Applied Catalysis A: General 198 (2000) 261–266
Partial oxidation of methane and ethane to synthesis gas over a
LiLaNiO/␥–Al2 O3 catalyst
Shenglin Liu, Guoxing Xiong∗ , Shishan Sheng, Weisheng Yang
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P.O. Box 110, Dalian 116023, China
Received 10 September 1999; received in revised form 23 October 1999; accepted 17 November 1999
Abstract
Partial oxidation of methane and ethane to synthesis gas over a LiLaNiO/␥–Al2 O3 catalyst was investigated with a flow
reactor, AAS, XPS, and XRD. Excellent reaction performance for CH4 –C2 H6 –O2 to synthesis gas over the LiLaNiO/␥-Al2 O3
is achieved at 1073 K, obtaining CO selectivity of 90–95% and CH4 conversion of ∼97%, with a wide range of C2 H6 content
in the feed and of space velocity. Meanwhile, 100, 200 and 500 h life tests of the LiLaNiO/␥-Al2 O3 for natural gas–O2
to synthesis gas were also performed. The results indicate that the LiLaNiO/␥-Al2 O3 catalyst not only possesses excellent
reaction performance (CH4 conversion ∼95%, CO selectivity ∼98%), good carbon deposition resistance, but also has a
relatively stable element component and a stable crystal phase structure during a 500 h life test experiment under conditions of
1123 K, natural gas/O2 ratio of 1.90 and space velocity of 2.7×105 l/(kg h). © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Partial oxidation of methane and ethane; Synthesis gas; LiLaNiO/␥-Al2 O3 catalyst; Crystal phase structure; Carbon deposition;
Sintering and loss of nickel
1. Introduction
There are abundant supplies of mixture gases containing CH4 and C2 H6 from natural gas, FCC (fluidized catalytic cracking) tail gas, refinery gas, etc.
Commonly, the amount of C2 H6 is relatively lower
than that of CH4 . With regard to the utilization of
methane, partial oxidation of methane (POM) to synthesis gas over nickel-based catalysts has received intensive attention [1,2]. For mixture gases containing
CH4 and C2 H6 , their conversion to synthesis gas is
also of significance (but has not gained adequate attention), because complete separation of ethane from
methane may not be economical [3]. Schmidt et al.
∗
Corresponding author.
[4,5] reported that synthesis gas could be produced
from CH4 , C2 H6 and C3 H8 , respectively, over a supported Rh catalyst with high selectivity and conversion. Yu et al. [6] investigated the effect of rare earth
metal oxides on the reaction performance of nickel
catalysts for the selective oxidation of nature gas to
synthesis gas. The results indicated that the rare earth
metal oxides like Y2 O3 and CeO2 were good promoters for better product yields and selectivities, and ceria could suppress the growth of nickel crystallites,
enhancing the catalyst stability and catalytic performance.
Sufficiently good performance for the POM reaction was reported for oxide systems such as NiO–CaO
[7], NiO–MgO [8], CoO–MgO [9], NiO–rare earth
oxides [10], Ni/Al2 O3 [11], NiO/␥-Al2 O3 [2]. Mean-
0926-860X/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 6 - 8 6 0 X ( 9 9 ) 0 0 5 1 7 - 7
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S. Liu et al. / Applied Catalysis A: General 198 (2000) 261–266
while, it was found that NiO/␥-Al2 O3 was also a good
catalyst for the partial oxidation of ethane (POE) to
synthesis gas [12]. However, it is well known that
nickel-based catalysts supported on ␥-Al2 O3 are usually unstable at high temperatures. The reason causing the deactivation of the NiO/␥-Al2 O3 catalyst is the
loss and sintering of nickel, as well as the deterioration of the support. In addition, carbon deposition over
the NiO/␥-Al2 O3 is also often considered as a possible cause of deactivation. Owing to these reasons, we
adopted alkali and rare earth metal oxides to modify
the NiO/␥-Al2 O3 catalyst. The results indicated that
modification with alkali and rare earth metal oxides
could not only stabilize the support ␥-Al2 O3 phase,
but also suppress the sintering and loss of nickel, and
in addition, enhance the ability of suppressing carbon deposition over the NiO/␥-Al2 O3 during a high
temperature reaction [2,13,14]. In the present paper,
reaction performance of a LiLaNiO/␥-Al2 O3 catalyst
for CH4 –C2 H6 –O2 reaction to synthesis gas and 500 h
life test of the LiLaNiO/␥-Al2 O3 for natural gas–O2
to synthesis gas were investigated.
