CATALYTIC REDUCTION OF NOx

摘要

A system for NOx reduction in combustion gases, especially from diesel engines, incorporates an oxidation catalyst to convert at least a portion of NO to NO2, particulate filter, a source of reductant such as NH3 and an SCR catalyst and methods for operating such a system are disclosed. Considerable improvements in NOx conversion and soot reduction are observed even at relatively low operating temperatures.

主权项

1. A system comprising:
a heavy duty diesel truck engine, the heavy duty diesel truck engine configured to produce an exhaust gas comprising particulate matter, NO, and NO2; an oxidation catalyst in exhaust gas communication with the heavy duty diesel engine, the oxidation catalyst configured to convert a substantial portion of the NO in the exhaust gas to NO2; a particulate trap in exhaust gas communication downstream of the oxidation catalyst, the particulate trap configured to react a portion of the enhanced NO2 in the exhaust gas with a substantial portion of the particulate matter in the particulate trap; a urea reductant injector positioned downstream of the particulate trap, the urea reductant injector configured to inject a metered dose of urea reductant into the exhaust gas; an SCR catalyst, the SCR catalyst configured to reduce the NO and NO2 in the exhaust gas;
wherein when the system is configured to operate at a sufficient temperature to react NO2 with particulate matter in the particulate trap, and the oxidation catalyst and the particulate trap are configured to together modify the exhaust gas such that it has an NO to NO2 ratio of about 4:1 to 1:3 when the exhaust gas exits the particulate trap.