Conversion Characteristics of Double-Layer Washcoat Tri-Metal Three-Way Catalyst Using High Cell Density Substrate

The research was conducted to evaluate conversion characteristics of three-way catalyst(TWC) with a double-layer washcoat to improve the light-off temperature and the thermal durability. The evaluations considered factors such as the PM loading ratio and loading quantity of the tri-metal catalyst for Rh-Pd-Pt configuration, the washcoat composition, and the cell density. The higher cell density of TWC can improve the light-off temperature because of the lower heat capacity of the substrate and the increase of the surface area. Loading quantity and ratio of precious metals has appropriate value to light-off performance in each cell density of substrate. A proper selection of the bottom layer washcoat loaded with Pd can promote thermal stability and the upper layer washcoat with an excellent ability of oxygen storage can improve the light-off performance and the durability of the double-layer TWC. The best TWC with double-layer was 9Hy(0.6×11×3) with 140cell/cm^2 substrate.