JP2010255583A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely avoid the deterioration of the activity of a second catalyst caused by a sulfur component desorbed from a storage catalyst, in an exhaust emission control device for an internal combustion engine. <P>SOLUTION: This exhaust emission control device for an internal combustion engine includes: an storage catalyst 26 having a property that absorbs a sulfur component contained in the exhaust gas; an Ag catalyst (a second catalyst) 34 containing Ag as a catalyst component; a sulfur desorbing means for executing sulfur desorption control that desorbs the sulfur component from the storage catalyst 26; and a flow passage selector means for selecting an exhaust gas flow passage so that the exhaust gas which has passed through the storage catalyst 26 is made to flow into the AG catalyst 34, and so that, when desorbing the sulfur component from the storage catalyst 26, the exhaust gas which has passed through the storage catalyst 26 is not made to flow into the AG catalyst 34. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  Japanese Patent Application Laid-Open No. 2004-169643 discloses a technique for generating nitrogen dioxide and ozone by generating plasma in exhaust gas and reducing particulate matter in the presence of an Ag catalyst by the nitrogen dioxide and ozone. Has been.

The Ag catalyst may react with sulfur oxides in the exhaust gas to form a compound such as Ag ₂ SO ₄ or AgS, and the activity may decrease. In Japanese Patent Laid-Open No. 2000-64827, when the Ag catalyst enters a temperature range where it is likely to combine with sulfur oxides, CO is generated by performing expansion stroke fuel injection, increasing the EGR rate, and the like. A technique for preventing the compounding with sulfur oxides is disclosed.

JP 2004-169643 A JP 2000-64827 A

  In the exhaust gas purification apparatus provided with the NOx storage catalyst, the NOx storage performance may deteriorate due to accumulation of sulfur components in the NOx storage catalyst. For this reason, sulfur desorption control for desorbing the sulfur component accumulated in the NOx storage catalyst and restoring the performance may be performed. In the case of an exhaust gas purification device in which an Ag catalyst is provided downstream of the NOx storage catalyst, a large amount of the desorbed sulfur component flows into the Ag catalyst when the sulfur component accumulated in the NOx storage catalyst is desorbed. However, there is a problem that the activity is reduced by forming sulfur compounds with Ag.

  The present invention has been made to solve the above-described problems, and is capable of reliably avoiding a decrease in the activity of the second catalyst due to the sulfur component desorbed from the storage catalyst. An object is to provide a purification device.

In order to achieve the above object, a first invention is an exhaust purification device for an internal combustion engine,
A storage catalyst having the property of storing sulfur components in exhaust gas;
A second catalyst having a property that the catalytic activity is reduced due to adhesion of a sulfur component;
Sulfur desorption means for performing sulfur desorption control for desorbing a sulfur component from the storage catalyst;
With
When desorbing the sulfur component from the storage catalyst, the exhaust gas after passing through the storage catalyst does not flow into the second catalyst.

The second invention is an exhaust emission control device for an internal combustion engine,
A storage catalyst having the property of storing sulfur components in exhaust gas;
A second catalyst having a property that the catalytic activity is reduced due to adhesion of a sulfur component;
Sulfur desorption means for performing sulfur desorption control for desorbing a sulfur component from the storage catalyst;
Normally, the exhaust gas that has passed through the storage catalyst is caused to flow into the second catalyst, and when the sulfur component is desorbed from the storage catalyst, the exhaust gas that has passed through the storage catalyst is used as the second catalyst. Flow path switching means for switching the flow path of the exhaust gas so as not to flow into the catalyst,
It is characterized by providing.

The third invention is the first or second invention, wherein
When the sulfur component is desorbed from the storage catalyst, exhaust gas after passing through the second catalyst flows into the storage catalyst.

According to a fourth invention, in any one of the first to third inventions,
An active oxygen supply device for supplying active oxygen to the second catalyst is provided.

  According to the first aspect, when the sulfur component is desorbed from the storage catalyst, the exhaust gas after passing through the storage catalyst can be prevented from flowing into the second catalyst. For this reason, it is possible to reliably prevent the sulfur component desorbed from the storage catalyst from adhering to the second catalyst. Therefore, it is possible to reliably prevent a decrease in the activity of the second catalyst due to sulfur poisoning.

