Removing nitrogen oxides during a lean-burn engine cold start

A method for the selective removal of NOx from a gaseous stream using lean NOx traps containing a catalyst that can catalyze the reduction of NOx to N2 and a compound that can store NOx as nitrates, comprising:

• heating a first lean trap to a temperature at which stored nitrates decompose and are released;
• cooling the first lean NOx trap in an environment that does not contain NOx;
• passing the gaseous stream through the first lean NOx trap;
• and
• passing the gaseous stream through a second lean NOx trap, the second lean NOx trap storing NOx released from the first lean NOx trap.

A method for reducing the total NOx released into the environment during operation from cold start to shut down of a vehicle containing an internal combustion engine comprising:

• operating the engine to produce an exhaust stream comprising NOx;
• passing the exhaust stream comprising NOx from the engine sequentially through a first LNT and a second LNT, wherein the LNTs comprise a catalyst that can catalyze the reduction of NOx to N2 and compounds that can store NOx as nitrates;
• shutting off the engine;
• and
• after shutting off the engine, regenerating the first LNT by heating it to a temperature at which it releases stored NOx.