Rh Nanoparticles Dispersed on ZrO2-CeO2 Migrate to Al2O3 Supports to Mitigate Thermal Deactivation via Encapsulation

Full-scale monolithic three-way catalysts (TWCs) comprisingRh,oxygen-scavenging ZrO2-CeO2 (ZC), and gamma-Al2O3 as a binder component were studiedafter real engine aging. The fatal irreversible deactivation thatoccurred under stoichiometric-lean-rich perturbation at 1000 degrees Cfor 40 h (SLR aging) was attributed to the complete encapsulationof Rh nanoparticles by ZC, leading to the physical blockage of gasadsorption. Preaging the catalyst under a rich condition at 1000 degrees Cfor 40 h (R aging) drastically mitigated this deactivation, i.e.,the catalyst with R-SLR combined aging sustained its catalyticperformance much better than the catalyst with SLR aging at the sametemperature (1000 degrees C) and total time (80 h). X-ray mapping andhigh-temperature environmental electron microscopic analyses suggestedthat R aging promoted the migration of Rh nanoparticles across theZC surface toward the boundary with the Al2O3 binder. Owing to the strong bonding with the Al2O3 surface, Rh nanoparticles were trapped at or near the boundary.Consequently, these Rh nanoparticles were unlikely to be fully coveredby ZC even under the SLR aging condition because the encapsulationwas induced through repetitive oxygen release/storage cycles at theRh/ZC interface. Thus, we propose that Rh nanoparticles in contactwith ZC and Al2O3 played crucial roles to hinderthe encapsulation caused by SLR aging at 1000 degrees C. Rh nanoparticlessupported on the dual-oxide support of ZC and Al2O3 were subjected to engine aging and chassis dynamometer tests.The deterioration extents of the TWC and oxygen storage capacity performanceswere successfully mitigated using this dual-oxide support formulation.