2. Experimental
2.1. Preparation of LiLaNiO/γ -Al2 O3 catalyst and
test of reaction performance
The LiLaNiO/␥-Al2 O3 catalyst was prepared by
the impregnation method. Appropriate amounts of
LiNO3 , Ni(NO3 )2 and La(NO3 )3 were impregnated
on ␥-Al2 O3 support for 24 h, dried at 393 K, and then
calcined in air at 823–1073 K for 4 h. The elemental
content of the catalyst is provided in Section 3. The
catalyst that has been operated for 100 h was labelled
as ‘catalyst’-100 h, e.g. LiLaNiO/␥-Al2 O3 -100 h,
etc.
The catalyst was tested in an atmospheric pressure
fixed-bed flow microreactor. Reaction performance
was tested using a microreactor with an internal diameter of 4 mm, and 100 mg catalyst was employed.
The 100, 200 and 500 h life tests of partial oxidation
of methane and ethane to synthesis gas were performed using a microreactor with an internal diameter
of 8 mm and 500 mg catalyst. The analysis methods
of the reaction products were the same as published
before [2].
2.2. Characterization of the catalyst
XPS characterization was performed using a VG
ESCA LABMK II spectrometer. Elemental analysis
was carried out with atomic absorption spectroscopy
(AAS). XRD characterization was performed with a
Riguku D/Max-RB X-ray diffractometer using a copper target at 40 kV×100 mA and scanning speed of
8◦ /min.
3. Results and discussion
3.1. Reaction performance of the LiLaNiO/γ -Al2 O3
catalyst for CH4 –C2 H6 –O2 reaction to synthesis gas
Under constant space velocity by keeping the
flow rate of CH4 (70 ml/min) and the total flow rate
(205 ml/min) of C2 H6 , O2 and He constant, the respective flow rates of C2 H6 , O2 and He were changed
to obtain different CH4 /C2 H6 /O2 ratios. The effect
of CH4 /C2 H6 /O2 ratio on the reaction performance
of the LiLaNiO/␥-Al2 O3 was studied (Table 1). The
results indicate that the catalyst can maintain excellent selectivity to synthesis gas with a wide range
of C2 H6 content in the feed (CO and H2 selectivity
are ∼93 and ∼99%, respectively). Furthermore, the
results (Table 1) indicate that the influence of space
velocity is not appreciable, i.e. the LiLaNiO/␥-Al2 O3
possesses good reaction performance with a wide
range of space velocity.
In order to examine the stability of LiLaNiO/␥Al2 O3 for CH4 –C2 H6 –O2 to synthesis gas reaction,
the 100 h life test experiment was carried out (Fig. 1).
During the 100 h of operation, methane conversion
remains ∼97% (both C2 H6 and O2 conversions are
>99.9%), no C2 H4 in the products appears. CO and
CO2 selectivities are ∼93 and ∼7%, respectively,
under the conditions of 1073 K, CH4 /O2 /C2 H6 /He
ratio of 39.0/41.2/19.8/74 and space velocity of
1.65×105 l/(kg h). These results indicate that besides
a good catalyst for both POM and POE [2,12–14],
LiLaNiO/␥-Al2 O3 is also a good catalyst for the
CH4 –C2 H6 –O2 to synthesis gas reaction. Longer life
test for partial oxidation of mixture gases containing
CH4 and C2 H6 , such as natural gas, to synthesis gas
over LiLaNiO/␥-Al2 O3 will be discussed in Section
3.2.
S. Liu et al. / Applied Catalysis A: General 198 (2000) 261–266
263
Table 1
Effect of CH4 /C2 H6 /O2 ratio on the reaction performance of LiLaNiO/␥-Al2 O3 (SV=1.65×105 l/(kg h); SVCH4 =4.2×104 l/(kg h);
T = 1073 K)a
Feed composition
Reaction performance
CH4 (%)
O2 (%)
C2 H6 (%)
XCH4 (%)
SCO (%)
SCO2 (%)
SH2 (%)
55.0
45.9
39.5
39.5
39.5
34.8
30.8
36.5
39.3
40.8
40.8
40.8
43.4
43.9
8.5
14.8
19.7
19.7b
19.7c
21.8
25.3
97.6
97.4
96.8
98.1
98.5
97.8
96.8
94.5
93.7
93.3
94.4
95.2
90.9
91.9
5.5
6.3
6.7
5.6
4.8
9.1
8.1
99.0
99.2
99.0
99.5
99.8
97.3
98.5
a
In all cases, both O2 and C2 H6 conversions are >99.9%
SV=3.3×105 l/(kg h); SVCH4 =8.4×104 l/(kg h)
c SV=6.6×105 l/(kg h); SV
5
CH4 =1.7×10 l/(kg h) XCH4 means CH4 conversion; SCO means CO selectivity, etc.
