CO and CO2 methanation over supported Ni catalysts

Article abstract of DOI:10.1016/j.cattod.2016.12.036

CO and CO₂ methanation was investigated over Ni catalysts supported on different supports such as γ-Al₂O₃, SiO₂, TiO₂, CeO₂, and ZrO₂. Among them, Ni/CeO₂ was determin

Full text of DOI:10.1016/j.cattod.2016.12.036

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CO and CO2 methanation over supported Ni catalysts
Thien An Le, Min Sik Kim, Sae Ha Lee, Tae Wook Kim, Eun Duck Park∗
Department of Chemical Engineering and Department of Energy Systems Research, Ajou University, 206, World Cup-Ro, Yeongtong-Gu, Suwon 16499,
Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
CO and CO2 methanation was investigated over Ni catalysts supported on different supports such as ␥-
Al2O3, SiO2, TiO2, CeO2, and ZrO2. Among them, Ni/CeO2 was determined to be the most active for CO and
CO2 methanation. These catalytic activities increased with increasing surface area of CeO2. To increase
the specific catalytic activity for CO and CO2 methanation, various Ni-CeO2 catalysts with different Ni
contents were prepared using co-precipitation method. The optimum Ni content was determined for
both reactions. The prepared catalysts were characterized with inductively coupled plasma-atomic emis-
sion spectroscopy, N2 physisorption, temperature-programmed reduction, temperature-programmed
desorption, and X-ray diffraction. The high Ni dispersion and strong CO2 adsorption appeared to be
responsible for the high catalytic activity for CO and CO2 methanation. This Ni-CeO2 can be applied to
the low-temperature CO and CO2 methanation reactor to achieve high single-pass conversions of CO and
CO2.
Received 1 September 2016
Received in revised form
26 November 2016
Accepted 16 December 2016
Available online xxx
Keywords:
CO Methanation
CO2 Methanation
Ni catalyst
Support effect
CeO2
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
production by water electrolysis, this consists of the Power-to-Gas
technology which connects the power grid with the gas grid by
Methane, which can be found as a main component in natural
gas and shale gas, is one of important energy resources and chemi-
cal feedstocks. Therefore, the infrastructure for its delivery has been
well developed and equipped throughout the nations. This enables
us to use methane as an energy carrier now and future.
Although methane can be found in nature, a synthetic natural
gas has been commercially produced from different starting mate-
rials including coal and biomass. In this process, syngas (a mixture
of CO and H2) is transformed into methane through CO methana-
tion, as follows:
transforming surplus power into a grid compatible gas [5].
Since Sabatier and Senderens first reported this reaction in 1902
[6], a number of works have been conducted for this reaction
[7–12]. Vannice [7] compared the catalytic activity for CO metha-
nation over various transition metals and found that the order of
decreasing activity was Ru > Fe > Ni > Co > Rh > Pd > Pt, Ir. Owing to
its high activity and relatively cheap price, nickel has been selected
as an active metal for CO and CO2 methanation. Besides active
metal, a support plays a critical role in the catalysis by stabilizing
the active site as well as enhancing the adsorption of key reac-
tants. Until now, lots of supports including ␥-Al2O3 [13], barium
hexaaluminate [14], SiO2 [13], MCM-41[15], meso-structured silica
nanoparticles (MSN) [15], SiC [16], HY [15], 5A zeolite [17], TiO2
[13], calcium titanate [18], ZrO2 [13], CeO2 [19–24], ceria–zirconia
binary oxide [25], Metal–organic frameworks (MOFs) [26], and
carbon nanofiber (CNF) [27] have been utilized for supported Ni
catalysts. However, only a few works have been disclosed on the
comparative study for CO or CO2 methanation over Ni catalysts
supported on different supports under same reaction conditions.
Takenaka et al. [13] compared the catalytic activity for CO metha-
nation over supported Ni catalysts and claimed that ZrO2 was the
best support among ␥-Al2O3, SiO2, TiO2, and ZrO2. Zhen et al. [15]
reported that the activity of CO2 methanation followed an order of
Ni/MSN > Ni/MCM–41 > Ni/HY > Ni/SiO2 > Ni/␥-Al2O3.
CO(g) + 3H2(g) ↔ CH4(g) + H2O(g); ꢀH◦298K = −206 kJ mol−1(1)
This reaction is also used in the purification process in hydrogen
and ammonia production plants [1]. Recently, selective CO metha-
nation in the presence of an excessive amount of CO2 has been
intensively studied to remove residual CO from the reformed gas
for the polymer electrolyte membrane fuel cells [2].
Besides CO methanation, a synthetic natural gas can be produced
from CO2 through CO2 methanation, as follows:
CO2(g) + 4H2(g) ↔ CH4(g) + 2H2O(g); ꢀH◦298K = −165 kJ mol−1
(2)
This is a rather simple chemical route among a variety of
catalytic CO2 hydrogenation techniques [3,4]. Together with H2
In this work, we carried out the comparative study for CO and
CO2 methanation over Ni catalysts supported on some selected sup-
∗
Corresponding author.
