Dehydrogenation of Propane with СО2 on Supported CrOx/SiO2 Catalysts

Article abstract of DOI:10.1134/S0036024418120403

Abstract: A systematic analysis was performed of the physicochemical properties of amorphous silicas (Acros, Degussa, KSKG) and CrO_x/SiO₂ catalysts prepared from them with 2, 3, 5, 7, and 10 wt % chromium. The supports and catalysts were characterized by BET, XRD, and UV–Vis diffuse reflectance spectroscopy. In the oxidative dehydrogenation of propane with carbon dioxide, the highest propylene selectivity (95%) was observed for the 5%?CrO_x/SiO₂ (Degussa) sample, and the highest propane conversion (53%) was reported on the 5%?CrO_x/SiO₂ (Acros) catalyst. The structure of chromium oxide particles on the support surface was studied by UV–Vis spectroscopy. The catalytic properties were correlated with the state of chromium.

Full text of DOI:10.1134/S0036024418120403

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2018, Vol. 92, No. 12, pp. 2403–2407. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © M.A. Tedeeva, A.L. Kustov, P.V. Pribytkov, A.V. Leonov, S.F. Dunaev, 2018, published in Zhurnal Fizicheskoi Khimii, 2018, Vol. 92, No. 12, pp. 1879–
1884.
PHYSICAL CHEMISTRY OF HYBRID NANOMATERIALS
AND MULTICOMPONENT SYSTEMS
Dehydrogenation of Propane with СО2
on Supported CrOx/SiO2 Catalysts
M. A. Tedeevaa, A. L. Kustova,b, P. V. Pribytkova,*, A. V. Leonova, and S. F. Dunaeva
aDepartment of Chemistry, Moscow State University, Moscow, 119991 Russia
bZelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
*е-mail: pribytkov@general.chem.msu.ru
Received May 21, 2018
Abstract—A systematic analysis was performed of the physicochemical properties of amorphous silicas
(Acros, Degussa, KSKG) and CrOx/SiO2 catalysts prepared from them with 2, 3, 5, 7, and 10 wt % chro-
mium. The supports and catalysts were characterized by BET, XRD, and UV–Vis diffuse reflectance spec-
troscopy. In the oxidative dehydrogenation of propane with carbon dioxide, the highest propylene selectivity
(95%) was observed for the 5% CrOx/SiO2 (Degussa) sample, and the highest propane conversion (53%) was
reported on the 5% CrOx/SiO2 (Acros) catalyst. The structure of chromium oxide particles on the support
surface was studied by UV–Vis spectroscopy. The catalytic properties were correlated with the state of chro-
mium.
Keywords: chromium oxides, silica gel, oxidative dehydrogenation of propane, propylene, carbon dioxide,
XRD, UV diffuse reflectance spectroscopy, specific surface area
DOI: 10.1134/S0036024418120403
The search for alternative sources of chemical raw lications that compared these catalysts on supports of
materials and new methods for the synthesis of valu- the same chemical nature but with different physical
able chemical compounds is currently one of the pri- properties. In [9], chromium oxide catalysts supported
on ordinary amorphous silicas SiO2 (SBET = 477 m2/g)
and SiO2 (SBET = 261 m2/g) were compared with those
on mesoporous silicas SBA-1 (SBET = 1181 m2/g) and
orities in scientific research. One such compound is
propylene, which serves as the starting substance for
the preparation of a number of valuable monomers
and polymers: acrolein, acrylic acid, acrylonitrile,
propylene oxide, cumene, polypropylene, and polyac-
rylonitrile. The conventional methods for the indus-
trial production of propylene are the thermal and cat-
alytic cracking of oil and natural gas and liquid-phase
catalytic cracking of gasolines. The oxidative dehydro-
genation of propane in the presence of oxygen has
recently been recognized as a promising method for
the production of propylene. The problem with this
method is coke deposition on the catalyst surface and
decreased activity after prolonged work.
SBA-15 (SBET = 750 m2/g). It was shown that the rate
of propylene formation increased almost proportion-
ally to the concentration of chromium in the form of
Cr6+, which was higher on catalysts with a larger spe-
cific surface area.
