Catalyst system for generating carbon monoxide for use with automotive catalysts
The present invention provides a catalyst system that may be used to regenerate NO x adsorber catalysts. It also provides methods for using these catalysts. According to the present invention, hydrocarbons are introduced into an exhaust gas stream upstream of a metal ion exchanged zeolite catalyst to generate CO. The metal ion exchanged zeolite catalyst is preferably a Cu-ZSM-5 catalyst that has a high loading of copper. The hydrocarbons are oxidized to carbon monoxide, and the carbon monoxide is then exposed to a NO x adsorber catalyst, which facilitates regeneration of that catalyst.
1. A catalyst system comprising:
a. a Cu-ZSM-5 catalyst, wherein said Cu-ZSM-5 catalyst has a copper loading between 125% and 275% exchanged;
b. a hydrocarbon addition apparatus, wherein said hydrocarbon addition apparatus is upstream of said Cu-ZSM-5 catalyst; and
c. a nitrogen oxide adsorber catalyst, wherein said nitrogen oxide adsorber catalyst is downstream of said Cu-ZSM-5 catalyst.
2. A catalyst system according to claim 1 , wherein said hydrocarbon addition apparatus comprises an in-cylinder with a late cycle injection apparatus.
3. A catalyst system according to claim 1 , wherein said hydrocarbon addition apparatus comprises a secondary fuel injector.
4. A catalyst system according to claim 1 , wherein the secondary fuel injector is located in an exhaust pipe.