Evolution of structural properties of three-way catalysts according to theageing procedure

The conversions of CO, NO and HC of TWC submitted to either cycling ageing (CA) or thermal ageing (TA) were compared. The results show a strong deacti vation with TA catalysts, whereas the loss of activity is very moderate whe n using CA ageing. To understand these differences, the catalysts were anal ysed with different physical techniques (microscopy, TPR, TPD, infrared). T hese techniques have put in evidence different compositions (bulk and surfa ce) between fresh, CA and TA catalysts. Indeed, TPR has allowed the distinc tion between two bulk phases on the fresh catalyst while only one phase rem ains on the CA catalyst. Equally, TPD and FTIR led to a partial elucidation of the surface composition and a good distinction of the different phenome na occurring during thermal ageing or oscillating ageing allowing the propo sition scheme to represent ageing of a TWC.