JP2002256926A - Exhaust emission control method and exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control method and an exhaust emission control device of an internal combustion engine having excellent NOx purifying performance while maintaining SOx resistance of an exhaust emission control catalyst. SOLUTION: This exhaust emission control method of the internal combustion engine has the exhaust emission control catalyst in an exhaust gas passage for reducing and purifying captured NOx to N2 in stoichimetric or rich by capturing the NOx in lean of the air-fuel ratio not less than 18, and has an exhaust gas temperature detecting means for detecting a temperature of exhaust gas flowing in the exhaust emission control catalyst, and purifies the NOx in the exhaust gas by contacting the exhaust gas with the exhaust emission control catalyst. When the exhaust gas temperature detected by the exhaust gas temperature detecting means is not less than a predetermined lower limit temperature and not more than an upper limit temperature, operation including the lean of the air-fuel ratio not less than 18 is performed, and when the exhaust gas temperature is not more than the lower limit temperature or not less than the upper limit temperature, the operation is performed in the stoichimetric or the rich of the air-fuel ratio not more than 14.7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to an exhaust gas purifying method and an exhaust gas purifying apparatus for an internal combustion engine such as an automobile capable of operating at least lean with an air-fuel ratio of 18 or more. About.

[0002]

2. Description of the Related Art In recent years, in the field of internal combustion engines mounted on vehicles and the like, attention has been paid to lean-burn internal combustion engines that increase the air-fuel ratio and make the fuel lean to burn due to environmental problems or problems such as reduction in fuel consumption. And various development proposals have been made.

[0003] Since the lean-burn internal combustion engine burns in an atmosphere having a high oxygen concentration, the three-way catalyst used in a conventional internal combustion engine burning at a stoichiometric air-fuel ratio has a problem particularly in the exhaust gas. The problem arises that the NOx component cannot be sufficiently purified. For this reason, in this type of lean burn internal combustion engine, a catalyst having a NOx absorption component is disposed in the exhaust passage of the internal combustion engine, and the NOx absorption component absorbs the NOx component in the exhaust gas during lean combustion of the fuel, It has been proposed that when the oxygen concentration in the exhaust gas becomes low, the absorbed NOx component is released and purified by another downstream NOx purification catalyst or the like.

[0004] On the other hand, fuels used in internal combustion engines usually contain sulfur components. Therefore, when the fuel is burned, the sulfur oxide SOx, mainly SO2, is contained in the exhaust gas. The SOx reacts with the NOx absorbing component or the NOx adsorbing component to lower the NOx absorbing performance or the NOx absorbing performance, which is a factor of so-called SOx poisoning. The technology described in Japanese Patent Application Laid-Open No. 11-81987 discloses a SOx absorbent and a NOx purification catalyst provided in an exhaust gas passage of an internal combustion engine,
The present invention has proposed a method for purifying exhaust gas which prevents or suppresses SOx poisoning of the NOx purification catalyst.

[0005]

By the way, the technology described in Japanese Patent Application Laid-Open No. H11-81987 discloses that in lean combustion of an internal combustion engine, a SOx absorbent absorbs SOx in exhaust gas to reduce NOx. The SOx resistance of the catalyst can be increased, but NO
In order to maintain the SOx resistance of the x purification catalyst, it is necessary to control the internal combustion engine to activate a special exhaust gas purification catalyst.
That is, before the absorbed SOx amount of the SOx absorbent in the lean combustion reaches saturation, the combustion of the internal combustion engine is set to a stoichiometric or rich combustion state, and control for removing SOx from the SOx absorbent during the state is performed. is necessary.

In the lean-burn internal combustion engine, as a technique for controlling the internal combustion engine to activate an exhaust gas purifying catalyst or the like, a technique described in Japanese Patent Application Laid-Open No. There is a technique described in Japanese Patent No. 288231. Each of these technologies detects an exhaust gas temperature or the like of an internal combustion engine, controls the fluctuation of the air-fuel ratio of the internal combustion engine based on the detection result, and activates the NOx catalyst and improves the purification performance. However, these techniques do not relate to controlling the internal combustion engine of an exhaust gas purifying catalyst to maintain the SOx resistance of the NOx purifying catalyst. The present invention has been made in view of the above-described problems, and the object thereof is to:
An object of the present invention is to provide an exhaust gas purifying method and an exhaust gas purifying apparatus for an internal combustion engine having excellent NOx purifying performance while maintaining the SOx resistance of the exhaust gas purifying catalyst.

[0007]

In order to achieve the above object,
An exhaust gas purifying method for an internal combustion engine according to the present invention includes an exhaust gas purifying catalyst provided in an exhaust gas flow path for trapping NOx in a lean air-fuel ratio of 18 or more and reducing and purifying the trapped NOx to N2 at stoichiometric or rich conditions. Exhaust gas temperature detection means for detecting the temperature of the exhaust gas flowing into the exhaust gas, applied to an internal combustion engine for purifying NOx in the exhaust gas by contacting the exhaust gas with the exhaust gas purification catalyst, the exhaust gas temperature detection means If the exhaust gas temperature detected in step 2 is equal to or higher than the predetermined lower limit temperature and equal to or lower than the predetermined upper limit temperature, the air-fuel ratio becomes 1
When the exhaust gas temperature is equal to or lower than the lower limit temperature or equal to or higher than the upper limit temperature, the air-fuel ratio
It is characterized by driving at stoichiometric or rich of 14.7 or less.