The aim of the present study was the synthesis of
the catalysts of propane dehydrogenation in the pres-
ence of CO2, containing chromium oxide deposited on
amorphous SiO2 of different grades (Acros, Degussa,
KSKG), and a comparative study of their physico-
In the dehydrogenation of propane on MOx/sup- chemical and catalytic properties.
port catalysts (M = Cr, Ga, Fe, In, W, V, and other
metals; support = SiO2, Al2O3, ZrO2, TiO2, ZSM-5,
EXPERIMENTAL
MCM-41, SBA-15, etc.), carbon dioxide was often
Synthesis of the Samples
used as the oxidizing agent [1–6]. At the same time,
the involvement of CO2 in propane dehydrogenation is
a solution to another important problem: greenhouse
gas utilization. When carbon dioxide was used, the
catalysts containing chromium, gallium, and tungsten
showed the best catalytic properties [1–6].
The catalysts were prepared by incipient wetness
impregnation from aqueous solutions of chromium
nitrate. As supports, granular silica gels SiO2 (Acros,
Degussa, and KSKG) were used. The previously
ground silica gel (0.25–0.5 mm fraction) was dried in
Chromium oxide catalysts on different supports air at 120°C for 6 h. The active component was then
were compared in [1, 2, 7, 8], but there were few pub- deposited by incipient wetness impregnation of silica
2403

2404
TEDEEVA et al.
Table 1. Specific surface areas of the CrOx/SiO2 catalysts
for KSKG, respectively. The on-line analysis of the
reaction products was performed using a Chromatec
Crystal 5000 gas chromatograph with a thermal con-
ductivity detector and an Мss316 column (3 m ×
2 mm, Hayesep Q 80/100 mesh). The column tem-
perature was varied according to the following pro-
gram: 40°С for 1.5 min, and then the temperature was
raised to 100°С at a rate of 15°С/min. The product
contents were calculated by the absolute calibration
method.
and the starting SiO2
Ssp, m2/g
Sample
SiO2 (Degussa)
5% Сr/SiO2 (Degussa)
SiO2 (KSKG)
5% Cr/SiO2 (KSKG)
SiO2 (Acros)
3% Cr/SiO2 (Acros)
3% Cr/SiO2 (Acros) after catalysis
5% Cr/SiO2 (Acros)
7% Cr/SiO2 (Acros)
10% Cr/SiO2 (Acros)
20% Cr/SiO2 (Acros)
156
155
231
231
532
520
511
460
433
414
410
RESULTS AND DISCUSSION
Physicochemical Properties of Supports and Catalysts
Table 1 presents the specific surface areas of the
starting SiO2 of different grades (Acros, Degussa, and
KSKG) and the catalysis prepared from it.
According to Table 1, the specific surface areas did
not change after the deposition of 5 wt % chromium
on SiO2 (Degussa, KSKG). For SiO2 (Acros), whose
starting surface area is two or three times larger than
that of SiO2 (Degussa, KSKG), the surface area
decreased slightly (by ~2%) when 3% chromium was
deposited and by ~13% when chromium load was 5%.
When the chromium concentration on the support
increased further, the specific surface area decreased
more slowly; the deposition of more than 10 wt %
chromium did not lead to a decrease in the surface
area. This is apparently due to the blocking of the nar-
rowest pores by chromium particles for SiO2 (Acros).
A similar decrease in the specific surface area during
the chromium deposition on SiO2 (KSKG) was also
gel with aqueous Cr(NO3)3 · 9H2O (Acros). The dried
samples were calcinated in air at 500°C for 4 h. The
resulting catalysts contained 2, 3, 5, 7, and 10 wt %
chromium.
Methods
The texture characteristics of the catalysts were
determined from the nitrogen adsorption isotherms
measured at 77 K. The specific surface area was calcu-
lated by the BET method; the pore size distribution
was determined from the desorption branch of the iso-
therm by the Barrett–Joyner–Halenda (BJH)
method.
The X-ray diffraction (XRD) analysis was per-
formed on a DRON-3 diffractometer using CuKα
radiation (35 kV, 25 mA, scanning at 2θ = 10°–60° at
a step of 0.1°).
