High-temperature methane oxidation over metallic monolith-supported zeolite catalysts containing Mn, Co, and Pd ions

Article abstract of DOI:10.1023/B:RUCB.0000009635.74059.7e

The high-temperature complete oxidation of methane over metallic monolith-supported zeolite catalysts containing isolated Mn, Co, and Pd ions was studied. The reaction involves heterogeneous and heterogeneous-homogeneous catalytic processes. The ratio between these processes depends on the temperature, feed rate, and the amount of catalyst charged in the reactor. In the heterogeneous catalytic process, the activity of the catalysts supported on the Fe-Cr-Al monolithic alloy decreases in the series Pd > Mn > Co > Fe-Cr-Al monolith and the reaction rate uniformly increases with increasing contact time. In the heterogeneous-homogeneous process, the reaction rate drastically increases and a 100% conversion of methane to CO₂ can be achieved by minor variations of the contact time. In this case, methane oxidation depends not only on the catalyst chemical composition but also on its external surface area and the reaction volume.

Full text of DOI:10.1023/B:RUCB.0000009635.74059.7e

Russian Chemical Bulletin, International Edition, Vol. 52, No. 9, pp. 1933—1939, September, 2003
1933
Highꢀtemperature methane oxidation over metallic monolithꢀsupported zeolite
catalysts containing Mn, Co, and Pd ions
ꢀ
K. I. Slovetskaya and L. M. Kustov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: Slovetskaya@mail.ru
The highꢀtemperature complete oxidation of methane over metallic monolithꢀsupported
zeolite catalysts containing isolated Mn, Co, and Pd ions was studied. The reaction involves
heterogeneous and heterogeneousꢀhomogeneous catalytic processes. The ratio between these
processes depends on the temperature, feed rate, and the amount of catalyst charged in the
reactor. In the heterogeneous catalytic process, the activity of the catalysts supported on the
Fe—Cr—Al monolithic alloy decreases in the series Pd > Mn > Co > Fe—Cr—Al monolith and
the reaction rate uniformly increases with increasing contact time. In the heterogeneousꢀ
homogeneous process, the reaction rate drastically increases and a 100% conversion of methꢀ
ane to CO2 can be achieved by minor variations of the contact time. In this case, methane
oxidation depends not only on the catalyst chemical composition but also on its external
surface area and the reaction volume.
Key words: methane, oxidation, monolith catalyst, zeolite, palladium, manganese, cobalt.
2 h at 500 °C. The catalysts 3% Mn/ZSMꢀ5, 2% Co/ZSMꢀ5,
and 1% Pd/ZSMꢀ5 were prepared by this procedure. The conꢀ
tent of the isolated metal ions in these samples corresponded to
the maximal value achievable by the introduction of these metꢀ
als in zeolite by a topochemical reaction.10—13
A search of catalysts for the highꢀtemperature hydroꢀ
carbon oxidation is an important problem despite the
numerous works that have been reported in the past
decade.1—8
The thermally stable (up to 1000 °C) highꢀsilica
ZSMꢀ5 zeolites containing isolated transition metal ions
are promising systems for highꢀtemperature methane
oxidation. We have found previously a good performance
of these systems in the highꢀtemperature complete oxidaꢀ
tion of methane.9—12
This work is aimed at studying the highꢀtemperature
methane oxidation over the metallic monolithsꢀsupported
ZSMꢀ5 zeolites containing isolated Pd, Mn, and Co ions.
It was of interest to find conditions favorable for the
heterogeneous catalytic and heterogeneousꢀhomogeneous
processes and to study sensitivity of these processes to the
catalyst chemical composition.
To prepare the monolith catalysts, the metalꢀcontaining zeoꢀ
lites were supported on a foil of the thermally stable Fe—Cr—A1
alloy with a thickness of 80 µm. The oxide layer was deposited by
electrophoretic precipitation according to a known procedure.14
Aluminum hydroxide sol was used as binder. A starting suspenꢀ
sion used for deposition contained a fine powder of ZSMꢀ5
(8.2 g L–1, particle size 5—10 µm) in an EtOH sol of aluminum
hydroxide (СА1О(ОН) = 8.2 g L–1), and the deposit thickness was
∼10 µm. After precipitation, the samples were dried in air for
36 h at 20 °C and then heated for 2 h at 500 °C. The smooth and
crimped foil layers covered on both sides with the zeolite were
lumped together and rolled into a tube with a height of 2.6 cm
and a crossꢀsection area of 4.1 cm2. The monoliths prepared had
40 triangle channels per 1 cm2. The amount of the catalyst in the
monoliths was 0.06—0.07 g. Such a deposition technique of the
catalysts on the metallic monoliths allowed us to operate with
small specimens of highly active catalysts at high feeding rates of
the reaction mixture.
