A copper catalyst on nonporous supports based on copper oxalate as a precursor

Article abstract of DOI:10.1134/S0036024410070083

A method for obtaining copper catalysts on nonporous supports by the thermal decomposition of copper oxalate in the absence of oxygen was suggested. The catalytic properties of the catalyst were studied in the model reaction of the conversion of propanol-2 into acetone and propylene. The influence of the content of copper in the catalyst, reaction temperature, and conditions of oxalate decomposition on the degree of alcohol conversion and ratio between reaction channels was studied. Electron photomicrographs were obtained, specific surface areas were measured, and X-ray powder patterns of the catalyst were recorded.

Full text of DOI:10.1134/S0036024410070083

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2010, Vol. 84, No. 7, pp. 1127–1131. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © Yu.N. Zhitnev, E.A. Tveritinova, F.M. Spiridonov, V.V. Lunin, 2010, published in Zhurnal Fizicheskoi Khimii, 2010, Vol. 84, No. 7, pp. 1249–1253.
CHEMICAL KINETICS
AND CATALYSIS
A Copper Catalyst on Nonporous Supports Based
on Copper Oxalate as a Precursor
Yu. N. Zhitnev, E. A. Tveritinova, F. M. Spiridonov, and V. V. Lunin
Faculty of Chemistry, Moscow State University, Moscow, Russia
eꢀmail: zhitnevyun@mail.ru
Received June 8, 2009
Abstract—A method for obtaining copper catalysts on nonporous supports by the thermal decomposition
of copper oxalate in the absence of oxygen was suggested. The catalytic properties of the catalyst were studꢀ
ied in the model reaction of the conversion of propanolꢀ2 into acetone and propylene. The influence of the
content of copper in the catalyst, reaction temperature, and conditions of oxalate decomposition on the
degree of alcohol conversion and ratio between reaction channels was studied. Electron photomicrographs
were obtained, specific surface areas were measured, and Xꢀray powder patterns of the catalyst were
recorded.
DOI: 10.1134/S0036024410070083
INTRODUCTION
rium conditions by explosive decomposition of copper
acetylacetonate in a vacuum was suggested. Copper
catalysts in the form of composite films were prepared
by lowꢀtemperature joint deposition of metal and
monomer vapors on a substrate with subsequent lowꢀ
temperature solidꢀstate polymerization [18]. In [19],
an effective copper catalyst was obtained by the depoꢀ
sition of atomic layers.
In recent years, the development of new technoloꢀ
gies has increased the demand for methods for the
preparation of transition metal nanosized particles,
including copper nanoparticles, which are used in
electronics and the production of composition materiꢀ
als. The use of copper nanoparticles in catalysis offers
promise.
According to stickler for nontraditional methods
for the preparation of copperꢀcontaining catalysts, the
traditional multistage scheme of synthesis, including
adsorption, drying, calcination, and reduction, subꢀ
stantially influences the structure of catalysts and
decreases catalytic activity, whereas the direct deposiꢀ
tion of metal particles on a support to a greater extent
contributes to the formation and conservation of
active catalytic centers.
Supports for copper catalysts are most often porous
compounds with developed surfaces, largely silica [5,
7, 9, 10, 12], alumina [11, 13, 14], and zinc oxide [6,
11] and also activated carbon [15, 16] and other carꢀ
bon forms [1–4].
Silica as a support for the synthesis of copper cataꢀ
lysts is used in quite different forms, including silica
gel [6, 7, 9, 10], aerosil [8, 21] and its varieties such as
cabꢀoꢀsil [21] and zeosil [5], and silica obtained by
burning rice husk [22]. Copper oxalate is extensively
used as a precursor of smallꢀsized copper particles [23,
24]. An analysis of the available data shows that the
conditions of oxalate decomposition (temperature,
gas atmosphere, rate of heating, etc.) can influence the
composition of decomposition products and size of
copper particles.
Copperꢀcontaining catalysts are extensively used in
industrial and laboratory syntheses. They catalyze
such important processes as hydrogenation and dehyꢀ
drogenation, hydration, oxidation, water gas converꢀ
sion, and neutralization of toxic gases. The methods
and conditions of catalyst preparation substantially
influence their catalytic activity. Traditional methods
for metal deposition on the surface of a support are
impregnation of a support with a solution of copper
salts followed by annealing and reduction [1–9], ion
exchange in the deposition of copper on the surface of
a support in the form of various complexes also folꢀ
lowed by annealing and reduction [8–10], and the
coprecipitation method, when copper catalysts are
obtained from insoluble copper salts (oxalates and carꢀ
bonates) and other metal salts (Zn, Al), which is folꢀ
lowed by washing, drying, and precipitate decomposiꢀ
tion [11, 12]. The method of chemical reduction is
also known. It includes preliminary surface sensitizaꢀ
tion with tin salts, the deposition of a platinum layer as
a catalyst of copper reduction on the surface, and subꢀ
sequent annealing [13–15].
Nontraditional methods of the preparation of copꢀ
perꢀcontaining catalysts include vaporꢀphase copper
deposition on activated carbon, when the precursor is
copper acetylacetonate [16]. In [17], a method for
In this work, we studied the catalytic behavior of
obtaining a copperꢀcarbon catalyst under nonequilibꢀ copper particles prepared by the thermal decomposiꢀ
1127

