ADVANCED THREE WAY CATALYST BASED ON IMPROVED PRECIOUS METALS LOADING METHOD AND THERMALLY DURABLE ZEOLITE-TYPE HYDROCARBON TRAP

摘要

Low temperature activity is prerequisite for catalytic converters as most of the emissionsoccur just after starting the engine (cold emissions). One of the efficient ways to improve cold emission, especially hydrocarbons (HC) isto apply close coupled layout. The thermal stability of the catalyst is a concern for close coupled layout, in particular, thermal stability of PGM and functional materials such as Ce-Zr oxide, Al_2O_3 and HC adsorbent zeolite materials. This is one of the reasons whyzeolites are not considered for closed coupled application. In order to realize application of close coupled layout for catalyst with high performance towards cold HC, the thermal stability of PGM and functional materials especially zeolite materials need to be improved significantly. We have developed a new loading method for Pd that is found to be effective in suppressing sintering of Pd during high temperature aging. With new loading method, the Pd dispersion after aging is higher than that obtained with conventional method. The three way catalyst (TWC) made by applying new loading method shows higher performance than conventional TWC. We have also utilized chemically modified β-zeolite (BEA) with Zrand P (Zr/P-BEA) as HC adsorbent which shows higher hydrothermal stability against hydrothermal aging at 1000°C. The Zr/P-BEA retains 80% of its initial SSA after aging while the unmodified BEA loses its SSA drastically during the aging. Vehicle evaluation with close coupled layoutconfirmed that, TWC prepared by new Pd loading method and including Zr/P-BEA (TWC + Zr/P-BEA), shows 15% lower value for cold HC emission than that of TWC. The strategies presented in this study can be utilized effectively for developing highly stable catalysts for close coupled layout for upcoming emission regulations such as BS6.