Experimental
Highꢀsilica zeolite TsVM (Si/Al = 20), structural analog of
ZSMꢀ5 (Nizhegorodskii Sorbent Co Ltd), was used for the prepaꢀ
ration of Mnꢀ and Coꢀcontaining zeolite catalysts, and ZSMꢀ5
(PQ Corporation, Si/Al = 25) was used for the preparation of
the Pdꢀcontaining catalyst. To introduce a metal, the starting
ammonium zeolite was impregnated to incipient wetness with
an aqueous solutions of Mn(NO3)2, Co(NO3)2, and Pd aminoꢀ
nitrile complex. The samples prepared were dried in air for 6 h at
20 °C and 4 h at 140 °C followed by calcination in an air flow for
Complete methane oxidation was conducted in a flow setup
at atmospheric pressure with the 10—1900 cm3 min–1 feed rate
of the initial gas mixture (2.5 vol.% СН4 in air). To study the
catalytic performance, the monoliths were placed on a grate
positioned 4 cm above the bottom of the quartz reactor (Fig. 1).
Nichrome wire of a heater was uniformly wound over the whole
length of the reactor and covered by a glass jacket only to proꢀ
vide fast heat exchange with environment. The temperature was
controlled and measured with a TPMꢀ10 thermal controller
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1832—1838, September, 2003.
1066ꢀ5285/03/5209ꢀ1933 $25.00 © 2003 Plenum Publishing Corporation

1934
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
1
Slovetskaya and Kustov
When the contact time (τ) was varied, an increase and deꢀ
crease in the amount of СО2 formed were reversible.
Methane oxidation over the Мn/ZSMꢀ5 catalyst was studꢀ
ied on both one and two monoliths positioned one above anꢀ
other. Methane oxidation over the other catalysts was studied
with one monolith. During the run, the temperature of the reacꢀ
tion mixture flow was increased from 500 to 720 °C and then
decreased to 600 or 500 °С, and new runs were performed to
verify the reproducibility of results and the thermal stability of
the catalyst. The activities of the cobalt and palladium catalysts
were also studied after their heat treatment in the reaction mixꢀ
ture at 800 and 900 °C. Conversions (α) of СН4 to СО2 found by
enhancing contact times coincided completely with those meaꢀ
sured upon the subsequent decrease in τ.
0.5 cm
2.3 cm
2
3
The reaction products were analyzed by GC on a column
packed with Polysorbꢀ1 (heat conductivity detector, helium carꢀ
rier gas, temperature 25 °C).
4
Earlier,10—13 in studies of methane oxidation over the cataꢀ
lysts used in this work, we measured the amounts of СН4 reacted
and those of СО2 formed, and no reaction products besides СО2
and Н2О were found. Therefore, in this work the amount of СО2
formed was used as the measure of methane conversion. In some
runs, the amount of СО2 was 2.5 0.02 vol.% and this correꢀ
sponded to complete oxidation of 2.50 vol.% СН4 contained in
the initial mixture.
2.6 cm
5
The activation energy of reaction was calculated from the
temperature dependence of the feed rates of the initial mixꢀ
ture (v), which correspond to the specified conversion α, or v•α
values when the kinetics was described by the zeroꢀorder equaꢀ
tion.18 The contact time for the monolith zeolite catalysts
was calculated as the ratio between the monolith volume and
the feed rate of the initial mixture. The feed rate of the initial
mixture at the specified conversion was taken as the catalyst
activity (А).19 Calculations were carried out by the equation
А = vαC/22.4mM, where С is the methane concentration in the
initial mixture and mM is the content of the transition metal in
the catalyst.