b
After 100 h of operation, the reactor was cooled
to room temperature in a flow of N2 . The catalyst
was then characterized by XRD and XPS. XRD results reveal that metallic nickel are present in the
used catalyst (Fig. 2). The ␥-Al2 O3 phase presents before the reaction. After operation, the ␥-Al2 O3 phase
in LiLaNiO/␥-Al2 O3 has hardly undergone any phase
tranformation to the ␣-Al2 O3 phase. The results indicate that the catalyst support of ␥-Al2 O3 is stable
during the CH4 –C2 H6 –O2 to synthesis gas reaction.
Carbon deposition of the used catalyst was characterized with XPS (Fig. 3). The prominent peak at a
binding energy of 284.6 ev in each spectrum is due to
adventitious carbon, while the peak at ∼288 ev may
be due to residual surface CO3 2− [11], and the peak
at ∼283 ev can be attributed to a graphitic or carbidic
surface carbon species. The results indicate that the
intensity of the graphitic or carbidic surface carbon
peak for used LiLaNiO/␥-Al2 O3 is similar to that for
the fresh one, i.e. the used catalyst has hardly any carbon deposition. It can be concluded from the results
that LiLaNiO/␥-Al2 O3 has high carbon deposition resistance during the high temperature reaction.
The stability of LiLaNiO/␥-Al2 O3 for partial oxidation of natural gas to synthesis gas (natural gas contains ∼91% CH4 , ∼6% C2 H6 , ∼3% C3 H6 and C4 H8 )
was tested using a microreactor with an internal diameter of 8 mm, and the weight of catalyst was 500 mg.
Fig. 1. Reaction performance of LiLaNiO/␥-Al2 O3 as
a function of time (CH4 /O2 /C2 H6 /He = 39.0/41.2/19.8/74;
SV=1.65×105 l/(kg h); 1073 K).
Fig. 2. XRD spectra of catalysts before and after the
CH4 –C2 H6 –O2 reaction (a): LiLaNiO/␥-Al2 O3 (before reaction)*
(b): LiLaNiO/␥-Al2 O3 -100 h; *Catalyst (before reaction): The catalyst that was cooled to room temperature in a flow of Ar, after
it was reduced by 5% H2 /Ar at 1123 K for 1 h.
3.2. Life test of LiLaNiO/γ -Al2 O3 for natural
gas–O2 to synthesis gas
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S. Liu et al. / Applied Catalysis A: General 198 (2000) 261–266
Fig. 3. C1s XPS spectra of the catalysts after the CH4 –C2 H6 –O2
reaction; (a): LiLaNiO/␥-Al2 O3 (fresh) (b): LiLaNiO/␥-Al2 O3
–100 h.
The results are shown in Fig. 4. Under conditions of
1123 K, natural gas/O2 ratio of 1.90 and space velocity of 2.7×105 l/(kg h), CH4 conversion and CO selectivity remain ∼95 and ∼98%, respectively, while
the conversions of C2 H6 , C3 H6 and C4 H8 are almost
100% during the 500 h of operation. These results indicate that the LiLaNiO/␥-Al2 O3 catalyst is quite stable during the high temperature reaction.
After the individual life test experiments for 100,
200 and 500 h, the reactor was cooled to room temperature in a flow of N2 in each case. The catalysts
were then investigated by XRD, AAS and XPS.
Fig. 4. Reaction performance of LiLaNiO/␥-Al2 O3 as a function of time (Natural gas /O2 =1.90/1; GHSV=2.7×105 l/(kg h);
T=1123 K).
Fig. 5. XRD spectra of the catalysts before and after reaction (a): ␥-Al2 O3 (b): LiLaNiO/␥-Al2 O3 (before reaction)*
(c): LiLaNiO/␥-Al2 O3 –100 h (d): LiLaNiO/␥-Al2 O3 –200 h (e):
LiLaNiO/␥-Al2 O3 -500 h; *Catalyst (before reaction): The catalyst
that was cooled to room temperature in a flow of Ar, after it was
reduced by 5% H2 /Ar at 1123 K for 1 h.