The UV–Vis spectra were recorded on a Shimadzu
UV-3600 Plus spectrophotometer equipped with
ISR-603 integrating sphere. The spectra were
recorded in the wavelength range 185–850 nm at room
temperature using BaSO4 as a standard and diluent of
the samples. The resulting spectra were treated with
the UVProbe program.
observed in [10], where Ssp = 346 m2/g for the initial
SiO2 (KSKG); when 5% Cr was deposited, Ssp
decreased to 307 m2/g, i.e., by ~11%. Note that for 3%
Cr/SiO2 (Acros), the surface area slightly decreased
after the catalytic propane dehydrogenation in the
presence of carbon dioxide due to the insignificant
coke deposition on its surface.
The crystalline structure of the synthesized
Cr(5%)Ox/SiO2 catalysts (Acros, Degussa, KSKG)
was studied by XRD. The diffraction pattern of the
Cr(5%)Ox/SiO2 (Degussa) sample shows the peaks
belonging to Cr2O3; for the Cr(5%)Ox/SiO2 (KSCG)
sample, there are peaks belonging to Cr2O3, which are
much less intense; for the Cr(5%)Ox/SiO2 (Acros)
sample, these peaks are not observed (Fig. 1).
Catalytic Tests
Dehydrogenation of propane into propylene in the
presence of СО2 was studied at atmospheric pressure
in a flow type steel reactor with an inner diameter of
4 mm. The С3Н8 + СО2 gas mixture was fed in the
reactor in a ratio of 1 : 2 v/v; the total flow rate of the
gas mixture was 30 mL/min. The catalyst load was 1 g.
The catalyst volume was 0.9 cm3 for SiO2 (Acros),
Based on these data, we can conclude that chro-
mium is mainly in the form of Cr2O3 in the SiO2
(Degussa) sample, some chromium is present as
Cr2O3 in CrOx/SiO2 (KSKG), and is not observed at
all in the form of Cr2O3 in SiO2 (Acros).
Additional information that confirms the structure
of chromium oxide particles on the support surface
was obtained by measuring the UV–Vis diffuse reflec-
0.48 cm3 for SiO2 (Degussa), and 0.45 cm3 for SiO2
(KSKG). The gas flow space velocity was 2000 h–1 for
the Acros sample, 3750 h–1 for Degussa, and 4000 h–1 tance spectra. Figure 2 shows these UV–Vis spectra of
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DEHYDROGENATION OF PROPANE
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Cr(VI)
(а)
Cr(III)
3a
3b
2a
2b
10 15 20 25 30 35 40 45 50 55 60
1a
1b
270
360
600
455
(b)
200
300
400
500
600
700
λ, nm
Fig. 2. UV–Vis diffuse reflectance spectra (а) before and
(b) after catalysis of the samples: (1) Cr(5%)O /SiO
x
2
(KSKG), (2) Cr(5%)O /SiO
(Acros), and (3)
x
2
Cr(5%)O /SiO (Degussa); А is absorption.
x
2
Cr(VI) and Cr(III) forms coexist in the samples. In
the 5% Cr/SiO2 (Degussa) sample, however, Cr(III)
predominates; in 5% Cr/SiO2 (Acros), chromium is
mainly in the form of Cr(VI). After catalysis, the con-
centration of chromium in the form of Cr(VI) and
Cr(III) decreased in all the samples, especially in
5% Cr/SiO2 (Acros); this may be due to coke forma-
tion on the surface of chromium oxide particles. Fig-
ure 3 shows the UV–Vis spectra of the fresh
CrOx/SiO2 (Acros) catalysts with 2–10 wt % chro-
mium.
10 15 20 25 30 35 40 45 50 55 60
(c)
Even with 2% Cr in the catalyst, chromium is
mainly in the form of Cr(VI), which does not change
when the chromium content increases to 10%. This
tendency is consistent with the data of [9], where the
=
477 m2/g) and 2–
10 15 20 25 30 35 40 45 50 55 60
2–7% Сr/SiO2-а (SBET
2θ, deg
7% Сr/SiO2-р (SBET = 261 m2/g) samples were stud-
ied.
