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

A 2nm-thick CeFeO x film was depositedonto & gamma;-Al2O3 by atomic layer deposition(ALD) and then compared to & gamma;-Al2O3-supportedCeO(2) and MgAl2O4-supported LaFeO3 films as a catalyst support for Pt. Scanning transmissionelectron microscopy (STEM) demonstrated that the CeFeO x film uniformly coated & gamma;-Al2O3, while X-ray diffraction (XRD) indicated that the film reversiblyunderwent a transition from a fluorite structure following oxidationto a perovskite structure after reduction at 1073 K. A 3.3 wt % Pt/CeFeO x /& gamma;-Al2O3 catalystshowed large (& SIM;10 nm) Pt particles after oxidation at 1073K, but the Pt dispersed uniformly over the support after reductionat 1073 K. While Pt/CeO x /& gamma;-Al2O3 exhibited high rates for CO oxidation and thewater gas shift (WGS) reaction after either oxidation or reductionat 1073 K, reaction rates for Pt/CeFeO x /& gamma;-Al2O3 and Pt/LaFeO3/MgAl2O4 depended strongly on the pretreatment conditions.Similar to Pt/LaFeO3/MgAl2O4, oxidizedPt/CeFeO x /& gamma;-Al2O3 exhibited significantly lower rates than Pt/CeO x /& gamma;-Al2O3 for CO oxidation,while reduced Pt/CeFeO x /& gamma;-Al2O3 exhibited much higher CO oxidation rates. Whilereduced Pt/CeFeO x /& gamma;-Al2O3 was relatively inactive for WGS, oxidized Pt/CeFeO x /& gamma;-Al2O3 wasnearly 10 times more active than Pt/CeO x /& gamma;-Al2O3. Based on these results, thepotential implications of the support composition and structure arediscussed.