Bimodal catalyst-urea SCR system for enhanced NOx conversion and durability

摘要

The present invention discloses a method for reducing NO_x in exhaust gases of an internal combustion engine. The purpose of this invention is to convert engine out NO_x (approximately 90% NO in diesel exhaust) into roughly a 50:50 mixture of NO and NO₂, while simultaneously oxidizing engine-out hydrocarbons which interfere with the reduction of NO_x by urea or ammonia. The present invention demonstrates that a 50:50 blend of NO and NO₂ is reduced more rapidly and with higher efficiency than a gas stream which is predominantly NO. In addition, catalyst in an engine exhaust that is a 50:50 mixture of NO and NO₂ is far more resistant to hydrothermal deterioration than using NO alone. In another embodiment of the present invention, a vehicle exhaust system utilizing the method of the present invention is provided.