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Synthesis

Gold Catalyst for Fuel Cells

Catalyst selectively oxidizes carbon monoxide in hydrogen-rich gas feed

by MICHAEL FREEMANTLE
June 6, 2005 | A version of this story appeared in Volume 83, Issue 23

CATALYSIS

Hutchings
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Credit: PHOTO BY MICHAEL FREEMANTLE
Credit: PHOTO BY MICHAEL FREEMANTLE

A catalyst consisting of gold nanocrystals supported on iron(III) oxide could potentially boost the efficiency of electricity-generating systems that combine a catalytic reformer with a polymer-electrolyte fuel cell.

The reformer converts an organic fuel, such as methanol or a hydrocarbon, into hydrogen, which is electrochemically oxidized by the fuel cell to generate electricity and water. Also produced in the reforming process are carbon dioxide, water, and carbon monoxide, a gas that poisons the platinum anode of the fuel cell.

"We have shown that gold, carefully prepared, is an effective catalyst for the preferential oxidation of CO in the presence of CO2, H2, and H2O under realistic fuel-cell conditions," says Graham J. Hutchings, a chemistry professor at Cardiff University, in Wales, who led the team that developed the catalyst [Chem. Commun., published online May 17, dx.doi.org/10.1039/b505295p].

Oxidation of CO in the presence of excess moist H2 and CO2 under industrially relevant conditions without oxidizing H2 or regenerating CO from H2 and CO2 by the reverse water gas shift reaction is a difficult objective, the authors note. So far, it's been achieved only by using a multistage reactor, they say.

The researchers prepare the Au/Fe2O3 catalyst by coprecipitation of Au3+ and Fe2O3. Subsequent calcination converts the cationic gold, which catalyzes the reverse water gas shift reaction, to metallic gold. The calcination temperature has a crucial influence on the selective CO oxidation activity of the catalyst. Calcining the catalyst twice--at 400 C and 550 C--gives a catalyst that removes more than 99.5% of the CO in the presence of moist H2 and CO2 at 80 C, the operating temperature of the fuel cell.

"This is the first time that this tough target has been achieved," Hutchings explains.

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