Comparative Analytical Study of Two Pt–Rh Three-way Catalysts

Abstract

Pt-Rh three-way catalysts (TWCs) of two formulations were examined by electron probe microanalysis (EPMA) and cross sectional transmission electron microscopy (TEM), in order to study the effect of accelerated aging on microstructure. Both formulations have Pt and Rh applied in separate washcoat layers, Rh in a zirconia-rich outer layer and Pt in an alumina-rich inner layer(s). Microstructural analyses show that in spite of the initial separation, the precious metals inter-diffuse between the washcoat layers and alloy during aging. Following dynamometer aging the two formulations exhibited significant differences in the precious metal (PM) particle size distributions and the correlation between PM particle size and composition. These differences are attributed to the increased transport of Pt due to the presence of ceria and zirconia in the alumina-rich inner washcoat of one formulation, compared to other formulation. The presence or absence of porosity > 1lm in diameter and differences in initial Pt distributions in the inner washcoat were also noted as possibly contributing to the PM particle growth. The transition alumina of one formulation, containing Ba, partially transformed to corundum during aging. The other formulation utilized a La-stabilized alumina which did not transform to corundum after aging.

Trapping mobile Pt species by PdO in diesel oxidation catalysts: Smaller is better

“…Yu-Yao and Kummer [9]reported that they were able to prepare low concentration precious metal catalysts via vapor phase transport from a metal foil to an alumina or ceria-alumina support. The transport of precious metals has also been found to lead to formation of alloys and bimetallic nanoparticles, as in the case of physically mixed Pt and Pd [10] catalysts and also Pt, and Rh catalysts [11]. In this previous work, the results were influenced by the catalyst formulation, for example the same nominal ratio of Pt and Pd gave very different extent of volatilization and transport.…”

Influence of Ageing Conditions on the Performance and Structure of Commercial Three-Way Catalysts

“…Haaß and Fuess [1] reported on the deactivation mechanism of model automotive catalysts and their structural characterisation. Because an extrapolation from model catalysts to commercial TWCs is not always possible, an understanding of deactivation processes of real life TWCs is definitely mandatory [2,3]. First results of activity measurements and structural investigations of commercial TWCs will be presented.…”

Assessing Economic Modulation of Future Critical Materials Use: The Case of Automotive-Related Platinum Group Metals

“…We illustrate the construction of the substitution curve model for the TWC. Data were collected for PGM loading in 24 TWCs, described in the technical literature. ,− Loadings were normalized on the basis of engine displacement to a common engine size of 2.5 L.…”

“…Data were collected for PGM loading in 24 TWCs described in the technical literature. (40,(46)(47)(48)(49)(50)(51)(52) Loadings were normalized based on engine displacement to a common engine size of 2.5 liters.…”