E-mail address: edpark@ajou.ac.kr (E.D. Park).
http://dx.doi.org/10.1016/j.cattod.2016.12.036
0920-5861/© 2016 Elsevier B.V. All rights reserved.
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ports such as ␥-Al2O3, SiO2, TiO2, CeO2, and ZrO2. Among them, the
Ni/CeO2 catalyst was selected as the best catalyst. Furthermore,
we have also found that the methanation activity over Ni/CeO2 is
proportional to the surface area of CeO2. Since these methanation
reactions are exothermic and thermodynamically limited at high
temperatures, it is quite desirable to carry out these reactions at low
temperatures to achieve high conversions of CO and CO2. There-
fore, a number of series Ni-CeO2 catalysts containing different Ni
contents were prepared by co-precipitation method and applied to
CO and CO2 methanation to find out the optimum Ni content. The
stability test was also carried out for the selected catalyst.
Powder X-ray diffraction (XRD) experiments were carried out
on a Rigaku D/Max instrument with a Cu K␣ source. The primary
crystallite sizes of the catalysts were determined using the Scherrer
equation [29],
0.9ꢀk˛1
B(2ꢁ) cos ꢁmax
L =
,
(3)
where L denotes the average particle size, 0.9 is the value in radians
when B(2␪) is the full width at half maximum (FWHM) of the peak,
␭
␪
is the wavelength of the X-ray radiation (0.15406 nm), and
is the angular position at the (111) peak maximum of Ni.
K␣1
max
The Ni content was confirmed using inductively coupled
plasma-atomic emission spectroscopy (ICP-AES) (Thermo Scientific
iCAP 6500).
2. Experimental
Hydrogen temperature-programmed reduction (H2-TPR) of the
sample was carried out on a Micromeritics Autochem 2910
equipped with a thermal conductivity detector (TCD). H2-TPR was
performed using 10 mol% H2/Ar at a flow rate of 30 mL/min in the
temperature range 40–900 ◦C at a heating rate of 10 ◦C/min. The
hydrogen consumption was calculated based on the H2-TPR pat-
terns of predetermined amount of Ag2O.
Temperature-programmed desorption (TPD) of the sample was
carried out on a Micromeritics Autochem 2910 equipped with a TCD
and mass spectrometric detector. A pulsed CO2 chemisorption was
conducted at room temperature by injection of 0.50 mL of 15 mol%
CO2 balanced with He in He stream. TPD was performed using He
at a flow rate of 30 mL/min in the temperature range 40–900 ◦C at a
heating rate of 10 ◦C/min. The ion signals recorded at m/e = 44 was
utilized for monitoring desorbed CO2.
2.1. Preparation of catalysts
Different supports, such as SiO2 (Zeochem, ZEOprep 60,
S
BET = 542 m2/g), TiO2 (Degussa, P25, SBET = 51 m2/g), ␥-Al2O3 (Alfa-
aesar, SBET = 162 m2/g), CeO2 (Rhodia, HSA20, SBET = 140 m2/g),
and CeO2 (Rhodia, SBET = 230 m2/g) were purchased and used as
received. Only ZrO2 (SBET = 50 m2/g) was prepared by precipita-
tion method from an aqueous solution of ZrO(NO3)2·2H2O (Junsei
Chemical) and Na2CO3 (Junsei Chemical). To change the surface
area of ceria, CeO2 (Rhodia, HSA20, SBET = 140 m2/g) was calcined
in air at 800 and 1000 ◦C, respectively. To differentiate each ceria
support with different surface areas, its surface area is denoted in
parenthesis, e.g. CeO2 (55) implies the ceria support with a surface
area of 55 m2/g, which was prepared through calcination of CeO2
(Rhodia, HSA20, SBET = 140 m2/g) at 800 ◦C.
Various supported Ni catalysts were prepared by wet impreg-
nation. 2.81 g of Ni(NO3)2·6H2O (Junsei Chemical) was dissolved
into 50 mL of deionized water and mixed with 5 g of support. The
excesswater was slowly removedusing a rotary evaporator(BUCHI,
Switzerland). The recovered powder was dried in an oven at 120 ◦C
for 12 h and calcined in an air stream at 500 ◦C for 3 h. These cal-
cined samples were reduced in a H2 stream at 500 ◦C for 1 h before
reaction. The Ni content was intended to be 10 wt% for supported
Ni catalysts.
NiaCe1-aOx (0.3 ≤ a ≤ 0.9) catalysts were prepared using a co-
precipitation method at room temperature. Ni(NO3)2·6H2O (Junsei
Chemical) and Ce(NO3)3·6H2O (Junsei Chemical) were first dis-
solved in deionized water to make solutions with different mole
fractions of Ni. Then, aqueous Na2CO3 solution was added drop-
wise under vigorous stirring to reach a final pH 9 and the slurry was
aged for 3 h without stirring at room temperature. The suspension
was filtered and washed with deionized water and dried at 110 ◦C
and calcined in air at 500 ◦C for 5 h. All the prepared catalysts were
reduced in hydrogen at 500 ◦C before reaction.
