Effect of Perovskite-Fluorite Phase Transition on the Catalytic Activity of Pt/CeFeO<sub><i>x</i></sub>
Kai Shen, Siwon Lee, Ohhun Kwon, Mengjie Fan, Raymond J. Gorte, John M. Vohs
Abstract
A 2 nm-thick CeFeO x film was deposited onto γ-Al 2 O 3 by atomic layer deposition (ALD) and then compared to γ-Al 2 O 3 -supported CeO 2 and MgAl 2 O 4 -supported LaFeO 3 films as a catalyst support for Pt. Scanning transmission electron microscopy (STEM) demonstrated that the CeFeO x film uniformly coated γ-Al 2 O 3, 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/CeFeO x /γ-Al 2 O 3 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/CeO x /γ-Al 2 O 3 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/CeFeO x /γ-Al 2 O 3 and Pt/LaFeO 3 /MgAl 2 O 4 depended strongly on the pretreatment conditions. Similar to Pt/LaFeO 3 /MgAl 2 O 4, oxidized Pt/CeFeO x /γ-Al 2 O 3 exhibited significantly lower rates than Pt/CeO x /γ-Al 2 O 3 for CO oxidation, while reduced Pt/CeFeO x /γ-Al 2 O 3 exhibited much higher CO oxidation rates. While reduced Pt/CeFeO x /γ-Al 2 O 3 was relatively inactive for WGS, oxidized Pt/CeFeO x /γ-Al 2 O 3 was nearly 10 times more active than Pt/CeO x /γ-Al 2 O 3 . Based on these results, the potential implications of the support composition and structure are discussed.