Patent ID: 8225597

Claim:
A system for a vehicle including an engine having an exhaust, the system comprising: a NOx reducing system coupled to the engine exhaust, said NOx reducing system including a catalytic unit, said catalytic unit including a first zeolite catalyst with a first NOx conversion performance in a first temperature range and a second NOx conversion performance, lower than said first NOx conversion performance, in a second temperature range, and a second zeolite catalyst with a third NOx conversion performance, lower than said first NOx conversion performance, in the first temperature range and a fourth NOx conversion performance, higher than said second and said third NOx conversion performances in the second temperature range, said first temperature range being higher than said second temperature range; and a controller configured to adjust an amount of reducing agent added to the NOx reducing system responsive to a temperature of the catalytic unit, the adjusting including increasing the amount of reducing agent added to the NOx reducing system as a temperature of the catalytic unit increases, and when the temperature of the catalytic unit is in the first temperature range, increasing the amount of reducing agent added to the NOx reducing system at a first rate, and when the temperature of the catalytic unit is in the second temperature range, increasing the amount of reducing agent added to the NOx reducing system at a second rate, said first rate being higher than said second rate, the reducing agent being an ammoniagenic agent including ammonia or aqueous urea.