Aftertreatment System Using LNT and SCR

Abstract

A multiple catalyst system for the treatment of exhaust gases generated by a combustion engine in an after treatment system. The system includes a substrate and a plurality of catalysts. The plurality of catalysts may provide a plurality of catalyst sections. A variety of different catalysts, as well as a variety of different combinations of catalysts, may be employed. Catalysts may include both catalysts that assist in the removal of nitrogen oxides from the exhaust gas during cold start operation of the engine, as well as catalysts that are generally more effective in removing nitrogen oxides after the temperature of the after treatment system and / or exhaust gas is elevated to normal operating temperatures.

Description

RELATED APPLICATIONS[0001]This application claims priority to U.S. application Ser. No. 61 / 737,199, having a filing date of Dec. 14, 2012, which is incorporated herein by reference.BACKGROUND[0002]Combustion engines may employ emission controls or systems that are configured to reduce the amount of nitrogen oxides (NOx), carbon dioxide (CO2), and / or iron (Fe), among others, which are present in the engine's exhaust gas. For example, one aspect of controlling such emissions may include the use of a Selective Catalytic Reduction (SCR) system. The SCR typically uses a catalyst and a reductant to convert NO in the exhaust gas into at least nitrogen gas and water. The reductant may be a liquid or gas, such as, for example, urea, anhydrous ammonia, or aqueous ammonia, among others.[0003]In some systems, the ammonia reductant is molecularly bounded to a solid host salt that is placed inside a metallic vessel, which may be referred to as a main unit. Through an exothermic reaction, the ammo...

AI Technical Summary

Benefits of technology

This patent is about a system for treating exhaust gases from combustion engines using a multiple catalyst system. The system includes a common substrate with multiple sections, each containing a different catalyst that helps with a specific exhaust gas treatment process. The first section has a lean NOx trap catalyst, while the second section has a selective catalytic reduction catalyst. The system works to reduce emissions of nitrogen oxides, selectively, using a combination of two different catalysts on a single substrate. The technical effect of this system is to provide more effective and efficient treatment of exhaust gases from combustion engines.

Problems solved by technology

However, in at least some systems, the effectiveness of the AMOx system may be impacted by the temperature of the exhaust gas, and more specifically, whether the exhaust gas has been heated to temperatures that promote the ability of the AMOx system to convert the ammonia into nitrogen gas and water.

For example, SCR systems are not typically effective in controlling NOx emissions at temperatures below 200° Celsius, which may present issues with compliance with emissions regulations.

However, higher fuel consumption is directly related to an increase in CO2 production, and may also increase the fuel consumption rate of engine.

Yet, with SCR systems, there may be a delay before the engine coolant reaches temperatures needed for the engine coolant to aid in the above-discussed exothermic reaction.

This delay in time may be further extended due to the temperature of the surrounding environment, such as, for example, during extreme cold weather conditions.

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