The journey of rhodium in Al2O3-CeO2-ZrO2 supported three-way catalysts

For increasing the noble metal efficiency and developing more robust emission control catalysts, an accurate understanding of their structural dynamics during operation is essential. This study systematically investigates the manifold interactions of Rh with various catalyst components in alumina/ceria-zirconia based washcoats by advanced in situ/operando characterization. Pronounced structural changes, which drastically affect the catalyst performance, were observed during short fuel-cut steps. Operando X-ray absorption spectroscopy and electron microscopy investigations revealed the formation of mobile metallic Rh particles under stoichiometric/rich reaction conditions. In contrast, Rh oxidation, volatilization and diffusion into the alumina surface/subsurface occurred above 950 ◦C during O2-rich steps. While the first phenomenon contributed to the redistribution of Rh on both supports, the partial relocation of Rh in low-loaded washcoats under lean reaction conditions was exclusively observed to occur from CeO2-ZrO2 to γ-Al2O3. Overall, the intimate interaction between the washcoat components prevented the loss of the noble metal due to volatilization.