Pd-, Pt-, and Rh-loaded Ce_0.6Zr_0.35Y_0.05O₂ three-way catalysts: An investigation on performance and redox properties

The redox behaviors, oxygen mobilities, and oxygen storage capacities of Ce_0.6Zr_0.4O₂ (CZ), Ce_0.6Zr_0.35Y_0.05O₂ (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 Ce_0.75Zr_0.25O₂, major; cubic ZrO_1.87, 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.