Catalytic activity of electrodeposited copper-containing compounds in conversion of carbon monoxide by steam

Article abstract of DOI:10.1134/S1070427211110048

Possibility of using an ultradisperse copper-containing powder produced by the electrolytic method as an efficient catalyst for conversion of carbon monoxide by steam was studied.

Full text of DOI:10.1134/S1070427211110048

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 11, pp. 1860−1865. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.V. Tesakova, V.I. Parfenyuk, A.A. Il’in, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 11, pp. 1774−1779.
PHYSICOCHEMICAL STUDIES
OF SYSTEMS AND PROCESSES
Catalytic Activity of Electrodeposited Copper-containing
Compounds in Conversion of Carbon Monoxide by Steam
a
a,b
b
M. V. Tesakova , V. I. Parfenyuk , and A. A. Il’in
a
Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
b
Ivanovo State University of Chemical Engineering, Ivanovo, Russia
Received October 11, 2010
Abstract—Possibility of using an ultradisperse copper-containing powder produced by the electrolytic method
as an efficient catalyst for conversion of carbon monoxide by steam was studied.
DOI: 10.1134/S1070427211110048
The reaction of conversion of CO by steam, used
in the technological cycle of hydrogen production in
manufacture of ammonia is carried out at medium
and low temperatures. The medium-temperature stage
is commonly performed with a mixture of iron and
chromium oxides as a catalyst, and the low-temperature
stage, with copper-containing catalysts including CuO,
ZnO, and Al O , prepared by the conventional methods
compared with uncatalyzed reactions; use of a catalyst
markedly raises the yield of the target product of the
reaction.
The goal of our study was to examine the catalytic
activity and operation selectivity of a nanosize copper-
containing powder produced by the electrochemical
reduction method in the low-temperature conversion
of carbon monoxide by steam in comparison with the
activity of catalysts synthesized by other methods.
2
3
of coprecipitation, mixing, decomposition of metal salts,
and mechanochemical synthesis [1].
Inthisstudy,wesuggesttoobtainacatalyticallyactive
copper-containing powder by using an electrochemical
method that is rather simple and practicable. The
method can yield a product with a prescribed particle
size and chemical composition by varying electrolysis
parameters and the concentration of an aqueous-organic
solvent [2].
EXPERIMENTAL
The nanosize copper-containing powder was
produced by electrolysis of a copper sulfate solution
in a water–isopropanol mixture [3, 4] in which
the working concentrations of copper sulfate and
isopropanol and the initial current density were found
by analysis of polarization curves. The electrolysis was
performed at the limiting current density at a constant
voltage maintained across the electrodes, with soluble
electrolytic-copper anodes a cylindrical steel anode.
The soluble anodes enable electrolysis during a rather
long time without adjustment of the electrolyte or any
adverse changes in the composition and particle size of
the powder obtained. The resulting precipitate was many
times washed with twice-distilled water to a constant
electrical conductivity of washing water and dried first
in air at room temperature and then in a drying box at
Introduction of an organic solvent in an aqueous
electrolyte solution makes it possible to obtain copper-
containing particles less than 100 nm in size and to
vary the chemical composition of the powder (raise the
content of copper oxides in the powder, compared with
that produced from an aqueous solution). The presence
of copper oxides in the powder provides its catalytic
activity in conversion of CO in the low-temperature
stage. The catalysis on small particles plays an extremely
important part in industrial chemistry. Catalyzed
reactions commonly occur at a lower temperature,
1
860