  According to the second invention, the exhaust gas after passing through the storage catalyst is normally allowed to flow into the second catalyst, and when the sulfur component is desorbed from the storage catalyst, the exhaust gas after passing through the storage catalyst. Can be prevented from flowing into the second catalyst. For this reason, it is possible to reliably prevent the sulfur component desorbed from the storage catalyst from adhering to the second catalyst. Therefore, it is possible to reliably prevent a decrease in the activity of the second catalyst due to sulfur poisoning.

  According to the third invention, when the sulfur component is desorbed from the storage catalyst, the exhaust gas after passing through the second catalyst can flow into the storage catalyst. As a result, even when the sulfur component is desorbed from the storage catalyst, exhaust gas before flowing into the storage catalyst can continue to flow to the second catalyst, so that harmful components can be purified in the second catalyst. it can. In addition, it is possible to avoid the second catalyst from being cooled while desorbing the sulfur component from the storage catalyst. Furthermore, sulfur desorption can be promoted by an increase in the exhaust gas temperature due to the reaction heat in the second catalyst.

  According to the fourth aspect of the invention, since active oxygen can be supplied to the second catalyst, the catalytic activity obtained by synergistic action of the active oxygen and the second catalyst enables high efficiency of CO even at low temperatures. Can be purified.

It is a figure for demonstrating the exhaust gas purification apparatus of Embodiment 1 of this invention. It is a block diagram of the system of Embodiment 1 of this invention. It is a figure for demonstrating the exhaust gas purification apparatus of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure for demonstrating the exhaust gas purification apparatus of Embodiment 2 of this invention. It is a figure for demonstrating the exhaust gas purification apparatus of Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining an exhaust emission control device according to a first embodiment of the present invention. As shown in FIG. 1, the system of this embodiment includes an internal combustion engine 10 that is used as a drive source for a vehicle. An internal combustion engine (hereinafter, simply referred to as “engine”) 10 of the present embodiment is an in-line four-cylinder diesel engine (compression ignition type internal combustion engine). The engine 10 of this embodiment includes a turbocharger 12. In FIG. 1, for convenience, the size of the exhaust passage and the catalytic converter on the downstream side of the turbine of the turbocharger 12 are exaggerated and drawn larger than the size of the engine 10.

  The intake air compressed by the compressor of the turbocharger 12 is distributed to each cylinder of the engine 10 through the intake manifold 14. Each cylinder is provided with a fuel injector 16 for injecting fuel directly into the cylinder. Each fuel injector 16 is supplied with high-pressure fuel stored in the common rail 18. Fuel in a fuel tank (not shown) is pressurized by the supply pump 20 and supplied to the common rail 18. Exhaust gases discharged from the cylinders merge at the exhaust manifold 22 and flow into the turbine of the turbocharger 12. The exhaust gas that has passed through the turbine flows through the exhaust passage 24.

The exhaust passage 24 is connected to the NOx storage catalyst 26. The NOx storage catalyst 26 is an NOx storage reduction (NSR) catalyst. As a catalyst component of the NOx storage catalyst 26, for example, a noble metal such as Pt (platinum) and a NOx storage material such as Ba (barium) are formed on the surface of a base material made of Al ₂ O ₃ (alumina), for example. Is supported. The NOx occlusion material can occlude NOx (nitrogen oxide) by forming nitrate (Ba (NO ₃ ) _{2 in} the case of Ba). In this specification, the term “occlusion” includes all concepts similar to “holding”, “adsorption”, “absorption”, and the like.

  In the engine 10, combustion is performed at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio during normal operation. For this reason, a large amount of oxygen is contained in the exhaust gas during normal operation. Therefore, NOx cannot be purified by a three-way reaction during normal operation. Thus, during normal operation, NOx contained in the exhaust gas is absorbed by the NOx storage catalyst 26 to prevent NOx from being discharged into the atmosphere.

  An exhaust fuel addition injector 27 for adding fuel to the exhaust gas is installed upstream of the NOx storage catalyst 26. The exhaust passage 25 on the downstream side of the NOx storage catalyst 26 is connected to the three-way valve 28. Exhaust passages 30 and 32 are further connected to the three-way valve 28. The exhaust passage 30 is connected to an Ag catalyst 34 containing Ag (silver) as a catalyst component. The Ag catalyst 34 may further contain any catalyst component other than Ag.

