Selective methanation of CO in the presence of CO2 in hydrogen-containing mixtures on nickel catalysts

Article abstract of DOI:10.1134/S0023158410060170

The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supported on CeO₂, γ-Al₂O ₃, and ZrO₂ in the reaction of selective CO methanation in the presence of CO₂ in hydrogen-containing mixtures (1.5 vol % CO, 20 vol % CO₂, 10 vol % H₂O, and the balance H₂) was performed at the flow rate WHSV = 26000 cm³ (g Cat)^-1 h^-1. It was found that commercial catalytic systems like NKM-2A and NKM-4A (NIAP-07-02) were insufficiently effective for the selective removal of CO to a level of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO ₂. This catalyst decreased the concentration of CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO₂ in the temperature range of 280-360°C at a selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concentration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO₂ catalyst was reached at a temperature of 300°C. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0023158410060170

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2010, Vol. 51, No. 6, pp. 907–913. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © M.M. Zyryanova, P.V. Snytnikov, Yu.I. Amosov, S.A. Ven’yaminov, E.Z. Golosman, V.A. Sobyanin, 2010, published in Kinetika i Kataliz, 2010, Vol. 51,
No. 6, pp. 938–944.
YOUNG
SCIENTISTS’ SCHOOL
Selective Methanation of CO in the Presence of CO2
in HydrogenꢀContaining Mixtures on Nickel Catalysts
,
b
,
b
,
,b
M. M. Zyryanovaa , P. V. Snytnikova *, Yu. I. Amosova ,
S. A. Ven’yaminova, E. Z. Golosmanc, and V. A. Sobyanina
,
b
aBoreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
bNovosibirsk State University, Novosibirsk, 630090 Russia
cOOO NIAPꢀKATALIZATOR, Novomoskovsk, Tula oblast, Russia
*eꢀmail: pvsnyt@catalysis.ru
Received February 2, 2010
Abstract—The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supꢀ
ported on CeO2, γꢀAl2O3, and ZrO2 in the reaction of selective CO methanation in the presence of CO2 in
hydrogenꢀcontaining mixtures (1.5 vol % CO, 20 vol % CO2, 10 vol % H2O, and the balance H2) was perꢀ
formed at the flow rate WHSV = 26000 cm3 (g Cat)–1 h–1. It was found that commercial catalytic systems like
NKMꢀ2A and NKMꢀ4A (NIAPꢀ07ꢀ02) were insufficiently effective for the selective removal of CO to a level
of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO2. This catalyst decreased the concentration of
CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO2 in the temperature range of 280–360°C at a
selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concenꢀ
tration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO2 catalyst was reached at a temperature of 300°C
.
DOI: 10.1134/S0023158410060170
INTRODUCTION
However, the process of selective CO oxidation is
associated with a number of problems. To determine
the amount of oxygen to be supplied to the reactor
inlet, the inlet concentration of CO should be continꢀ
uously monitored. Otherwise, the desired degree of
In recent years, lowꢀtemperature protonꢀexchange
membrane fuel cells (PEMFCs) have been considered
as attractive devices for transport power generation (as
an alternative to internal combustion engines) or porꢀ removal will not be reached in an oxygen deficiency or
an additional amount of hydrogen will be consumed in
an excess of oxygen to decrease the process efficiency.
In addition, nitrogen will also be supplied to the reacꢀ
tor if air will be used as a source of oxygen to result in
an undesirable dilution of the gas mixture.
Another possible way of removing CO from a
hydrogenꢀcontaining gas is the selective methanation
of CO
table (electronic instrumentation and communication
facilities) and fixed applications (main and standby
power supply devices, in particular, in hardꢀtoꢀreach
areas). Either pure hydrogen or a hydrogenꢀcontaining
mixture can serve as fuel for PEMFCs. This mixture is
generated on site in a fuel processor from traditional
hydrocarbon materials (natural gas, propane–butane
mixtures, gasoline, and diesel fuel) or oxygenꢀcontainꢀ
ing compounds (alcohols and ethers) using catalytic
(steam, oxygen, or autothermal) conversion followed
by the steam conversion of CO. The hydrogenꢀconꢀ
taining mixture thus prepared usually contains 0.5–
2 vol % CO, which is a poison for the PEMFC anode,
and its concentration in the mixture should be
decreased to a level of <10 ppm (in the case of a Pt
anode) or 100 ppm (Pt–Ru anode) [1–3]. The selecꢀ
tive oxidation of CO in hydrogenꢀcontaining mixtures
is an efficient process for the removal of carbon monꢀ
oxide. In the past 15 years, much effort has been
directed toward the development of stable, highly
active, and selective catalysts for this reaction all round
the world. As a result, a large number of various systems
mainly containing Au, Pt, Ru, Rh, Co, and Cu supꢀ
ported on various carriers have been proposed [2, 3].
