A study of ageing effect: Migration of rhodium under air atmosphere

摘要

Rh is the most important element for the current TWC technology. However, the deterioration of Rh is occurred during the high-temperature ageing under an air condition, leading to Rh migration. From the EPMA results, the migration of Rh was found to really take place, resulting in the formation of new Rh - support interaction. This was also supported by the formation of RhAlOx on the catalyst surface, which was confirmed by XPS, in the aged "Rh/CZ + Al" sample. Although Rh/CZ showed higher NO reduction than Rh/Al under dynamic conditions, "Rh/ CZ + Al" and "Rh/Al + CZ" after high-temperature ageing showed similar NO reduction performance, which seems to be a sum of the activity of Rh/CZ and Rh/Al. This was explained by the Rh migration. The results of H2TPR and FT-IR spectroscopy following CO adsorption revealed that many of Rh particles are still present on CZ even after the high-temperature ageing because of Rh - CZ interaction.