6
Fig. 1. Scheme of the reactor for highꢀtemperature methane
oxidation to СО2: 1, inlet of the reaction mixture; 2, spiral of the
heater; 3, glass jacket; 4, monolith catalyst; 5, thermocouple;
6, outlet of the reaction products to analyzer.
with an accuracy of 0.1%. The temperature gradient over the
reactor height measured at 500 and 700 °C was 1 °C cm–1. The
runs were performed in an air flow, which was fed with the
reaction mixture to a top of the reactor. A thermocouple for
temperature controlling was placed in the center of the reactor.
The feed rate for air was the same as that for the reaction mixꢀ
ture, thus eliminating a possible high temperature gradient,
which could be created by the heater. The isothermicity in the
catalyst layer during oxidation was verified by the kinetic
method15, according to which the specific reaction rates should
remain constant when the catalyst charge changes at a speciꢀ
fied temperature. The specific activity (reaction rate) of the
3% Mn/ZSMꢀ5 monolith catalyst was found to remain constant
upon doubling the catalyst bed depth of the reactor. When the
charge of the catalyst was increased by 2, 3, and 4 times, its
specific activity remained constant.16 This indicates that the
heterogeneous catalytic methane oxidation occurs under the
isothermal conditions in the kinetic region over the whole cataꢀ
lyst volume.15—17
The desired temperature of methane oxidation, which was
continuously measured with a temperature controller, remained
constant during all the runs. A temperature increase due to the
heat evolution during oxidation was monitored with a thermoꢀ
couple located under the grate with the catalyst. When the temꢀ
perature increased, the thermocouple response was transmitted
to the thermal controller, which turned off the heater. Fast heat
exchange with environment resulted in establishing a desired
temperature, so that the isothermal conditions were maintained
in the reaction volume.
Results and Discussion
We studied the activity of the monolith zeolite cataꢀ
lysts in a highꢀtemperature region (500—900 °C). Under
these conditions the massꢀtransfer processes and homoꢀ
geneousꢀheterogeneous chain reactions can affect the
heterogeneous catalytic methane oxidation. To determine
whether the heterogeneous catalytic or homogeneousꢀhetꢀ
erogeneous chain reactions occur, we used the specific
kinetic features20—22 typical of these processes.
The main features of the heterogeneous catalytic proꢀ
cess are as follows: (1) specific activity is independent of
the catalyst charge and the volume of the reaction space;
(2) drastic changes in the reaction rate when varying the
contact time are absent; (3) activation energy for methꢀ
ane oxidation is lower than that for the homogeneousꢀ
heterogeneous process.
The main features of the homogeneousꢀheterogeneous
chain process are as follows: (1) specific activity changes
when the catalyst charge or the reaction space volume is

CH4 combustion on ZSMꢀ5 metal monolith catalysts Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
1935
α (%)
α (%)
100
80
100
80
3
1
2
4
3
2
1
60
60
4
40
40
20
20
0.8 v–1/s cm–3
0
0.2
0.4
0.6
0
5
10
15
20
25
30
τ/s
Fig. 2. Methane conversion to СО2 (α) vs. reverse gas feed rate
(v–1) in the empty reactor at 650 (1), 670 (2), 700 (3), and
720 °C (4).
Fig. 3. Methane conversion to СО2 (α) vs. contact time (τ) over
the metallic monolith without oxide coverage at 600 (1), 620 (2),
680 (3), and 700 °C (4).
varied; (2) reaction rate increases dramatically when the
contact time increases slightly; (3) activation energy for
methane oxidation is higher than that for the heterogeꢀ
neous catalytic process but lower than that for the homoꢀ
geneous reaction.
The catalyst 3% Мn/ZSMꢀ5 is thermally stable in the
temperature range studied. As can be seen in Fig. 4, a, the
methane conversion at 500 °С increases steadily with inꢀ
creasing contact time and is independent of the catalyst
charge in the reactor (viz., one or two monoliths) at the
same contact times. In the runs with two monoliths at
Methane oxidation in empty reactor. No methane oxiꢀ
dation to СО2 in the empty reactor was found at temperaꢀ
tures below 650 °С. An induction period was observed at
650 °С, and during this period the СН4 conversion inꢀ
creases slightly from 5 to 9% with decreasing feed rate of
the initial mixture but then increases sharply to 97—100%
(Fig. 2). Such a sharp increase in the reaction rate is
typical of radicalꢀchain processes. At higher temperatures,
the methane oxidation rate sharply increases at higher
feed rates of the initial mixture and the СН4 conversion is
at most 6—10% during the induction period. The activaꢀ
tion energy for methane oxidation in the empty reactor
calculated from the temperature dependence of the feed
α (%)
a
100
600 °C
80
600 °C
1
2
60
40
20
500 °C
rate of the initial mixture at α ≈ 100% is 200 15 kJ mol–1
.
