Abstract
The effect of water treatment and Fe doping on Pt sintering at high temperature was studied for 1wt%Pt/Al2O3 catalysts. After aging for 5h at 700 and 800°C, the water-treated catalysts had higher Pt dispersions than the corresponding untreated catalysts, indicating that Pt sintering was suppressed by water treatment. The degree of improvement depended on Fe content. X-ray diffraction and Pt LIII and Fe K edge X-ray absorption fine structure measurements indicated that Pt was not alloyed with Fe species; that metallic Pt particles and trivalent Fe species existed in all of the aged catalysts; and that both water treatment and Fe content did not affect the Pt and Fe valence states. Thus, the effective suppression of Pt sintering in catalysts with low Fe content (molar ratio of Fe/Pt≈1) at 700–800°C is probably due to iron oxides on the alumina surface functioning as pinning sites for Pt nanoparticles. In contrast, high Fe contents (molar ratio of Fe/Pt≳5) promoted Pt sintering, but lowered the propane oxidation temperature. This is probably due to the promotion of dissociative adsorption of the propane CH bond during the oxidation reaction.
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