Exhaust gas processing apparatus and method

Abstract

An apparatus and a method for processing exhaust gas are provided. The apparatus includes a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst containing an oxygen storage material and a precious metal sequentially disposed along an exhaust gas flow direction. The apparatus also includes a front lambda sensor disposed upstream of the LNT, a rear lambda sensor disposed downstream of the oxygen storage catalyst, and a temperature sensor configured to measure a temperature of exhaust gas.

What is claimed is: 
     
         1 . An exhaust gas processing apparatus, comprising:
 a lean NOx trap (LNT);   a temperature sensor configured to measure a temperature of an exhaust gas;   a selective catalytic reduction (SCR) catalyst; and   an oxygen storage catalyst containing an oxygen storage material and a precious metal, wherein the LNT, the SCR and the oxygen storage catalyst are sequentially disposed along an exhaust gas flow direction, and wherein a front lambda sensor is disposed upstream of the LNT, a rear lambda sensor is disposed downstream of the oxygen storage catalyst.   
     
     
         2 . The exhaust gas processing apparatus of  claim 1 , wherein the oxygen storage catalyst includes a ceria catalyst containing ceria as an oxygen storage material. 
     
     
         3 . The exhaust gas processing apparatus of  claim 1 , wherein the SCR catalyst is formed by coating an SCR catalyst layer on a porous filter configured to collect a particulate material in diesel exhaust gas. 
     
     
         4 . The exhaust gas processing apparatus of  claim 1 , wherein the SCR catalyst and the oxygen storage catalyst form an integral catalyst which uses one porous filter, and wherein the integral catalyst comprises:
 a porous filter;   an SCR catalyst layer coated on an exhaust inlet of the filter; and   an oxygen storage material catalyst layer coated on an exhaust gas outlet of the filter and containing an oxygen storage material and a precious material.   
     
     
         5 . The exhaust gas processing apparatus of  claim 4 , wherein the filter is a porous filter configured to collect a particulate material in diesel exhaust gas. 
     
     
         6 . The exhaust gas processing apparatus of  claim 4 , wherein the filter includes a plurality of multi-layered filter walls, and wherein facing surfaces of the plurality of filter walls form alternating exhaust inlets and outlets. 
     
     
         7 . The exhaust gas processing apparatus of  claim 1 , wherein a diesel particulate filter is disposed between the LNT and the SCR catalyst. 
     
     
         8 . The exhaust gas processing apparatus of  claim 7 , wherein the SCR catalyst and the oxygen storage catalyst form an integral catalyst which uses one support, and the integral catalyst is formed by coating the SCR catalyst layer and the oxygen storage material containing an oxygen storage material and a precious metal on a front area and a rear area of the support through a zone coating method. 
     
     
         9 . The exhaust gas processing apparatus of  claim 4 , wherein the oxygen storage material includes ceria. 
     
     
         10 . The exhaust gas processing apparatus of  claim 1 , wherein the SCR catalyst layer of the SCR catalyst contains a zeolite catalyst. 
     
     
         11 . The exhaust gas processing apparatus of  claim 1 , wherein a rich operation for eliminating NOx occluded in the LNT is maintained until lambda values of the front lambda sensor and the rear lambda sensor coincide with each other during rich operation. 
     
     
         12 . A method of controlling an exhaust gas processing apparatus, wherein a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst containing an oxygen storage material and a precious metal are sequentially disposed along an exhaust gas flow direction, and wherein a front lambda sensor is disposed upstream of the LNT, and a rear lambda sensor is disposed downstream of the oxygen storage catalyst, the method comprising:
 measuring a temperature, by a temperature sensor, of exhaust gas disposed within the exhaust path, and   eliminating NOx, by the SCR catalyst during a rich operation when NH 3  generated by the LNT and NOx in the exhaust gas react with each other in the SCR catalyst.   
     
     
         13 . The exhaust gas processing method of  claim 12 , further comprising:
 eliminating, by a precious metal contained in the oxygen storage catalyst, carbon monoxide (CO) and hydrocarbon (HC) in the exhaust gas.   
     
     
         14 . The exhaust gas processing method of  claim 12 , further comprising:
 maintaining a rich operation for eliminating NOx occluded in the LNT until the lambda values of the front lambda sensor and the rear lambda sensor coincide.   
     
     
         15 . The exhaust gas processing method of  claim 14 , wherein the α is a time period (tbt) from a rich operation starting time until a time that lambda values of the front lambda sensor and the rear lambda sensor coincide, the method further comprising:
 measuring, by a temperature sensor, a temperature of the exhaust gas. 
 
     
     
         16 . The exhaust gas processing method of  claim 12 , wherein the oxygen storage catalyst is a ceria catalyst containing ceria as an oxygen storage material. 
     
     
         17 . The exhaust gas processing method of  claim 12 , wherein the SCR catalyst is formed by coating an SCR catalyst layer on a porous filter configured to collect a particulate material in diesel exhaust gas. 
     
     
         18 . The exhaust gas processing method of  claim 12 , wherein a diesel particulate filter is disposed between the LNT and the SCR catalyst. 
     
     
         19 . The exhaust gas processing method of  claim 12 , wherein the SCR catalyst layer of the SCR catalyst contains a zeolite catalyst. 
     
     
         20 . The exhaust gas processing method of  claim 17 , wherein the SCR catalyst layer of the SCR catalyst contains a zeolite catalyst.