Pd doped CaCo x Zr 1-x O 3- δ perovskites for automotive emissions control

Abstract

CaCoxZr1-xO3-δ (x = 0, 0.3, 0.5, 0.7 and 0.9) perovskites with and without Pd doping were synthesized for the first time and reported here to show outstanding redox property and oxygen storage capacity (OSC) compared to the ceria-based oxygen storage materials (OSMs). The studied perovskites retain their main phase of orthorhombic Lakargiite CaZrO3 structure, and were characterized by x-ray fluorescence (XRF), x-ray diffraction (XRD), temperature programmed reduction (TPR) and dynamic redox cycle measurements. Partial substitution of Co by Zr at B sites enhanced the perovskite structural crystallinity and stability, material reducibility and OSC properties, giving optimized OSM composition when x was around 0.5. Further kinetic studies showed a first order reaction mechanism with an activation energy (Ea) of 0.159 eV for CaCo0.5Zr0.5O3-δ. For Pd-containing samples, Pd was present in both forms of bulk Pd2+ and surface Pd0, and the amount of surface Pd0 increased with increasing Pd loading. Pd dopant also facilitated the Co reduction and improved the catalyst reducibility. Under simulated exhaust conditions at fuel lean-rich conditions (stoichiometric numbers of 1.16, 1.07 and 0.95), Pd-doped CaCo0.6-yZr0.4PdyO3 (y = 0.05 and 0.1) samples showed profound catalytic activity towards C3H6 and CO oxidation (T50s < 280 °C at fuel lean-rich), suggesting their potential application for automotive emissions control.