Design of a novel Pd three-way catalyst: Integration of catalytic functions in three dimensions

Performance of Pd catalysts for three-way conversion of HC/CO/NO is characterized using simulated auto exhaust gas over a wide temperature range from 423 to 823 K. For Pd catalysts, HC/CO/NO conversions increase sharply around 570 K. Introduction of ceria in Pd catalysts reduces NO conversion at low temperature around 600 K, while increases NO conversion at high temperature around 770 K. The lower NO conversion is attributed to a lower Pd function resulted by intimate Pd-Ce interaction. The enhanced NO conversion at high temperature is related to a higher oxygen storage capacity provided by ceria. In addition, base metal oxide additives are found to enhance Pd catalysts performance over the wide temperature range tested. An integrated Pd only catalyst washcoat architecture, consisting of a Pd top layer and a Pd-Ce bottom layer, is designed to maximize HC/CO/NO performance over a wide operating temperature range. Engine and vehicle evaluation results show that this Pd catalyst, integrating Pd sites and oxygen storage components in three dimensions, is superior in three-way performance to current Pt/Rh catalysts, and can be applied to meet stringent Californian low emission vehicle standards.