CO + 3H2 = CH4 + H2O,
ΔH° = –206 kJ/mol.
(I)
The advantages of selective CO methanation over
selective oxidation consist in that it is not necessary to
add oxygen (air) to the reaction mixture and the
resulting methane, which is not a poison for PEMFCs,
can further be used in an afterburner of anodic gases.
Because the initial concentration of CO is low, the
amount of hydrogen consumed for CO methanation is
also small. The main problem is the side methanation
of CO2
CO2 + 4H2 = CH4 + 2H2O,
ΔH° = –165 kJ/mol.
(II)
Because the concentration of CO2 in the hydrogenꢀ
containing mixture usually is 15–20 vol %, considerꢀ
907

908
ZYRYANOVA et al.
able hydrogen losses can occur. The reverse reaction of oped at the Novomoskovsk Institute of Nitrogen
steam CO conversion can also facilitate an increase in Industry in cooperation with the Zelinsky Institute of
the concentration of CO:
CO2 + H2 = CO + H2O,
Organic Chemistry, Russian Academy of Sciences, a
correlation of the specific surface area of nickel with
activity, thermal stability, and agglomeration resisꢀ
tance of supported particles was demonstrated [24,
25]. Unfortunately, the catalytic properties of these
catalysts under the reaction conditions of selective CO
methanation remained unstudied. Recently, we proꢀ
posed nickel–cerium catalysts that exhibited high
activity and selectivity in the reaction of selective CO
methanation in the presence of CO2 in hydrogenꢀconꢀ
taining mixtures [17, 18].
ΔH° = 41 kJ/mol. (III)
The preliminary adsorption removal of CO2 (analoꢀ
gous to industrial processes of hydrogen production) is
often inappropriate because of a considerable increase
in the size of a fuel processor. Thus, highly active and
selective catalysts for CO methanation are required;
these catalysts should prevent the occurrence of CO2
methanation reactions and the reverse reaction of
steam CO conversion.
The process of selective CO methanation in the
presence of CO2 has long been known [4]. It has been
found that rutheniumꢀ and nickelꢀcontaining catalysts
are sufficiently effective for performing the selective
methanation of CO. Interest in studies in this area has
quickened in the past few years [5–22]. The majority
of researchers are agreed that Ru [5–15] and Ni [13–
22] systems are the most promising catalysts, the propꢀ
erties of which can be changed using various supports,
promoting additives, and preparation techniques. It is
believed that nickel catalysts rank below ruthenium
catalysts in performance characteristics because they
require a long reductive pretreatment, are pyrophoric,
and rapidly lose activity in contact with air. At the
same time, their main advantage (which is a crucial
factor for use in a fuel processor for widespread appliꢀ
cations) is much lower cost, as compared with rutheꢀ
nium systems.
In this work, we synthesized nickelꢀcontaining catꢀ
alysts on CeO2, ZrO2, and γꢀAl2O3 supports, studied
their catalytic properties in the reaction of selective
CO methanation in the presence of CO2 in hydrogenꢀ
containing mixtures, and compared their activity with
that of commercial samples of nickel–alumina and
nickel–alumina–calcium catalysts manufactured at
the Novomoskovsk Institute of Nitrogen Industry.
EXPERIMENTAL
Preparation of the Catalysts
The table lists the catalysts, their main composiꢀ
tions, and specific surface areas.
The NiCe, NiCeAl, NiAl, and NiZr catalysts were
prepared by incipient wetness impregnation.
Cerium oxide was prepared from cerium nitrate by
calcination in air at 400°C for 2 h. The specific surface
area of CeO2 was 82 m2/g.
In this context, it is pertinent to develop stable
nonpyrophoric, active, and highly selective catalysts
containing no expensive precious metals for the selecꢀ
tive methanation of CO in the presence of CO2.
γꢀAl2O3 as spherical granules 0.25–0.50 mm in
diameter was used. The specific surface area of
γ
ꢀAl2O3 was 120 m2/g.
