Chung-Zong Wan

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

Abstract 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.

Smart Pd TWC technology to meet stringent standards

Abstract This work highlights the use of model gas reactions to probe and elucidate the properties of complex palladium catalysts. Palladium loading in the catalyst is directly related to hydrocarbon and nitrogen oxide activity, while ceria, an oxygen storage component, improves carbon monoxide performance. An approach, Strategic Material Architecture at Reaction Temperatures (SMART), is discussed as it is applied to palladium automotive catalysts. It will be demonstrated that the catalyst design must incorporate features to achieve early light-off, high temperature performance, thermal resistance, sulfur poisoning tolerance and good TWC activity over a broad range of conditions. A highly integrated Pd catalyst washcoat design is shown to obtain high TWC performance typical of that seen in Rh-based catalysts. A correlation of model gas reaction data with dynamometer aged and vehicle evaluated catalysts will be demonstrated.