Methane oxidation over metallic monolith. Methane
oxidation over the metallic monolith begins at 600 °С,
i.e., under the conditions when the reaction in the empty
reactor does not occur (Fig. 3). The СН4 to СО2 converꢀ
sion smoothly increases to 20% with increasing contact
time as shown by the initial segment of the kinetic curve.
Then the reaction rate drastically increases and the conꢀ
version achieves 80—100%. The activation energy of
methane oxidation calculated from the temperature deꢀ
pendence of the feed rate of the initial mixture is the same
0
10
20
30
τ/s
α (%)
100
80
b
720 °C
720 °C
670 °C
670 °C
60
40
at α = 15% and α ≈ 100% and is equal to 160 10 kJ mol–1
.
1
2
The contact time, which corresponds to a sharp increase
of the methane conversion, decreases from 7 to 0.6 s with
increase in the temperature from 600 to 650 °С.
Methane oxidation over catalyst 3% Mn/ZSМꢀ5.
Complete oxidation of СН4 to СО2 over the catalyst
3% Мn/ZSMꢀ5 supported on the metallic monoliths was
studied in the temperature range of 500—720 °С at the
contact times of 0.5—35 s and conversions of 8—99%.
20
0
1
2
3
τ/s
Fig. 4. Methane conversion to СО2 (α) vs. contact time (τ) over
the metallic monolith catalyst containing 3% Mn/ZSMꢀ5 at
500 and 600 °C (a), 670 and 720 °C (b). The runs were perꢀ
formed over one (1) and two monoliths (2).

1936
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
Slovetskaya and Kustov
600, 670, and 720 °С, the methane conversion monotoꢀ
nously increases with contact times without sharp jumps
as was obsreved in the runs at 500 °С. The conversion at
670 and 720 °С in the range from 8 to 99% (Fig. 4, b)
increases proportionally to the contact time, indicating
the zero order of the reaction. The same reaction order
was found at 500 and 600 °С but at the conversion beꢀ
low 20%. The activation energy for methane conversion
to СО2 is 130 10 kJ mol–1. The same activation energy
has been found for the pelleted sample.10 This coinciꢀ
dence indicates that the nature of СН4 to СО2 oxidation
over the 3% Мn/ZSMꢀ5 catalyst remains unchanged when
the reaction was conducted over the catalyst supported on
the metallic monolith and the reaction temperature was
increased to 720 °С.
Thus, the specific activity of the catalyst
3% Mn/ZSMꢀ5 in the form of two monoliths is indepenꢀ
dent of its amount; sharp changes in the reaction rate with
a slight variation of the contact time (by 10—15%) are not
found, and the activation energy is substantially lower
than those of the homogeneous process in the empty reꢀ
actor and homogeneousꢀheterogeneous process over the
metallic monolith. On the basis of the above kinetic feaꢀ
tures one can conclude that methane oxidation over two
monoliths of the 3% Mn/ZSMꢀ5 catalyst is the heterogeꢀ
neous catalytic process.
on the plot of α vs. τ (see Fig. 4, a, b). As indicated by the
first section (α < 20—30%), the methane conversion nearly
coincides with that over two monoliths, i.e., the reaction
is a heterogeneously catalyzed process. At α > 20—30%, a
slight increase in the contact time (by 10—15%) results in
a sharp increase in the reaction rate and in methane conꢀ
version to СО2 up to 94—100%. The desired temperature
remains constant during the whole run. The contact time
at which the above transition occurs decreases from 3 to
0.6 s as temperature increases from 600 to 700 °С. The
activation energy calculated from the temperature depenꢀ
dence of the feed rate of the initial mixture at α ≈ 100% is
155 5 kJ mol–1. This value is higher than the activation
energy of the heterogeneous process (130 kJ mol–1
)
and that of methane oxidation in the empty reactor
(200 kJ mol–1).
