Pd-Supported Interaction-Defined Selective Redox Activities in Pd−Ce_0.7Zr_0.3O₂−Al₂O₃ Model Three-Way Catalysts

Abstract

Effects of Pd-supported interactions toward redox behaviors concerning three-way catalytic reactions and oxygen-buffering effects are investigated through stepwise changing Pd-loading locations over ceria−zirconia and alumina. Through light-off tests and kinetics, texture, and surface studies, discrepant but redistributable Pd−A 2 O 3 and Pd−Ce 0.7 Zr 0.3 O x interfaces are defined and analyzed. Pd species are inclined to promote the transformation of Ce 4+ to Ce 3+ and maintain themselves as fine particles on ceria−zirconia surfaces. Oxygen spillover promoted by Pd n + /Pd 0 −Ce 4+ /Ce 3+ redox couples benefits the oxygen-buffering effect, but is limited by the increase of reaction temperatures and ceria−zirconia reducibility. This strong oxidative interaction overcomes the possibility of ceria-related anionic vacancies in facilitating NO dissociation and, thus, improves CO conversion only. Stochiometric light-off tests show higher activities for NO reduction and C 3 H 8 oxidation on a Pd−Al 2 O 3 interface, where the different morphologies and redox states of Pd-supported interfaces should be the main contributing factors for efficient molecular bond dissociation.