Effects of the Precious Metal Composition in the Double Layer Wash-coat Tri-metal TWC for Low Emission Vehicles

In this paper, the effects of the precious metals composition in the double-layer washcoat TWC were examined by the conversion efficiency and the catalytic reaction. The double-layer tri-metal three-way catalyst (TWC) was designed to achieve a high conversion performance and a high thermal durability. The catalytic performance on the PMs loading weight was impacted by the dispersion of the PMs in washcoats. In the results of the CO-pulse chemisorption experiment, the over amount of the optimum PMs loading weight decreases the PMs dispersion in washcoats and the catalytic performance. This was accelerated on the thermal aged catalyst. TPD (temperature-programmed desorption), TPR (temperature-programmed reduction), TEM (transmission electron microscope) and BET analysis were conducted to discuss the effect of the double-layer on both the catalytic reaction and thermal stability.