Exhaust gas purification apparatus, exhaust gas purification method, and sulfur component trapping agent for internal combustion engine

Abstract

An object of the present invention is to provide a new exhaust gas purification apparatus for an internal combustion engine operated under a condition of an air fuel ratio leaner than a theoretical air fuel ratio, a method for purification of exhaust gas and an exhaust gas purification catalyst, which is suitable for suppressing degradation of the NOx purification catalyst by sulfur components. An exhaust gas purification apparatus for an internal combustion engine, which comprises an exhaust gas passage for an internal combustion engine into which exhaust gas of lean air fuel ratio and rich or stoichiometric air fuel ratio flows, a NOx trapping catalyst that functions to trap NOx in the exhaust gas when the air fuel ratio is lean, a sulfur component trapping agent for trapping sulfur components in the exhaust gas, which is disposed before the NOx trapping catalyst, and a catalyst for oxidizing the sulfur components, which is disposed before the sulfur component trapping agent, wherein the sulfur component trapping agent has a trapping rate of 85 % or more of an amount of inflow sulfur in a trapping test at a flow rate of 150 ppm SO 3 -5% O 2 —balance being N 2 gas per 1.5 moles of the sulfur trapping agent at 300° C. and a space velocity of 30,000/h for 1 hour; and the sulfur component trapping agent has a release rate of sulfur amount of 5 % or less of sulfur trapped in the sulfur component trapping agent in a release test under a flow of a 3000 ppm H 2 -600 ppm C3H6-3000 ppm O 2 -3.5 % CO—balance being N 2 gas at a temperature elevation rate of 10° C. /min from 250 to 750° C. at an sulfur component trapping agent entrance, after the trapping test.

1 . An exhaust gas purification apparatus disposed in an exhaust gas passage of an internal combustion engine having a NOx purification catalyst, which comprises a sulfur component trapping agent for trapping sulfur components, which is arranged before the NOx trapping catalyst and a catalyst for oxidizing the sulfur components, disposed before the sulfur component trapping agent, wherein the sulfur component trapping agent does not substantially release the trapped sulfur components under the conditions of the internal combustion engine.  
   
   
       2 . An exhaust gas purification apparatus for an internal combustion engine, which comprises an exhaust gas passage for an internal combustion engine into which exhaust gas of lean air fuel ratio and rich or stoichiometric air fuel ratio flows, a NOx trapping catalyst that functions to trap NOx in the exhaust gas when the air fuel ratio is lean, a sulfur component trapping agent for trapping sulfur components in the exhaust gas, which is disposed before the NOx trapping catalyst, and a catalyst for oxidizing the sulfur components, which is disposed before the sulfur component trapping agent, wherein the sulfur component trapping agent has a trapping rate of 85% or more of an amount of inflow sulfur in a trapping test at a flow rate of 150 ppm SO 3 -5% O 2 —balance being N 2  gas per 1.5 moles of the sulfur component trapping agent at 300° C. and a space velocity of 30,000/h for 1 hour; and the sulfur component trapping agent has a release rate of sulfur amount of 5% or less of sulfur trapped in the sulfur component trapping agent in a release test under a flow of a 3000 ppm H 2 —600 ppm C 3 H 6 -3000 ppm O 2 —3.5% CO—balance being N 2  gas at a temperature elevation rate of 10° C./min from 250 to 750° C. at an sulfur component trapping agent entrance, after the trapping test.  
   
   
       3 . An exhaust gas purification apparatus for an internal combustion engine, which comprises an exhaust gas passage for an internal combustion engine into which exhaust gas of lean air fuel ratio and rich or stoichiometric air fuel ratio flows, a NOx trapping catalyst that functions to trap NOx in the exhaust gas when the air fuel ratio is lean, a sulfur component trapping agent for trapping sulfur components in the exhaust gas, which is disposed before the NOx trapping catalyst, and a catalyst for oxidizing the sulfur components, which is disposed before the sulfur component trapping agent, wherein the sulfur component trapping agent has a trapping rate of 60% or more of an amount of inflow sulfur in a trapping test at a flow rate of 150 ppm H 2 S—0.5% O 2 —balance being N 2  gas at 300° C. of the sulfur trapping agent and a space velocity of 30,000/h for 1 hour.  
   
   
       4 . An exhaust gas purification apparatus for an internal combustion engine, which comprises a NOx trapping catalyst for trapping NOx, which is disposed in an exhaust gas passage, a sulfur component trapping agent disposed before the NOx trapping catalyst for trapping sulfur components, and a catalyst disposed before the sulfur component trapping agent for oxidizing the sulfur components, wherein the sulfur component trapping agent contains at least one of alkali metals and alkaline earth metals and a total amount of Pt, Pd and Rh is at least 0.4% by weight of the sulfur component trapping agent.  
   
   
       5 . The exhaust gas purification apparatus according to  claim 1 , wherein the sulfates contained in the sulfur component trapping agent has a melting temperature or decomposition temperature of 750° C. or higher.  
   
