Patent ID: 8245500

Claim:
A system for reducing the percentage of nitrogen dioxide and nitrogen monoxide in an exhaust gas stream of an internal combustion engine, comprising: a) a first catalyst for selective reduction of a portion of said nitrogen oxides to nitrogen and ammonia; b) a second catalyst for selective reduction of a portion of said nitrogen oxides and said ammonia to molecular nitrogen; c) an injector upstream of said first catalyst for injecting at least a hydrocarbon compound into said exhaust gas stream; d) a sensor disposed downstream of at least one of said first and second catalysts for sensing concentration of at least ammonia in said exhaust gas stream after passage of said exhaust gas stream through said at least one of said first and second catalysts; and e) a programmed controller in communication in a feedback loop with said sensor and said injector for injecting an amount of said hydrocarbon that will produce a predetermined concentration of ammonia and nitrogen oxides at said sensor according to an algorithm programmed into said controller.