In the operation including the lean operation with the air-fuel ratio of 18 or more, the lean combustion having the air-fuel ratio of 18 or more and the stoichiometric or rich combustion having the air-fuel ratio of 14.7 or less are periodically repeated. It is desirable. Further, it is desirable that the operation including the lean operation with the air-fuel ratio of 18 or more be switched from lean combustion to stoichiometric or rich combustion before reaching the maximum amount of NOx that can be captured by the exhaust gas purifying catalyst in lean combustion.

Further, it is preferable that the exhaust gas temperature detecting means is provided upstream of the exhaust gas purifying catalyst, and the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst is 300 to 7
When the temperature is 00 ° C., it is desirable to perform an operation including lean combustion with an air-fuel ratio of 18 or more, and when the exhaust gas temperature is less than 300 ° C. or higher than 700 ° C., it is desirable to operate with a stoichiometric or rich air-fuel ratio of 14.7 or less .

[0010] As described above, the present inventors provide NOx in an exhaust gas flow path of an internal combustion engine that can be operated at least with a lean air-fuel ratio of 18 or more (hereinafter referred to as lean). An exhaust gas purifying method and an exhaust gas purifying apparatus for an internal combustion engine for purifying exhaust gas by providing an exhaust gas purifying catalyst for trapping (absorbing and adsorbing) and reducing and purifying the trapped NOx to N2 in stoichiometric or rich conditions, and as a result, Provide exhaust gas temperature detection means upstream of the exhaust gas purification catalyst to detect the exhaust gas temperature, perform operation control including lean combustion with an air-fuel ratio of 18 or more according to the exhaust gas temperature, and perform stoichiometric or rich air-fuel ratio 14.7 or less. It has been found that it is effective for the exhaust gas purifying catalyst to perform the operation control only by selecting the air-fuel ratio and to control the air-fuel ratio.

That is, the upper limit temperature and the lower limit temperature of the exhaust gas temperature are determined in advance, and when the exhaust gas temperature detected by the exhaust gas temperature detecting means is equal to or higher than the lower limit temperature and equal to or lower than the upper limit temperature, an operation including a lean air-fuel ratio of 18 or higher is performed. When the exhaust gas temperature is lower than the lower limit temperature or higher than the upper limit temperature, it is possible to perform control to operate only with stoichiometric or rich air-fuel ratio of 14.7 or less, thereby reducing the SOx resistance of the exhaust gas purifying catalyst. It is effective to maintain excellent NOx purification performance while maintaining it.

At this time, the upper and lower limits of the exhaust gas temperature are as follows:
It is determined in advance from both the SOx resistance and the NOx purification performance of the exhaust gas purification catalyst. The exhaust gas contains a trace amount of SOx, and oxidation of SO2 proceeds in a lean state where oxygen is excessive, and the SOx is captured by the exhaust gas purification catalyst. As a result, lean NOx trapping performance decreases. So-called SOx poisoning occurs. This SOx poisoning has a lean exhaust gas temperature of 30.
It is largest at 0 ° C.

On the other hand, when the temperature of the exhaust gas rises to 300 ° C. or higher (preferably 350 ° C. or higher), SOx trapping by the exhaust gas purifying catalyst is suppressed, and SOx poisoning is reduced. Furthermore,
When the stoichiometric or rich exhaust gas is brought into contact with the exhaust gas purification catalyst at an exhaust gas temperature of 500 ° C. or higher, SOx trapped by the exhaust gas purification catalyst is reduced and removed. Therefore, at an exhaust gas temperature of 300 ° C. or higher, SOx poisoning of the exhaust gas purification catalyst can be reduced by performing an operation of periodically repeating lean, stoichiometric, or rich.

On the other hand, the lean NOx purification performance decreases at an exhaust gas temperature of 600 ° C. or higher, greatly decreases at 650 ° C. or higher, and becomes impractical at 700 ° C. or higher. Therefore,
The upper limit of the exhaust gas temperature at which the operation of periodically repeating lean, stoichiometric or rich operation is desirably 700 ° C. Preferably it is 650 ° C, and 600 ° C is optimal. From the above, it is preferable that the exhaust gas temperature for performing operation control including lean operation is 300 ° C. or more and 700 ° C. or less. Desirably, the temperature is 350 ° C. or more and 650 ° C. or less. The temperature is preferably 350 ° C. or more and 600 ° C. or less.

