Exhaust gas treatment system including a four-way catalyst and urea SCR catalyst and method of using the same

A method of using an exhaust gas treatment system for a diesel engine comprising a diesel oxidation catalyst (DOC) in fluid communication with the diesel engine to receive an exhaust gas flow therefrom;

• a hydrocarbon (HC) injection device located between the engine and the DOC that is configured to periodically and selectively inject a hydrocarbon, CO or H2 material, or a combination thereof, into the exhaust gas flow;
• a urea selective catalytic reduction (U-SCR) catalyst in fluid communication with the DOC to receive the exhaust gas flow therefrom;
• and a four-way catalyst in fluid communication with the U-SCR to receive the exhaust gas flow therefrom, the four-way catalyst comprising a monolithic wall-flow substrate having a plurality of porous cell walls that incorporates a lean nitrogen oxides (NOX) trap disposed on the porous cell walls and a diesel particulate filter (DPF);
• a second injection device that is configured to periodically and selectively inject urea or ammonia, or a combination thereof, into the exhaust gas flow between the DOC and the U-SCR catalyst;
• and a controller that is configured to control operation of the engine and periodic and selective injection of the hydrocarbon, CO or H2 material, or combination thereof, and periodic and selective injection of the urea or ammonia, or combination thereof, and determine an amount of NOX in the exhaust gas flow, the method comprising:
• configuring the controller to operate in a first mode to minimize consumption of the urea or ammonia, or a combination thereof, and minimize NOX conversion in the U-SCR catalyst or in a second mode to minimize consumption of the hydrocarbon, CO or H2 material, or combination thereof, and minimize NOX conversion in the four-way catalyst;
• operating the engine to produce the exhaust gas flow, and
• periodically and selectively injecting at least one of the hydrocarbon, CO or H2 material, or combination thereof, or the urea or ammonia, or combination thereof, into the exhaust gas flow using the controller to operate the exhaust gas treatment system in the first mode or the second mode.

An exhaust gas treatment system for a diesel engine, comprising:

• a diesel oxidation catalyst (DOC) in fluid communication with the diesel engine to receive an exhaust gas flow therefrom, the DOC disposed in a DOC housing;
• a hydrocarbon injection device located between the engine and the DOC that is configured to inject a hydrocarbon, CO or H2 material, or a combination thereof, into the exhaust gas flow;
• a urea selective catalytic reduction (U-SCR) catalyst in fluid communication with the DOC to receive the exhaust gas flow therefrom, the U-SCR catalyst disposed in a U-SCR catalyst housing;
• a second injection device that is configured to inject urea or ammonia, or a combination thereof, into the exhaust gas flow between the diesel engine and the U-SCR;
• a four-way catalyst in fluid communication with the U-SCR catalyst to receive the exhaust gas flow therefrom, the four-way catalyst comprising a monolithic wall-flow substrate having a plurality of porous cell walls that incorporates a lean nitrogen oxide trap disposed on the porous cell walls and a diesel particulate filter;
• and
• a controller that is configured to control operation of the exhaust gas aftertreatment system and periodic and selective injection of the hydrocarbon, CO or H2 material, or combination thereof using the hydrocarbon injection device, and periodic and selective injection of the urea or ammonia, or combination thereof using the second injection device, and determine an amount of NOX in the exhaust gas flow, the controller configured to operate in a first mode to minimize consumption of the urea or ammonia, or a combination thereof, and minimize NOX conversion in the U-SCR catalyst or in a second mode to minimize consumption of the hydrocarbon, CO or H2 material, or combination thereof, and minimize NOX conversion in the four-way catalyst.