Partial oxidation of methane to syngas over plasma treated Ni-Fe/La2O3 catalyst

Article abstract of DOI:10.1246/cl.2002.1068

Ni-Fe/La₂O₃ catalyst prepared by a glow discharge plasma treatment following calcinations thermally exhibits higher activity and selectivity compared to the Ni-Fe/La₂O₃ prepared conventionally. At the same react

Full text of DOI:10.1246/cl.2002.1068

1068
Chemistry Letters 2002
Partial Oxidation of Methane to Syngas over Plasma Treated Ni-Fe/La2O3 Catalyst
Jian-guo Wang,y;yy Chang-jun Liu,Ãy;yy Yue-ping Zhang,y;yy Xin-li Zhu,y;yy Jijun Zou,y;yy Kai-lu Yu,y;yy and Baldur Eliassonyyy
yState Key Laboratory of C1 Chemistry and Technology and School of Chemical Engineering, Tianjin University,
Tianjin 300072, P. R. China
yyTianjin University-ABB Plasma Greenhouse Gas Chemistry Laboratory, Tianjin University, Tianjin 300072, P. R. China
yyyEnergy and Global Change, ABB Corporate Research Ltd., CH5405, Switzerland
(Received June 21, 2002; CL-020521)
Ni-Fe/La2O3 catalyst prepared by a glow discharge plasma
treatment following calcinations thermally exhibits higher
activity and selectivity compared to the Ni-Fe/La2O3 prepared
conventionally. At the same reaction temperature, the CH4
conversion, CO selectivity and H2 selectivity obtained from the
plasma prepared Ni-Fe/La2O3 are5–9%, 4–7% and9–15% higher
than those from the conventional Ni-Fe/La2O3 catalyst, respec-
tively. At the same methane conversion, the reaction temperature
with the plasma prepared Ni-Fe/La2O3 is at least 100 ꢀC lower
than that with the conventional Ni-Fe/La2O3.
The catalꢀyst (40–60 mesh; 40 mg), reduced by a flowing H2
for 1h at 650 C, was then placed in a 6 mm i.d. quartz-tube flow
reactor. The feed was the mixture of CH4 : O2 ¼ 2 : 1. The feed
and the product gases were analyzed by an on-line gas
chromatograph (HP4890) using a thermal conductivity detector
(TCD) with a TDX-01column.
Figure 1 shows the effect of the temperature on methane
conversion. In the following discussions, the conventional
catalyst is referred to as Ni-Fe/La2O3(C), and the plasma treated
catalyst is referred to as Ni-Fe/La2O3(P). The reaction initiation
temperature with Ni-Fe/La2O3(P) was ca. 25 ꢀC lower, compared
to that with Ni-Fe/La2O3(C). The methane conversion obtained
from Ni-Fe/La2O3(P) was 5–9% higher than that from Ni-Fe/
La2O3(C) at the same temperature. At the same methane
conversion, the reaction temperature with Ni-Fe/La2O3(P) is at
least 100 ꢀC lower than that with Ni-Fe/La2O3(C). The oxygen
conversion was 100% for both cases. Especially, the initiation
temperature for Ni-Fe/La2O3(P) was 600 ꢀC, while the reaction
started at about 750 ꢀC for Ni/Al2O3 catalyst.11 The Ni-Fe/
La2O3(P) catalyst shows better low temperature activity. The
effect of the temperature on CO and H2 selectivity were presented
in Figure 2 and Figure 3. The CO and H2 selectivity for Ni-Fe/
La2O3 (P) were 4–7% and 9–15% higher, respectively, than those
for Ni-Fe/La2O3(C). The H2/CO ratio in syngas produced was
1.8–2.0 for Ni-Fe/La2O3(P), which is excellent for further
synthesis. The CO selectivity was more than 85% for Ni-Fe/
La2O3(P).
An intense investigation has been conducted worldwide on
the utilization of methane for the production of more valuable
chemicals since 1980s. The commercial methane utilization,
however, still requires a multi-step process via syngas. The
industrialized syngas production technology is the steam
reforming of methane.1;2 But there exist some drawbacks with
the steam reforming of methane. The steam reforming is an
energy intensive reaction. The H2/CO ratio of syngas produced is
not suitable for further synthesis directly. As an alternative
approach, the partial oxidation of methane into syngas has drawn
more and more attentions recently.3{6
Ni based catalysts have been extensively investigated for the
partial oxidation of methane into syngas.7{10 The catalysts tested,
however, require a high temperature activation. In addition, the
catalysts easily lose their activity due to the serious carbon
deposit. Choudhary et al.11 reported a reduced reaction
temperature with enhanced catalytic activity and improved CO
selectivity by adding noble metal to Ni/Al2O3 catalyst. Nakagawa
et al.12 presented a La2O3 supported Ni catalysts that show some
activity at lower temperatures. But a significant amount of carbon
deposition was detected in the La2O3-supported Ni (10 wt%)
catalyst.12 In this work, we attempt to use plasma treatment
following thermal calcinations to achieve a better low tempera-
ture activity of La2O3 supported Ni catalysts with Fe as a
promoter.
70
60
Ni-Fe/La2O3(C)
Ni-Fe/La2O3(P)
50
40
30
20
10
0
The conventional wetness impregnation has been applied for
the catalyst preparation (Ni : Fe : La2O3 ¼ 7 : 3 : 90). The
La2O3 support was first impregnated in an aqueous solution of
Ni (NO3)2 and Fe (NO3)3. After impregnation, the resulted
sample was then divided into two parts: one for calcinations at
600 ꢀC for 6 h after drying at 90 ꢀC for 16 h, and the other for
400
500
600
700
800
900
1000
Temperature /°C
Figure 1. Effect of reaction temperature on CH4 conversion.
Reaction conditions: P ¼ 1 atm, GHSV ¼ 10000 cm3/gꢁh,
CH4/O2 ¼ 2.
ꢀ
plasma treatment for only 1h before further calcinations at 600 C
for 6 h. In this work, we have successfully utilized a dc glow
discharge for plasma treatment of catalyst. The catalyst was
located in the ‘‘positive column’’ of glow discharge13 that was
generated at ca. 12 Pa and at room temperature using argon as the
glow discharge plasma-forming gas.
It has been considered that the catalytically active species can
be highly dispersed on the support during the plasma treatment
and the particle size was also uniform after the calcinations of the
plasma treated catalyst. Thereby the activity and selectivity of Ni-
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
1069
100
selectivity. It would support that the highly dispersion of active
species on the support induced from plasma treatment lead to
enhanced activity and better selectivity. Further catalyst char-
acterization is being conducted for better understanding of
plasma-enhanced activity.
Ni-Fe/La2O3(C)
Ni-Fe/La2O3(P)
90
80
70
60
Supports from the Foundation for University Key Teacher by
the Ministry of Education of China and ABB Corporate Research
Ltd., Switzerland are very appreciated.
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