  Normally, the three-way valve 28 is in a state where the exhaust passage 25 communicates with the exhaust passage 30. That is, normally, the exhaust gas that has passed through the NOx storage catalyst 26 flows into the Ag catalyst 34 through the exhaust passage 30 as indicated by the arrow in FIG. On the other hand, the three-way valve 28 can be switched to a state where the exhaust passage 25 communicates with the exhaust passage 32.

An ozone injection nozzle 36 is provided on the upstream side of the Ag catalyst 34. The ozone injection nozzle 36 is provided with a plurality of ejection holes for ejecting a gas containing ozone. In the illustrated configuration, the ozone injection nozzle 36 is disposed in front of the Ag catalyst 34 in a casing common to the Ag catalyst 34. An ozone supply device 38 is connected to the ozone injection nozzle 36. The ozone supply device 38 includes an air pump, an ozone generator, a flow rate adjustment valve, and the like. The air taken in by the air pump is sent to the ozone generator and is subjected to high pressure discharge. Thereby, ozone (O ₃ ) is generated from oxygen in the air. The ozone supply device 38 can inject ozone into the exhaust gas upstream of the Ag catalyst 34 by sending the gas containing ozone to the ozone injection nozzle 36.

  FIG. 2 is a block diagram of the system of this embodiment. As shown in FIG. 2, the system of this embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 includes various actuators including the fuel injector 16, the exhaust fuel addition injector 27, the three-way valve 28, and the ozone supply device 38, a crank angle sensor 40 that detects a crank angle of the engine 10, and an intake air amount of the engine 10. Various sensors including an air flow meter 42 that detects the position of the vehicle, an accelerator position sensor 44 that detects the position of the accelerator pedal of the vehicle on which the engine 10 is mounted, and a vehicle speed sensor 46 are electrically connected.

There is a limit to the amount of NOx that can be stored by the NOx storage catalyst 26. Therefore, before the NOx occlusion amount of the NOx occlusion catalyst 26 reaches the limit, the reducing agent supply control for reducing and purifying NOx occluded in the NOx occlusion catalyst 26 is executed. When the reducing agent is supplied to the NOx storage catalyst 26 and the oxygen concentration in the NOx storage catalyst 26 decreases, NOx is desorbed from the storage material. The desorbed NOx reacts with the reducing agent by the action of the noble metal catalyst and is reduced and purified to N ₂ .

  In the present embodiment, as a method of supplying the reducing agent to the NOx storage catalyst 26, fuel as a reducing agent is added from the exhaust fuel addition injector 27 into the exhaust gas. The present invention is not limited to such a method, and the reducing agent may be supplied by performing post injection or low temperature rich combustion in the engine 10.

  When NOx reduction is performed by the NOx storage catalyst 26, CO is generated by the reaction. This CO also reacts with NOx as a reducing gas. However, a part of the generated CO may not react with NOx and may flow out downstream of the NOx storage catalyst 26. In addition, a part of the reducing agent supplied to the NOx storage catalyst 26 may become excessive, and may flow out downstream of the NOx storage catalyst 26 as HC.

  In the present embodiment, CO or HC flowing out downstream of the NOx storage catalyst 26 when the reducing agent is supplied to the NOx storage catalyst 26 can be purified (oxidized) in the Ag catalyst 34. In particular, in the present embodiment, by supplying ozone from the ozone injection nozzle 36, even when the temperature of the Ag catalyst 34 is low, HC and CO can be sufficiently purified using ozone.

The reactivity between ozone and HC is relatively high, but the reactivity between ozone and CO is low. However, according to the knowledge of the present inventors, a catalyst using Ag (silver) exhibits excellent CO oxidation activity from a low temperature when ozone coexists. This is presumably because Ag reacts with ozone to change to Ag ₂ O or AgO, which is a stronger oxidant, and CO is oxidized to CO ₂ by this Ag ₂ O or AgO. In this way, in the present embodiment, by supplying ozone from the ozone injection nozzle 36, even when the temperature of the Ag catalyst 34 is low, such as immediately after startup or in a light load region, the NOx storage catalyst 26 is reduced during NOx reduction. HC and CO flowing out from the fuel can be reliably purified.

