Pd-, Pt-, and Rh-Loaded Ce0.6Zr0.35Y0.05O2 Three-Way Catalysts: An Investigation on Performance and Redox Properties

Abstract

The redox behaviors, oxygen mobilities, and oxygen storage capacities of Ce0.6Zr0.4O2 (CZ), Ce0.6Zr0.35Y0.05O2 (CZY), and 0.5 wt% M/CZY (M=Pd, Pt, Rh) as well as the three-way catalytic performance of the noble metal-loaded CZY materials have been investigated. It is observed that at a space velocity of 60,000 h−1 and in an atmosphere close to the theoretical air-to-fuel ratio (i.e., 14.6), the CZY-supported precious metal catalysts showed good three-way catalytic activity. X-ray diffraction investigations revealed that there are two phases (cubic Ce0.75Zr0.25O2, major; cubic ZrO1.87, minor) in CZ, CZY, and 0.5 wt% M/CZY. These materials are porous and large in surface area. According to the results of Ce 3d X-ray photoelectron spectroscopic studies, the doping of Y3+ ions into the CZ lattice would cause the concentrations of oxygen vacancies and Ce3+ ions to increase. The results of H2(or CO)–O2 titration and temperature-programmed reduction–reoxidation experiments indicate the presence of a reversible redox behavior of Ce4+/Ce3+ couples. The results of 18O/16O isotope exchange studies show that in the presence of oxygen vacancies and noble metals, the mobility of lattice oxygen on/in CZY is promoted. Based on the above outcomes, we suggest that by incorporating Y3+ ions into CZ and loading Pd, Pt, or Rh on CZY, one can enhance (i) lattice oxygen mobility, (ii) Ce3+ ion concentration, and (iii) oxygen uptake capacity of the CZY solid solution, generating a class of materials suitable for the catalytic conversion of automotive exhaust.