Oxidation of CO on Mn-containing catalysts prepared by pyrolysis of metal β-diketonates on synthetic ceramic foam

Article abstract of DOI:10.1007/s11176-005-0473-x

New catalytic systems for oxidation of CO to CO₂ were developed. These systems are based on composite Mn, Mn-Ni, and Mn-Cu coatings and are prepared by gas-phase thermolysis of metal β-diketonates on a ceramic foam support. The relative activity of the new catalytic systems was examined. The kinetic and activation parameters of the oxidation of CO on these catalysts were determined. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11176-005-0473-x

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Russian Journal of General Chemistry, Vol. 75, No. 10, 2005, pp. 1599 1602. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 10, 2005,
pp. 1676 1680.
Original Russian Text Copyright
2005 by Tsyganova, Didenkulova, Shekunova, Aleksandrov.
Oxidation of CO on Mn-Containing Catalysts Prepared
by Pyrolysis of Metal -Diketonates on Synthetic Ceramic Foam
E. I. Tsyganova, I. I. Didenkulova, V. M. Shekunova, and Yu. A. Aleksandrov
Research Institute of Chemistry, Lobachevsky Nizhni Novgorod State University, Nizhni Novgorod, Russia
Received September 15, 2004
Abstract New catalytic systems for oxidation of CO to CO2 were developed. These systems are based on
composite Mn, Mn Ni, and Mn Cu coatings and are prepared by gas-phase thermolysis of metal -diketonates
on a ceramic foam support. The relative activity of the new catalytic systems was examined. The kinetic and
activation parameters of the oxidation of CO on these catalysts were determined.
Catalytic oxidation of CO to CO2 is an efficient
way of rendering harmless gaseous exhausts from
automobile transport and industrial enterprises. It was
shown previously [1 4] that Mn-containing catalysts
are active in conjugate oxidation reduction of a mix-
ture of nitrogen oxides and CO. Therefore, proceeding
with systematic studies of catalytic systems prepared
by vacuum thermolysis of transition metal -diketo-
nates on synthetic ceramic foam [5 8], we studied
the catalytic activity of Mn, Mn Ni-, and Mn Cu-
containing catalysts in oxidation of CO to CO2.
tions, we deposited solid metal-containing products by
gas-phase vacuum thermolysis of metal -diketonates:
Mn and Cu acetylacetonates M(acac)2 and Ni hexa-
fluoroacetylacetonate Ni(hfacac)2. The composition of
the catalysts and the conditions of their preparation
are given in Table 1.
Thermolysis of metal -diketonates yields compo-
site coatings containing metals, their oxides, carbides,
and free carbon; the coating composition depends on
the deposition parameters [10]. Vacuum pyrolysis of
Cu(acac)2 at 300 400 C yields metallic Cu in a mix-
ture with a nonstoichiometric oxide. Pyrolysis of
Ni(hfacac)2 yields NiO containing up to 1 wt % C.
Pyrolysis of Mn(acac)2 yields highly pure ultradis-
persed (200 500 ) manganese oxides [11].
The catalyst supports were prepared from KhIPEK
synthetic ceramic foam (SCF) [TU (Technical Specif-
ications) 5759-010-10657190 97] [9].
Onto synthetic ceramic foam of various composi-
Table 1. Composition of catalysts for oxidation of CO to CO2 and conditions of their preparation
Catalyst no.
Catalyst composition
Support Ib + 3% Mnc
Metal source
Deposition conditionsa Metal source content, wt %
1
2
Mn(acac)2
Mn(acac)2
Cu(acac)2
Mn(acac)2
Ni(hfacac)2
Mn(acac)2
Mn(acac)2
Cu(acac)2
Mn(acac)2
Ni(acac)2
400 C, 1 h
350 C, 1 h
12.1
12.1
Support I + 3% Mnc
3% Cuc
+
9.53
3
Support I + 3% Mnc
3% Nic
+
400 C, 1 h
12.1
17.4
12.1
12.1
4
5
Support IId + 3% Mnc
Support II + 3% Mnc
3% Cuc
400 C, 1 h
350 C, 1 h
+
+
9.53
6
Support II + 3% Mnc
3% Nic
400 C, 1 h
12.1
17.4
a
b
The coatings were deposited by gas-phase thermolysis in a vacuum. Support I: synthetic ceramic foam of the composition
c
Fe O /P O /B O /KhIPEK I [9]. Mn-, Mn Cu-, and Mn Ni-containing coatings consist of metals, oxides, carbides, and free
carbon. Support II: GAZ slime/SCF [GAZ slime is a waste from the electroplating production of the Nizhni Novgorod Automobile
Plant (GAZ)], wt %: Cr 0.017; Fe , Fe 4.5; Mn 0.01; Zn 4.5; PO 22.37; P O 16.72; Cu 0.01; Ni 0.87; SO 0.9;
2
3
2
5
2 3
d
3+
2+
3+
2+
2+
3
2+
2+
2
4
2
5
4
Cl 0.9.
1070-3632/05/7510-1599 2005 Pleiades Publishing, Inc.