In the exhaust gas purifying method of the present invention, it is preferable to provide an exhaust gas purifying catalyst so as to be in the above-mentioned exhaust gas temperature range. Specifically, since the exhaust gas temperature gradually decreases before being discharged to the outside air from immediately below the internal combustion engine,
In order to keep the temperature in the above-mentioned preferable temperature range, it is preferable to install an exhaust gas purifying catalyst on the internal combustion engine side so that the temperature does not decrease.

For example, in an automobile, the vehicle speed is 30-1.
At 00 km / h, the exhaust gas purifying catalyst is installed on the internal combustion engine side so that the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst is 350 to 650 ° C. Note that at a vehicle speed of 120 km / h or more, the exhaust gas temperature has a possibility of being 700 ° C. to 900 ° C. Accordingly, in the present invention, the exhaust gas purifying catalyst
In order to obtain high NOx purification performance while maintaining x properties, the exhaust gas purification catalyst also needs to have heat resistance.

The structure of the exhaust gas purifying catalyst of the present invention and the improvement in heat resistance will be described below. First, the configuration of the exhaust gas purifying catalyst will be described. The exhaust gas purifying catalyst is coated with a porous inorganic oxide on a monolith structure, and the porous inorganic oxide carries a NO oxidizing material that oxidizes NO to NO2 and a NOx trapping material that traps the oxidized NO2. Is desirable. The NOx trapping material has at least one selected from an alkali metal and an alkaline earth metal.

The NOx trapping material of the catalyst for trapping NOx by absorption preferably has at least one selected from the group consisting of Na, K, Cs, Ba and Sr. Also, in order to obtain high NOx purification performance in a high temperature range where the exhaust gas temperature is 500 ° C or higher, Na, K,
It is preferable to have at least one selected from Cs.

At least one selected from the group consisting of Na, K, Cs, Ba, and Sr is used as a NOx adsorbent for a catalyst that traps NOx by adsorption.
It is desirable to have at least one selected from i, Si and Mn. In order to obtain high NOx purification performance in a high temperature range where the exhaust gas temperature is 500 ° C. or higher, it is preferable to have at least one selected from Na, K, and Cs. NO oxidizer
It has at least one selected from Pt, Rh, and Pd. Also,
Pt, Rh, and Pd are captured lean by a reducing agent such as HC and CO that coexist in the exhaust gas in stoichiometric or rich conditions.
It also has the effect of reducing and removing Ox.

When a cordierite honeycomb, which is usually used as a monolith structure, is used, the thermal deterioration of the exhaust gas purifying catalyst is caused by thermal aggregation of alkali metal or alkaline earth metal,
And the reaction of alkali metal or alkaline earth metal with cordierite honeycomb is considered to be the main cause. Therefore, in order to increase the heat resistance of the exhaust gas purifying catalyst, it is necessary to improve the two causes. As a method of suppressing thermal aggregation of an alkali metal or an alkaline earth metal, first, an alkali metal or an alkaline earth metal and Mn and Ti
Is desirable. The composite oxide includes crystalline and non-crystalline.

Next, an oxide having heat resistance and hardly forming an alloy or a composite oxide with an alkali metal or an alkaline earth metal between porous inorganic oxide particles in a coat layer on the monolith structure. (Hereinafter referred to as anchor material) is desirable. By the anchor material, contact of the porous inorganic oxide particles is suppressed, and NOx between the porous inorganic oxide particles is reduced.
The movement of the trapping material is suppressed.

Further, since it is difficult to form an alloy or a composite oxide between the anchor material and the alkali metal or alkaline earth metal, migration to the porous inorganic oxide particles or the monolith structure via the anchor material is suppressed. Is done. for that reason,
The reaction between the alkali metal or alkaline earth metal and the cordierite honeycomb is suppressed.

As the anchor material, it is desirable that the melting point of the oxide of the anchor material is 2500 ° C. or more and the electronegativity of ions of the anchor material is 7.0 to 5.0. The melting point corresponds to the heat resistance of the anchor material, and the electronegativity corresponds to the reactivity of the anchor material with the alkali metal or alkaline earth metal. Since the electronegativity of the alkali metal or the alkaline earth metal is low, if the electronegativity of the anchor material is small, it will show the same basicity as the alkali metal or the alkaline earth metal, and the anchor material and the alkali metal or Reactivity with alkaline earth metals is reduced.

When the melting point is 2500 ° C. or higher, heat resistance can be obtained. 6. The electronegativity of the ions of the anchor material is 7.
By being 0 or less, the reaction between the alkali metal or alkaline earth metal and the anchor material is suppressed. When the electronegativity is less than 5.0, the melting point of the oxide is 2500 ° C.
It is not preferable because it becomes lower.

As the anchor material, Ca and Mg are preferable, but MgO is particularly preferable. The melting point of MgO is 2826 ° C
(Source: Chemical Society of Japan, Basic Handbook of Chemistry I, 4th revised edition, p. 16)
9), and the MgO particles are stably present in the coat layer even when subjected to a heat load of about 800 to 1000 ° C. Also,
The electronegativity of the ions is 5.0 (Source: Catalysis Society of Japan, Catalyst Engineering Course 10, p752).
It is difficult to form an alloy or a composite oxide with an alkali metal or an alkaline earth metal.

