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The palladium oxidation state of an SiO 2 -supported palladium catalyst was quantitatively determined by Pd L 3 -edge XANES (X-ray absorption near-edge structure) analysis. By changing the time of CO-reduction pre-treatment at 673 K, a series of 5 wt% Pd-loaded SiO 2 catalysts (PdO x/2 /SiO 2 ) containing different amounts of the Pd metal and PdO phases were prepared, and the average oxidation number (x) was estimated from the number of CO 2 molecules formed during the CO-reduction treatment. L 3 -edge XANES spectra of these samples and a reference sample (Pd powder) were recorded, and the white line area of the spectra was evaluated. A good linear relationship was confirmed between the white line area intensity and the average oxidation number (x), indicating that the oxidation state of Pd in structurally unknown Pd samples could be quantitatively determined by a simple XANES analysis. To demonstrate the utility of this method in a catalytic study, the effect of the oxidation number (x) on the CO oxidation activity of PdO x/2 /SiO 2 was also examined, and metallic Pd 0 sites in PdO x/2 /SiO 2 were shown to be active species.

Pd/TiO2–CeO2 is proposed as a promising catalyst for low-temperature oxidation of CO with 100 °C lower light-off temperature than Pd/Al2O3.

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