Catalyst System for the Reduction of NOx and NH3 Emissions

Abstract

This catalyst system simultaneously removes ammonia and enhances net NOx conversion by placing an NH 3 —SCR catalyst formulation downstream of a lean NOx trap. By doing so, the NH 3 —SCR catalyst adsorbs the ammonia from the upstream lean NOx trap generated during the rich pulses. The stored ammonia then reacts with the NOx emitted from the upstream lean NOx trap-enhancing the net NOx conversion rate significantly, while depleting the stored ammonia. By combining the lean NOx trap with the NH 3 —SCR catalyst, the system allows for the reduction or elimination of NH 3 and NOx slip, reduction in NOx spikes and thus an improved net NOx conversion during lean and rich operation.

1 - 10 . (canceled) 
   
   
       11 . A method for the reduction of nitrogen oxides and ammonia from diesel engine exhaust gas, said method comprising:
 storing nitrogen oxides present in the exhaust gas in a nitrogen oxide adsorber during lean cycles with a lean exhaust gas air ratio;   reducing stored nitrogen oxides from the nitrogen oxide adsorber during rich pulses, which contain a rich exhaust gas air ratio, and thereby generating ammonia;   adsorbing and storing ammonia in a NH 3 —SCR catalyst arranged downstream of the nitrogen oxide adsorber;   reacting the stored ammonia with nitrogen oxides in the NH 3 —SCR catalyst;   operating the engine under lean conditions during lean cycles;   during lean cycles, oxidizing carbon monoxide and hydrocarbons contained in the exhaust gas in an oxidizing catalytic converter arranged upstream of the nitrogen oxide adsorber and NH 3 —SCR catalyst;   operating the engine under rich conditions during rich cycles.   
   
   
       12 . The method according to claim  1 , further comprising filtering particulate matter in the exhaust gas.