For comparison, NiO nanoparticles were synthesized as
described in the previous work [28]. Briefly, an aqueous
Ni(NO3)2·6H2O (Junsei Chemical) solution was added drop-
wise to the poly(ethylene glycol)-block-poly (propylene)-block-
poly(ethylene glycol) (PEG-PPG-PEG, Mn = 8400, Aldrich) mixture
in which PEG-PPG-PEG was mixed with NaOH (Samchun Chemi-
cal) in deionized water. The resulting mixture was stirred at room
temperature for 1 h, centrifuged, washed three times with water
and then with isopropanol (Aldrich), and dried at 50 ◦C for 12 h.
The dried powder was calcined at 500 ◦C for 2 h in an air stream.
2.3. Catalytic activity test
The catalytic activity tests were conducted at atmospheric pres-
sure using a continuous fixed bed reactor system. Generally, 0.10 g
of the catalyst that had been retained between 45 and 80 mesh
sieves was loaded into the quartz reactor (internal diameter = 3 mm
and length = 345 mm) and brought into contact with a feed com-
posed of 1 mol% CO or CO2, 50 mol% H2, and 49 mol% He at a flow
rate of 100 mL/min. The mass flow rate of each gas was controlled
with a mass flow controller (MFC) (Brooks Instrument). The reac-
tion temperature was measured by a thermocouple placed in the
catalyst bed.
In order to obtain the kinetic data for CO and CO2 methanation,
50 mg of the catalyst was diluted with 0.15 g of ␣-Al2O3 to avoid the
generation of hot spot in the catalyst bed. The steady-state activity
data at different temperatures were measured only when CO or CO2
conversion was less than 15%.
The reactants and products were separated using a packed col-
umn filled with Carbosphere® and capillary Poraplot Q column, and
analyzed using an online gas chromatographer (HP 6890) fitted
with a TCD and flame ionization detector. The conversion of CO and
CO2 and carbon yields to CH4, CO, C2H6, and C3H8 were calculated
using the following equations:
CO conversion (%) = ([CO]in − [CO]out)/[CO]in × 100,
CO2 conversion (%) = ([CO2]in − CO2]out)/[CO2]in × 100,
(4)
(5)
Carbon yield to CH4(%) = [CH4]out/([CO]in + [CO2]in) × 100, (6)
Carbon yield to CO(%) = [CO]out/[CO2]in × 100,
(7)
2.2. Characterization of catalysts
Carbon yield to C2H6(%) = (2 × [C2H6]out)/([CO]in + [CO2]in
× 100,
)
The specific surface area of the sample was measured on a
Micromeritics ASAP 2020 system and calculated by the Brunauer-
Emmett-Teller (BET) method. Prior to the measurement, the sample
was degassed under vacuum for 6 h at 200 ◦C.
(8)
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Ni/CeO2 (230)
Ni/γ-Al2O3
Ni/CeO2 (230)
Ni/γ-Al2O3
Ni/ZrO2
Ni/ZrO2
Ni/TiO2
Ni/SiO2
Ni/TiO2
Ni/SiO2
20
40
60
80
0
200
400
600
800
2 theta (deg.)
Fig. 2. X-ray diffraction patterns of supported Ni catalysts reduced at 500 ◦C. (ꢀ)
Anatase, JCPDS 21-1272, (᭹) Rutile, JCPDS 21-1276, (ꢁ) ZrO2, JCPDS 37-1484, (᭿)
␥-Al2O3, JCPDS 10-0425, (ꢂ) CeO2, JCPDS 43-1002, (ꢂ) Ni, JCPDS 04-0850.
Temperature (oC)
Fig. 1. H2-TPR profiles of supported Ni catalysts.