  Sulfur oxides are generated in the exhaust gas of the engine 10 as a result of combustion of sulfur contained in fuel such as light oil. The NOx storage material of the NOx storage catalyst 26 has the property of absorbing not only NOx but also this sulfur oxide. That is, the NOx storage material accumulates sulfur components in the exhaust gas as sulfates or sulfites. As the sulfur component accumulates in the NOx storage catalyst 26, the NOx storage capacity of the NOx storage catalyst 26 decreases. Further, since the sulfur component accumulated in the NOx occlusion material is less likely to desorb than NOx, the sulfur component is not desorbed from the NOx occlusion material even when NOx reduction is performed.

  Therefore, in this embodiment, when it is determined that the amount of sulfur deposited on the NOx storage catalyst 26 has reached a predetermined saturated storage amount, the accumulated sulfur is recovered in order to restore the NOx storage capacity of the NOx storage catalyst 26. Sulfur desorption control is performed to desorb components.

In order to desorb the sulfur component from the NOx occlusion catalyst 26, a reducing agent is supplied to the NOx occlusion catalyst 26 in a state where the temperature of the NOx occlusion catalyst 26 is maintained at a temperature higher than the temperature at which the sulfur component can be desorbed. Necessary. At this time, if odorous hydrogen sulfide (H ₂ S) is generated by the sulfur component desorbed from the NOx storage catalyst 26, the exhaust odor may become a problem. For this reason, in this embodiment, the reducing agent supply amount and the like are controlled so that the sulfur component accumulated in the NOx storage catalyst 26 is desorbed as SO ₂ .

If the exhaust gas after passing through the NOx storage catalyst 26 flows into the Ag catalyst 34 during execution of the sulfur desorption control as described above, a large amount of SO ₂ flows into the Ag catalyst 34. Ag is easier to combine with SO ₂ than other noble metals such as Pd. That is, Ag tends to form compounds such as Ag ₂ SO ₄ and AgS in the presence of SO ₂ . When a compound such as Ag ₂ SO ₄ or AgS is formed, there is a problem that the catalytic activity of Ag is lowered.

In order to solve the above problems, in the present embodiment, the exhaust gas after passing through the NOx storage catalyst 26 is not allowed to flow into the Ag catalyst 34 by switching the three-way valve 28 when performing the sulfur desorption control. It was decided. FIG. 3 is a diagram for explaining an exhaust gas flow path during execution of sulfur desorption control. As shown in FIG. 3, when the sulfur desorption control is executed, the three-way valve 28 is switched to a state where the exhaust passage 25 is communicated with the exhaust passage 32. In this state, as shown in FIG. 3, the exhaust gas after passing through the NOx storage catalyst 26 is exhausted through the exhaust passage 32 without flowing into the Ag catalyst 34. For this reason, since SO ₂ desorbed from the NOx storage catalyst 26 does not flow into the Ag catalyst 34, it is possible to reliably prevent a decrease in catalyst activity due to Ag forming a sulfur compound.

  FIG. 4 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is repeatedly executed every predetermined time. According to this routine, first, it is determined whether or not the sulfur storage amount of the NOx storage catalyst 26 has reached the saturated storage amount (step 100). This determination method may be any method, but as an example, the determination can be made based on the travel distance of the vehicle. That is, it can be determined that the sulfur accumulation amount reaches the saturated occlusion amount at every predetermined travel distance (for example, every 20000 km).

  If it is determined in step 100 that the sulfur accumulation amount has not reached the saturated occlusion amount, it can be determined that it is not necessary to execute the sulfur desorption control yet. In this case, control is performed to inject ozone as required from the ozone injection nozzle 36 (step 102).