XRD tests were performed to determine the crystal phases of these catalysts (Fig. 5). Only peaks for
␥-Al2 O3 and metallic nickel appear, while those for
NiO and NiAl2 O4 do not appear, namely, the ␥-Al2 O3
support has not undergone crystalline transformation
into ␣-Al2 O3 . Metallic nickel does not aggregate
obviously between 100 and 500 h of operation. It
can be concluded that the crystal phase structure of
LiLaNiO/␥-Al2 O3 is stable during the high temperature reaction [13].
According to our experience [15], for LiLaNiO/␥Al2 O3 , carbon deposition result from TG is in agreement with that from XPS, namely, the bigger the
carbon deposition result from TG, the stronger the
intensity of the peak at ∼283 ev [11] from XPS is.
In addition, the amount of carbon deposition is very
low and that of the used LiLaNiO/␥-Al2 O3 is limited
(only 500 mg ). Therefore, TG measurement of the
used catalyst was not performed, taking into consideration that a considerable amount of the sample is
needed. Carbon deposition of the used catalyst was
only characterized by the XPS technique (Fig. 6).
During the high temperature reaction, the samples all
have a peak at ∼288 ev that may be due to residual
surface CO3 2− [11], but the intensity of the peak
does not increase with reaction time, which indicates
that it does not affect the reaction performance of
LiLaNiO/␥-Al2 O3 . An important point is that, dur-
S. Liu et al. / Applied Catalysis A: General 198 (2000) 261–266
Fig. 6. C1s XPS spectra of the catalysts after reaction
(a): LiLaNiO/␥-Al2 O3 -100 h (b): LiLaNiO/␥-Al2 O3 -200 h (c):
LiLaNiO/␥-Al2 O3 -500 h.
ing the 500 h of operation, the catalyst only has a
little graphitic or carbidic surface carbon species,
due to the fact that the asymmetrically broad peak
does not obviously change. These results reveal that
LiLaNiO/␥-Al2 O3 has excellent carbon deposition
resistance during the high temperature reaction.
The AAS technique was used to investigate the
loss of the elements in these catalysts. The results are
shown in Table 2. The losses of lithium and nickel in
the samples are not obvious during the high temperature reaction. Even after 500 h of operation, the lithium
and nickel loss-percentages of LiLaNiO/␥-Al2 O3 are
only 16 and 8%, respectively. Mclean [16] reported
Table 2
Element contents (wt%) of the catalysts at different reaction time
Element
B-0 h
B-100 ha
B-200 h
B-500 h
Ni
Li
La
10.0
1.00
5.00
9.8
0.90
4.92
9.6
0.87
4.96
9.2
0.84
4.94
B-100 h means that LiLaNiO/␥-Al2 O3 (B) has been operated
for 100 h, etc.
a
265
that when the catalysts were reduced or used at a high
temperature, the rare earth oxides migrated to the surface of the nickel grains. A part of the nickel was
covered or embedded by the rare earth oxides. Nickel
was restrained over the surface and could not migrate
freely. So, the growth and loss of nickel were suppressed. Xiong et al. [14] found that the introduction of
Li and La could not only stabilize the support ␥-Al2 O3
phase, but also suppress the sintering and loss of nickel
on the NiO/Al2 O3 during the high-temperature POM
process. Levy et al. [17] pointed out that the thermal
stability of transition alumina is sensitive to many factors such as inhomogeneity, lattice strain, ionic radii
of impregnates, and the coordination of the latter with
oxygen. Lithium stabilizes a spinel alumina by the formation of a mixed bulk phase (Al8 [Al12 Li4 ] O32 ).
Such a structure may suppress the loss of lithium
of LiLaNiO/␥-Al2 O3 . This work is still in progress.
The results indicate that the LiLaNiO/␥-Al2 O3 catalyst has a relatively stable element component. Moreover, the reaction performance does not decrease during the 500 h life test experiment, which implies that
this amount of lost nickel is not enough to cause any
change of reaction performance under such reaction
conditions.
Acknowledgements
The authors would like to thank Prof. Z. Yu and
Prof. W. Chu for their help and beneficial discussion.
Meanwhile the authors are grateful to the Chinese
Ministry of Science and Technology for the financial
support.
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