Development of Advanced Diesel Oxidation Catalysts

The lower temperatures encountered with European Stage III/IV turbo charged direct injection (DI) Diesel engines with additional features such as cooled exhaust gas recirculation (EGR), compared to Stage II engines, means that modern light duty Diesel engine exhaust gas will rarely exceed temperatures of around 550° - 650°C under full load conditions, and under normal driving conditions, temperatures as low as 120°C will be common. The development of high activity Diesel oxidation catalysts (DOCs) having good low temperature performance is therefore key for achieving hydrocarbon (HC) and carbon monoxide (CO) conversions to meet Stage III and IV legislation. It is shown that extended operation of conventional DOC technology, at the lower temperatures encountered on modern Diesel engines, introduces an important mechanism of catalyst deactivation by accumulation of soot/coke and associated sulfur. This paper describes the development of new DOC technology with emphasis on performance following both low and high temperature operation. A turbo charged DI common rail Diesel engine powered passenger vehicle equipped with the new catalyst technology has been shown to pass the European Stage III legislation after 80,000 km vehicle ageing.