  On the other hand, when it is determined in step 100 that the sulfur accumulation amount has reached the saturated occlusion amount, it can be determined that the sulfur desorption control needs to be executed. In order to desorb the sulfur component of the NOx occlusion catalyst 26, the temperature (bed temperature) of the NOx occlusion catalyst 26 is higher than a predetermined temperature at which the sulfur component can be desorbed (hereinafter referred to as “sulfur desorption temperature”). There is a need to. For this reason, when sulfur desorption control is requested, the ECU 50 executes control for increasing the temperature of the NOx storage catalyst 26 to the sulfur desorption temperature or higher. Any method may be used to raise the temperature of the NOx storage catalyst 26. For example, a method of supplying HC to the NOx storage catalyst 26 by engine control such as post injection or fuel injection from the exhaust fuel addition injector 27, a heater The method of heating with is mentioned. The ECU 50 estimates the temperature of the NOx storage catalyst 26 based on the operating state history or detects it with a sensor. When it is determined that the temperature of the NOx storage catalyst 26 has reached the sulfur desorption temperature, the supply of the reducing agent is started.

  In the routine shown in FIG. 4, it is determined in step 104 whether or not the supply of the reducing agent for desorbing the sulfur component from the NOx storage catalyst 26 has been executed. If it is determined in step 104 that the reducing agent has been supplied, the three-way valve 28 is switched to the state shown in FIG. 3 (step 106) and the injection of ozone from the ozone injection nozzle 36 is stopped. (Step 108). As described above, since the supply of the reducing agent is started when the temperature of the NOx storage catalyst 26 reaches the sulfur desorption temperature, in the above step 104, instead of determining whether or not the supply of the reducing agent has been executed. Thus, it may be determined whether or not the temperature of the NOx catalyst 26 has reached the sulfur desorption temperature.

According to the routine processing shown in FIG. 4 described above, the three-way valve 28 is switched to the state shown in FIG. 3 when the supply of the reducing agent for desorbing the sulfur component from the NOx storage catalyst 26 is executed. Therefore, the exhaust gas after passing through the NOx storage catalyst 26 is exhausted through the exhaust passage 32 without flowing into the Ag catalyst 34. For this reason, it is possible to reliably prevent SO ₂ desorbed from the NOx storage catalyst 26 from being combined with Ag of the Ag catalyst 34, and to reliably prevent a decrease in the activity of the Ag catalyst 34.

  In the exhaust purification device of the present embodiment, the exhaust passage 32 may be configured to join the exhaust passage 48 on the downstream side of the Ag catalyst 34.

In the present embodiment, ozone is supplied as the active oxygen into the exhaust gas. However, in the present invention, other types of active oxygen (for example, O ⁻ , O ²⁻ , O ₂ ⁻⁾ are used instead of ozone. , O ₃ ⁻ , O _n ^−, etc.) can also be used. In this embodiment, the ozone supply device 38 is outside the exhaust gas flow path. However, in the present invention, the present invention is not limited to such a configuration, and a high voltage is applied to the ozone generator arranged in the exhaust gas flow path. Then, discharge may be performed to generate active oxygen such as ozone from oxygen in the exhaust gas.

  Moreover, the property that the catalytic activity is lowered by the adhesion of sulfur component is not only found in Ag but also in Fe (iron) catalyst, noble metal catalyst and the like. For this reason, the present invention can be preferably applied to an exhaust purification device provided with an Fe catalyst or a noble metal catalyst instead of the Ag catalyst 34.

  In the above-described embodiment, the Ag catalyst 34 is the “second catalyst” in the first invention, the ozone injection nozzle 36 and the ozone supply device 38 are the “active oxygen supply device” in the fourth invention, Each corresponds. Further, the “flow path switching means” according to the first aspect of the present invention is realized by the ECU 50 executing the processing of steps 100 and 104 described above.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 5 and FIG. 6. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Simplify or omit. FIG. 5 is a diagram for explaining an exhaust emission control apparatus according to the second embodiment of the present invention.

  As shown in FIG. 5, the exhaust passage 24 through which the exhaust gas that has passed through the turbine of the turbocharger 12 passes is connected to a three-way valve 52. Exhaust passages 54 and 56 are further connected to the three-way valve 52. The exhaust passage 54 is connected to a three-way valve 58. Exhaust passages 60 and 62 are further connected to the three-way valve 58. The exhaust passage 60 is connected to the NOx storage catalyst 26. An exhaust passage 64 is connected to the opposite side of the NOx storage catalyst 26. The exhaust passage 64 is connected to the Ag catalyst 34. An exhaust passage 66 is connected to the opposite side of the Ag catalyst 34. The exhaust passage 66 is connected to a three-way valve 68. The above-described exhaust passage 56 and the exhaust passage 70 are further connected to the three-way valve 68. The three-way valves 52, 58 and 68 are electrically connected to the ECU 50. The block diagram of the system according to the present embodiment is the same as that shown in FIG.

