Direct Observation of Rhodium Aluminate (RhAlOx) and Its Role in Deactivation and Regeneration of Rh/Al2O3 under Three-Way Catalyst Conditions

To improve the performance of three-way catalysts (TWC), it is essential to further develop our understanding of the microstructure-performance relationships in next-generation TWC. Light-off measurement combined with comprehensive structural imaging using advanced characterization techniques reveals the correlation between catalyst activity and atomic-scale morphology of deactivated and regenerated Rh/Al2O3 catalysts. Using scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS), and extended X-ray absorption fine structure spectroscopy (EXAFS), we show direct evidence of rhodium aluminate (RhAlOx); its formation and disappearance can be attributed to the deactivation and regeneration of Rh/gamma-Al2O3. Specifically, regeneration relies on the ability to restore active nanometer-sized Rh nanoparticles from inactive RhAlOx in which the preferential interstitial sites of inactive Rh are found to be the octahedral sites of the cubic spinet gamma-Al2O3. A deep understanding of the long-debated deactivation mechanism in Rh/Al2O3 will enable more efficient usage of Rh in TWC applications.