Promoting effect of Pd addition to Ni0.2Mg0.8Al 2O4 in oxidative steam reforming of methane

Article abstract of DOI:10.1246/cl.2006.1072

Addition of Pd to Ni_0.2Mg_0.8Al₂O ₄ promoted oxidative steam reforming of methane, and it gave high activity under high partial pressure of steam and low W/F, where Ni _0.2Mg_0.8Al₂

Full text of DOI:10.1246/cl.2006.1072

1
072
Chemistry Letters Vol.35, No.9 (2006)
Promoting Effect of Pd Addition to Ni Mg Al O
0
:2
0:8
2
4
in Oxidative Steam Reforming of Methane
1
;2
1
1
Mohammad Nurunnabi, Yuya Mukainakano, Shigeru Kado,
1
ꢀ1
Kimio Kunimori, and Keiichi Tomishige
Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565
1
2
(Received June 27, 2006; CL-060724; E-mail: tomi@tulip.sannet.ne.jp)
Addition of Pd to Ni0:2Mg0:8Al2O4 promoted oxidative
Table 1. Properties of the catalysts
steam reforming of methane, and it gave high activity under high
partial pressure of steam and low W=F, where Ni0:2Mg0:8Al2O4
showed very low activity. The Ni0:2Mg0:8Al2O4 requires the H2
reduction pretreatment; however, Pd/Ni0:2Mg0:8Al2O4 can be
activated automatically by the reactant gases of oxidative
reforming of methane.
Ni
Pd
H2 consa
H2 adc
Dredb
Ddispd
BET content content
/m2 gꢂ1 /10ꢂ4 /10ꢂ6
ꢂ6
ꢂ6
Catalysts
/10
/10
/%
/%
ꢂ1
ꢂ1
mol g
mol g
ꢂ1
ꢂ1
mol g mol g
Ni0:2Mg0:8Al O
2
4
23.9
13.4
13.4
0
0
816
1222
21
61
90
—
20.4
56.2
5.0
9.2
Pd/Ni0:2Mg0:8Al2O4 23.9
Pd/MgAl2O4 29.9
9.4
9.4
4.2 39.3
aTotal amounts of hydrogen consumption in TPR profiles (283–
1123 K).
Oxidative steam reforming of methane is one of attractive
methods for the production of hydrogen for fuel cells and the
synthesis gas for gas-to-liquid process because the oxidative
reforming is more energy efficient than conventional steam
b
Reduction degree of Ni: the ratio of reduced Ni to total Ni.
Total amount of hydrogen adsorption at 298 K.
c
d
Dispersion: (2 ꢁ H2 adsorption)/(Pd + reduced Ni) ꢁ 100. The
1
–7
loading amount of Pd was 0.1 mass%, and it is assumed that all Pd
reforming of methane. This difference can be mainly due to
the heating methods: The oxidative reforming is internal-heating
and the conventional reforming is external-heating. On the other
hand, in the oxidative reforming of methane, it has been reported
that the Ni catalysts can be deactivated by the oxidation of Ni
metal species.5 In this letter, we report that the addition of Pd
to Ni0:2Mg0:8Al2O4 spinel enhanced the catalyst reducibility,
and this can be related to high activity in oxidative steam reform-
ing of methane. Furthermore, Ni0:2Mg0:8Al2O4 modified with Pd
can be activated easily with the reactant gases of the oxidative
reforming, although the activation of Ni0:2Mg0:8Al2O4 needs
H2 reduction at high temperature.
atoms were reduced as Pd2 + H2 ! Pd + 2H .
þ
0
þ
α
2 3
-Al O
,8
MgO
2 4
NiAl O
2 4
Ni0.2Mg0.8Al O
Ni0:2Mg0:8Al2O4 was prepared by the solid reaction method
from NiO (Wako Pure Chemical Industries Ltd., Japan), MgO
2 4
MgAl O
(
Aerosil Corporation, Japan). The mixture of NiO, MgO, and
Al2O3 with the appropriate composition was calcined in air at
UBE Material Industries Ltd., Japan), and Al2O3 (Nippon
36 37 38 39 40 41 42 43 44 45 46
2 theta /degrees
1
423 K for 12 h. As a reference, MgAl2O4 and NiAl2O4 were
Figure 1. XRD patterns of the samples after the calcination at
1
also prepared by the calcinations at 1423 K for 12 h. The loading
of Pd on Ni0:2Mg0:8Al2O4 and MgAl2O4 was performed by the
impregnation of Ni0:2Mg0:8Al2O4 and MgAl2O4 with aqueous
solutions of Pd(NO3)2 (N.E. Chemcat Corp, Japan). The loading
423 K for 12 h.
9
ous report. The amount of deposited carbon during the reaction
was negligible in all the cases. Characterization results are also
listed in Table 1.
ꢂ6
amount of Pd was 0.1 mass% (9:4 ꢁ 10 mol/g-cat), and BET
surface areas of these catalysts are listed in Table 1.
Figure 1 shows the XRD patterns of the MgAl2O4,
ꢃ
Oxidative steam reforming of methane was carried out in a
fixed bed flow reaction system. In usual case, the catalysts were
pretreated by hydrogen under atmospheric pressure at 1123 K for
Ni0:2Mg0:8Al2O4, and NiAl2O4. The peaks around 43 can be as-
signed to MgO and ꢀ-Al2O3 found as impurities. According to
10
the X-ray powder diffraction data file, it is found that MgAl2O4
1
1
0
.5 h. In the self-activation test, the catalysts were used without
