Low temperature hydrocarbon oxidation Diesel Oxidation Catalyst (DOC) with improved PM oxidation capability

Pollutants emitted from an internal combustion engine need to be controlled to improve quality of air. The pollutants emitted from a diesel engine are – carbon monoxide (CO), unburnt hydrocarbons (HCs), oxides of nitrogen (NOx) and particulate matter (PM). These pollutants can be controlled using after treatment systems which comprise of – a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF) and a selective catalytic reduction (SCR) unit. With increasing vehicle density and lower speed driving scenarios, there is a need to improve the rate of oxidation and reduction in after treatment systems at lower exhaust gas temperatures for effectively decreasing pollutant emissions. There is a need to lower the light off temperature (T50 – Temperature at which 50% conversion is achieved) for unburnt hydrocarbons (HCs) to improve quality of air during cold start conditions. In this work, the light off temperatures for representative HCs were lowered using various techniques, such as decreasing basicity of the catalyst support, adding promoters of d block elements, and modifying the pore size distribution of the washcoat. Light off temperatures were evaluated for the developed washcoat (Catalyst B) and conventional washcoat (Catalyst A) using a Synthetic Gas Test Bench (SGTB) at space velocity of 60,000 h-1. The light off temperatures for THC and CO were lowered by 23 and 40°C fresh, and 12 and 9°C aged respectively for a catalyst having similar Platinum Group Metal (PGM) loading and substrate volume. The performance of the developed catalyst was evaluated on an engine test bench in Non-Road Steady State (NRSC) and Non-Road Transient Cycle (NRTC) tests, and compared with the benchmark catalyst. A significant improvement in THC emission reduction – 45% in NRSC test and 17% in NRTC test and PM emission reduction – 27% in NRSC test and NRTC test was achieved. The improvement was achieved by lowering the light off temperature for THC and decreasing opacity using the developed catalyst formulation. The diesel fuel oxidation performance of developed washcoat (Catalyst B) and conventional washcoat (Catalyst A) was evaluated on engine test bench at steady state condition. Diesel fuel was dosed upstream of DOC to raise pre DPF exhaust gas temperature to regenerate accumulated soot in DPF. Catalyst A and B was evaluated as aged. Catalyst B was able to oxidise fuel at lower temperatures even at 220°C DOC inlet exhaust gas temperature and exhaust gas temperature at DOC outlet was raised up to 620°C while Catalyst A was able to raise exhaust gas temperature at DOC outlet up to 553°C at DOC inlet exhaust gas temperature of 220°C. A similar trend was observed at DOC inlet exhaust gas temperature of 250°C and 300°C.