Comparison of precious metal doped and impregnated perovskite oxides for TWC application

• Behavior of Pd-doped LaFeO3 evolves toward Pd-impregnated LaFeO3 upon aging.
• Activation energy of Pd-impregnated LaFeO3 for CO oxidation is low compared to Pd.
• Rh-doped CaTiO3 evolves toward Rh-impregnated CaTiO3 upon aging.
• Activation energy of Rh-impregnated CaTiO3 for CO oxidation is comparable to Rh.
• Aging leads to higher CO oxidation rates for both forms of both catalysts.

Four high-surface-area (50–60 m2/g) perovskite-based powder catalysts, Pd-doped LaFeO3, Pd-impregnated LaFeO3, Rh-doped CaTiO3, and Rh-impregnated CaTiO3, were characterized by scanning transmission electron microscopy and CO oxidation measurements in fresh and redox-aged (14 h at 800 °C) states. Both intrinsic catalytic activity and stability were significantly higher in Pd-doped LaFeO3 than in Rh-doped CaTiO3 under lean to stoichiometric reaction conditions. Activities of doped were initially lower than impregnated versions, though aging led to convergence in the catalytic performance for both systems. A mixture of metallic and cationic forms of Pd appear to contribute to activity in the Pd catalysts, whereas metallic Rh particles, which can easily segregate onto the surface of CaTiO3 in Rh-doped CaTiO3 upon aging, are the likely source of catalytic activity in the Rh catalysts.

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