Abstract
Precious metal (PM) dispersions on CeO 2-containing supports were examined. When dispersions were evaluated by the H 2–O 2 titration method, the CeO 2-containing supports hide the true redox of PM because of the large oxygen storage-reduction capacity of the oxide, resulting in higher apparent dispersions than the exact values. When Pt dispersions on the CeO 2 support were evaluated by the ordinary CO pulse method, CO was adsorbed on the CeO 2 support as carbonate species accompanying the oxidation with lattice oxygen. Therefore, the dispersions estimated from the CO uptake were also higher than the exact value. Infrared spectra also clearly evidenced the presence of carbonate species after CO adsorption. To prevent the CO adsorption on CeO 2 as the carbonate species, we treated Pt/CeO 2 with CO 2 before CO adsorption. The strong bands arising from carbonate species on CeO 2 were observed in the infrared spectra. When CO was adsorbed on CO 2-terated Pt/CeO 2, CO was selectively adsorbed on the surface atoms of Pt particles. By the O 2–CO 2–H 2–CO pulse method, the amount of CO adsorbed on surface atoms of the Pt particles could be separated, and a precise dispersion was determined.
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