Specifically, in the exhaust gas purifying catalyst, a mixture of a porous inorganic oxide and MgO is coated on a monolith structure, and at least one selected from an alkali metal and an alkaline earth metal is coated on the coating layer. Preferably, at least one selected from noble metals, at least one selected from rare earth metals, and titanium and Mn are supported. Furthermore, by using a metal honeycomb for the monolith structure of the exhaust gas purifying catalyst, it is possible to prevent a reaction between the monolith structure and the alkali metal and alkaline earth metal, and to obtain excellent heat resistance.

As described above, according to the method for purifying exhaust gas of an internal combustion engine of the present invention, a high NOx purification performance is obtained by using an exhaust gas purification catalyst having heat resistance and maintaining the SOx resistance of the exhaust gas purification catalyst. Can be When NOx trapping is absorption, switching to rich or stoichiometric reduces the oxygen concentration and may release trapped NOx. In this case, a NOx reduction catalyst for reducing and purifying NOx is provided downstream of the exhaust gas purification catalyst, such as a three-way catalyst, in stoichiometric or rich conditions,
An exhaust gas purification method for reducing and purifying released NOx is also possible.

The method for preparing the NOx purification catalyst and the NOx reduction catalyst according to the present invention includes an impregnation method, a kneading method, a coprecipitation method, a sol-gel method,
Any of a physical preparation method such as an ion exchange method and a vapor deposition method and a preparation method utilizing a chemical reaction can be applied. As a starting material for the NOx purification catalyst and the NOx reduction catalyst, a nitrate compound,
Various compounds such as acetic acid compounds, complex compounds, hydroxides, carbonate compounds, organic compounds, and dinitrodiamine complexes, and metals and metal oxides can be used.

As the porous carrier in the method for purifying exhaust gas of an internal combustion engine of the present invention, metal oxides such as titania, silica, silica-alumina and composite oxides can be used in addition to alumina. Alumina is preferred as a carrier having heat resistance. INDUSTRIAL APPLICABILITY The internal combustion engine of the present invention is suitable for a gasoline-powered vehicle or a diesel-powered vehicle capable of performing stratified or homogeneous lean combustion that performs oxidizing atmosphere operation with an air-fuel ratio of 18 or more and stoichiometric or rich operation.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an exhaust gas purifying method and an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows an automobile equipped with an internal combustion engine having the exhaust gas purifying apparatus according to the first embodiment of the present invention.

The automobile A has an internal combustion engine 100 disposed in front of the automobile A. The internal combustion engine 100 includes an internal combustion engine main body 1.
Exhaust gas from the internal combustion engine body 1 flows into the exhaust gas purifying catalyst 10 through the exhaust pipe 13, and is discharged from the rear of the automobile A through the exhaust gas purifying catalyst 10. The internal combustion engine 100 is a lean burn in-cylinder injection internal combustion engine, and can intentionally repeat lean combustion with an air-fuel ratio of 18 or more and stoichiometric or rich combustion with an air-fuel ratio of 14.7 or less.
The exhaust gas purifying catalyst 10 includes a NOx trapping material, a NO oxidizing material, and N
The exhaust gas temperature is detected by an exhaust gas temperature sensor 8, and information on the exhaust gas temperature is input to an internal combustion engine control unit (control device) 11 and constantly monitored.

FIG. 2 shows an internal combustion engine 10 according to this embodiment shown in FIG.
0, the internal combustion engine 100 includes an internal combustion engine body 1 having an injector 5 and a spark plug 6 and capable of performing lean burn, an air cleaner 12, an air flow sensor 2, and a throttle valve 3. An exhaust system having an oxygen concentration sensor 7, an exhaust gas temperature sensor 8, a catalyst outlet gas temperature sensor 9, an exhaust gas purifying catalyst 10, and the like, and an internal combustion engine control unit (control device) 11 are provided. Note that an A / F sensor may be used instead of the oxygen concentration sensor 7.

Although not shown, the internal combustion engine control unit 11 has I / O and L as input / output interfaces.
It comprises an SI, an arithmetic processing unit MPU, a storage device RAM and ROM storing a large number of control programs, a timer counter, and the like. The intake air to the internal combustion engine main body 1 is input from the air cleaner 12, filtered by the air cleaner 12, measured by the air flow sensor 2, and supplied to the combustion chamber 1 a of the internal combustion engine main body 1 via the slot valve 3. Then, in the combustion chamber 1a, the fuel comes into contact with the fuel injected from the injector 5 to form an air-fuel mixture.

A signal from a sensor such as the air flow sensor 2 is input to the internal combustion engine control unit 11, and the internal combustion engine control unit 11 evaluates the operating state of the internal combustion engine and the state of the exhaust gas purifying catalyst 10 to determine the operating air-fuel ratio. The fuel concentration of the air-fuel mixture is set to a predetermined value by controlling the injection time of the injector 5 and the like. The air-fuel mixture in the combustion chamber 1a is ignited by a spark plug 6 controlled by a signal from the internal combustion engine control unit 11 and burns.
The combustion exhaust gas is guided to an exhaust gas purification system and purified by an exhaust gas purification catalyst 10 provided in the exhaust gas purification system.