Thus, during methane oxidation to СО2 over one
monolith, one can observe that at the temperaꢀ
tures 600—720 °С and α > 20—30% under isothermal
conditions, the amount of СО2 increases markedly with
a low (10—15%) variation of the contact time. In addiꢀ
tion, with increasing catalyst amount in the reaction volꢀ
ume there is a decrease in the reaction rate. Finally, the
activation energy enhances compared to those typical of
the heterogeneous catalytic regime. The kinetic feaꢀ
tures of the reaction allow suggestion that methane oxidaꢀ
tion to СО2 over one monolith at 600—720 °С and
α > 20—30% is the heterogeneousꢀhomogeneous chain
process.
The externalꢀdiffusion retardation does not affect the
heterogeneous catalytic complete oxidation of СН4 up to
720 °С and α ≈ 99%, and this is confirmed by the absence
of sharp kinks on the logarithmic dependence of α•v
on 1/T (Fig. 5) and the fact that the plots of methane
conversion vs. contact time for two different catalyst layꢀ
ers in the reactor at two temperatures of 500 and 600 °С
coincide (see Fig. 4, a).
Since in the experiments with one monolith one can
simultaneously study methane oxidation in both heteroꢀ
geneous catalytic and heterogeneousꢀhomogeneous proꢀ
cesses, the performance of the palladium and cobalt cataꢀ
lysts was studied under these conditions.
When the catalyst charge is halved (viz., one of monoꢀ
liths is removed), methane oxidation changes drastically.
Beginning from 600 °С, one can distinguish two sections
Methane oxidation over catalyst 1% Pd/ZSМꢀ5. Comꢀ
plete methane oxidation to СО2 over the catalyst
1% Pd/ZSМꢀ5 supported on a metallic monolith was studꢀ
ied at the temperatures of 500—720 °С and conversions of
10—100% (Fig. 6, a, b). In this temperature range at the
conversions up to 40—50%, the methane conversion
gradually increases with increasing contact time. The acꢀ
lg(α•v)
6.6
6.4
6.2
6.0
5.8
5.6
5.4
5.2
tivation energy calculated at α = 30% is 84 5 kJ mol–1
.
The reaction rate sharply increases with further increasing
the contact time and the conversion reaches 97—100%.
When the reaction temperature is increased from 550 to
720 °С, the contact time relevant to this increase deꢀ
creases from 3 to 0.5 s. The activation energy calculated
at conversions close to 100% is 156 5 kJ mol–1. Thus, for
methane oxidation over the palladium catalyst as well as
over the Mnꢀcontaining catalyst, one can distinguish two
regions, which differ essentially in the kinetic features and
activation energies. One can assume that in these regions,
two different mechanisms, the heterogeneous catalytic
and chain heterogeneousꢀhomogeneous mechanisms, are
operative in the reaction.
1.025
1.075
1.125
1.175
T –1•103/K–1
Fig. 5. Activity of the metallic monolith catalyst containing
3% Mn/ZSMꢀ5 vs. inverse temperature in complete methane
oxidation (α is conversion, v is the feed rate of the initial mixture).

CH4 combustion on ZSMꢀ5 metal monolith catalysts Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
1937
α (%)
energy over the pelleted catalyst 2% Со/ZSMꢀ5, which
was calculated for heterogeneous catalytic oxidation of
СН4 at 450—500 °С in the kinetic regime.12
a
100
80
2
3
The second section of the plot of methane converꢀ
sions vs. contact time (see Fig. 7) shows that the methane
conversion to СО2 under isothermal conditions sharply
increases at α > 20% achieving 95—100%. The increase in
α is likely due to the transition from the heterogeneous
catalytic process to the chain heterogeneousꢀhomogeꢀ
neous process. The contact time at which this transition
occurs decreases from 3.5 to 0.5 s with an increase in
temperature from 600 to 700 °С. The activation energy of
the heterogeneousꢀhomogeneous process is 165 kJ mol–1
as in the case of the manganese and palladium catalysts.
Hence, two pathways of methane oxidation to СО2
occur over the Pdꢀ, Mnꢀ, and Coꢀcatalysts as well as over
the metallic monolith without an oxide layer: one is a
heterogeneously catalyzed reaction and another is a
chain heterogeneousꢀhomogeneous reaction. Their ratio
changes with the feed rate of the initial mixture, reaction
temperature, and a depth of the catalyst bed (charge).
Only heterogeneousꢀhomogeneous methane oxidation
occurs in the empty reactor. The above findings allow
some general conclusions to be drawn on the kinetic feaꢀ
tures of highꢀtemperature methane oxidation.