Fig. 1. X-ray diffraction patterns of the samples: (а)
Cr(5%)O /SiO (Degussa), (b) Cr(5%)O /SiO (KSKG),
x
2
x
2
and (c) Cr(5%)O /SiO (Acros); for comparison, the peak
x
2
Oxidative Dehydrogenation of Propane on the
CrOx/SiO2 Catalyst in the Presence of СО2
positions of Cr O are given (JCPDS 04-312).
2
3
To compare the support effects on the catalyst
activity, the CrОх/SiO2 catalysts were prepared using
SiO2 Acros, Degussa, and KSKG.
the Cr(5%)Ox/SiO2 (Acros, Degussa, KSKG) cata-
lysts measured before and after the catalytic tests.
Before catalysis, all the three samples showed four
bands in the range 200–700 nm. The UV bands at 270
and 360 nm relate to the O2– → Cr6+ charge transfer
for chromium ions in the tetrahedral environment
[11–16]. The bands at 455 and 600 nm correspond to
the octahedral coordination of Cr3+ in Cr2O3 or CrOx
Propane is dehydrogenated in the presence of СО2
by the reaction
С3Н8 + СО2 → С3Н6 + СО + Н2О.
In addition to propylene, by-products such as
methane, ethane, and ethylene formed. The results of
clusters [11–16]. The UV–Vis spectra indicate that the the catalytic tests are shown in Figs. 4 and 5.
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2406
TEDEEVA et al.
σ, %
60
Cr(VI)
360
270
Cr(III)
455
50
40
600
30
d
c
20
10
0
b
1
2
a
3
200
300
400
500
600
700
λ, nm
550
600
650
700
T, °С
Fig. 3. UV–Vis diffuse reflectance spectra of fresh sam-
ples: (a) Cr(2%)O /SiO (Acros), (b) Cr(5%)O /SiO
2
x
2
x
Fig. 4. Temperature dependences of propane conversion
on the catalysts: (1) Cr(5%)O /SiO (Acros), (2)
(Acros), (c) Cr(7%)O /SiO
(Acros), and (d)
x
2
Cr(10%)O /SiO (Acros); А is absorption.
x
2
x
2
Cr(5%)O /SiO (KSKG), and (3) Cr(5%)O /SiO
x
2
x
2
(Degussa); σ is conversion.
δ, %
100
σ, %
70
80
60
40
20
0
2
1
60
50
40
30
20
10
0
1
2
3
3
550
600
650
700
T, °С
550
600
650
700
T, °С
Fig. 5. Temperature dependences of propylene selectivity
(δ) on the catalysts: (1) Cr(5%)O /SiO (Acros), (2)
x
2
Fig. 6. Temperature dependences of propane conversion
(σ) on the catalysts: (1) Cr(3%)O /SiO (Acros), (2)
Cr(5%)O /SiO (KSKG), and (3) Cr(5%)O /SiO
x
2
x
2
x
2
(Degussa).
Cr(5%)O /SiO (Acros), and (3) Cr(7%)O /SiO (Acros).
x 2 x 2
propane conversion and propylene selectivity are
shown in Figs. 6 and 7.
The highest conversion of propane (67%) was
observed for the catalyst with 3 wt % Cr at T = 700°C.
The highest propylene selectivity (83%) was found for
the catalyst with 7 wt % Cr at T = 600°C.
The highest propylene selectivity of 95% was
observed for 5% Cr/SiO2 (Degussa) at T = 600°C; the
highest propane conversion of 53% and propylene
yield of 34% were determined for 5% Cr/SiO2 (Acros)
at T = 700°C.
For further studies, the (3, 5, 7%)Cr/SiO2 (Acros)
Thus, the oxidative dehydrogenation of propane in
catalyst samples were prepared. The dependences of the presence of carbon dioxide on chromium oxide
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DEHYDROGENATION OF PROPANE
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lysts and supports. This study was financially sup-
ported by the Russian scientific Foundation (project
no. 14-50-00126).
δ, %
100
1
2
80
60
40
20
0
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Translated by L. Smolina
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 92 No. 12 2018