FIG. 3 is a control block diagram of the internal combustion engine control unit (control device) 11 of the present embodiment. The control device 11 includes an exhaust gas temperature detection unit 111, a lean and rich or stoichiometric operation control unit 112, and a stoichiometric or rich operation control unit 113.

FIG. 4 shows a control flow based on the control block of the control device 11 of FIG. Step 10
In 01, the exhaust gas temperature sensor 8 detects the exhaust gas temperature T, and in step 1002, the exhaust gas temperature detector 111 determines whether the exhaust gas temperature T is 350 ° C or more and 650 ° C or less. If it is determined that this is the case, the routine proceeds to step 1003, where it is recognized that the internal combustion engine 100 may intentionally repeat lean and stoichiometric or rich combustion.
At 2, lean and stoichiometric or rich combustion operation control is performed.

On the other hand, in step 1002, the exhaust gas temperature
If it is determined that the temperature has become lower than 300 ° C. or higher than 650 ° C., the process proceeds to step 1004, in which the stoichiometric or rich operation control unit 113 is operated to cause the internal combustion engine 100 to execute only the stoichiometric or rich combustion operation.

As a control method in the lean and stoichiometric or rich combustion operation control unit 112, for example, the amount of trapped NOx and SOx in the lean is estimated, and a predetermined NOx and Sx are determined.
When the Ox trapping amount is exceeded, control is performed to set stoichiometric or rich operation. By the operation control of the internal combustion engine as described above, the exhaust gas under all the internal combustion engine combustion conditions of the lean operation, the stoichiometric operation, or the rich operation is effectively purified.

FIG. 5 shows an automobile B equipped with an internal combustion engine having an exhaust gas purification control device according to a second embodiment of the present invention.
The same components as those in the first embodiment of the present invention shown in FIG. 1 are denoted by the same reference numerals.

The automobile B has an internal combustion engine 100 disposed at a front portion thereof. The internal combustion engine 100 includes an internal combustion engine main body 1.
Exhaust gas from the internal combustion engine main body 1 flows into the exhaust gas purifying catalyst 10 through the exhaust pipe 13, and is discharged from the rear of the automobile B through the exhaust gas purifying catalyst 10 and the NOx reduction catalyst 13. The internal combustion engine 100 is a lean burn in-cylinder injection internal combustion engine, and can intentionally repeat lean combustion with an air-fuel ratio of 18 or more and stoichiometric or rich combustion with an air-fuel ratio of 14.7 or less. Next, the exhaust gas purification catalyst used in the exhaust gas purification control devices of the two embodiments will be described in detail.

[Catalyst used] In selecting the exhaust gas purifying catalyst, NOx is trapped by adsorption in a lean state, and the trapped NOx is not desorbed even if the oxygen concentration in the exhaust gas is reduced. As a representative example of purification by reduction to N2, the following Example Catalyst 1 and Example Catalyst 2 were examined.

(Example Catalyst 1) In the production of Example Catalyst 1, a slurry composed of alumina powder and an alumina precursor and adjusted to nitric acid acid was coated on a metal honeycomb, dried and fired, and the apparent appearance of the honeycomb was measured. Volume 1
An alumina-coated honeycomb coated with 200 g of alumina per liter was obtained. The alumina-coated honeycomb was impregnated with a solution of Ce nitrate in water, dried at 200 ° C, and then fired at 600 ° C.

Next, a dinitrodiammine Pt nitric acid solution, a nitric acid Rh, and a nitric acid Pd were added to the calcined alumina-coated honeycomb.
And a mixture of Mn nitrate and K acetate was impregnated, dried at 200 ° C., and subsequently fired at 600 ° C. Finally, K acetate and N nitrate
impregnated with a mixed solution of a, Li nitrate and titania sol,
And then calcined at 600 ° C. From the above, for an apparent volume of 1 L of the honeycomb, Ce: 27 g, Rh:
0.14g, Pt: 2.8g, Pd: 1.4g, K: 15.6g, Na: 12.4g, Li: 1.6g, Ti:
Example catalyst 1 containing 4.3 g, Mn: 13.7 g was obtained (Table 1).
Example catalyst 1).

(Example Catalyst 2) Example catalyst 2 is the same as example catalyst 1 except that it is composed of alumina powder and a precursor of alumina, and MgO (average particle size: 30 μm, MgO-alumina mixed slurry to which specific surface area: 1 m2 / g) was added was coated on a metal honeycomb, and then dried and fired, so that MgO-alumina coated with 190 g of alumina and 10 g of MgO per liter of apparent volume of the honeycomb was obtained. Example catalyst 2 using coated honeycomb
(Example Catalyst 2 in Table 1).