60
40
1
20
0
2
4
6
8
10
τ/s
α (%)
b
100
80
3´
2´
1´
60
40
20
0
0.2
0.6
1.0
τ/s
Fig. 6. Methane conversion to СО2 (α) vs. contact time (τ) over
the metallic monolith catalyst containing 1% Pd/ZSMꢀ5 at
500 (1), 550 (2), 600 °C (3) (a) and 650 (1´), 700 (2´),
720 °C (3´) (b).
The heterogeneous catalytic process prevails at low
contact times and СН4 conversions below 50%. The
catalytic activity decreases in the series Pd/ZSMꢀ5 >
> Mn/ZSMꢀ5 > Co/ZSMꢀ5 > Fe—Cr—Alꢀmonolith
(Fig. 8, a, Table 1). The activation energy for methane
Methane oxidation over catalyst 2% Со/ZSМꢀ5. On
inspecting the plot of methane to СО2 conversion vs.
contact time obtained for the catalyst 2% Со/ZSMꢀ5 supꢀ
ported on the metallic monolith (Fig. 7), one can also
find two sections. At α < 25%, the conversion is proporꢀ
tional to the contact time, and this is typical of a zeroꢀ
order heterogeneous reaction. The activation energy calꢀ
culated at α = 20% and temperatures of 550—700 °С is
198 10 kJ mol–1. This value coincides with the activation
α (%)
a
100
2
1
3
80
4
60
40
20
α (%)
0
2
4
6
8
τ/s
100
α (%)
80
4
3
2
100
80
b
60
40
20
60
5
40
2
1
1
4
20
3
0
0.5
1.0
1.5
τ/s
0
2
4
6
8
τ/s
Fig. 8. Methane conversion to СО2 (α) vs. contact time (τ) at
600 (a) and 700 °C (b) over the catalysts 1% Pd/ZSMꢀ5 (1),
2% Co/ZSMꢀ5 (2), 3% Mn/ZSMꢀ5 (3), Fe—Cr—Alꢀmonoꢀ
lith (4) and in the empty reactor (5).
Fig. 7. Methane conversion to СО2 (α) vs. contact time (τ) over
the metallic monolith catalyst containing 2% Co/ZSMꢀ5 at
550 (1), 600 (2), 650 (3), and 700 °C (4).

1938
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
Slovetskaya and Kustov
Table 1. Catalytic activity (A) and activation energy (E) for
complete methane oxidation at 500 °C and 33% conversion
v/mL min–1
1000
800
600
400
200
1
2
3
4
5
Catalyst
А
Е
/mol (g metal h)–1
/kJ mol–1
1% Pd/ZSMꢀ5
3% Mn/ZSMꢀ5
2% Со/ZSMꢀ5
4.4
84
130
193
160
—
0.12
0.029
—
0.35
0.17
Fe—Cr—Alꢀmonolith
a
10% Pd/Al2O3
0.3% Рt/Аl2O3/Ni b
CeO2, barium
—
hexaaluminatec
0.01
—
600
640
680
T/°C
a See Ref. 23.
b See Ref. 24.
c See Ref. 7.
Fig. 9. Activity (feed rate of the reaction mixture (v) at ∼100%
methane conversion) vs. reaction temperature over various zeoꢀ
lite metallic monolith catalysts: 1, empty reactor; 2, metallic
monolith; 3, Mn/ZSMꢀ5; 4, Co/ZSMꢀ5; 5, Pd/ZSMꢀ5 (650 °C).
oxidation over these catalysts increases in the same seꢀ
quence. The zeolite catalysts studied in this work exceed
in the specific activity measured at 500 °С the oxide
Ba—Alꢀcatalyst for methane combustion in gas turꢀ
bines.1—8 In addition, the activity of the Pdꢀzeolite cataꢀ
lyst is many times higher than those of aluminumꢀpallaꢀ
dium and aluminumꢀplatinum catalysts (see Table 1). The
high activity of metalꢀcontaining zeolite catalysts is due
to the presence of metals in the zeolite lattice in the form
of isolated ions.
activity from the monolith with the supported Pdꢀzeolite
catalyst.