CATALYTIC ACTIVITY OF ELECTRODEPOSITED COPPER-CONTAINING COMPOUNDS
a)
(b)
1861
(
2
0 μm
150 nm
Fig. 1. Electron micrographs of powders. (a) Without addition of an organic solvent, (b) with addition of isopropyl alcohol; the same
for Fig. 2.
8
0°C for 20–30 min until a powder with a constant mass
was formed.
The specific surface area of the catalysts obtained
version of carbon monoxide by steam were determined
on a flow-through installation in the temperature range
1
80–240°C [8]. The tests were made in a gaseous reac-
2
tion mixture of composition (vol %): H 55, CO 12, CO2
was determined by the BET technique from thermal
desorption of argon for a helium–argon mixture. The
shape and size of powder particles was determined by
transmission electron microscopy (TEM); micrographs
were obtained on an EMV-100L electron microscope
with a resolution of 0.3 nm at an accelerating voltage of
9
, and He 24, at a steam : gas ratio of 0.7. A weighed
portion of the catalyst was 0.5 g. The volumetric rate of
–1
gaseous mixture delivery to the catalyst was 5000 h .
The catalyst was placed in a quartz glass reactor and
heated in the reaction mixture, with temperature raised
–
1
at a rate of 4 deg min . The compositions of the starting
gaseous reaction mixture and the final gaseous reaction
mixture after the reactor were determined chromato-
graphically on a Tsvet-100 gas chromatograph.
1
00 keV (Fig. 1).
The chemical composition of the powders was
analyzed by electron diffraction and thermogravimetric
methods [5] and by X-ray phase analysis. The
diffraction pattern formed by accelerated electrons was
obtained on transmission electron microscope in the
microdiffraction mode from areas up to 2 μm in size.
To determine the chemical composition of the samples
under study, we measured ring diameters, calculated
the corresponding interplanar spacings, and compared
the results with reference data [6]. Among the probable
phases, we found those in whose lattice the dhkl sequence
we found is observed. The measurement accuracy of the
electron diffraction patterns is about 0.1% relative to the
measured value of interplanar spacings.
The catalytic activity of the samples was evaluated
by the conversion of CO in the reaction of conversion of
carbon monoxide by steam and by the output capacity
of the catalyst (for CO). The reaction of CO conversion
is satisfactorily described by a kinetic equation of
a first-order reaction [9]. To calculate the throughput P
–
1 –1
(
ml g s ) of the catalyst, we used the equation derived
by transforming the equation for the rate constant of the
first-order reaction, adapted to the process under study,
in which CO is converted by steam [10]:
1
The X-ray diffraction analysis of the powders
was made on a DRON-3M diffractometer with
monochromatized CuK radiation (λ = 0.154 nm) at
angles in the range 20–70°. Diffraction spectra were
obtained at a measurement step of 0.01° and scanning
rate of 2 deg min on the scale. The phase composition
was found by comparing the interplanar spacings
obtained from diffraction patterns and the corresponding
diffraction peak intensities with values from the PDF
X-ray database [7].
ln ——— (1 + n)R
(1 + X)
P = ————————— ,
0gcat
6
–1
where R is the flow rate of dry gas (ml min ); X, CO
–
1
conversion; g , catalyst mass (g); and n, steam-to-gas
cat
ratio.
To find the amount of by-products formed in the
conversion reaction and determine the operation
selectivity of the catalyst, we subjected the condensate
to a chromatographic analysis on a Kristall Lyuks
chromatograph.
The catalytic properties of the ultradisperse copper-
containing powders we obtained in the reaction of con-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 11 2011

1862
TESAKOVA et al.
The results of our analysis of the granulometric
composition of the powders obtained (Figs. 2a and
b) suggest that key role is played in the formation of
ultradisperse particles by the organic solvent and, in
particular, isopropyl alcohol. Introduction of isopropyl
alcohol into the electrolyte makes it possible to produce
by the electrochemical method a copper-containing
powder with a particle size smaller than 100 nm and a
sufficiently narrow particle size distribution. As follows
from Fig. 2b, only a small number of particles (about 10–
perse powder particle can be characterized as a druse of
polycrystalline copper with oxidized surface. The X-ray
diffraction method is less sensitive than the electron dif-
fraction analysis. The sensitivity threshold of this meth-
od is 2–10 wt %. Presumably, the amount of copper(II)
2
A, %
(a)
1
5% of the total amount of particles) are more than 100
nm in size, with the main mass of powder particles (85–
0%) having size smaller than 100 nm. The powder with
100-nm particles, produced from an aqueous-organic
9
<
solution, was subjected to electron and X-ray diffraction
analyses. The results of the electron diffraction analysis
demonstrated that the powders contain metallic copper
–
–
–
–
–
–
–
and oxides Cu O and CuO (Table 1).
2
An analysis of the X-ray diffraction pattern in Fig. 3
A, %
(b)
confirmed that the powders contain Cu and Cu O. Apos-
2
sible reason for the absence of peaks corresponding to
copper(II) oxide found by electron diffraction analysis
in the X-ray diffraction patterns is that copper(II) oxide
covers copper-containing particles in the form of a thin
layer and its amount is insufficient for being detected
by X-ray phase analysis. The structure of an ultradis-
Table 1. Radii of rings in electron diffraction patterns,
calculated interplanar spacings, and reference data for Cu,
Cu O, and CuO
–39
–99
–149
–349
–500
2
Reference data
Fig. 2. Histograms of the particle size distribution of the
powders obtained. (A) Content.
R, mm
d , Å
Compound
Cu
hkl
d , Å
I, %
100
53
33
9
hkl
17.54
20.00
33.15
34.75
12.00
14.87
24.00
28.00
14.50
19.32
21.00
23.00
37.00
2.06
1.81
1.09
1.04
3.01
2.43
1.51
1.29
2.49
1.87
1.72
1.57
0.98
2.08
1.81
1.09
1.04
3.00
2.45
1.51
1.28
2.51
1.85
1.70
1.57
0.98
3
100
44
31
100
20
8
Cu O
2
2
θ, deg
CuO
8
Fig. 3. X-ray diffraction pattern of the ultradisperse copper-
containing powder. (2θ) Bragg angle.
3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 11 2011