To prepare the CeO2/
An analysis of publications devoted to selective CO
methanation on Niꢀcontaining catalysts allowed one
to recognize several supports: MgO [13], Al2O3 [13,
15], TiO2 [13], and ZrO2 [13, 19]. Among them,
Ni/ZrO2 systems exhibited the best characteristics. It
was found [15, 19] that the main factor affecting process
selectivity is the dispersity of supported nickel particles
and the degree of nickel interaction with the support.
Thus, in the series of test samples with various nickel
concentrations (from 0.6 to 15 wt %), a 1.6 wt %
Ni/ZrO2 catalyst was found most effective; the disperꢀ
sity of nickel particles in this catalyst was high [19]. At a
concentration of Ni in the catalyst higher than 3 wt %,
the agglomeration of nickel particles was observed,
γꢀAl2O3 support, γꢀAl2O3 was
impregnated with a required amount of an aqueous
solution of cerium nitrate and then dried in air at
110°C for 2 h and calcined at 400°C for 2 h.
Zirconium oxide was prepared by precipitation
from an aqueous solution of zirconyl nitrate at a conꢀ
stant value of pH 10. A 5% aqueous solution of ammoꢀ
nia was used as a precipitating agent. The resulting
precipitate was filtered off and washed with water and
then with ethanol on filter. The resulting mass was
dried in air for two days and then calcined in air at
500°C for 4 h.
The resulting supports were impregnated with an
which resulted in a decrease in the process selectivity. aqueous solution of a nickel salt and dried in air for 2 h
at 110°C. The preparation procedure was described in
more detail elsewhere [17].
Before performing the catalytic experiments, the
resulting powdered NiCe and NiZr catalysts were pelꢀ
letized and crushed, and a fraction with a particle size
of 0.25–0.50 mm was taken.
The domestic knowꢀhow for the development of
nickel catalysts for the methanation of carbon oxides
also suggests a considerable effect of nickel concentraꢀ
tion and dispersity on the properties of catalysts [23–
25]. Thus, for a series of nickel–alumina (NKMꢀ1,
which is currently referred to as NIAPꢀ07ꢀ01 in accorꢀ
dance with technical specifications) and nickel–aluꢀ
In this work, we studied nickelꢀcontaining catalysts
mina–calcium catalysts (NKMꢀ2A and NKMꢀ4A, taken from several pilot batches manufactured at the
which are currently referred to as NIAPꢀ07ꢀ02) develꢀ Novomoskovsk Institute of Nitrogen Industry: NIAPꢀ
KINETICS AND CATALYSIS Vol. 51
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2010

SELECTIVE METHANATION OF CO IN THE PRESENCE OF CO2
909
Characteristics of the commercial and synthesized nickel catalysts for CO methanation
Concentration
of Ni, wt %
Sample
Catalyst
S
BET, m2/g
Support components
Series of synthesized catalysts
1.9
NiCe
2 wt % Ni/CeO2
75
115
120
35
CeO2
NiCeAl
NiAl
NiZr
2 wt % Ni/8 wt % CeO2/Al2O3
2 wt % Ni/ ꢀAl2O3
2 wt % Ni/ZrO2
1.9
1.8
1.9
γ
ꢀAl2O3, CeO2
ꢀAl2O3
γ
γ
ZrO2
Commercial methanation catalysts manufactured at the Novomoskovsk Institute of Nitrogen Industry
*
ꢀAl2O3, CaCO3, СA2
NIAPꢀ07ꢀ02
Pellets
28.6
209
γ
NKMꢀ2А (t)
NKMꢀ2А (e1)
NKMꢀ2А (e2)
NKMꢀ4А (k)
Pellets
30.6
14.3
7.7
137
149
177
156
AlOOH,
γ
ꢀAl2O3, CaCO3, СА2
ꢀAl2O3, СА2, gibbsite
ꢀAl2O3, CaCO3, СА2
ꢀAl2O3, СА2, graphite,
Al(OH)3, boehmite
CaCO3, ꢀAl2O3, СА2, graphite
γꢀAl2O3, boehmite, CaCO3
Extrudates 1 mm in diameter
Extrudates 1.5 mm in diameter
Ring
CaCO3,
γ
AlOOH,
γ
27.3
CaCO3, γ
NKMꢀ4А (t)
NKMꢀ4А (e1)
Pellets
Extrudates 1 mm in diameter
27.6
13.4
178
235
γ
*Notation used in the chemistry of cements: C = CaO, A = Al O , CA —calcium dealuminate.