Carbon yield to C3H8(%) = (3 × [C3H8]out)/([CO]in + [CO2]in
× 100,
)
lowest TPR peak can be found over Ni/CeO2. It is generally accepted
that the smaller metal oxide particle can be reduced at a lower tem-
perature than the larger ones as long as the interaction between a
metal oxide particle and a support can be neglected. Therefore, it
can be said that the smallest NiO nanoparticles are formed on ceria
support, which results in the formation of the smallest Ni particles
after reduction. This is consistent with the XRD patterns of Ni/CeO2
reduced at 500 ◦C in which very weak XRD peaks corresponding to
the metallic Ni were observed (Fig. 2). In the case of Ni/␥-Al2O3,
no XRD peak representing the metallic Ni can be obtained. This
can be explained that most Ni oxides on ␥-Al2O3 were not reduced
at 500 ◦C based on its H2-TPR patterns where the main peak was
observed at 678 ◦C. It can be conclude that there exists a strong
interaction between NiO and ␥-Al2O3 surface. Based on the H2-TPR
patterns, the interaction between NiO and TiO2 surface seems to
be weaker than that between NiO and ␥-Al2O3 surface but much
stronger than those between NiO and other supports such as CeO2,
SiO2, and ZrO2. The amount of hydrogen consumed during H2-TPR
experiments were calculated and listed in Table 1. It is worth noting
that the amount of consumed hydrogen was larger for the Ni cata-
lysts supported on reducible metal oxides such as CeO2, TiO2, and
ZrO2 than for the ones supported on irreducible metal oxides such
as ␥-Al2O3 and SiO2. Especially, the amount of consumed hydrogen
was the largest for Ni/CeO2 even though the high-temperature TPR
peak centered at 795 ◦C due to the reduction of bulk CeO2 was not
(9)
where [CO]in and [CO2]in represent the concentration of CO and
CO2 in the feed stream and [CO]out, [CO2]out, [CH4]out, [C2H6]out
and [C3H8]out denote the concentration of CO, CH4, C2H6, and C3H8
in the output stream, respectively. The difference between CO or
CO2 conversion and total carbon yield in all experiments is within
an experimental error.
,
3. Results and discussion
3.1. Supported Ni catalysts prepared by wet impregnation
The physical properties of Ni catalysts supported on different
supports such as ␥-Al2O3, SiO2, TiO2, CeO2, and ZrO2 are presented
in Table 1. The BET surface area of each supported Ni catalyst was
lower than that of the support itself. This can be explained by the
pore filling in the catalyst preparation step. The ratio of reduction
in the BET surface area after an impregnation of Ni was significant
for the Ni catalysts supported on the supports with high surface
areas and small average pore diameters.
To find out the reducibility of nickel oxide species on different
supports, H2-TPR patterns were obtained for supported Ni catalysts
calcined in air at 500 ◦C, as shown in Fig. 1. It is worth noting that the
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Table 1
Physicochemical properties of supported Ni catalysts.
Catalyst
SBET (m2/g)
Pore volume (cm3/g)
Average pore
Crystallite size of
Ni (nm)b
H2 consumption
(mmol H2/g)c
diameter (nm)a
Ni/CeO2 (230)
Ni/ZrO2
Ni/SiO2
Ni/TiO2
Ni/␥-Al2O3
117
36
380
31
0.13
0.11
0.58
0.26
0.22
4.4
11.8
6.1
32.8
7.4
n.d.
12
11
17
n.d.
2.4
1.5
1.2
1.5
1.2
130
a
Average pore diameter was determined by BJH model.
b
c
Crystallite size of Ni was determined by Scherrer formula for supported Ni catalysts reduced at 500 ◦C.
H2 consumption was determined based on the H2-TPR.
Fig. 3. Catalytic performance of supported Ni catalysts for CO methanation. Reaction conditions: 1 mol% CO, 50 mol% H2, 49 mol% He, F/W = 1000 mL/min/gcat.
considered. This also supports that there exists a strong interaction
between Ni and ceria support.
The catalytic performance for CO and CO2 methana-
tion was evaluated over Ni catalysts supported on different
The amount of CO2 chemisorbed at room temperature was
determined to be 232, 39, 9, 3, 1 ␮mol CO2/gcat. for Ni/CeO2,
Ni/ZrO2, Ni/␥-Al2O3, Ni/TiO2, and Ni/SiO2, respectively. The CO2-
TPD patterns were obtained as shown in Fig. 5. All the catalysts
except for Ni/CeO2 has only weak low-temperature TPD peak,
which implies that there exist only weak basic sites for CO2
chemisorption. On the other hand, a rather broad and strong TPD
peak was also observed around 500 ◦C over Ni/CeO2. This strong
CO2 chemisorption might have a beneficial effect on the catalytic
activity for CO2 methanation.
Since ceria was selected as the best support for these reactions,
a further work was carried out to find out the effect of surface area
of ceria on the catalytic activities. H2-TPR patterns were obtained
for Ni/CeO2 catalyst with different surface areas, as shown in Fig. 6.
The H2-TPR patterns can be separated into three different parts.
A first weak TPR peak is found around 220 ◦C with a rather broad
shoulder at lower temperatures. This might be due to the reduc-
tion of very small NiO particles weakly interacting with ceria. The
second sharp TPR peak is observed around 320 ◦C. This is owing to
the reduction of NiO particles and surface ceria. The surface ceria
can be reduced easily by hydrogen dissociated on the metallic Ni.
The high-temperature TPR peak is ascribed to the reduction of bulk
ceria. Fig. S4 clearly shows that the peak intensity of the first TPR
peak decreased with decreasing surface area of the support. This
can be interpreted that the number of very small NiO particles
decreases with decreasing surface area of the support. Fig. 7 reveals
that the intensity of the XRD peaks was strengthened with decreas-
ing surface area of the support. The crystallite sizes of ceria and Ni
were calculated to be increased with decreasing surface area of the
support, as shown in Table 2.
supports. Fig.
