Effect of Thermal Aging on the Structure and Activity of a Commercial Three-Way Catalyst for Natural Gas Vehicle Exhaust

The effect of thermal aging on the catalytic activity and structural attributes of a commercial Pd/Rh/Al 2 O 3 /CeO 2 –ZrO 2 three-way catalyst is investigated. Comprehensive characterization of the fresh and laboratory-aged catalysts reveals that substantial agglomeration of the active metal and support particles occurs, weakening the metal–support interactions. The pretreatment conditions significantly influence the activity of the fresh and aged catalysts in different ways. O 2 pretreatment does not impact the activity of the fresh catalyst but reduces the light-off temperatures over the aged catalyst. Similar in situ CO DRIFTS spectra of the fresh and aged catalysts after O 2 pretreatment suggest a partial restoration of the aged catalyst surface. H 2 pretreatment leads to an increase in the CO and NO activity of the fresh as well as the aged catalyst, and is explained by the increase in the metallic Pd 0 fraction. The decrease in activity of the aged catalyst is the least with O 2 pretreatment and is suggested as a method to partially restore the activity.