[0045]

[Table 1]

Test Example 1 In order to examine the heat resistance of the catalysts 1 and 2 of the above example, the NOx purification rates before and after the heat treatment were examined. The catalyst fired at 600 ° C. was used as an initial product, and 83
A catalyst heat-treated by air calcination at 0 ° C. for 60 hours was used as a heat-resistant product. The gas used for the test was a lean model gas simulating lean burn exhaust gas and a stoichiometric model gas simulating stoichiometric air-fuel ratio combustion, with a catalyst volume of 6 cc and SV of 3
It was set to 0,000 / h.

The composition of the lean model gas is as follows: NOx: 600 pp
m, C3H6: 500ppm, CO: 0.1%, CO2: 10%, O2: 5%, H2O:
10%, N2: Residual. The composition of the stoichiometric model gas is N
Ox: 1000ppm, C3H6: 600ppm, CO: 0.5%, CO2: 5%, O2:
0.5%, H2: 0.3%, H2O: 10%, N2: balance.

The test was performed according to the following procedures. The mixture was heated to 500 ° C. while flowing a stoichiometric model gas. The flow of the stoichiometric model gas was stopped, and the temperature was maintained at a predetermined temperature of 200 to 700 ° C. At a predetermined temperature, after allowing the stoichiometric model gas to flow through the catalyst layer for 3 minutes, immediately switch to the lean model gas.
Allowed to flow for 3 minutes. A test in which the stoichiometric model gas and the lean model gas alternately flow through the catalyst layer every three minutes (hereinafter, repeated test) was continued for 18 minutes. The NOx purification rate is switched from stoichiometric model gas to lean model gas.
The reduction rate of the NOx concentration before and after circulation of the catalyst layer after 1 minute was defined as the reduction rate. The definition formula was the following formula (1).

[0049]

## EQU1 ## NOx purification rate = (NOx concentration before flowing through the catalyst layer−NOx concentration after flowing through the catalyst layer) / (NOx concentration before flowing through the catalyst layer) × 100 Equation (1) (Test results) FIG. Example catalyst 1 and example catalyst 2
3 shows measurement results of NOx purification rates at various temperatures before and after heat treatment. NOx purification rate of initial product is 300-7
At 00 ° C., both Example Catalyst 1 and Example Catalyst 2
70-100%.

After the heat treatment, the NOx purification rate on the low temperature side is 30
40-50% at 0 ° C, 50-6 at 350 ° C
It was 0%. Below 300 ° C, the NOx purification rate is 30-
Since it is as low as 40%, the lower limit temperature for obtaining a high NOx purification rate is considered to be 300 ° C, preferably 350 ° C.

The NOx purification rate on the high temperature side was 10% at 700 ° C., 40% at 650 ° C., and 50-60% at 600 ° C. If the temperature is higher than 700 ° C., it is considered that a practical NOx purification rate cannot be obtained. Further, in consideration of the SOx resistance, it is desirable that the upper limit temperature for the lean operation is as high as possible. Therefore, the upper limit temperature for lean operation is
700 ° C. is the highest temperature. In consideration of NOx purification performance, 650 ° C. is preferable, and 600 ° C. is suitable.
However, when the temperature is 600 ° C. or lower, the temperature becomes close to the lower limit temperature for the lean operation, and the lean operation region is narrowed, which is not preferable.

From the above, the lower limit temperature (300-
(350 ° C) or higher, and in a temperature range below the upper limit temperature (600-700 ° C), perform lean and stoichiometric or rich operation,
In other temperature ranges, it was found that NOx in exhaust gas can be efficiently purified by stoichiometric or rich operation. At 200-700 ° C, switching to stoichiometric model gas, the NOx purification rate after 3 minutes was almost
100%.

[Test Example 2] SOx resistance at 250-500 ° C was measured using Example Catalyst 1 calcined at 700 ° C for 5 hours.
Sex was examined. The gas used for the test was SOx poisoning gas in a stoichiometric atmosphere, SOx poisoning gas in a lean atmosphere, and a stoichiometric model gas, the catalyst volume was 6 cc, and the SV was 30,000 / h.

The composition of the SOx poisoning gas in the stoichiometric atmosphere is S
Ox: 1500ppm, NOx: 1000ppm, C3H6: 600ppm, CO: 0.5%,
CO2: 5%, O2: 0.5%, H2: 0.3%, H2O: 10%, N2: balance. The composition of SOx poisoning gas in lean atmosphere is SOx: 1500
ppm, NOx: 600ppm, C3H6: 500ppm, CO: 0.1%, CO2: 10
%, O2: 5%, H2O: 10%, N2: balance.

The test was performed according to the following procedures. After the catalyst was set in the reaction tube, the initial NOx purification rate at 350 ° C. was measured by the method described in Test Example 1. SOx poisoning treatment: The temperature was maintained at a predetermined temperature of 250 to 500 ° C., and SOx poisoning gas in a stoichiometric atmosphere or SOx poisoning gas in a lean atmosphere was allowed to flow for one hour. 1 hour later N
The mixture was cooled to room temperature while flowing two gases. The NOx purification rate after SOx poisoning at 350 ° C. was measured by the method described in Test Example 1. Regeneration treatment: After heating to 600 ° C. in an N 2 atmosphere, stoichiometric model gas was passed for 10 minutes. The flow of the stoichiometric model gas was stopped, and the mixture was cooled to 350 ° C. The NOx purification rate after reprocessing at 350 ° C. was measured by the method of Test Example 1.

