Activity–Property Relationships and Thermal Stability of Fully Formulated Pt–Pd–Rh-Based Three-Way Catalysts

In this study, the effects of support formulation on the properties, activity, and hydrothermal stability of fully formulated platinum group metals (PGM; Pd–Pt–Rh)-based three-way catalysts (TWCs) were investigated. Activity of a series of commercial catalysts, i.e. PGM/La–Al, PGM/Ce–Zr–Y, PGM/Ce–Zr–Al, PGM/Ce–Zr–La-Al, PGM/Ce–Zr–La–Y-Nd, and PGM/Ce–Zr–La-Y, with Pd, Pt, and Rh loadings of 1, 2, and 0.2 wt %, respectively, was tested toward CO and C3H6 oxidation and NO reduction under fresh and aged states. The Euro V aging protocol (i.e., under air and 10% H2O at 1050 °C) was employed for hydrothermal aging. Catalyst characterization was conducted using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy-Dispersive Spectroscopy (EDS), X-ray Fluorescence (XRF), Inductively coupled Plasma (ICP), hydrogen-temperature-programmed reduction (H2-TPR), Brunauer–Emmett–Teller (BET), and field emission scanning electron microscopy (FE-SEM) techniques. H2-TPR analysis confirms that high loading of ceria-zirconia leads to higher H2 consumption and in high-ceria, Y-doped samples (i.e., Ce–Zr–Y and Ce–Zr–La-Y) reducibility can be enhanced after aging. Catalytic performance tests show that alumina-containing samples, despite their higher BET surface area, exhibit lower activities due to their low H2 consumption. The C3H6 and NO light-off behavior of the fresh samples indicates that T50 (i.e., the temperature at which CO/C3H6/NO conversion is 50%) generally decreases with increasing H2 consumption. Among the aged samples, PGM/Ce–Zr–Y exhibited the highest activity, despite its significantly low BET surface area, due to the combined influence of high H2 consumption (i.e., enhanced oxygen mobility) and Y-induced stabilization of precious metal dispersion after aging. Overall, the results demonstrate that preserved catalytic activity after severe hydrothermal aging arises from the combined effects of reducibility, noble metal crystallite size (i.e., maintained dispersion), and support composition, highlighting the role of rare-earth promoters-particularly yttrium- and ceria-zirconia content in improving redox behavior and catalyst durability.