When the catalyst amount is doubled (viz., two instead
of one monoliths are used), a decrease rather than an
increase in the reaction rate was observed down to the
value, which is immeasurable under the experimental conꢀ
ditions. The structural characteristics of the system (viz.,
the external surface area (S) and reaction volume (Vr)),
which would be capable of markedly affecting the rate of
methane oxidation through the heterogeneousꢀhomogeꢀ
neous chain mechanism,20—22,25—28 are the same for all
the catalysts and metallic monolith under study. The ratio
S/Vr is constant in the runs with both one and two monoꢀ
liths. When the heterogeneousꢀhomogeneous process ocꢀ
curs in the absence of the catalyst and when the S/Vr ratio
changes markedly, the methane conversions decrease
more than 2 times (see Fig. 8) and the activation energy
The heterogeneousꢀhomogeneous chain process of
methane oxidation occurs at higher contact times and is
accompanied by a sharp increase in the СО2 amount inꢀ
duced by small changes of the feed rate of the gas mixture.
The heterogeneousꢀhomogeneous chain process begins at
550 °С over the most active catalyst and at 600 °С over all
the rest catalysts, i.e., by 50 °С lower than in the empty
reactor. As can be seen in Fig. 8, a, chemical composition
of the catalysts affects the rate of the heterogeneousꢀhoꢀ
mogeneous process at 600 °С. Transition from the heteroꢀ
geneous catalytic to significantly faster heterogeneousꢀ
homogeneous chain process occurs at different contact
times over various catalysts. These differences (Fig. 8, b)
vanish upon the further increase in temperature. As can
be seen in Fig. 9, the СН4 conversions to СО2 close to
100% are achieved at nearly the same volume feed rates
for the gas mixture (contact times) over all the catalysts
including the metallic monolith. The activation energies
of the heterogeneousꢀhomogeneous process unlike those
of the heterogeneous catalytic processes are also the same
for all the catalysts and equal to 160 5 kJ mol–1. Hence,
chemical composition of the catalysts studied, while
strongly affecting the catalyst activity in methane oxidaꢀ
tion via the heterogeneous catalytic mechanism, does not
essentially influence methane oxidation through the hetꢀ
erogeneousꢀhomogeneous chain mechanism. The metalꢀ
lic monolith without the oxide coverage does not differ in
increases from 165 to 200 kJ mol–1
.
Hence, the catalytic highꢀtemperature methane oxiꢀ
dation can occur both through heterogeneous catalytic
mechanism and through the heterogeneousꢀhomogeneous
chain mechanism. In the first case, chemical compoꢀ
sition of the catalyst is a determining factor for the methꢀ
ane conversion, while in the second case, the S/Vr ratio is
one of the decisive factors. It follows that one should be
careful in prediction of the catalytic activity at high
temperatures on the basis of the data obtained under
the conditions of the heterogeneous catalytic mechaꢀ
nism only.
The authors are grateful to A. V. Kucherov and S. S.
Goryashchenko for providing the samples of the metalꢀ
containing zeolite catalysts and to M. P. Vorob´eva
for the preparation of monolith catalysts and useful disꢀ
cussion.

CH4 combustion on ZSMꢀ5 metal monolith catalysts Russ.Chem.Bull., Int.Ed., Vol. 52, No. 9, September, 2003
1939
[Kinet. Catal., 2000, 41 (Engl. Transl.)]; Pat. RF 2078611;
Byul. Izobret. [Invention Bulletin], 1997, 64 (in Russian).
16. K. I. Slovetskaya, A. A. Greish, M. P. Vorob´eva, and L. M.
Kustov, Izv. Akad. Nauk, Ser. Khim., 2001, 1512 [Russ. Chem.
Bull., Int. Ed., 2001, 50, 1589].
References
1. M. F. Zwinkels, S. G. Jaras, and P. G. Menon, Catal. Rev.
Sci. Eng., 1993, 35, 319.
2. Z. R. Ismagilov and M. A. Kerzentsev, Catal. Rev. Sci. Eng.,
1990, 32, 51.
17. Ch. N. Satterfield, Mass Transfer in Heterogeneous Catalysis,
Interscience, New York, 1970.
3. P. G. Menon, M. F. M. Zwinkels, E. M. Iohanson, and
S. G. Jaras, Kinet. Katal., 1993, 39, 670 [Kinet. Catal., 1993,
39 (Engl. Transl.)].