   
       6 . The exhaust gas purification apparatus according to to  claim 1 , wherein the sulfur component trapping agent is disposed below the engine.  
   
   
       7 . The exhaust gas purification apparatus according to  claim 1 , which further comprises a filter disposed in upstream of the NOx trapping catalyst, wherein an upstream side of the filter is provided with a catalyst for oxidizing the sulfur components and a downstream side of the filter is provided with the sulfur component trapping agent.  
   
   
       8 . The exhaust gas purification apparatus according to  claim 1 , which further comprises a filter disposed at upstream of the NOx trapping catalyst, wherein the sulfur component trapping agent if formed on part of the filter, and the catalyst for oxidizing sulfur components is formed on another part of the filter.  
   
   
       9 . The exhaust gas purification apparatus according to  claim 4 , wherein an amount of the alkali metals or the alkaline earth metals is 1 to 4 moles or less in terms of (alkali metals /2+alkaline earth metals).  
   
   
       10 . The exhaust gas purification apparatus according to  claim 1 , wherein the catalyst for oxidizing sulfur components contains at least one of Pt, Pd and Rh.  
   
   
       11 . The exhaust gas purification apparatus according to  claim 1 , wherein the NOx trapping catalyst contains at least one of alkali metals and alkaline earth metals and at least one of noble metals, and has a function to trap SOx under a lean air fuel condition and a function to release SOx in a rich or stoichiometric air fuel condition by heating the catalyst to 500° C. or higher.  
   
   
       12 . The exhaust gas purification apparatus according to  claim 1 , wherein the sulfur component trapping agent is replaceable with another.  
   
   
       13 . A sulfur component trapping agent containing an ingredient for trapping sulfur components in an exhaust gas, wherein the ingredient has a trapping rate of 85% or more of an amount of inflow sulfur in a trapping test at a flow rate of 150 ppm SO 3 -5% O 2 —balance being N 2  gas per 1.5 moles of the sulfur trapping agent at 300° C. and a space velocity of 30,000/h for 1 hour; and the sulfur component trapping agent has a release rate of sulfur amount of 5% or less of sulfur trapped in the sulfur component trapping agent in a release test under a flow of a 3000 ppm H 2 —600 ppm C 3 H 6 —3000 ppm O 2 —3.5% CO—balance being N 2  gas at a temperature elevation rate of 10° C./min from 250 to 750° C. at an sulfur component trapping agent entrance, after the trapping test.  
   
   
       14 . The sulfur component trapping agent according to  claim 13 , wherein the sulfur component trapping agent contains at least one selected from the group consisting of alkali metals, alkaline earth metals, Ce, Al, Y, La and Ni.  
   
   
       15 . A sulfur component trapping agent for trapping sulfur in an exhaust gas, which comprises a honeycomb substrate made of cordierite or metal, a porous support, and a sulfur trapping agent supported on the porous support, wherein the sulfur trapping agent contains 1 to 4 moles of at least one of alkali metals and alkaline earth metals in (molar number of alkali metals /2+molar number of alkaline earth metals) as conversion of elements, and the total amount of Pt+Pd+Rh is 0.4% by weight or more per the sulfur component agent.  
   
   
       16 . A method of purification of an exhaust gas from an internal combustion engine, which uses the sulfur component trapping agent according  claim 13 .  
   
   
       17 . A method of purification of an exhaust gas for an internal combustion engine, which comprises oxidizing sulfur components in the exhaust gas, trapping and accumulating the sulfur components in a sulfur component trapping agent, and purifying NOx in the exhaust gas with a NOx purifying catalyst.  
   
   
       18 . The method of purification of an exhaust gas according to  claim 16 , which comprises a step for releasing the sulfur components from the NOx purifying catalyst, wherein the releasing step is carried out by changing the air fuel ratio to rich or stoichiometric and elevating temperature of the NOx purifying catalyst to 500° C. or higher.  
   
   
       19 . A method of diagnosis of degradation of a sulfur component trapping agent in an exhaust gas purification apparatus comprising a NOx purification catalyst, a sulfur component trapping agent disposed before the NOx purification catalyst, and a sulfur component oxidizing catalyst disposed before the sulfur component trapping agent, which comprises measuring NOx purification rates before and after a step of releasing a sulfur component from the NOx purification catalyst and diagnosing a degradation of the sulfur component trapping agent based on a difference or ratio of the NOx purification rates.  
   
   
       20 . A system for diagnosis of degradation of a sulfur component agent in an exhaust gas purification apparatus comprising a NOx purification catalyst for trapping NOx, a sulfur component trapping agent disposed before the NOx purification catalyst for trapping sulfur components, a sulfur component oxidizing catalyst disposed before the sulfur component trapping agent, which comprises means for diagnosing the sulfur component trapping agent in accordance with the diagnosis method defined in  claim 19  for every sulfur component releasing step, and means for indicating replacement of the sulfur component trapping agent when the sulfur component trapping agent is degraded to a predetermined level.