Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-02-06
2004-08-17
Langel, Wayne A. (Department: 1754)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C423S247000, C423S437200, C423S655000, C423S656000, C429S010000
Reexamination Certificate
active
06777117
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a water-gas-shift-reaction catalyst used for converting and removing carbon monoxide (CO) in a gas which is rich in hydrogen through a water gas shift reaction, a method for removing carbon monoxide in a hydrogen gas using such catalyst, and a fuel cell generation system using such catalyst.
BACKGROUND ART
A reformed gas which is rich in hydrogen is produced by a steam reforming reaction of a hydrocarbon gas, liquid or solid, or a fuel such as methanol or the like with steam, and such reformed gas contains carbon monoxide as a by-product. The reformed gas is used for a supply of hydrogen as a fuel in a fuel cell electricity generation system.
It is contemplated that among fuel cells, a polymer electrolyte fuel cell (or solid polymer fuel cell) is used for a vehicle, a compact generator and a domestic co-generation system since it operates at a lower temperature, produces a higher power density, and is expected to be compact and light and to have a shortened operation period.
The polymer electrolyte fuel cell uses a perfluorosulfonic acid based polymer membrane as a proton conductive solid electrolyte and operates at a temperature between 50° C. and 100° C. However, since the polymer electrolyte fuel cell operates at such a lower temperature, it is likely to be poisoned by an impurity contained in the reformed gas which is rich in hydrogen. Particularly, platinum used for an electrode in a fuel cell unit is likely to be poisoned by CO, and generation performance of the unit is degraded when CO is contained in the reformed gas beyond a certain predetermined concentration.
Thus, a CO removal unit is provided downstream a reforming unit which produces the reformed gas rich in hydrogen from the fuel, and CO is selectively converted and removed through a water gas shift reaction (CO+H
2
O→CO
2
+H
2
) so that a concentration of CO in the reformed gas is usually reduced to not greater than 1%. A catalyst for the water gas shift reaction is used for the CO removal as a CO conversion catalyst, and hitherto a Cu—Zn based catalyst has been conventionally used. It is noted that in the generation system using the polymer electrolyte fuel cell, a selective oxidation reaction unit is additionally provided downstream the CO removal unit so that the CO concentration in the hydrogen gas is further reduced for example to not larger then 50 ppm, and the hydrogen gas of which CO concentration is thus reduced is supplied to a fuel cell unit.
DISCLOSURE OF INVENTION
However, since an activity of the Cu—Zn based catalyst is low, a large amount of the catalyst has to be used in order that the CO concentration in the hydrogen gas is reduced to not larger than 1%. Further, its activity ages, and therefore the catalyst has be replaced with a fresh catalyst periodically. Therefore, it is difficult to apply the Cu—Zn based catalyst to a fuel cell generation system wherein start and stop are repeatedly carried out, and in particular to a compact fuel cell generation system.
The present invention has been made considering the problem as described above, and an object of the present invention is to provide a catalyst for a water gas shift reaction which can removes CO effectively in a hydrogen gas preferably within a broader temperature range and which can be used for the removal of CO contained in the hydrogen gas. Such catalyst can be used as a catalyst which accelerates a water gas shift reaction when CO is removed from a gas rich in hydrogen which is formed particularly in a fuel cell generation system.
Another object of the present invention is to provide a method for reducing carbon monoxide in a hydrogen gas in which method the hydrogen gas containing carbon monoxide contacts with the catalyst for the water gas shift reaction catalyst as described above.
A further object of the present invention is to provide a fuel cell generation system characterized in that a hydrogen gas which contains carbon monoxide contacts with the catalyst for the water gas shift reaction, and an obtained hydrogen gas of which carbon monoxide content is reduced is supplied to a fuel cell unit.
In the first aspect, the present invention provides a catalyst for a water gas shift reaction characterized in that at least platinum is supported as an active component on a metal oxide carrier.
In the catalyst according to the present invention, the metal oxide carrier is preferably at least one selected from the group consisting of zirconia, alumina, titania, silica, silica-magnesia, zeolite, magnesia, niobium oxide, zinc oxide and chromium oxide (it is to be noted that a metal herein includes also silicon). Among those oxides, zirconia is particularly preferable. Also, a carrier of zirconia, alumina, silica, silica-magnesia, zeolite, magnesia, niobium oxide, zinc oxide or chromium oxide coated with titania may be used as the metal oxide carrier.
As to the catalyst according to the present invention, an amount of the active component supported by the carrier is preferably between0.1% by weight and 10.0% by weight converted into a platinum metal expression based on a weight of the carrier (that is, based on a weight of the carrier itself which does not include the active component, which is also applicable hereinafter to the amount of the a supported active component).
According to one embodiment, rhenium is supported as another active component in addition to platinum in the catalyst of the present invention. In this case, an amount of supported rhenium (converted into a rhenium metal expression) is preferably between 0.1% by weight and 10.0% by weight based on a weight of the carrier.
In a further embodiment, at least one other metal selected from the group consisting of yttrium, calcium, chromium, samarium, cerium, tungsten, neodymium, praseodymium, magnesium, molybdenum and lanthanum is further supported as a further active component in the catalyst of the present invention in addition to platinum and rhenium optionally present as described above. In this case, an amount of the further supported active component(s) (converted into a metal expression) is in total preferably between 0.1% by weight and 10.0% by weight based on a weight of the carrier.
As to the catalyst according to the present invention, any suitable manner may support the active component on the carrier. For example, a salt of a metal which is suitable for the active component is dissolved in a suitable solvent such as water, and thus obtained solution is mixed with the carrier (for example in a powder form) to produce a mixture (for example a slurry) before the mixture is dried (preferably dried by heating), so that the carrier is obtained as the catalyst for the water gas shift reaction on which carrier the active component is supported.
The obtained catalyst for the water gas shift reaction is preferably subjected to firing thereafter. In the present invention, firing means a treatment wherein the carrier on which the active component is supported is kept at an elevated temperature, and makes it possible to produce a catalyst of which activity is higher. For example, the carrier is kept at a temperature between 400° C. and 600° C. (for example, 500° C.) for a period between one hour and six hours (for example, two hours) in a suitable atmosphere (for example, in air or in an inert atmosphere).
In other embodiment, in place of or before firing, the catalyst for the water gas shift reaction which is produced by the above supporting is preferably subjected to a washing treatment. The washing treatment is carried out using water, preferably warm water and more preferably hot water (for example, boiling water). Concretely, the washing treatment is so carried out that the carrier which includes the active component thereon is dispersed in water which is agitated, and then the carrier is separated (for example, by filtration) followed by drying.
In the second aspect, the present invention provides a process of producing a catalyst for a water gas shift reaction which removes carbon monoxide in a hydrogen ga
Hashimoto Noboru
Higashi Hirokazu
Igarashi Akira
Kinugawa Kensaku
Mizobuchi Manabu
Langel Wayne A.
Matsushita Electric & Works Ltd.
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