rhodium selenochloride Rh Se Cl (an interpretation of
fect is observed in the thermogram (Fig. 1) at around
20°C and corresponds to the decomposition of rhodium
2
9
6
the latter was reported in [15]), which points to profound
changes in the molecular structure. The doublet at 318
3
selenochloride with sublimation of selenium, evolution
of Se Cl vapor, and its condensation on cold parts of
–1
and 311 cm corresponds to bond vibrations ν(Rh–Se)
2
2
the reactor. The black powder obtained as a result of the
thermal treatment has the following experimentally found
composition (%): Rh 40.20, Se 59.80 at a composition
with somewhat lowered frequency. The broad absorption
band peaked at 270 cm is associated with the vibrations
ν(Se–Se).
–1
calculated for RhSe (%): Rh 39.345 and Se 60.55. This
It should be noted that RhSe , product formed in the
2
2
compound is rather thermally stable, with an endother-
mic effect observed only at 780°C. In this case, a gray
product with metallic shine is formed, which has an
experimentally found composition (%): Rh 57.03 and
thermal decomposition of Rh Se Cl at 320°C, has low
2
9
6
crystallinity, which hinders an unambiguous identification
of its structure. However, the positions and intensities of
broadened diffraction peaks (Fig. 3) indicate that the cubic
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 89 No. 2 2016

236
VOLKOV et al.
I, %
surface [19]. However, it seems to be impossible to obtain
the spectrum of thermal desorption of ammonia from
the starting Rh Se Cl compound because selenium and
2
9
6
Se Cl vapors are released as the temperature increases
2
2
from 160 to 320°C.
Figures 4a and 4b show spectra of thermal desorption
of ammonia from the products RhSe and RhSe formed
2
in the thermal decomposition of rhodium selenochloride.
Analysis of the spectra shows that the RhSe sample
2
contains acid centers of varied strength, with peaks of the
thermal desorption of ammonia at 150, 350, and 480°C.
The total concentration of the acid centers is 0.023 mmol
2
θ, deg
Fig. 3. X-ray diffraction pattern of RhSe , product of thermal
transformations of rhodium selenochloride Rh Se Cl at T =
20°C. (I) Relative intensity and (2θ) Bragg angle.
2
NH /g. The spectrum of thermal desorption of ammonia
3
2
9
6
from the RhSe sample has no pronounced peaks, and
the total concentration of acid centers sharply decreases
3
phase RhSe is present in this product [17]. The diffraction
to become only 0.008 mmol NH /g. Thus, rhodium is
2
3
pattern of the product formed in thermal transformation
of Rh Se Cl at 780°C shows that it contains the RhSe
hexagonal phase [18] of the NiAs structural type and
elementary rhodium.
reduced in the course of thermal transformation at 780°C
to the oxidation states +2 and 0, and the product being
formed loses its acid properties.
2
9
6
The results obtained in the study indicate that rho-
The presence of the selenium and chlorine ligands in
Rh Se Cl may indicate that acid centers are present on its
dium selenochloride mostly decomposes to RhSe in the
course of a preliminary treatment of a catalyst formed by
2
2
9
6
X, arb. units
(a)
(b)
X, arb. units
Catharometer
readings
Titration
Titration
Catharometer
readings
T, °C
T, °C
Fig. 4. Spectra of thermal desorption of ammonia for (a) RhSe and (b) RhSe. (X) Signal from catharometer and (T) temperature. Total
2
acidity (mmol NH /g): (a) 0.023 and (b) 0.008.
3
C, %
(a)
(b)
S, %
3
00
320
340 T, °C
T, °C
Fig. 5. (a) Conversion C of glycerol and (b) selectivity S for liquid reaction products (1) acrolein and (1a) acetaldehyde on the catalysts
1) Ga/H–ZSM-5 and (2) RhSe2/Ga/H–ZSM-5 vs. temperature T.
(
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 89 No. 2 2016

CATALYTIC PROPERTIES OF RhSe /Ga/H-ZSM-5 SYSTEM
237
2
Y, %
ride Rh Se Cl and a gallium-containing zeolite Ga/H–
2 9 6
ZSM-5 in a flow of nitrogen at the process temperatures.
It was shown that the starting rhodium selenochloride
Rh Se Cl is stable up to 160°V. Raising the temperature
to 320°C results in its decomposition to rhodium sel-
enide, the presence of which provides an increase in the
catalytic activity of Ga/H–ZSM-5 in the reaction under
study. It was found that the promotion of Ga/H–ZSM-5
2
1
1
0
5
0
5
2
9
6
with rhodium selenide RhSe raises the yield of the target
2
product acrolein from 13 to 19% at 340°C.
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3
00
320
340
T, °C
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2
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2
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