METHOD FOR TREATING NOX IN EXHAUST GAS AND SYSTEM THEREFORE

摘要

The present invention relates to a method for the treatment of an exhaust gas comprising NO x , wherein the method comprises the step of subjecting the exhaust gas to an exhaust gas treatment system comprising, in order of the exhaust stream: (a) a first NO x storage catalytic converter (2,2'); (b) a catalytic converter (3) for selective catalytic reduction (SCR) downstream of the first NO x storage catalytic converter; and (c) a catalytic converter (4) having oxygen storage capacity downstream of the SCR catalytic converter; wherein the exhaust gas treatment system is operated in alternating rich and lean phases, wherein the rich phase is terminated when the amount of reducing components leaving the first NO x storage catalytic converter is at least 0.05 times the amount of reducing components consumed by the first NO x storage catalytic converter during the time interval beginning when the air/fuel ratio upstream of the first NO x storage catalytic converter turns from lean to rich conditions and ending when the air/fuel ratio downstream of the first NO x storage catalytic converter turns from lean to rich conditions.
Optionally there can be provided a close coupled three-way or diesel oxidation or NO x storage catalytic converter (1,1').