1128
ZHITNEV et al.
per oxalate deposited on the surface of supports was
dried and loaded into an ampule for evacuation
placed into an electric furnace with controlled temꢀ
perature. Evacuation was performed first at room
temperature to a pressure of 7 Pa. The selected
decomposition temperature was then established,
and evacuation continued to complete copper
oxalate decomposition (~2 Pa). Copper oxalate +
support mixtures had the compositions 0.5, 1.0, 5.0,
and 10% (recalculated to pure copper). The decomꢀ
position temperature was varied from 280 to 450°С
.
Copper oxalate deposited on surfaces and the prodꢀ
ucts of copper oxalate thermal decomposition were
fairly firmly held by surfaces. The microelectronic
photograph (Fig. 1) shows that the surface of lamp
glass was fairly uniformly covered by copper partiꢀ
cles.
100 μm
Fig. 1. Photomicrograph of the products of copper oxalate
decomposition on the surface of lamp glass particles.
Xꢀray diffraction patterns of catalyst samples were
obtained on a TROE diffractometer, the specific surꢀ
face area of supports and catalysts was determined by
the Brunauer–Emmett–Teller method from the lowꢀ
temperature adsorption of nitrogen on a GKhꢀ1 gasꢀ
ometer. Electron photomicrographs of catalyst samꢀ
ples were obtained using a JSMꢀ6390LA IEOL scanꢀ
ning electron microscope.
ТG, %
90
DSC
,
mW/mg
4
−
6.88%
3
2
1
70
50
264.8°C, 1.143 mW/mg
−
48.48%
The catalytic activity of copper catalysts was studꢀ
ied by the pulsed microcatalytic method [17] in the
dehydrogenation and dehydration of propanolꢀ2. The
temperature of the catalytic reaction was maintained
326.3°C, 44.31%
0
500
100
200
300
400
T, °C
constant to within 1 K and varied from 120 to 350°С
.
Catalytic transformation products were analyzed
chromatographically on a Chromꢀ5 chromatograph
with a flame ionization detector and a column with
PorapakꢀN. The thermogram of the decomposition of
copper oxalate was recorded on a NETZSCH STA 409
PC/PG thermoanalyzer.
Fig. 2. Thermogram of copper oxalate (in argon atmoꢀ
sphere).
tion of copper oxalate deposited on nonporous mateꢀ
rials, such as crystalline quartz, quartz glass, and usual
glass of luminescent lamps (the latter contains K, Na,
and Mg oxides in addition to silica). Such a method
for copper deposition allows the content of copper to
be varied over a wide range. The use of nonporous supꢀ
ports minimized the role played by supports in cataꢀ
lytic reactions and allowed the catalytic behavior of
copper itself to be studied in more detail. The catalytic
activity of the products synthesized was studied for the
example of the conversion of propanolꢀ2 into propyꢀ
lene and acetone.
RESULTS AND DISCUSSION
The catalysts were comparatively estimated
according to two parameters, the degree of initial alcoꢀ
hol conversion and reaction selectivity with respect to
the yield of acetone (the dehydrogenation channel).
The specific surface areas of the nonporous materials
used almost coincided and were of 0.15 0.03 m2/g,
which allowed them to be used as fairly inert diluents.
Estimates of the effectiveness of catalyst samples on
these supports under comparable conditions showed
the absence of support nature effects. All subsequent
studies were therefore performed using luminescent
lamp glass as a support.
EXPERIMENTAL
Support samples without preliminary chemical
treatment were prepared by grinding in a porcelain
mortar. Fractions of 0.5–1.0 mm particles were used
in experiments. Copper oxalate was deposited on the
surface of a nonporous support by pouring together
The thermogravimetric curve of copper oxalate is
shown in Fig. 2. This curve was used to select the temꢀ
equimolar copper sulfate and oxalic acid solutions. perature interval for decomposition (250–450°С).
The precipitate was centrifuged and washed with disꢀ Catalyst samples containing 1% copper were used to