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TSYGANOVA et al.
1
2
2
(a)
(b)
3
80
60
40
20
3 4
4
1
0
200 300 400 500 600 700 800
T, C
100 200 300 400 500 600 700
Fig. 1. Comparison of the catalytic activities of the catalysts in a pulse system with CO containing O . Support: (a) I and
2
3
1
3
(b) II; F 0.5 cm s ; fraction 0.3 0.5 mm; m/F 1.3 g s cm . Catalyst: (a) (1) 2, (2) 1, (3) 3, and (4) straight support I;
(b) (1) 6, (2) 5, (3) 4, and (4) straight support II.
The catalytic activity of the catalysts was evaluated
in a pulse microcatalytic system under comparable
conditions. All the catalysts were preliminarily heated
in the reactor at 500 C for 3 h in a helium flow to
attain the stationary catalytic activity. The system
reached a steady state after two or three admissions
of a CO air mixture into the microcatalytic system.
The temperature dependences of the conversion of CO
into CO2 are shown in Figs. 1 and 2.
700 C [12, 13]. The resulting catalyst MnO2/SCF (3%
Mn in terms of metal) at 360 C and m/F 0.37 g s cm
3
(where m is the catalyst weight and F, flow rate of the
carrier gas) afforded 65% conversion of CO to CO2.
Thus, this catalyst was more active than the Mn Cu-
containing catalyst prepared in this study. The catalyst
MnO2/SCF + V2O5 prepared using a vanadium-
modified ceramic foam was less active [12]. On this
catalyst, the conversion of CO to CO2 at 600 C was
as low as 23%. The Mn-containing catalysts prepared
by impregnation of synthetic ceramic foam with
potassium permanganate, K2O MnO2/SCF, showed
a high activity. The amount of the active phase (in
terms of Mn) varied from 6 to 30%. The activity of
these catalysts depended on the amount of the intro-
duced Mn in a complex fashion, being the highest
with 14% Mn. On this catalyst, the conversion of CO
to CO2 started at 200 C, and 100% conversion was
With respect to the catalytic activity on support I
(Fig. 1a), the catalysts can be ranked in the following
order (comparison for 50% conversion in the ascend-
ing hysteresis branch): 2 > 1 > 3. The Mn Cu-con-
taining catalyst was the most active: The conversion
of CO to CO2 started at 100 C, and 100% conversion
was attained at 550 C. This catalyst exhibited a
clockwise hysteresis. The Mn- and Mn Ni-contain-
ing catalysts were less active. The Mn-containing
catalyst showed a counterclockwise hysteresis, and
the Mn Ni-containing catalyst, no hysteresis. The
activity of straight support I was considerably lower
than that of the metal-containing catalysts.
3
reached at 400 C (at m/F 0.5 g s cm ) [12]. A high
activity was also shown by Mn-containing cobaltites
MnCo2O4/ -Al2O3 prepared by impregnation of the
support with the nitrates; the content of the active Mn
phase was 20%. The 100% conversion of CO to CO2
was attained at 170 C [1].
Previously we studied the activity of Mn-contain-
ing catalysts prepared by impregnation of support I
with an aqueous solution of Mn(III) orthophosphate,
followed by thermolysis in a helium atmosphere at
The dependence of the conversion of CO to CO2
in the presence of oxygen with catalysts on support II
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OXIDATION OF CO ON Mn-CONTAINING CATALYSTS
1601
1
(a)
(b)
1
80
60
40
2
4
4
2
3
3
20
0
300 400 500 600 700 800
T, C
100 200 300 400 500 600 700
Fig. 2. Comparison of the catalytic activities of the catalysts in a pulse system with oxygen-free CO. Support: (a) I and
3
1
3
(b) II; F 0.5 cm s ; fraction 0.3 0.5 mm; m/F 1.3 g s cm . Catalyst: (a) (1) 2, (2) 1, (3) 3, and (4) straight support I;
(b) (1) 5, (2) 6, (3) 4, and (4) straight support II.
is shown in Fig. 1b. The conversion curves have a
complex oscillating character with a clockwise hys-
teresis. The conversion of CO to CO2 on straight
support II starts at 200 C, at 300 C it reaches 40%,
remaining on this level up to 700 C, after which it
starts to increase again. The independence of the con-
version of CO to CO2 from temperature in the range
300 750 C may be due to the occurrence of dispro-
This order is similar to that observed with CO con-
taining O2. However, in the absence of CO the cata-
lyst activities decrease, and the conversion curves
shift toward higher temperatures by 100 200 C com-
pared to the oxidation of CO in the presence of O2.
The Mn Cu-containing catalyst appeared to be the
most active under these conditions: The CO conver-
sion on this catalyst started at 200 C, and 50% con-
version was attained at 400 C.
portionation: 2CO
CO2 + C. The catalysts can be
ranked in the following order with respect to their
activity (for 50% convesion, ascending branch): 6 >
5 > 4 > straight support II. The Mn- and Mn Cu-
containing catalysts on support I are more active than
those on support II.
On support II (Fig. 2b), the conversion of CO to
CO2 in the absence of O2 drastically decreased, and
10% conversion was attained only at 550 700 C. The
catalysts are ranked in the order (for 10% conversion)
5 > 6 > 4 > straight support II. Thus, the Mn Cu-
containing catalyst was the most active under these
conditions also. Oscillation phenomena and hysteresis
were observed on none of the catalysts under these
conditions. Thus, the activity of Mn-containing cata-
lysts in the absence of O2, when CO is oxidized by
the lattice oxygen, is determined by the nature of the
support, as in the case of the Zr-, Fe-, Cr-, Ni-, and
Cu-containing catalysts [8]. The catalytic activity of
straight supports I and II in the absence of O2 is very
low and approximately equal ( 5% conversion at
700 C). Support I contains metal oxides that readily
release lattice oxygen in the oxidation of CO to CO2,
whereas support II mainly consists of metal salts that
The oxidation of CO to CO2 under the examined
conditions is in total a first-order reaction [5].
The conditions of the kinetic experiments and the
activation parameters of the heterogeneous-catalytic
oxidation of CO in the presence of oxygen on the ex-
amined catalysts are listed in Table 2. The activation
energies suggest the kinetic control of the reaction.
To determine the mechanism of oxidation of CO to
CO2, we studied the oxidation of oxygen-free CO on
all the catalysts (Fig. 2). For this process, the catalysts
on support I (Fig. 2a) are ranked in the following
order (for 50% conversion): 2 > 1 > 3 > support I.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

