Low Temperature Hydrocarbon Oxidation Diesel Oxidation Catalyst (DOC) with Improved Particulate Matter Oxidation Capability 2021-26-0201

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 (LOT or T50, the temperature at which 50% conversion is achieved) for unburnt hydrocarbons (HCs) to improve quality of exhaust air during cold start conditions.

In this work, the LOT 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. The LOT were evaluated for the developed washcoat (Catalyst B) compared to a conventional benchmark washcoat (Catalyst A) using a Synthetic Gas Test Bench (SGTB) procedure at a space velocity of 60000 h^-1. The LOT for THC and CO were lowered by 23°C and 40°C as fresh and 12°C and 9°C as aged, respectively, for a catalyst having the same Platinum Group Metal (PGM) loading and substrate volume.

The performance of the developed catalyst was also evaluated on an engine test bench over Non-Road Steady State (NRSC) and Non Road Transient Cycle (NRTC) tests, and compared with the benchmark catalyst. Significant improvements in HCs and PM emission reduction of 45% and 27% in NRSC and 17% and 27% in NRTC tests were achieved. These improvements were achieved by lowering the LOT for HCs and decreasing the opacity with developed catalyst formulation.

The diesel fuel oxidation performance of developed washcoat Catalyst B and benchmark washcoat Catalyst A were evaluated on the engine test bench under steady state conditions. Diesel fuel was dosed upstream of the DOC to raise the pre-DPF exhaust gas temperature to actively regenerate the DPF by PM oxidation. The catalysts were evaluated as aged. At a DOC inlet temperature of 220°C, Catalyst B raised the pre-DPF temperature up to 620°C, whereas Catalyst A only raised the temperature to 553°C. A similar trend was observed for DOC inlet temperatures of 250°C and 300°C.