Catalyst for oxidation of gaseous compound

Details Catalyst for oxidation of gaseous compound Catalyst for oxidation of gaseous compound

2002-06-11

2004-04-13

Nguyen, Cam N. (Department: 1754)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S047000, C429S047000

Reexamination Certificate

active

06720100

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an oxidation catalyst of a gaseous compound, particularly a catalyst for promoting an oxidation reaction of a gaseous compound by oxygen ions supplied through a solid electrolyte under an environment where no oxygen molecules are present, more particularly relates to an oxidation catalyst of a gaseous compound which can be suitably used for a solid electrolyte fuel cell.
BACKGROUND ART
A solid electrolyte fuel cell can promise a higher efficiency of power generation compared with thermal power generation etc., so is being widely researched at the present.
The applicant proposed the solid electrolyte fuel cell shown in FIG. 1 in Japanese Unexamined Patent Publication (Kokai) No. 2000-348736.
The solid electrolyte fuel cell shown in
FIG. 1
has a solid electrolyte element
16
A comprised of an oxygen ion conducting type solid electrolyte substrate
10
and electrodes
12
and
14
a
formed on the two surfaces of this solid electrolyte substrate
10
.
The solid electrolyte substrate
10
is comprised of a zirconia (YSZ) fired body stabilized by 8 mol % of yttria (Y
2
O
3
)
One electrode
12
is comprised of lanthanum strontium manganoxide [(La
0.8
Sr
0.15
)
0.90
MnO
3
], is supplied with oxygen, and acts as a cathode.
The other electrode
14
a
is substantially comprised of a porous platinum layer, is supplied with methane gas as a fuel, and acts as an anode.
The oxygen (O
2
) supplied to the cathode
12
is ionized at the interface between the cathode
12
and solid electrolyte substrate
10
and becomes oxygen ions (O
2−
) which are conducted through the solid electrolyte substrate
10
to the anode
14
a
. These oxygen ions (O
2−
) react with the methane (CH
4
) gas supplied to the anode
14
a
to generate water (H
2
O), carbon dioxide (CO
2
), hydrogen (H
2
), and carbon monoxide (CO). At the time of this reaction, electrons are emitted from the oxygen ions at the anode
14
a
, so a potential difference is caused between the cathode
12
and the anode
14
a
. If the cathode
12
and the anode
14
a
are electrically connected by an output line
18
, the electrons of the anode
14
a
flow through the output line
18
in the direction of the cathode
12
(direction of arrow mark in figure) and electricity can be output from the solid electrolyte fuel cell.
The anode
14
a
is comprised of a porous platinum layer
22
a
formed on one surface of the solid electrolyte substrate
10
and an oxidation catalyst layer
22
b
formed on the outer surface carrying metal oxide particles comprised of PdCoO
2
. The oxidation catalyst layer
22
b
promotes the oxidation reaction between the oxygen ions (O
2−
) and methane at the anode
14
a.
The solid electrolyte fuel cell shown in
FIG. 1
, by using the above oxidation catalyst, can improve the power generating characteristic compared with conventional solid electrolyte fuel cells using cermet particles comprised of nickel (Ni) and nickel oxide (Nio) as an oxidation catalyst.
In the solid electrolyte fuel cell shown in
FIG. 1
, the PdCoO
2
metal oxide particles used as the oxidation catalyst were ones obtained by double decomposition or high temperature pressure synthesis. To obtain the PdCoO
2
, in double decomposition, PdCl2 and CoO are made to react for double decomposition under a high temperature and high pressure, while with high temperature pressure synthesis, PdO and CoO are sealed in a platinum tube and heated.
With each of these methods, the metal oxide particles obtained are large and uneven in size, so have been pulverized to make the particles finer and then sieved to obtain a uniform particle size. This is because the finer the metal oxide particles making up the oxidation catalyst, the higher the oxidation action obtained.
There are however the problems that there are limits to how fine the particles can be made by pulverization and that the cost of manufacture of the oxidation catalyst rises due to the need of the pulverization process.
DISCLOSURE OF INVENTION
The present invention has as its object the provision of an oxidation catalyst of a gaseous compound superior in oxidation action comprised of fine metal oxide particles.
To achieve the above object, the oxidation catalyst of a gaseous compound of the present invention comprises a catalyst for promoting an oxidation reaction of a gaseous compound by oxygen ions supplied through a solid electrolyte under an environment where no oxygen molecules are present, characterized by
comprising metal oxide particles produced by firing a precipitate comprised of a mixture of two types of metal hydrates obtained by coprecipitation from a mixed solution of two types of metal salts of different metal positive ions dissolved together, the composition of the metal oxide particles being expressed by the formula:
ABO
2
where, A is one element selected from the group consisting of Pd, Pt, Cu, and Ag,
B is one element selected from the group consisting of Co, Cr, Rh, Al, Ga, Fe, In, Sc, and Tl.
Typically, by firing a precipitate comprised of a mixture of Pd(OH)
2
and Co(OH)
2
obtained by coprecipitation from a mixed solution of PdCl
2
and CoCl
2·
6H
2
O dissolved together, it is possible to obtain fine metal oxide particles comprised of PdCoO
2
.
By the conventional double decomposition or high temperature pressure synthesis, depending on the mixed state or particle size of the starting material, there is an effect on the particle size of the metal oxide particles finally obtained and as a result an effect on the catalytic action of the oxidation catalyst.
The precipitate obtained by mixing two types of metal hydrates obtained by coprecipitation is comprised of fine particles of an even particle size, so the metal oxide particles obtained by firing the precipitate are also fine and uniform in particle size. By using the metal oxide particles as an oxidation catalyst, it is possible to obtain a high oxidation action.


REFERENCES:
patent: 3862023 (1975-01-01), Johnson
patent: 4173518 (1979-11-01), Yamada et al.
patent: 4384986 (1983-05-01), Lecloux et al.
patent: 4492811 (1985-01-01), Switzer
patent: 6379830 (2002-04-01), Sato et al.
patent: 270203 (1987-07-01), None
patent: 602864 (1993-12-01), None
patent: A-47-33225 (1972-11-01), None
patent: 49-104873 (1974-10-01), None
patent: B-57-44374 (1982-09-01), None
patent: 2000-348736 (2000-12-01), None

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