3
shows that the temperature achieving
100% CO conversion increased in the following order:
Ni/CeO2 < Ni/ZrO2 < Ni/TiO2 < Ni/SiO2 < Ni/␥-Al2O3. The highest
catalytic activity of Ni/CeO2 can be ascribed to the smallest Ni
particle size. On the other hand, the lowest catalytic activity of
Ni/␥-Al2O3 must be due to the incomplete reduction of Ni oxides
under present reductive pretreatment conditions. Besides Ni
dispersion, the support effect cannot be neglected because Ni/ZrO2
and Ni/TiO2 which have large Ni particles exhibit the higher
catalytic activity compared with Ni/SiO2 with small Ni particles.
Methane was determined to be a major product irrespective of
supports for all reaction temperatures. Besides methane, ethane
and propane were also detected at low temperatures (Fig. S1).
The carbon yields to ethane and propane appear to be depen-
dent on the support. High carbon yields to ethane and propane
were observed over Ni/ZrO2. Fig. 4 exhibits that the temperature
achieving 100% CO2 conversion increased in the following order:
Ni/CeO2 < Ni/SiO2 < Ni/ZrO2 < Ni/TiO2 ∼ Ni/␥-Al2O3. This seems to
be closely related to the Ni dispersion as long as the Ni species
are fully reduced. Methane was a predominant product during
CO2 methanation. The formation of ethane was observed only
over Ni/CeO2 and only CO was detected as a byproduct over the
other supported Ni catalysts (Fig. S2). The activation energy for
CO methanation of Ni/␥-Al2O3, Ni/SiO2, Ni/TiO2, Ni/CeO2, and
Ni/ZrO2 was determined to be 153, 100, 90, 115, and 87 kJ/mol,
respectively, based on the Arrhenius plot (Fig. S3). These values
are similar with those in the previous reports [23]. Note that the
activation energy of Ni/␥-Al2O3, in which most Ni oxides were not
reduced, is much higher than those of other catalysts.
The catalytic performance for CO and CO2 methanation was
evaluated over Ni/CeO2 catalysts with different surface areas.
Figs. 8 and 9 show that the catalytic activities for both reactions
increased with increasing surface area of the support. Methane is
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Fig. 4. Catalytic performance of supported Ni catalysts for CO2 methanation. Reaction conditions: 1 mol% CO2, 50 mol% H2, 49 mol% He, F/W = 1000 mL/min/gcat.
Table 2
Physicochemical properties of Ni/CeO2 catalysts with different surface areas.
Catalyst
SBET (m2/g)
Pore volume
(cm3/g)
Average pore
Crystallitesize(nm)b
H2 consumption
(mmol H2/g)c
diameter (nm)a
CeO2
Ni
Ni/CeO2 (230)
Ni/CeO2 (140)
Ni/CeO2 (55)
Ni/CeO2 (19)
117
94
44
0.13
0.22
0.22
0.15
4.4
9.3
20.1
39.9
9
8
18
37
n.d.
9
21
27
2.4
2.5
2.3
2.2
15
a
Average pore diameter was determined by BJH model.
b
c
Crystallite size of Ni was determined by Scherrer formula for supported Ni catalysts reduced at 500 ◦C.
H2 consumption was determined based on the H2-TPR.
Ni/CeO2 (19)
Ni/CeO2 (55)
Ni/CeO2 (140)
Ni/CeO2 (230)
800
Ni/CeO2 (230)
0
200
400
600
Ni/ZrO2
Temperature (oC)
Ni/SiO2
Fig. 6. H2-TPR profiles of Ni/CeO2 with different surface areas.
Ni/TiO2
3.2. Ni-CeO2 catalysts prepared by co-precipitation
Ni/Al2O3
200
400
600
800
Various Ni-CeO2 catalysts with different Ni contents were pre-
pared by co-precipitation method to increase the specific catalytic
activity. The physical properties of a series of Ni-CeO2 catalysts are
listed in Table 3. The BET surface areas of Ni-CeO2 catalysts were
larger than that of unsupported NiO catalysts. However, there was
no correlation between the BET surface area and the Ni content for
Ni-CeO2 catalysts. On the other hand, the pore volume and average
pore diameter increased with increasing Ni content.
H2-TPR patterns were obtained for Ni-CeO2 catalysts calcined
in air at 500 ◦C to find out the reducibility of nickel oxide species,
as shown in Fig. 10. For comparison, H2-TPR pattern of unsup-
ported NiO is also displayed. The main TPR peak is shifted to a
higher temperature with increasing Ni content for Ni-CeO2 cat-
alysts. Compared with H2-TPR patterns of Ni/CeO2 catalysts, TPR
Temperature (oC)
Fig. 5. CO2-TPD profiles of supported Ni catalysts.
the major product for both CO and CO2 methanation. In the case
of CO methanation, ethane and propane were also observed as
byproducts (Fig. S5). On the other hand, the formation of propane
was not detected for CO2 methanation (Fig. S6). CO formation was
confirmed over Ni/CeO2 (19) which had the lowest catalytic activ-
ity. Therefore, it can be concluded that the Ni dispersion is a critical
factor to control the catalytic activity for Ni/CeO2 catalysts.