(Test Results) Table 2 shows the NOx purification rate with respect to the SOx poisoning temperature in a lean combustion atmosphere. NOx purification rate after SOx treatment is 70% at SOx poisoning temperature 250 ° C, 68% at 300 ° C, 73% at 350 ° C, 400 ° C
At 78 ° C. and 80% at 500 ° C. SOx poisoning temperature 30
At 0 ° C., the NOx purification rate decreased most.

On the other hand, the NOx purification rate after the regeneration treatment is 250
At −300 ° C., the recovery was not complete, but at 350 ° C. or higher, it almost recovered to the initial stage. From the above, the lower limit temperature of the lean operation for suppressing SOx poisoning and facilitating the regeneration is desirably 300 ° C or higher, and 350 ° C or higher.
It became clear that the above was more suitable.

[0058]

[Table 2]

Test Example 3 The effect of the regeneration treatment temperature was examined using the catalyst of Example 1 calcined at 700 ° C. for 5 hours. The test method was performed using the method of Test Example 2. However, SOx
The processing temperature was 350 ° C. in all tests. Regeneration processing conditions were: regeneration processing temperatures 400, 500, 600 ° C.
The regeneration processing time was 10 minutes. NOx purification rate is 350 ℃
Was measured.

(Test Results) Table 3 shows the NOx purification rate with respect to the regeneration processing temperature in the lean combustion. At the reprocessing temperature of 400 ° C., the NOx purification rates are almost equal after the SOx treatment and after the regeneration treatment, and no recovery is observed. However, 500 ° C
In the regeneration process at 600 ° C., the NOx purification rate has recovered. From the above, it has been clarified that when the exhaust gas purification catalyst is brought into contact with a stoichiometric or rich exhaust gas having an exhaust gas temperature of 500 ° C. or higher, SOx trapped in the lean is removed.

[0061]

[Table 3]

FIG. 7 shows an automobile C equipped with an internal combustion engine having an exhaust gas purifying apparatus according to a third embodiment of the present invention. The automobile C includes a pre-catalyst 20 and an exhaust gas purifying catalyst 10 as catalysts. The same components as those in the first embodiment of the present invention shown in FIG. 1 are denoted by the same reference numerals.

The pre-catalyst 2 is located immediately downstream of the internal combustion engine 100.
0, the exhaust gas purifying catalyst 10 is provided downstream of the pre-catalyst 20, and the air-fuel ratio is operated near stoichiometric or rich when the internal combustion engine is started or in a low temperature range equal to or lower than the lean operation lower limit temperature. When NOx in the exhaust gas in the low temperature range cannot be sufficiently purified only by the exhaust gas purification catalyst 10, the use of the precatalyst 20 is effective.

Since exhaust gas temperature loss is avoided immediately below the internal combustion engine, a relatively high exhaust gas temperature can be obtained immediately below the internal combustion engine from the start of the internal combustion engine. However, in steady state operation, the temperature rises to a very high temperature (for example, 900-1000 ° C.).
Therefore, the function of the pre-catalyst 20 is required to purify exhaust gas in the vicinity of stoichiometric or rich and to have high heat resistance. The components of the precatalyst 20 include, for example, three-way catalyst components such as noble metals and rare earth metal oxides.

By the combination of the precatalyst 20 and the exhaust gas purifying catalyst 10 having the above function, the exhaust gas can be purified in a wide temperature range. As described above, the three embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various designs may be made without departing from the spirit of the present invention described in the appended claims. It can be changed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an automobile equipped with an internal combustion engine having an exhaust gas purification device (exhaust gas purification catalyst) according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an overall configuration of an exhaust gas purifying apparatus for an internal combustion engine in FIG. 1;

FIG. 3 is a control block diagram of a control device of the exhaust gas purifying apparatus of FIG. 2;

FIG. 4 is a control flowchart of an exhaust gas purification control device of FIG. 2;

FIG. 5 is a diagram showing an automobile equipped with an internal combustion engine having an exhaust gas purification device (exhaust gas purification catalyst and NOx reduction catalyst) according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the NOx purification performance of the exhaust gas purification catalyst of the present invention.

FIG. 7 is a diagram showing an automobile equipped with an internal combustion engine having an exhaust gas purifying apparatus (a pre-catalyst and an exhaust gas purifying catalyst) according to a third embodiment of the present invention.

