Abstract
Detailed analyses of the adsorption of carbon monoxide on platinum show that a previously unknown surface compound, “carbon monoxide monohydrate,” is formed utilizing two adjacent platinum sites, one covered by linear carbon monoxide and the other by a co-adsorbed water molecule. At high coverages of carbon monoxide, the surface concentration of “carbon monoxide monohydrate” is limited by the number of adsorbed water sites. “Reduced carbon dioxide” on platinum is identified as a two-electron reduction species from carbon dioxide and has a rate constant for oxidation higher than that of “carbon monoxide monohydrate.” Oxidation of methanol produces “reduced carbon dioxide” but interactions between “reduced carbon dioxide” and adsorbed water sites cannot be identified at present. Indications of a strong interaction are seen from the effect of “reduced carbon dioxide” on the adsorbed hydrogen isotherms on platinum at those water adsorption sites. This work shows that the unpoisoned catalyst sites available for hydrogen oxidation in the presence of carbon monoxide should not be treated in the same way as the same catalyst sites in the absence of carbon monoxide. The structure of adsorbed water at the platinum catalyst surface may be the most important factor in controlling the oxidation of hydrogen in reformed natural gas.
Published Version
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