Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon monoxide component
Utility Patent
1995-03-20
2001-01-02
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon monoxide component
C423S437200, C429S010000, C502S074000
Utility Patent
active
06168772
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a catalyst for selective oxidation of carbon monoxide in reformed gases of which a main component is a hydrogen gas employed as a fuel for such as a fuel cell and a process of the oxidation of carbon monoxide in reformed gases.
While a platinum based catalyst is employed in a solid polymer electrolyte fuel cell (PEMFC) as in a phosphoric acid fuel cell (PAFC), the solid polymer electrolyte fuel cell is operated under a low temperature (ordinarily at or below 100° C.) different from the phosphoric acid fuel cell so that the poisoning of a catalyst with carbon monoxide more seriously takes place. A reformed gas prepared by reforming methane or the like in the consideration of a cost is frequently employed as a supply source of hydrogen in a fuel employed in these fuel cells, but, for example, about 1% of carbon monoxide is contained in the reformed gas for PAFCs, which results in the poisoning of the electrocatalyst of the said polymer electrolyte fuel cells so as not to provide desired cell performances.
Because of this poisoning, in order to obtain the desired cell performances employing the reformed gas. It is required to supply the reformed gas after the amount of the carbon monoxide is reduced to one-hundredth of the original amount. In accordance with this concept, Gottesfeld et al. have proposed {circle around (1)} a process of oxidizing in advance coexisting carbon monoxide to nonpoisonous carbon dioxide by means of a &ggr;-alumina supporting platinum (3% in weight) and {circle around (2)} a process of oxidizing coexisting carbon monoxide to carbon dioxide on the electrocatalyst of a fuel cell (M. T. Paffett, S. Gottesfeld et al., “The Treatment of CO Poisoning in Low Temperature Fuel Cells by the Injection of Oxygen or Air into the Anode Feed Stream”, 1990 Fuel Cell Seminar Pre-Publication).
Since, however, the selectivity of the oxidation reaction with the oxygen is low in these reactions, a large amount of the hydrogen which is a main component of the reformed gas and is to be used as a fuel is concurrently oxidized and wasted so that the lowering of the fuel utilization is caused. The reason why the large amount of the hydrogen gas is oxidized is that the catalyst is exposed on the support of the &ggr;-alumina and the ordinary electrocatalyst (carbon black) and onto the catalyst are adsorbed by the oxygen and carbon monoxide which is then oxidized to carbon dioxide and concurrently with this oxidation the hydrogen is also adsorbed and oxidized. Since the adsorption rate of the hydrogen is proportional to the partial pressure of the hydrogen in the gas phase, the amount of the hydrogen oxidized supposedly becomes large.
SUMMARY OF THE INVENTION
The present Invention has been made to overcome the above drawbacks. Accordingly, an object of the present invention is to provide a catalyst for selectively oxidizing carbon monoxide in reformed gases employed as a fuel of a fuel cell.
Another object of the invention is to provide a catalyst which enables the depression of an amount of hydrogen wasted due to oxidation thereof and maintains the fuel utilization efficiency in addition to the selective oxidation of the carbon monoxide.
A further object of the invention is to provide a process of preparing said catalyst.
A first aspect of the present invention is a catalyst for selective oxidation of carbon monoxide in reformed gases which comprises a support having apertures of which a diameter is a molecular level dimension and a catalyst supported thereon.
A second aspect of the present invention is a process of oxidation of carbon monoxide in reformed gases which comprises contacting a reformed gas containing a large amount of hydrogen and a small amount of carbon monoxide with a catalyst comprising a support having apertures of which a diameter is a molecular level dimension and a catalyst supported thereon while supplying oxygen for selectively oxidizing the carbon monoxide.
In accordance with these aspects, a small amount, usually at a concentration of about 1%, of carbon monoxide existing in original reformed gases can be selectively oxidized to nonpoisonous carbon dioxide by the function of the catalyst such as a platinum while depressing the waste of hydrogen due to its oxidation. Accordingly, when the reformed gases prepared according to the process of this invention is employed as a fuel of a fuel cell, substantially no poisoning occurs because only a small amount of the carbon monoxide is left, and the high cell performances and the high fuel utilization rate can be obtained because the hydrogen is not wasted. More than 90% of the introduced oxygen is employed only for the oxidation of the carbon monoxide so as to remarkably lower the decrease of the hydrogen due to its oxidation and when it is employed as a fuel of a fuel cell, the fuel utilization rate is not lowered.
REFERENCES:
patent: 3631073 (1971-12-01), Cohn et al.
patent: 5244852 (1993-09-01), Lachman et al.
patent: 5258340 (1993-11-01), Augustine et al.
patent: 5292991 (1994-03-01), Lachman et al.
patent: 5432021 (1995-07-01), Wilkinson et al.
Akubuiro et al, “Dispersion and Support Effects in Carbon Monoxide Oxidation over Platinum,” 1985 (No Month)Applied Catalysis,14, 215-227.*
Arent Fox Kinter Plotkin & Kahn PLLC
Langel Wayne
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