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1602
TSYGANOVA et al.
Table 2. Conditions of kinetic experiments and activation
parameters of catalytic oxidation of CO to CO2 (F
metal -diketonates [10]. The catalysts obtained were
annealed in air at 600 C for 1 h.
1
0.5 cm3 s , CO/O2 ratio 1/8)
The kinetics of heterogeneous-catalytic oxidation
of CO to CO2 was studied by the pulse version of the
gas-chromatographic method [5]. The conversion of
CO was calculated from the CO2 peaks by the calibra-
tion method. The procedure for kinetic measurements
Catalyst Temperature T,
C
Ea,
kJ mol
logk0
1
no.
range, C ( 50%)
1
200 690
650 200
140 450
507 190
200 780
200 750
327 700
700 330
300 700
540
507
335
385
670
725
620
570
615
4.33 0.09 68.34 1.76a
3.13 0.14 48.95 1.84b is described in [5].
2.67 0.07 36.83 0.84a
2
3.06 0.28 40.34 2.88b
REFERENCES
3
4
5
3.18 0.13 60.53 2.09c
1.59 0.58 38.41 4.14c
2.47 0.07 44.77 1.09a
3.46 0.23 62.70 3.76b
2.73 0.17 48.07 2.38c
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a
c
b
Ascending hysteresis branch. Descending hysteresis branch.
No hysteresis.
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C
Ea
kJ mol
logk0
1
no.
range, C ( 50%)
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1
2
3
4
5
6
365 675
192 540
435 763
500 800
400 750
375 750
635
425
775
725
700
750
3.73 0.25
3.81 0.24
4.95 0.86 104.46 3.55
2.94 0.09
5.24 0.74
3.44 0.42
50.45 3.39
46.11 1.42
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70.35 3.55
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do not exhibit such a property. The activation param-
eters of oxidation of CO to CO2 under these condi-
tions are given in Table 3. The activation energies are
typical of kinetically controlled reactions.
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Organometallic Compounds to Preparation of In-
organic Coatings and Materials ), Moscow: Nauka,
1983, p. 197.
Supports based on KhIPEK ceramics were prepared
according to TU 5759-010-10657190 97 [9] by in-
troducing various additives. Prior to catalyst prepara-
tion, the ceramic samples (fraction 0.3 0.5 mm) were
annealed for 1 h at 500 C. A definite portion of a
metal -diketonate (for support : promoting additive
ratios, see Table 1) was added to the support, the
sample was placed in a 60-ml glass ampule, and the
ampule was evacuated and placed in an oven heated
to the required temperature, which was chosen taking
into account the optimal conditions of thermolysis of
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005