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NiO
Ni0.9Ce0.1Ox
Ni0.8Ce0.2Ox
Ni0.7Ce0.3Ox
Ni0.6Ce0.4Ox
Ni0.5Ce0.5Ox
Ni0.3Ce0.7Ox
0
200
400
600
800
Temperature (oC)
Fig. 10. H2-TPR profiles of NiO and Ni-CeO2 catalysts with different Ni contents.
Fig. 7. X-ray diffraction patterns of Ni/CeO2 catalysts with different surface areas
reduced at 500 ◦C. (ꢁ) CeO2, JCPDS 43–1002, (*) Ni, JCPDS 04-0850.
reached the minimum value for Ni0.7Ce0.3Ox and Ni0.8Ce0.2Ox, and
increased with further increasing Ni contents.
peaks were observed at higher temperatures for Ni-CeO2 catalysts,
which implies that there exists a stronger interaction between NiO
and ceria in Ni-CeO2 catalysts than in Ni/CeO2 ones. The amount
of consumed hydrogen during H2-TPR experiment increased with
increasing Ni content (Table 3).
X-ray diffraction patterns were obtained for Ni-CeO2 catalysts
reduced at 500 ◦C (Fig. S7). The crystallite size of Ni was calcu-
lated and listed in Table 3. It decreased with increasing Ni content,
The catalytic performance for CO and CO2 methanation was
evaluated over Ni-CeO2 and unsupported Ni catalysts. As shown in
Figs. 11 and 12, the Ni-CeO2 catalysts were superior to unsupported
Ni catalysts in all cases. The highest catalytic activity was obtained
over Ni0.8Ce0.2Ox catalyst for both reactions. Methane was deter-
mined to be a major product for both reactions. Besides methane,
ethane and propane were also detected at low temperatures for CO
100
100
Ni/CeO2 (230)
Ni/CeO2 (230)
Ni/CeO2 (140)
Ni/CeO2 (55)
Ni/CeO2 (140)
Ni/CeO2 (55)
80
80
Ni/CeO2 (19)
60
Ni/CeO2 (19)
60
40
20
0
40
20
0
150
200
250
300
350
150
200
250
300
350
Temperature (oC)
Temperature (oC)
Fig. 8. Catalytic performance of Ni/CeO2 with different surface areas for CO methanation. Reaction conditions: 1 mol% CO, 50 mol% H2, 49 mol% He, F/W = 1000 mL/min/gcat.
Ni/CeO2 (230)
Ni/CeO2 (140)
Ni/CeO2 (55)
Ni/CeO2 (19)
100
80
60
40
20
0
100
80
60
40
20
0
Ni/CeO2 (230)
Ni/CeO2 (140)
Ni/CeO2 (55)
Ni/CeO2 (19)
150
200
250
300
350
150
200
250
300
350
Temperature (oC)
Temperature (oC)
Fig. 9. Catalytic performance of Ni/CeO2 with different surface areas for CO2 methanation. Reaction conditions: 1 mol% CO2, 50 mol% H2, 49 mol% He, F/W = 1000 mL/min/gcat.
Please cite this article in press as: T.A. Le, et al., CO and CO2 methanation over supported Ni catalysts, Catal. Today (2016),
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7
Table 3
Physicochemical properties of Ni-CeO2 catalysts with different Ni contents.
Catalyst
SBET (m2/g)
Pore volume
(cm3/g)
Average pore
Crystallite size of
Ni (nm)b
H2 consumption
(mmol H2/g)c
diameter (nm)a
NiO
Ni0.3Ce0.7Ox
(wt.%)
22
91
0.18
0.09
32.8
5.5
33
n.d.
13
1.5
Ni0.5Ce0.5Ox
(25 wt.%)
Ni0.6Ce0.4Ox
(34 wt.%)
Ni0.7Ce0.3Ox
(44 wt.%)
Ni0.8Ce0.2Ox
(58 wt.%)
Ni0.9Ce0.1Ox
(75 wt.%)
83
89
73
64
76
0.17
0.22
0.33
0.42
0.44
8.9
32
22
12
12
16
4.4
5.6
7.9
10
11.5
19.8
21.5
22.5
13
a
Average pore diameter was determined by BJH model.
b
c
Crystallite size of Ni was determined by Scherrer formula for Ni-CeO2 catalysts reduced at 500 ◦C.
H2 consumption was determined based on the H2-TPR.