CATALYTIC ACTIVITY OF ELECTRODEPOSITED COPPER-CONTAINING COMPOUNDS
1863
oxide does not exceed this value and, therefore, cannot
be determined in this way. The techniques we used mu-
tually supplement each other and enable the most objec-
tive and fullest estimate of the qualitative composition
of the powders obtained. The powders contain copper
The selectivity of the catalyst is also highly impor-
tant for the process of CO conversion because the steam
condensate can be repeatedly used in manufacture of
ammonia [12]. The content of accumulated organic ad-
–1
mixtures in the condensate should not exceed 15 mg l .
Performing the technological cycle with recycling of the
condensate saves raw materials and energy resources,
diminishes the expenditure for preliminary water treat-
ment and desalination, makes shorter the blowing stage,
and lowers the loss of heat.
and copper oxides Cuo and Cu O, with the amount of
2
copper(II) oxide not exceeding 10 wt %.
Copper-containing catalysts are widely used in
production of ammonia, methanol, and caprolactam. The
catalytic conversion of copper monoxide with steam,
catalyzed by copper-containing catalysts, is a constituent
of the industrial process for hydrogen production from
natural gas. The conversion of carbon monoxide by
steam occurs in accordance with the reaction equation
A chromatographic analysis of the reaction process
demonstrated that, with the copper-containing powder
produced by the electrochemical method used as
a catalyst, the condensate contains no methanol,
acetone, or butanol; the contents of acetaldehyde and
2-propanol are, respectively, seven and six times lower
than those with the industrial sample (Table 3). The
СО + Н О ⇄ СО + Н .
2
2
2
–
1
The copper-containing powder exhibits a high
catalytic activity in the reaction of CO conversion at
a temperature of 200°C, which is due to its large specific
surface area. With this catalyst, the conversion of CO in
the reaction is 87% [11].
total content of impurities is 4.04 mg l . The presence
of acetaldehyde, methyl acetate, ethyl acetate, ethanol,
and 1- and 2-propanol in the condensate indicates that
there occur side processes in which carbon monoxide is
hydrogenated:
ItcanbeseeninTable2thatcopper-containingpowders
produced by electrochemical precipitation surpass
at low temperatures all catalysts obtained using other
methods. At 180°C, the throughput of electrochemically
precipitated copper-containing powders is more than two
times that of the industrial KCO catalyst. At 220°C, the
difference between catalysts of different types becomes
less pronounced. At his temperature only the catalysts
produced by the mechanochemical method is 6% better.
In the range of optimal temperatures (200°C for the
electrochemically precipitated powder and 240°C for
the industrial catalyst), the catalyst we obtained has the
best characteristics.
2
СО + 4Н = С Н ОН + Н О,
2 2 5 2
2
СО + 3Н = СН СОН + Н О,
2 3 2
3
СО + 6Н = С Н ОН + 2Н О,
2 3 7 2
3
СО + 4Н = СН СООСН + Н О,
2 3 3 2
4СО + 6Н = С Н СООСН + 2Н О.
2
2
5
3
2
The electrolytically produced copper-containing
powder has a high selectivity and surpasses in this
regard the industrial sample, which is probably due to
Table 2. Activities of the copper-containing powder and catalysts produced by other methods in conversion of CO by steam at
various temperatures
Catalyst throughput, ml g–1 s–1, at indicated temperature, °C
Catalyst preparation method
1
80
200
220
240
12.4
13.2
13.7
11.7
Precipitation from ammonia carbonate solutions
Industrial KCO sample
4.9
5.1
–
8.7
–
9.6
Mechanochemical synthesis from salts
Electrochemical precipitation
7.5
–
14.2
11.3
10.5
13.5
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 11 2011

1864
TESAKOVA et al.
Table 3. Yield of by-products in the test conversion of carbon monoxide by steam
Content in the condensate, mg l–1
Σ,
mg l
Catalyst
–
1
methyl ethyl
acetate acetate
acetaldehyde
methanol 2-propanol 1-propanol ethanol acetone butanol
Copper-containing
powder
0
.76
.52
2.09
–
0.17
–
–
0.77
4.85
0.07
–
0.18
–
–
–
4.04
Industrial KCO
sample
5
0.48
0.48
0.28
11.77
the decrease in the reaction temperature to 200°C.
Н О + K ⇄ КН О;
2
2
The high catalytic activity of the catalyst under study
is due to the size-related characteristics of the powder
and its chemical composition. The particle size smaller
than 100 nm and the considerable amount of cuprous ox-
ide in the powder predetermine its large specific surface
area (51 m g ) and presence of a large number of active
centers. Despite the wide application of copper-contain-
ing catalysts, the nature of their active centers remains
a matter of discussion [13]. The published information
about active forms of copper in the reaction of CO con-
version is rather contradictory: in [14], it is assumed that
metallic copper in finely dispersed state is assumed to be
active; according to other data, the active centers include
surface reaction
KСО + KН О ⇄ KСО + KН ;
2
2
2
and desorption of reaction products
2
–1
KСО ⇄ K + СО ,
2
2
KН ⇄ K + Н .
2
2
CONCLUSIONS
An electrolytically produced copper-containing
powder used as a catalyst for conversion of carbon
monoxidebysteammakeslowerthereactiontemperature
and diminishes the yield of by-products, compared with
catalysts obtained using other methods.
+
2+
Cu ions [15, 16] or Cu aggregates formed as a surface
solid solution on ZnO on highly dispersed CuO and on
the surface of metallic copper [13, 17].
Probably, copper in the oxidation state +1, which
has high electron affinity, is responsible for the catalytic
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