Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1
세타-알루미나 담지 니켈 촉매상에서 메탄의 이산화탄소 개질 반응
백승찬, 노현석, 유중문, 전기원, 박상언*
한국화학연구원 화학기술부 분자활성공학실
Carbon Dioxide Reforming of Methane over θ-Al2O3 Supported Ni Catalysts
Seung-Chan Baek, Hyun-Seog Roh, Zhong-Wen Liu, Ki-Won Jun, Sang-Eon Park*
Catalysis Center for Molecular Engineering, Korea Research Institute of Chemical Technology, P. O.
Box 107, Yuseong, Daejeon 305-600, Korea
INTRODUCTION
In recent years, a renewable study on carbon dioxide reforming of methane (CDR) to produce
synthesis gas is becoming an attractive and challenging subject for the chemical utilization of natural
gas and carbon dioxide, which are substances intimately related to greenhouse effect and energy
resources [1]. This reaction produces synthesis gas having a low H2/CO ratio, which is suitable for
Fisher-Tropsch synthesis and oxo-synthesis. Catalytic reforming of methane with carbon dioxide to
synthesis gas has been considered as one of the most promising technologies for utilization of CO2.
However, the major problem encountered in this reaction is rapid catalyst deactivation by coke
deposition on the catalyst surface. The major interest in CDR originates from the demand of the
production of liquid hydrocarbons and oxygenates, e.g. acetic acid, formaldehyde, and oxoalcohols
since this reaction gives synthesis gas with a low H2/CO ratio [2]. However, there is no established
commercial process for this reaction because of fatal coking on the reforming catalyst. For this reason,
a number of studies have been focused on the development of a promising catalyst for CDR [1-7]. The
catalysts based on noble metals have been found to be less sensitive to carbon deposition [7]. However,
considering the high cost and limited availability of noble metals, it is more practical in the industrial
standpoint to develop Ni-based catalysts with high performance and high resistance to carbon
deposition. Therefore, it is necessary to develop a new supported Ni catalyst having high activity and
stability suitable for CDR.
As a catalyst for the reforming reaction, Ni/γ-Al2O3 catalyst has been used [8,9]. However, Ni/γAl2O3 is usually unstable at high temperature ( > 700oC) because of the thermal deterioration of the γAl2O3 support as well as phase transformation into α-Al2O3. Therefore, it is necessary to modify the γAl2O3 support in order to obtain thermally stable support for the reforming reaction. In our recent
studies, we have successfully performed partial oxidation of methane (POM) over Ni/θ-Al2O3 with
high activity as well as high stability [10]. However, Ni/θ-Al2O3 was not stable in CDR. Thus, we
aimed to modify θ-Al2O3 with suitable materials.
Lercher et al. [11] have recently reported that Pt/ZrO2 showed excellent performance in CDR.
However, they have failed to apply Ni/ZrO2 with high Ni loading to the same reaction due to a serious
plug of the reactor by coke formation. On the contrary, we have successfully performed CDR over Ni
supported on ZrO2 and modified ZrO2 catalysts [12,13]. Moreover, Ni/Ce-ZrO2 exhibited both high
activity and stability in steam reforming of methane (SRM) [14,15], POM [16,17], and oxy-SRM
(OSRM) [14,17], owing to the ability to make mobile oxygen species, easier reducibility of Ce-ZrO2
and so on. Also, Montoya et al. [18] applied Ni/Ce-ZrO2 system to CDR. However, Ni/Ce-ZrO2 is
difficult to commercialize due to the high price of Ce-ZrO2.
In our previous study, Ni-Mg/ZrO2 exhibited the best activity and stability during CDR [15].
Herein we investigated nickel-based catalyst using θ-Al2O3 as a support for CO2 reforming of methane,
wherein the support was modified by magnesium oxide. Consequently, we have successfully
performed CO2 reforming reaction over Ni/θ-Al2O3 with high activity and high stability.
EXPERIMENTAL
Support materials employed in this study was θ-Al2O3 (SBET = 167 m2/g) prepared by heat treatment
at 900 oC for 12 h. The temperature was carefully increased with the heating rate of 1 oC/min.
