Integrated NOx and PM reduction devices for the treatment of emissions from internal combustion engines

Abstract

One concept of the inventors relates to a system and method in which a particulate filter comprises at least about 40% by weight of an NOx adsorbant. The filter can be used as both an NOx trap and a particulate filter. By constructing the filter elements using a substantial amount of NOx adsorbant, a large volume of NOx adsorbant can be incorporated into the particulate filter, which substantially reduces the volume and expense of an exhaust system that includes both a catalytic diesel particulate filter and an NOx trap having a large quantity of NOx adsorbant. In a preferred embodiment, the filter also oxidizes NO to NO2. In another preferred embodiment, an SCR catalyst is position downstream of the filter elements.

Description

FIELD OF THE INVENTION [0001] The present invention relates to the field of pollution control devices for internal combustion engines, especially diesel engines and lean burn gasoline engines. BACKGROUND OF THE INVENTION [0002] NOx emissions from vehicles with internal combustion engines are an environmental problem recognized worldwide. Several countries, including the United States, have long had regulations pending that will limit NOx emissions from vehicles. Manufacturers and researchers have put considerable effort toward meeting those regulations. In conventional gasoline powered vehicles that use stoichiometric fuel-air mixtures, three-way catalysts have been shown to control NOx emissions. In diesel powered vehicles and vehicles with lean-burn gasoline engines, however, the exhaust is too oxygen-rich for three-way catalysts to be effective. [0003] Several solutions have been proposed for controlling NOx emissions from diesel powered vehicles and lean-burn gasoline engines. O...

AI Technical Summary

Benefits of technology

[0011] One concept of the inventors relates to a system and method in which a particulate filter comprises at least about 40% by weight of an NOx adsorbant. The filter can be used as both an NOx trap and a particulate filter. By constructing the filter elements using a substantial amount of NOx adsorbant, a large volume of NOx adsorbant can be incorporated into the particulate filter, which substantially reduces the volume and expense of an exhaust system that includes both a catalytic diesel particulate filter and an NOx trap having a large quantity of NOx adsorbant. In a preferred embodiment, the filter also oxidizes NO to NO2. In another preferred embodiment, an SCR catalyst is position downstream of the filter elements.

Problems solved by technology

NOx emissions from vehicles with internal combustion engines are an environmental problem recognized worldwide.

Manufacturers and researchers have put considerable effort toward meeting those regulations.

In diesel powered vehicles and vehicles with lean-burn gasoline engines, however, the exhaust is too oxygen-rich for three-way catalysts to be effective.

These techniques alone, however, will not solve the problem.

Reduction of NOx in an oxidizing atmosphere is difficult.

It has proved challenging to find a lean-burn NOx catalyst that has the required activity, durability, and operating temperature range.

Lean-burn NOx catalysts also tend to be hydrothermally unstable.

A noticeable loss of activity occurs after relatively little use.

The introduction of a reductant, such as diesel fuel, into the exhaust is generally required and introduces a fuel economy penalty of 3% or more.

Currently, peak NOx conversion efficiency with lean-burn catalysts is unacceptably low.

SCR can achieve NOx reductions in excess of 90%, however, there is concern over the lack of infrastructure for distributing ammonia or a suitable precursor.

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