18. S. L. Kiperman, Vvedenie
v kinetiku geterogennykh
kataliticheskikh reaktsii [Introduction to the Kinetics of Heteroꢀ
geneous Reactions], Nauka, Moscow, 1964, 545 (in Russian).
19. A. V. Sagalovich and A. L. Klyachko, Usp. khim., 1971, 40,
1237 [Russ. Chem. Rev., 1971, 40 (Engl. Transl.)].
20. Ya. B. Gorokhovatskii, T. P. Kornienko, and V. V. Shalya,
Geterogennoꢀgomogennye reaktsii [Heterogeneousꢀhomogeꢀ
neous Reactions], Tekhnika, Kiev, 1972, 28; 126 (in Russian).
21. M. Yu. Sinev, L. Ya. Margolis, and V. N. Korchak, Usp.
khim., 1995, 64, 378 [Russ. Chem. Rev., 1995, 64 (Engl.
Transl.)].
22. S. L. Kiperman, Kinet. Katal., 1994, 35, 45 [Kinet. Catal.,
1994, 35 (Engl. Transl.)].
23. G. Grohhi, C. C. Crisiani, M. Vallentini, and E. Proaconi,
Proc. of 12th Cong. on Catalysis, 2000, 130C, 274.
24. O. Yu. Pod´yacheva, Ph. D. (Chem.) Thesis, Tomsk State
Univ., Tomsk, 1998.
4. J. G. McCarty, Nature, 2000, 403, 35.
5. A. G. Ersson, H. M. J. Kusar, P. G. Menon, and S. G. Jaras,
Eng. Symp. «Environmente Catalysis 2 — Catalysis for Green
Chemistry», Stockholm (Sweden), 2001, 8ꢀPꢀ53.
6. F. J. Cadele Santos Aires, S. Romirer, G. Garcia Cervantes,
E. Rogenmond, and J. S. Bertollint, Eng. Simp. 1th «New
Materials for New Improved Processes», 2001, 1ꢀ0ꢀ13.
7. A. J. Zarur and J. Y. Ying, Nature, 2000, 403, 65.
8. R. A. M. Giacomuzzi, M. Portinaari, M. Rossetti, and
L. Forni, Proc. of 12th Int. Cong. on Catalysis, 2000,
130A, 197.
9. A. V. Kucherov, A. A. Slinkin, S. S. Goryashchenko, and
K. I. Slovetskaya, J. Catal., 1989, 118, 459.
10. S. S. Goryashchenko, K. I. Slovetskaya, M. A. Alimov, and
A. A. Slinkin, Kinet. Katal., 1992, 33, 350 [Kinet. Catal.,
1992, 33 (Engl. Transl.)].
25. V. S. Arutyunov and O. V. Krylov, Okislitel´nye
prevrashcheniya metana [Oxidative Methane Conversions],
Nauka, Moscow, 1998, 267; 298.
26. M. V. Polyakov and I. E. Neimark, Zh. Fiz. Khim., 1938,
15, 355.
11. S. S. Goryashchenko, K. I. Slovetskaya, and A. A. Slinkin,
Kinet. Katal., 1994, 35, 106 [Kinet. Catal., 1994, 35 (Engl.
Transl.)].
12. S. S. Goryashchenko, M. A. Alimov, E. A. Fedorovskaya,
K. I. Slovetskaya, and A. A. Slinkin, Kinet. Katal., 1994, 35,
588 [Kinet. Catal., 1994, 35 (Engl. Transl.)].
27. I. I. Bobrova, N. N. Bobrov, V. V. Chesnokov, and V. N.
Parmon, Kinet. Katal., 2001, 42, 882 [Kinet. Catal., 2001, 42
(Engl. Transl.)].
13. A. V. Kucherov and M. Shelef, Catal. Lett., 2001, 71, 19.
14. M. P. Vorob´eva, A. A. Greish, A. V. Ivanov, and L. M.
Kustov, Appl. Catal. A, 2000, 199, 257.
28. N. A. Vasil´eva and V. N. Panfilov, Kinet. Katal., 2002, 43,
189 [Kinet. Catal., 2002, 43 (Engl. Transl.)].
15. I. I. Bobrova, V. V. Chesnokov, N. N. Bobrova, V. I.
Zaikovskii, and V. N. Parmon, Kinet. Katal., 2000, 41, 25
Received June 25, 2002;
in revised form July 1, 2003