Patent ID: 6996975

Claim:
An exhaust treatment apparatus, comprising: a first ammonia injector configured to inject a first charge of ammonia into an exhaust stream; a first catalyst bed positioned to receive the exhaust stream with the first charge of ammonia and adapted to catalyze a reaction between NO x and ammonia to reduce NO x ; a second ammonia injector for injecting a second ammonia charge into an effluent from the first catalyst bed; a second catalyst bed positioned to receive the effluent from the first catalyst bed with the second charge of ammonia and adapted to catalyze a reaction between NO x and ammonia to reduce NO x ; and an NO x sensor positioned downstream of the first catalyst bed, and a controller; wherein the apparatus is adapted for use in a vehicle exhaust system; the controller controls the second ammonia charge based at least in part on data from the NO x sensor; and the second ammonia charge is controlled to be less than a stoichiometric amount a stoichiometric amount being an amount of ammonia just sufficient to reduce all the NO x remaining after the first catalyst bed to N 2 .