Supported Ni catalysts were prepared by the impregnation method, namely, impregnating appropriate
amounts of Ni(NO3)2∙6H2O on supports for 24 h and dried at 60 - 80 oC and then calcined at 550 oC for
화학공학의 이론과 응용 제8권 제1호 2002년
Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1
6 h in air. Catalytic activity tests were carried out using a conventional fixed-bed microreactor [3]. The
reaction temperature was measured and controlled by a thermocouple inserted directly into the top
layer of the catalyst bed. Each catalyst was reduced in the reactor with 5% H2/N2 at 700 oC for 1 h
prior to each catalytic measurement. Reactant gas was composed of CH4:CO2:N2 = 1:1:1. N2 was
employed as a reference gas for calculating both CH4 and CO2 conversions. Effluent gases from the
reactor were analyzed by a gas chromatograph (Chrompack CP9001) equipped with a thermal
conductivity detector (TCD). GC column used in this study was a Fused Silica capillary column
(CarboPLOT P7).
RESULTS AND DISCUSSION
The supported Ni catalysts mentioned above were tested at 800 oC and space velocity of 108,000
mL/h∙gcat. CH4 conversion with time on stream is presented in Figure 1. In the case of Ni/MgAl 2O4
catalyst, the activity decreased sharply during the reaction. On the contrary, Ni/θ-Al2O3 catalyst
showed high initial activity (95% CH4 conversion), but the activity decreased gradually. Furthermore,
Ni/MgO/θ-Al2O3 catalyst exhibited the highest activity as well as stability. The initial activity (97 %
CH4 conversion) of Ni/MgO/θ-Al2O3 catalyst was maintained during the reaction for 22 h..
Table 1 summarizes the precoating effect on CH4 conversion, H2 yield, CO yield, and H2/CO ratio.
All the catalysts except Ni/MgO/θ-Al2O3 showed unstable activity during the reaction process. On the
contrary, Ni/MgO/θ-Al2O3 showed stable activity for more than 22 h. This is due to the fact that
Ni/MgO/θ-Al2O3 has less carbon deposition on the catalyst surface compared with Ni/θ-Al2O3 and
Ni/MgAl2O4 catalyst.
CH4 conversion (%)
100
90
Ni/MgO/¥è-Al2O3
80
Ni/¥è-Al2O3
70
60
50
40
30
Ni/MgAl2O4
20
10
0
0
2
4
6
8
10 12 14 16 18 20 22 24
Time on stream (h)
Fig. 1. Comparison of catalytic activity with time on stream. (Reaction conditions: P = 1 atm, T =
800 ℃, CH4:CO2:N2 = 1:1:1, GHSV = 108,000 mL/h∙gcat).
화학공학의 이론과 응용 제8권 제1호 2002년
Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1
Table 1. CH4 conversion, CO2 conversion, H2 selectivity, CO selectivity, and H2/CO ratio over
Ni/support catalyst. (Reaction conditions: P = 1 atm, T = 800 ℃, CH4:CO2:N2 = 1:1:1, GHSV =
108,000 mL/h∙gcat)*.
Catalyst
XCH4 (%)
XCO2 (%)
YH2 (%)
YCO (%)
H2/CO ratio
Ni/MgO/θ-Al2O3
97
96
93
94
0.99
Ni/θ-Al2O3
81
78
75
79
0.95
Ni/MgAl2O4
28
19
25
31
0.80
*
( measured after 14 h)
100
90
80
CH4 conv.
CO2 conv.
Conversion (%)
70
60
50
40
30
20
10
0
0
20 40 60 80 100 120 140 160 180 200 220 240
Time on stream (h)
Fig. 2. Changes in catalytic activity with time on stream. (Cat. = Ni/MgO/θ-Al2O3, Reaction
conditions: P = 1 atm, T = 800 ℃, CH4:CO2:N2 = 1:1.2:1, GHSV = 17,280 mL/h∙gcat).
We have successfully performed CDR over Ni/MgO/θ-Al2O3 in mild reaction condition. Fig. 2
shows CH4 conversion and CO2 conversion. It was found that Ni/MgO/θ-Al2O3 exhibited stable
activity without significant decrease in the mild reaction condition (T = 800 ℃, CH4:CO2:N2 = 1:1.2:1,
GHSV = 17,280 mL/h∙gcat) The catalytic activity of Ni/MgO/θ-Al2O3 was maintained during the
reaction for 220 h. Thus, it is concluded that Ni/MgO/θ-Al2O3 showed the highest activity as well as
high stability.
In summary, Ni/MgO/θ-Al2O3 catalyst reveals high activity as well as stability in the CO2
reforming reaction due to high resistance to carbon.
화학공학의 이론과 응용 제8권 제1호 2002년
Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1
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