100
80
60
40
20
0
100
80
60
40
20
0
Ni0.3Ce0.7Ox
Ni0.3Ce07Ox
Ni0.5Ce0.5Ox
Ni0.6Ce0.4Ox
Ni0.7Ce0.3Ox
Ni0.8Ce0.2Ox
Ni0.9Ce0.1Ox
Ni
Ni0.5Ce0.5Ox
Ni0.6Ce0.4Ox
Ni0.7Ce0.3Ox
Ni0.8Ce0.2Ox
Ni0.9Ce0.1Ox
Ni
150
200
250
300
350
150
200
250
300
350
Temperature (oC)
Temperature (oC)
Fig. 11. Catalytic performance of Ni-CeO2 catalysts with different Ni contents for CO methanation. Reaction conditions: 1 mol% CO, 50 mol% H2, 49 mol% He,
F/W = 1000 mL/min/gcat.
Ni0.3Ce0.7Ox
Ni0.3Ce0.7Ox
Ni0.5Ce0.5Ox
Ni0.6Ce0.4Ox
Ni0.7Ce0.3Ox
Ni0.8Ce0.2Ox
Ni0.9Ce0.1Ox
Ni
100
80
60
40
20
0
100
80
60
40
20
0
Ni0.5Ce0.5Ox
Ni0.6Ce0.4Ox
Ni0.7Ce0.3Ox
Ni0.8Ce0.2Ox
Ni0.9Ce0.1Ox
Ni
150
200
250
300
350
150
200
250
300
350
Temperature (oC)
Temperature (oC)
Fig. 12. Catalytic performance of Ni-CeO2 catalysts with different Ni contents for CO2 methanation. Reaction conditions: 1 mol% CO2, 50 mol% H2, 49 mol% He,
F/W = 1000 mL/min/gcat.
methanation (Fig. S8). However, only ethane was observed for CO2
methanation (Fig. S9).
Since CO and CO2 methanation are highly exothermic reactions,
the thermal stability was checked for the best catalyst. The catalytic
activities for CO and CO2 methanation of Ni0.8Ce0.2Ox catalyst after
a reaction at 400 or 500 ◦C for 24 h were compared with those of the
fresh Ni0.8Ce0.2Ox catalyst (Figs. S11 and S12). The catalytic activity
appeared to be decreased slightly after a reaction at high temper-
atures. The crystalline sizes of Ni of the catalyst after a reaction
at 400 and 500 ◦C for 24 h were determined to be 16 and 19 nm,
Compared with Ni-based catalysts reported previously, the
Ni0.8Ce0.2Ox catalyst can be classified into most active catalyst
group for CO methanation (Fig. S10). Its activation energy is deter-
mined to be 133 kJ/mol, which is slightly higher than that of Ni/CeO2
catalysts. On the other hand, the activation energy for CO2 metha-
nation was calculated to be 95 kJ/mol.
Please cite this article in press as: T.A. Le, et al., CO and CO2 methanation over supported Ni catalysts, Catal. Today (2016),
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respectively. The crystalline sizes of CeO2 of the catalyst after a
reaction at 400 and 500 ◦C for 24 h were also estimated to be 9
and 12 nm, respectively. This increase in the crystalline size of Ni
and CeO2 is responsible for the decreased catalytic activity for CO
and CO2 methanation after reaction at high temperatures. Owing
to the thermodynamic limitations for CO and CO2 methanation, it
is quite plausible to carry out these reactions at low temperatures
to achieve high conversions of CO and CO2. Therefore, this highly
active Ni0.8Ce0.2Ox catalyst can be installed in the first methana-
tion reactor in a series of adiabatic reactors with inter-stage coolers
to initiate reaction at low temperatures. This catalyst can be also
applied to a low-temperature methanation reactor in which the
reaction temperature is well controlled not to cause catalyst sin-
tering and low single-pass conversions of CO or CO2 due to the
thermodynamic limitation.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.cattod.2016.12.
036.
References
[1] M.V. Twigg (Ed.), Catalyst Handbook, 2nd ed., Manson Publishing, London,
1996.
[2] E.D. Park, D. Lee, H.C. Lee, Catal. Today 139 (2009) 280.
[3] W. Wang, S. Wang, X. Ma, J. Gong, Chem. Soc. Rev 40 (2011) 3703.
[4] H. Ban, C. Li, Y. Zhang, F. Meng, H. Zheng, Z. Li, Rev. Adv. Sci. Eng. 4 (2015) 126.
[5] M. Götz, J. Lefebvre, F. Mörs, A.M. Koch, F. Graf, S. Bajohr, R. Reimert, T. Kolb,
Renew. Energy 85 (2016) 1371.
[6] P. Sabatier, J.B. Senderens, C.R. Acad. Sci. Paris 134 (1902) 514.
[7] M.A. Vannice, J. Catal 37 (1975) 448.
[8] B. Mao, S.S.K. Ma, X. Wang, H. Su, S.H. Chan, Catal. Sci. Technol. 6 (2016) 4048.
[9] M.A.A. Aziz, A.A. Jalil, S. Triwahyono, A. Ahmad, Green Chem. 17 (2015) 2647.