tilled water to a negative reaction for sulfate ions. Copꢀ study the influence of the temperature of precursor
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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A COPPER CATALYST ON NONPOROUS SUPPORTS BASED
rel, %
1129
c
η
, %
100
90
80
70
60
50
40
30
20
10
0
100
80
60
40
20
0
4
3
2
'
2
2
1
1
1
'
3
'
3
120
160
200
240
280
320
360
T, °C
200
240
280
320
360
T, °C
Fig. 4. Reaction temperature dependence of the relative
contents of reagents ( in the reaction medium for (
Fig. 3. Temperature dependences of the degree of converꢀ
sion ( ) of propanolꢀ2 on catalysts containing ( ) 0.5,
) 1, ( ) 5, and ( ) 10% copper.
c
1–
rel)
η
1
3
) 1 and ( ) 5% catalysts; (
1
'–
3
'
1, 1') propanolꢀ2, (2, 2')
(2
3
4
acetone, and (3, 3') propylene.
(copper oxalate) decomposition (Tdecomp) on alcohol dence shows the occurrence of the transition from
conversion (
η
) at 250°С:
kinetically to diffusion controlled conditions, which
can be caused by the porous structure of copper crysꢀ
tallites.
T
decomp, °С
280
25
330
44
360
37
450
0
η
, %
A comparison of the fraction of the residual copꢀ
per oxalate mass from the thermogram (Fig. 2)
obtained in the argon atmosphere (44.31%) with that
theoretically calculated for copper oxalate on the
assumption that, in the absence of oxygen, oxalate
decomposes thermally to free copper and carbon
dioxide only (41.91%) shows that real oxalate
decomposition products contain copper oxides in
addition to free copper. The presence of oxides also
follows from the Xꢀray pattern of the products of
copper oxalate pyrolysis (Fig. 6).
Alcohol conversion is maximum for catalysts
obtained by the decomposition of copper oxalate at
330°С
.
Data on catalytic conversion of propanolꢀ2 with
catalyst samples containing 0.5, 1.0, 5.0, and 10.0%
copper under comparable conditions (Fig. 3) show
that conversion increases as the content of copper
grows. Conversion for the sample with 1% copper
reaches ~50% at 250°С (at a 100% selectivity for the
dehydrogenation channel).
Typical dependences of the yields of products and
the degree of alcohol conversion on reaction temperaꢀ
ture for catalysts containing 1 and 5% copper are
shown in Fig. 4. We see that catalytic alcohol converꢀ
sion is observed already at 170°С and reaches 50%
(75%) at 250°С with a high reaction selectivity with
respect to acetone (the dehydrogenation channel). No
propylene (the dehydration channel) was observed in
the reaction with the catalyst containing 1% copper
over the temperature range 210–330°С. Electron
photomicrographs show that copper is largely formed
as particles with a porous structure and size from
150 nm to several m (Fig. 5).
µ
The efficient activation energy calculated from
the temperature dependence of the degree of proꢀ
panolꢀ2 conversion for catalysts with different copꢀ
per contents was ~28 and 82 kJ/mol. The depenꢀ
2 μm
Fig. 5. Electron photomicrograph of a copper crystallite.
Vol. 84 No. 7 2010
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A

1130
100
ZHITNEV et al.
80
60
40
20
0
20
40
60
2θ, deg
Fig. 6. Xꢀray pattern of copper oxalate pyrolysis products obtained under dynamic vacuum conditions (residual pressure ~2 Pa).
4. J. Ma, N. M. Rodriguez, M. A. Vannice, and
We estimated the size of elementary crystallites
from the Xꢀray diffraction patterns. This gave ~40–
60 nm for copper and ~40 nm for copper oxide. It
was shown that copper oxalate thermal decomposiꢀ
tion products deposited on the surface of a nonpoꢀ
rous support exhibited fairly high catalytic activity
and selectivity (with respect to the dehydrogenation
channel) already at moderate temperatures (200–
250°С) in propanolꢀ2 dehydrogenation and dehyꢀ
dration. The reactivity of these catalysts depended
strongly on the conditions of copper oxalate thermal
decomposition.
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