2
3
2
07ꢀ02, NKMꢀ4A (k), NKMꢀ4A (t), NKMꢀ4A (e1),
The compositions of gas mixtures at the reactor
NKMꢀ2A (t), NKMꢀ2A (e1), and NKMꢀ2A (e2). The inlet and outlet were analyzed using a Kristall 2000
table summarizes the concentrations of nickel in the chromatograph equipped with a flameꢀionization
samples and the main composition of the catalysts. detector with a methanizer containing an NKMꢀ4
The procedures used for the preparation of these cataꢀ nickel catalyst. The test mixture was separated on a
lysts were described elsewhere [24, 25]. To perform the column packed with Porapak Q. The sensitivity of the
catalytic experiments, commercial catalysts were determination of CO, CO2, CH4, and other gaseous
crushed and a fraction with a particle size of 0.25– hydrocarbon concentrations was 1 ppm. Error in the
0.5 mm was taken.
concentration measurements was no higher than
3
rel. %.
Before performing the experiments, all of the cataꢀ
lyst samples were prereduced immediately in a reactor
in a flow of 5% H2 in He at 400°C for 2 h.
In the course of reaction, we monitored the formaꢀ
tion of not only methane but also other hydrocarbons.
We found that, under the reaction conditions used, the
total concentration of hydrocarbons other than methꢀ
ane was no higher than a few ppm.
The course of the reaction of selective CO methaꢀ
nation was characterized by the inlet CO concentraꢀ
tion, the outlet CH4 concentration, and selectivity
The concentrations of main components in the
catalysts were determined using inductively coupled
plasma atomic emission spectrometry on an Optima
instrument.
The specific surface areas (SBET) of samples were
determined on an ASAPꢀ2400 instrument from full
isotherms of lowꢀtemperature nitrogen adsorption at
(
S
), which was calculated from the equation
FCinO − F
out
CO
–196°C
.
,
×100%
(1)
S =
out
CH4
F
in
CO
where
is the molar concentration of CO at the
F
Catalytic Experiments
out
out
reactor inlet;
and
are the molar concentraꢀ
FCO
F
CH4
The reaction of selective CO methanation in the
presence of CO2 in hydrogenꢀcontaining mixtures was
studied in a quartz flow reactor at atmospheric pressure.
The reactor was a Uꢀshaped tube 40 cm in length with
inner and outer diameters of 3 and 5 mm, respectively.
A weighed portion (0.25 g) of a catalyst was placed in
the reactor. To avoid the release of flour catalyst partiꢀ
cles with a gas flow to the offtake capillary system, a filꢀ
ter was arranged at the reactor outlet. The reaction temꢀ
tions of CO and CH4, respectively, at the reactor outlet.
Selective CO methanation was studied using a gas
mixture with the following composition: CO, 1.5 vol %;
CO2, 20 vol %; H2O, 10 vol %; and the balance H2. The
supply rate of the mixture (standard temperature and
pressure) on a catalyst weight basis (WHSV) was
26000 cm3 (g Cat)–1 h–1 in all of the experiments.
To prevent the formation of volatile Ni(CO)4, the
perature was determined using a Chromel–Alumel formation of which is thermodynamically possible at
thermocouple placed at the center of a catalyst bed. < 150°C, the reaction was performed over the temꢀ
T
KINETICS AND CATALYSIS Vol. 51
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910
[CO]out, ppm
ZYRYANOVA et al.
perature range of 170–400°C. Initially, the reactor was
heated to 170°C in a flow of He; thereafter, the reacꢀ
tion mixture was supplied and the catalytic experiꢀ
ments were started.
(a)
104
103
102
RESULTS AND DISCUSSION
Figure 1 shows the temperature dependence of (a)
the outlet concentration of carbon monoxide, (b) the
outlet concentration of methane, and (c) selectivity
for the commercial catalysts NIAPꢀ07ꢀ02, NKMꢀ4A
(k), NKMꢀ4A (t), NKMꢀ2A (t), and NKMꢀ2A (e2).
The catalysts NKMꢀ2A (e1) and NKMꢀ4A (e1) were
found inactive under reaction conditions, and they are
not given in Fig. 1.
1
2
3
4
5
150
200
250
300
350
Temperature, °C
It can be seen that catalysts containing 27.3–
30.6 wt % Ni exhibited high activity; among them,
NIAPꢀ07ꢀ02 was found the most active (the CO and
CH4 outlet concentration curves were shifted to the
region of lower temperatures with respect to other catꢀ
alysts). This catalyst decreased the concentration of
CO to 570 ppm at 250°C. The selectivity of CO methꢀ
anation was as low as 68% at the specified temperaꢀ
ture. This is reasonable taking into account the fact
that these systems were initially developed for the
combined removal of CO and CO2 from a hydrogenꢀ
containing gas mixture.
