Exhaust emission purifying apparatus

Abstract

The present invention provides an exhaust emission purifying apparatus. In the exhaust emission purifying apparatus, while an ammonia adsorbent is coated on a predetermined length portion on the exhaust inflow side of a carrier of a catalytic converter which reduces and purifies NOx in exhaust gas, a NOx reduction catalyst is coated on the remaining portion on the exhaust outflow side of the carrier of the catalytic converter. On the other hand, a first layer containing the ammonia adsorbent and the NOx reduction catalyst in a mixed state and a second layer containing a hydrolysis catalyst are coated in that order on a carrier surface of the catalytic converter. In a transition of an engine operation state, NOx is reduced and purified with the use of ammonia adsorbed to the ammonia adsorbent.

1 . An exhaust emission purifying apparatus comprising:
 a catalytic converter which reduces and purifies nitrogen oxide in exhaust gas with the use of ammonia generated from a urea aqueous solution by hydrolysis;   a urea aqueous solution tank which stores the urea aqueous solution therein;   an injection nozzle through which the urea aqueous solution is injection-supplied to the exhaust upstream side of the catalytic converter; and   a urea aqueous solution supply device which supplies the urea aqueous solution stored in the urea aqueous solution tank, to the injection nozzle at a flow rate corresponding to an engine operation state,   wherein while an ammonia adsorbent is coated on a predetermined length portion on the exhaust inflow side of a carrier of the catalytic converter, a nitrogen oxide reduction catalyst is coated on the remaining portion on the exhaust outflow side of the carrier of the catalytic converter.   
     
     
         2 . The exhaust emission purifying apparatus according to  claim 1 , wherein the carrier is a diesel particulate filter. 
     
     
         3 . An exhaust emission purifying apparatus comprising:
 a catalytic converter which reduces and purifies nitrogen oxide in exhaust gas with the use of ammonia generated from a urea aqueous solution by hydrolysis;   a urea aqueous solution tank which stores the urea aqueous solution therein;   an injection nozzle through which the urea aqueous solution is injection-supplied to the exhaust upstream side of the catalytic converter; and   a urea aqueous solution supply device which supplies the urea aqueous solution stored in the urea aqueous solution tank, to the injection nozzle at a flow rate corresponding to an engine operation state,   wherein a first layer containing an ammonia adsorbent and a nitrogen oxide reduction catalyst in a mixed state and a second layer containing a hydrolysis catalyst are coated in that order on a carrier surface of the catalytic converter.   
     
     
         4 . The exhaust emission purifying apparatus according to  claim 3 , wherein the carrier is a diesel particulate filter.