and NiAl2O4 have a spinel structure. The peaks of Ni0:2-
Mg0:8Al2O4 were positioned between those of MgAl2O4 and
NiAl2O4. This indicates that Ni0:2Mg0:8Al2O4 also has a spinel
structure. Table 2 represents the effect of partial pressure
ratios in oxidative steam reforming of methane. In the case of
Ni0:2Mg0:8Al2O4, methane conversion decreased remarkably
with increasing steam pressure. This behavior indicates that Ni
metal species was oxidized under high steam partial pressure
at this W=F condition. Similar tendency has been observed in
hydrogen reduction pretreatment. The partial pressure ratio of
reactants was CH4/H2O/O2 = 2/1.5/1 and 2/4/1. The operat-
ing total pressure was 0.1 MPa; 30 mg of catalyst was used. Con-
tact time W=F was used as 0.43 and 0.13 g h mol . The effluent
gas was analyzed with a gas chromatograph. CH4 conversion
ꢂ1
and CO selectivity were estimated on the basis of our previous
8
report. The methods of temperature programmed reduction with
H2 (H2-TPR) and H2 chemisorption were described in our previ-
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.9 (2006)
1073
Reaction temperature / K
73 823 873 923 973 1023 1073
Table 2. Effect of partial pressure ratios on methane conver-
sion, CO selectivity, and H2/CO ratio in oxidative steam reform-
ing of methane
7
a
100
10
8
2 4
Ni0.2Mg0.8Al O
CH4 conv.
CO sel.
/%
8
6
4
2
0
0
0
0
0
Catalysts
CH4/H2O/O2
H2/CO
/%
6
Ni0:2Mg0:8Al2O4
2/1.5/1
93
12
72
69
94
94
87
5
2.4
0
4
2
/4/1
2/1.5/1
/4/1
2/1.5/1
/4/1
Pd/MgAl2O4
93
90
87
76
1.8
2.2
2.6
3.3
2
2
0
Pd/Ni0:2Mg0:8Al2O4
0
30 60 90 120 150 180 210
Time on stream / min
2
Reaction temperature / K
73 823 873 923 973 1023 1073
Equilibrium
2/1.5/1
/4/1
>99
>99
79
59
2.8
4.1
7
2
1
00
10
8
a
0
.1% Pd/MgAl
2
O
4
Reaction conditions: catalyst weight = 30 mg, W=F ¼ 0:13 g h
80
60
40
20
0
ꢂ1
mol , reaction temperature = 1073 K, H2 reduction pretreatment =
1123 K.
6
4
with increasing reaction temperature. Similar behavior was also
observed on Pd/Ni0:2Mg0:8Al2O4 and, moreover, methane con-
version was much higher than that of Pd/MgAl2O4 in all reac-
tion temperature range. This behavior indicates that the Pd/
Ni0:2Mg0:8Al2O4 can be activated by the CH4 + H2O + O2 at
2
0
0
30 60 90 120 150 180 210
Time on stream / min
7
73 K and the reduction of Ni species in Ni0:2Mg0:8Al2O4 can
Reaction temperature / K
773 823 873 923 973 1023 1073
be also promoted by the addition of Pd drastically. Equilibrium
conversion and selectivity were almost the same as the obtained
results on Pd/Ni0:2Mg0:8Al2O4 at each reaction temperature in
Figure 2. In addition, this is also related to much higher activity
100
10
8
80
60
40
20
0
6
6
of Pd/Ni0:2Mg0:8Al2O4 than those reported. High activity of
4
Pd/Ni0:2Mg0:8Al2O4 can be related to higher reduction degree
of Ni and larger amount of hydrogen adsorption than
Ni0:2Mg0:8Al2O4 (Table 1). Furthermore, the previous results
suggest that the alloying of Pd with Ni can influence the catalytic
2
0
2 4
.1% Pd/Ni0.2Mg0.8Al O
0
0
30 60 90 120 150 180 210
Time on stream / min
1
2,13
performance.
the Pd–Ni alloy formation by EXAFS analysis.
In the present case, we have already confirmed
1
4
Figure 2. Results of CH4 conversion, CO selectivity, and H2/
CO ratio in oxidative steam reforming of methane during the re-
action temperature increasing over the catalysts without H2 pre-
treatment. ( ) CH4 conversion, ( ) CO selectivity, ( ) H2/CO.
A part of this study is supported by a Industrial Technology
Research Grant (No. 05A43002C) from the New Energy and
Industrial Technology Development Organization (NEDO) of
Japan.
Reaction conditions: catalyst weight = 30 mg, CH4/H2O/
ꢂ1
O2 = 2/1.5/1, W=F ¼ 0:43 g h mol
.
6
References
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most constant under both partial pressure conditions. Another
important point is that Pd/Ni0:2Mg0:8Al2O4 exhibited much
higher methane conversion than Ni0:2Mg0:8Al2O4 and Pd/
MgAl2O4 under all the partial pressure conditions.
1
2
3
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7
8
9
(
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1
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1
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Published on the web (Advance View) August 23, 2006; doi:10.1246/cl.2006.1072