[CH4]out, %
12
(b)
1
2
3
4
5
10
8
6
4
According to published data [24, 25] for the NKMꢀ1
(an analog of the catalyst NIAPꢀ07ꢀ02), NKMꢀ2A,
and NKMꢀ4A series, the optimum compositions of
catalysts for the methanation of CO and CO2 present
in a hydrogenꢀcontaining mixture in amounts of 0.3–
2.5 vol % contained ~27.5 wt % Ni. In this case, the
maximum specific surface area of nickel, thermal staꢀ
bility, and catalyst strength were reached. Nevertheꢀ
less, as can be seen in Fig. 1, the test commercial catꢀ
alysts did not allow us to reach the required degree of
CO removal in the reaction of selective CO methanaꢀ
tion in the presence of CO2 in spite of a nearꢀoptimum
composition.
Figure 2 shows the results of testing the catalytic
activity of NiCe, NiCeAl, NiAl, and NiZr samples. It
can be seen that the NiAl catalyst exhibited the lowest
activity and selectivity. The methanation reactions of
CO and CO2 were not observed on this catalyst until a
temperature of ~350°C. A further increase in the temꢀ
perature resulted in the formation of methane because
of both CO and CO2 methanation. In this case, the
fraction of reacted CO2 rapidly increased, and this
manifested itself in a decrease in selectivity to 60%
even at 420°C. It is most likely that the low activity of
this catalyst was related to the formation of inactive
nickel aluminate on the catalyst surface and the hinꢀ
dered reduction of nickel to the metal state [24, 25].
2
0
150
200
250
300
350
Temperature, °C
S
, %
(c)
100
80
60
40
20
0
1
2
3
4
5
150
200
250
300
350
Temperature, °C
Fig. 1. Temperature dependence of the concentrations of
(a) CO and (b) CH at the reactor outlet and (c) selectivꢀ
ity in the course of the reaction of selective CO methanaꢀ
tion in the presence of CO in a hydrogenꢀcontaining
4
The NiZr catalyst exhibited a low activity (the conꢀ
centration of CO at the reactor outlet decreased to
1 vol % at 350°C, Fig. 2); the reaction selectivity was
100%. The high selectivity of NiZr catalysts in the
2
mixture on the commercial catalysts (
) NKMꢀ4A (t), ( ) NKMꢀ2A (e2), (
and ( ) NIAPꢀ07ꢀ02.
1
) NKMꢀ4A (k),
4) NKMꢀ2A (t),
(
2
3
5
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2010

SELECTIVE METHANATION OF CO IN THE PRESENCE OF CO2
911
reaction of selective CO methanation in the presence
[CO]out, ppm
104
of CO2 was also demonstrated previously [13, 19].
The supporting of cerium oxide onto the surface of
alumina had a positive effect on the activity and selecꢀ
tivity of the NiAl catalyst. As can be seen in Fig. 2, on
the NiCeAl catalyst, a minimum concentration of CO
at the reactor outlet (1600 ppm) was observed at 380°C
and 70% selectivity. Note that 100% selectivity was
(a)
103
observed on this catalyst to a temperature of 330°C
.
102
101
We call attention to the fact that Xavier et al. [26]
observed previously an increase in the activity of the
Ni/Al2O3 catalyst in the CO methanation reaction
upon doping with cerium oxide. Xavier et al. [26]
related this effect to an increase in the dispersity of
nickel in the presence of cerium oxide; in turn, this
resulted in a decrease in the temperatures required for
the reduction of supported particles and the methanaꢀ
tion of CO. Barrault et al. [27] also observed a decrease
in the reduction temperature of nickel particles supꢀ
1
2
3
4
150
200
250
300
350
400
450
Temperature, °C
[CH4]out, vol %
ported on CeO2, as compared with the Ni/γꢀAl2O3 and
Ni/SiO2 systems. On the whole, this is consistent with
the results of this work.
