Exhaust gas treatment unit for internal combustion engines and processes for operatin therm

A process for treating an exhaust gas comprising:

• a. exposing a rich exhaust gas to a first catalyst unit to generate ammonia;
• b. storing said ammonia of step (a) in a second catalyst unit, wherein said second catalyst unit is located downstream of said first catalyst unit;
• c. exposing a lean exhaust gas to a third catalyst unit wherein said third catalyst unit is located downstream of said first catalyst unit and upstream of said second catalyst unit and wherein said lean exhaust gas comprises nitrogen oxides;
• d. oxidizing said nitrogen oxides to form oxidized nitrogen oxides;
• and
• e. exposing said oxidized nitrogen oxides to said second catalyst unit.

A process for treating exhaust gas comprising:

• a. exposing a first lean exhaust gas comprised of nitrogen oxides to a fourth catalyst unit, wherein said fourth catalyst unit temporarily stores said nitrogen oxides;
• b. releasing said temporarily stored nitrogen oxides in the presence of a rich gas composition;
• c. exposing said temporarily stored nitrogen oxides and said rich gas composition to a first catalyst unit to generate ammonia, wherein said first catalyst unit is located downstream of said fourth catalyst unit;
• d. storing said ammonia of step (c) in a second catalyst unit, wherein said second catalyst unit is located downstream of said first catalyst unit;
• e. exposing a second lean exhaust gas to a third catalyst unit located downstream of said first catalyst unit and upstream of said second catalyst unit, wherein said lean exhaust gas is comprised of nitrogen oxides;
• f. oxidizing said nitrogen oxides of step (e) to form oxidized nitrogen oxides;
• and
• g. exposing said oxidized nitrogen oxides to said second catalyst unit.