Pd/Support Interface-Promoted Pd−Ce_0.7Zr_0.3O₂−Al₂O₃ Automobile Three-Way Catalysts: Studying the Dynamic Oxygen Storage Capacity and CO, C₃H₈, and NO Conversion

Abstract

The effect of the Pd−support interface on the dynamic oxygen storage capacity (DOSC) and three-way catalytic activities were investigated using Pd chromatographically distributed between Ce0.7Zr0.3O2 and Al2O3. CO−He pulse, H2-TPR, and XPS show that the Pd−(Ce, Zr) Ox interface promotes a higher degree of oxygen releasing than the Pd−(Al2O3) interface while maintaining the oxidized states of Pd. Pd promotion at the Pd−(Ce, Zr) Ox interface depends on the oxygen species of ceria−zirconia, and promotion takes place on surface oxygen and subsurface oxygen species. Dynamic CO−O2 transient measurement shows that DOSC is greatly promoted by the Pd−(Ce, Zr) Ox interface. The transient results indicate that the Pd−(Ce, Zr) Ox interface accelerates the oxygen spillover and back-spillover between Pd and the support oxide, but this phenomenon is not obvious for the Pd−(Al2O3) interface. Higher CO oxidation activity was obtained over a catalyst with a higher degree of Pd−(Ce, Zr) Ox interface in proportion to its DOSC performance. A two-step CO oxidation mechanism at the Pd−(Ce, Zr) Ox interface includes oxygen migration and its reaction with the adsorbed CO. Higher NO reduction and C3H8 oxidation rates were obtained with a catalyst with more Pd−(Al2O3) interface, showing negative correlation with the DOSC performance.