(b)
4
3
2
1
1
2
3
4
Among the synthesized samples containing 2 wt %
Ni, the NiCe catalyst exhibited the best catalytic charꢀ
acteristics. It provided the occurrence of the selective
CO methanation reaction in the presence of CO2 with
100% selectivity to a temperature of 260°C, at which
the concentration of CO at the reactor outlet was 0.4
vol % (see Fig. 2). The minimum CO concentration of
10 ppm at the reactor outlet was reached at 300°C and
80% selectivity. A further increase in the temperature
resulted in a gradual increase in the outlet concentraꢀ
tion of CO and a decrease in selectivity, which were as
high as 60 ppm and 40% at 360°C, respectively. Note
that this catalyst decreased the concentration of CO to
<100 ppm over the temperature range of 280–360°C
at >40% selectivity; this makes it possible to use the
resulting hydrogenꢀcontaining mixture for feeding
PEMFCs with Pt–Ru anodes.
It is well known that nickelꢀcontaining catalysts are
pyrophoric systems, and they often lose activity in
contact with air because of the agglomeration of the
active component. To reveal the effect of air (oxygen)
on the catalytic properties of the NiCe system, we perꢀ
formed the following experiments: After performing
standard catalytic experiments, the reactor with the
NiCe catalyst was cooled in a reaction atmosphere to
160°C and then purged with an inert gas (1 min) and
air to cool it to 25°C; then, it was repeatedly heated to
160°C (2 h) and purged with an inert gas (1 min). After
this treatment, a reaction mixture was supplied to the
reactor and catalytic experiments were performed.
Figure 3 shows the temperature dependence of the
outlet concentrations of CO and CO2 and selectivity in
the course of the reaction of selective CO methanation
on the NiCe catalyst immediately after contact with
air (the measurements were performed as the temperꢀ
ature was increased from 160 to 360°C) and in the subꢀ
sequent experiment (the measurements were perꢀ
0
150
200
250
300
350
400
450
Temperature, °C
S
, %
100
80
60
40
20
0
(c)
1
2
3
4
150
200
250
300
350
400
450
Temperature, °C
Fig. 2. Temperature dependence of the concentrations of
(a) CO and (b) CH at the reactor outlet and (c) selectivity
in the course of the reaction of selective CO methanation
in the presence of CO in a hydrogenꢀcontaining mixture
4
2
on the catalysts (
) NiZr.
1) NiCe, (2) NiCeAl, (3) NiAl, and
(
4
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2010

912
[CO]out, ppm
ZYRYANOVA et al.
formed as the temperature was decreased from 360 to
160°C). It can be seen that the activity of the NiCe
catalyst (Figs. 3a, 3b) measured immediately after
contact with air was lower than that in the subsequent
experiment. This was most likely due to the surface
oxidation of supported nickel particles in air; then,
these particles were reduced immediately in the reacꢀ
tion atmosphere. Note that, in the subsequent experiꢀ
ment, the observed temperature dependence of the
outlet concentrations of CO and CH4 and selectivity
was consistent with that obtained in standard catalytic
experiments (Fig. 2). In the following temperature
increase–decrease cycles over the range of 160–
360°C without contact with air, changes in the activity
of the NiCe catalyst were not observed.
(a)
104
103
102
101
1
2
150
200
250
250
250
300
300
300
350
400
This suggests that the NiCe catalyst is stable to
agglomeration in air, and it recovers its activity in the
reaction of selective CO methanation without any
additional pretreatment immediately before the action
of a reaction atmosphere.
Temperature, °C
[CH4]out, vol %
(b)
4
3
2
1
1
2
CONCLUSIONS
The study of the catalytic properties of NKMꢀ2A
and NKMꢀ4a (NIAPꢀ07ꢀ02) commercial methanaꢀ
tion catalysts did not allow us to recommend them for
use in the reaction of selective CO methanation in the
presence of CO2. Among the test systems, 2 wt %
Ni/CeO2 is the most promising catalyst. This catalyst
retained its activity after contact with air and
decreased the concentration of CO from 1.5 vol % to
100 ppm in the presence of 20 vol % CO2 over the temꢀ
perature range of 280–360°C at >40% selectivity. The
minimum CO outlet concentration of 10 ppm at 80%
0
150
200
350
400
Temperature, °C
selectivity was reached at 300°C
.
It is reasonable to focus the subsequent studies on
the optimization of the composition and preparation
procedure of the NiCe system in order to increase its
activity and to extend the range of conditions under
which the reaction of selective CO methanation
occurs in the presence of CO2.
S, %
100
80
60
40
20
0
(c)
ACKNOWLEDGMENTS
This study was supported by the Federal Specialꢀ
Purpose Program “Scientific and Educational Cadres
of Innovative Russia” for 2009–2013 (State Contract
no. P185 of July 16, 2009).
1
2
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