[10] J. Gao, Q. Liu, F. Gu, B. Liu, Z. Zhong, F. Su, RSC Adv. 5 (2015) 22759.
[11] S. Rönsch, J. Schneider, S. Matthischke, M. Schlüter, M. Götz, J. Lefebvre, P.
Prabhakaran, S. Bajohr, Fuel 166 (2016) 276.
4. Conclusion
Ni/CeO2 was determined to be the most active for CO and CO2
methanation among Ni catalysts supported on different supports
such as ␥-Al2O3, SiO2, TiO2, CeO2, and ZrO2. These catalytic activ-
ities increased with increasing surface area of CeO2. The high Ni
dispersion and an intimate contact between Ni and ceria appeared
to be responsible for the high catalytic activity for CO methanation.
Furthermore, strong CO2 adsorption on CeO2 is beneficial for CO2
methanation. A further increase in the specific catalytic activity for
CO and CO2 methanation can be made using Ni-CeO2 catalyst pre-
pared by co-precipitation method. The best catalyst, Ni0.8Ce0.2Ox,
has the high Ni content and small Ni particles. This catalyst can be
applied to the low-temperature CO or CO2 methanation reactor to
achieve high single-pass conversions of CO and CO2.
[12] X. Su, J. Xu, B. Liang, H. Duan, B. Hou, Y. Huang, J. Energy Chem. 25 (4) (2016)
553.
[13] S. Takenaka, T. Shimizu, K. Otsuka, Int. J. Hydrogen Energy 29 (2004) 1065.
[14] J. Gao, C. Jia, J. Li, F. Gu, G. Xu, Z. Zhong, F. Su, Ind. Eng. Chem. Res. 51 (31)
(2012) 10345.
[15] M.A.A. Aziz, A.A. Jalil, S. Triwahyono, R.R. Mukti, Y.H. Taufiq-Yap, M.R. Sazegar,
Appl. Catal. B 147 (2014) 359.
[16] Y. Yu, G.-Q. Jin, Y.-Y. Wang, X.-Y. Guo, Fuel Process. Technol. 92 (12) (2011)
2293.
[17] A. Borgschulte, N. Gallandat, B. Probst, R. Suter, E. Callini, D. Ferri, Y. Arroyo, R.
Erni, H. Geerlings, A. Zuttel, Phys. Chem. Chem. Phys. 15 (2013) 9620.
[18] C. Jia, J. Gao, J. Li, F. Gu, G. Xu, Z. Zhong, F. Su, Catal. Sci. Technol. 3 (2) (2013)
490.
[19] S. Tada, T. Shimizu, H. Kameyama, T. Haneda, R. Kikuchi, Int. J. Hydrogen
Energy 37 (7) (2012) 5527.
[20] M.M. Zyryanova, P.V. Snytnikov, R.V. Gulyaev, Yu.I. Amosov, A.I. Boronin, V.A.
Sobyanin, Chem. Eng. J. 238 (2014) 189.
[21] B. Nematollahi, M. Rezaei, E. Nemati Lay, Int. J. Hydrogen Energy 40 (2015)
8539.
Acknowledgments
[22] M.V. Konishcheva, D.I. Potemkin, P.V. Snytnikov, M.M. Zyryanova, V.P.
Pakharukova, P.A. Simonov, V.A. Sobyanin, Int. J. Hydrogen Energy 40 (2015)
14058.
[23] B. Nematollahi, M. Rezaei, E. Nemati Lay, J. Rare Earth 33 (2015) 619–628.
[24] E. Rombi, M.G. Cutrufello, L. Atzori, R. Monaci, A. Ardu, D. Gazzoli, P. Deiana, I.
Ferinoa, Appl. Catal. A 515 (2016) 144.
[25] F. Ocampo, B. Louis, L. Kiwi-Minsker, A.-C. Roger, Appl. Catal. A 392 (2011) 36.
[26] W. Zhen, B. Li, G. Lu, J. Ma, Chem. Commun. 51 (2015) 1728.
[27] W. Zhang, Q. Ge, H. Xu, Sci. Adv. Mater. 3 (6) (2011) 1046.
[28] P. Lakshmanan, M.S. Kim, E.D. Park, Appl. Catal. A 513 (2016) 98.
[29] A. Patterson, Phys. Rev. 56 (10) (1939) 978.
This work was supported by the New & Renewable Energy Core
Technology Program (20123010040010) and Human Resources
Program in Energy Technology (No. 20154010200820) of the Korea
Institute of Energy Technology Evaluation and Planning (KETEP),
granted financial resource from the Ministry of Trade, Industry &
Energy, Republic of Korea. This work was also supported by C1
Gas Refinery Program through the National Research Foundation
of Korea (NRF) funded by the Ministry of Science, ICT & Future
Planning (2015M3D3A1A01064899).
Please cite this article in press as: T.A. Le, et al., CO and CO2 methanation over supported Ni catalysts, Catal. Today (2016),
http://dx.doi.org/10.1016/j.cattod.2016.12.036