Effect of Perovskite-Fluorite Phase Transition on the Catalytic Activity of Pt/CeFeOx

A 2 nm-thick CeFeOx film was deposited onto γ-Al2O3 by atomic layer deposition (ALD) and then compared to γ-Al2O3-supported CeO2 and MgAl2O4-supported LaFeO3 films as a catalyst support for Pt. Scanning transmission electron microscopy (STEM) demonstrated that the CeFeOx film uniformly coated γ-Al2O3, while X-ray diffraction (XRD) indicated that the film reversibly underwent a transition from a fluorite structure following oxidation to a perovskite structure after reduction at 1073 K. A 3.3 wt % Pt/CeFeOx/γ-Al2O3 catalyst showed large (∼10 nm) Pt particles after oxidation at 1073 K, but the Pt dispersed uniformly over the support after reduction at 1073 K. While Pt/CeOx/γ-Al2O3 exhibited high rates for CO oxidation and the water gas shift (WGS) reaction after either oxidation or reduction at 1073 K, reaction rates for Pt/CeFeOx/γ-Al2O3 and Pt/LaFeO3/MgAl2O4 depended strongly on the pretreatment conditions. Similar to Pt/LaFeO3/MgAl2O4, oxidized Pt/CeFeOx/γ-Al2O3 exhibited significantly lower rates than Pt/CeOx/γ-Al2O3 for CO oxidation, while reduced Pt/CeFeOx/γ-Al2O3 exhibited much higher CO oxidation rates. While reduced Pt/CeFeOx/γ-Al2O3 was relatively inactive for WGS, oxidized Pt/CeFeOx/γ-Al2O3 was nearly 10 times more active than Pt/CeOx/γ-Al2O3. Based on these results, the potential implications of the support composition and structure are discussed.