  Normally, the three-way valve 52 is in a state where the exhaust passage 24 is in communication with the exhaust passage 54, the three-way valve 58 is in a state in which the exhaust passage 54 is in communication with the exhaust passage 60, and the three-way valve 68 is in a state where the exhaust passage 66 is in the exhaust passage. 70 to communicate with each other. Thus, as indicated by the arrows in FIG. 5, the exhaust gas that has passed through the turbine of the turbocharger 12 passes through the NOx storage catalyst 26, then flows into the Ag catalyst 34, and is discharged through the exhaust passage 70. . In this state, CO and HC flowing out of the NOx storage catalyst 26 can be purified by the Ag catalyst 34.

  FIG. 6 is a diagram for explaining an exhaust gas flow path during execution of sulfur desorption control. When the sulfur desorption control is executed, the three-way valves 52, 58 and 68 are switched in the directions shown in FIG. That is, when the sulfur desorption control is performed, the exhaust gas that has passed through the turbine of the turbocharger 12 first passes through the Ag catalyst 34, and then passes through the NOx storage catalyst 26 and is discharged from the exhaust passage 62. The exhaust fuel addition injector 27 is installed on the exhaust passage 64 side. Thereby, the reducing agent can be supplied to the NOx storage catalyst 26 by the exhaust fuel addition injector 27 when the sulfur desorption control is executed.

As described above, in this embodiment, when the sulfur component accumulated in the NOx storage catalyst 26 is desorbed, the exhaust gas after passing through the NOx storage catalyst 26 does not flow into the Ag catalyst 34, so the NOx storage catalyst 26. It is possible to reliably prevent the catalytic activity of the Ag catalyst 34 from being reduced by combining SO ₂ desorbed from the Ag with the Ag of the Ag catalyst 34.

  Furthermore, in the present embodiment, the exhaust gas before flowing into the NOx storage catalyst 26 can continue to flow through the Ag catalyst 34 even during execution of the sulfur desorption control. For this reason, harmful components can be purified in the Ag catalyst 34 even during execution of sulfur desorption control. Further, it is possible to avoid the Ag catalyst 34 from being cooled during execution of the sulfur desorption control. Furthermore, sulfur desorption can be promoted by an increase in exhaust gas temperature due to heat of reaction at the Ag catalyst 34.

  Since the control of this embodiment is the same as that of Embodiment 1 except for the points described above, the flowchart is omitted.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Turbocharger 16 Fuel injector 26 NOx storage catalyst 27 Exhaust fuel addition injector 28, 52, 58, 68 Three-way valve 34 Ag catalyst 36 Ozone injection nozzle 38 Ozone supply device 50 ECU

Claims (4)

A storage catalyst having the property of storing sulfur components in exhaust gas;
A second catalyst having a property that the catalytic activity is reduced due to adhesion of a sulfur component;
Sulfur desorption means for performing sulfur desorption control for desorbing a sulfur component from the storage catalyst;
With
An exhaust gas purification apparatus for an internal combustion engine, wherein when the sulfur component is desorbed from the storage catalyst, exhaust gas after passing through the storage catalyst does not flow into the second catalyst. A storage catalyst having the property of storing sulfur components in exhaust gas;
A second catalyst having a property that the catalytic activity is reduced due to adhesion of a sulfur component;
Sulfur desorption means for performing sulfur desorption control for desorbing a sulfur component from the storage catalyst;
Normally, the exhaust gas that has passed through the storage catalyst is caused to flow into the second catalyst, and when the sulfur component is desorbed from the storage catalyst, the exhaust gas that has passed through the storage catalyst is used as the second catalyst. Flow path switching means for switching the flow path of the exhaust gas so as not to flow into the catalyst,
An exhaust emission control device for an internal combustion engine, comprising:   The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein when the sulfur component is desorbed from the storage catalyst, the exhaust gas after passing through the second catalyst flows into the storage catalyst. .   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising an active oxygen supply device that supplies active oxygen to the second catalyst.

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