[Explanation of symbols]

2: air flow sensor, 3: throttle valve, 5: injector, 6: spark plug, 7: oxygen concentration sensor,
8: Exhaust gas temperature sensor, 10: Exhaust gas purification catalyst, 11:
Internal combustion engine control unit, 12: air cleaner, 1
4: NOx reduction catalyst, 20: pre-catalyst, 100: internal combustion engine, 101: exhaust pipe, A, B, C: automobile

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/10 F01N 3/28 301C 3/20 301P 3/24 F02D 41/02 330A 3/28 301 45 / 00 312Z B01D 53/36 ZAB F02D 41/02 330 101B 45/00 312 B01J 23/64 104A (72) Inventor Kojiro Okude 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Electric Power & Electric Machinery Co., Ltd. Inside the Research Laboratory (72) Inventor Toshio Yamashita 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Inside Power and Electricity Development Laboratory, Hitachi, Ltd. (72) Inventor Yuichi Kitahara 2520 Takada, Daijita, Hitachinaka City, Ibaraki Pref. (72) Inventor Osamu Kuroda Oita High School, Hitachinaka City, Ibaraki Prefecture 2520 F-term in Hitachi, Ltd. Automotive Equipment Group (reference) HA10 HA36 3G301 HA01 HA04 HA15 JA25 LB04 MA01 MA12 NA08 NE13 NE14 NE15 NE17 NE19 PD02Z PD11Z 4D048 AA06 AB02 AB07 BA01X BA03X BA07Y BA10Y BA14X BA15Y BA18Y BA19X BA28X BA30X BA31X BA33X BA39X BA02DA03 DA02A02 DA02A02 DA02A02 DA02A BA04A BA06A BA17 BA20A BA20B BB02A BB04A BB04B BB06A BB06B BC01A BC02A BC02B BC03A BC03B BC04A BC04B BC06A BC08A BC10A BC10B BC12A BC13A BC16A BC16B BC38A BC43A BC43B BC50A BC50BBCA BCBC BC BC BC BC BC

Claims (15)

[Claims] An exhaust gas purifying catalyst for trapping NOx in a lean air-fuel ratio of 18 or more and reducing and purifying the trapped NOx to N2 in stoichiometric or rich conditions is provided in an exhaust gas passage, and a temperature of exhaust gas flowing into the exhaust gas purifying catalyst is provided. An exhaust gas purification method for an internal combustion engine that includes exhaust gas temperature detection means for detecting the exhaust gas and contacts the exhaust gas with the exhaust gas purification catalyst to purify NOx in the exhaust gas, wherein the exhaust gas temperature detected by the exhaust gas temperature detection means is predetermined. If it is above the lower limit temperature and below the upper limit temperature,
When the exhaust gas temperature is equal to or lower than the lower limit temperature or equal to or higher than the upper limit temperature, the exhaust gas of the internal combustion engine is operated at a stoichiometric or rich air fuel ratio of 14.7 or less when the air-fuel ratio includes a lean operation of 18 or more. Purification method. 2. The operation including lean operation with an air-fuel ratio of 18 or more includes lean combustion with an air-fuel ratio of 18 or more and an air-fuel ratio of 1 or more.
The exhaust gas purification method for an internal combustion engine according to claim 1, wherein the stoichiometric or rich combustion of 4.7 or less is periodically repeated. 3. The operation including the lean operation with the air-fuel ratio of 18 or more switches from lean combustion to stoichiometric or rich combustion before reaching the maximum amount of NOx that can be captured by the exhaust gas purifying catalyst in lean combustion. Item 3. The method for purifying exhaust gas of an internal combustion engine according to Item 2. 4. The exhaust gas temperature detecting means is provided upstream of the exhaust gas purifying catalyst.
The method for purifying exhaust gas of an internal combustion engine according to any one of the above. 5. When the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst is 300 to 700 ° C., an operation including lean combustion with an air-fuel ratio of 18 or more is performed. When the exhaust gas temperature is lower than 300 ° C. or higher than 700 ° C., The exhaust gas purification method for an internal combustion engine according to any one of claims 1 to 4, wherein the operation is performed at a stoichiometric or rich air-fuel ratio of 14.7 or less. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying catalyst has at least one selected from an alkali metal and an alkaline earth metal. Method. 7. The exhaust gas purifying catalyst comprises at least one selected from the group consisting of alkali metals and alkaline earth metals, and P
The exhaust gas purification method for an internal combustion engine according to any one of claims 1 to 5, comprising at least one selected from the group consisting of t, Rh, and Pd. 8. The exhaust gas purifying catalyst, wherein a monolith structure is coated with a mixture of a porous inorganic oxide and MgO,
At least one selected from alkali metals and alkaline earth metals, at least one selected from noble metals, at least one selected from rare earth metals, and titanium and Mn are supported on the coat layer. Claim 1
The exhaust gas purifying method for an internal combustion engine according to any one of claims 1 to 5. 9. The exhaust gas purifying method for an internal combustion engine according to claim 8, wherein the monolith structure uses a metal honeycomb. 10. A lean air-fuel ratio of 18 or more
an exhaust gas purifying catalyst provided in an exhaust gas passage for trapping x and reducing and purifying the trapped NOx to N2 in stoichiometric or rich; exhaust gas temperature detecting means for detecting the temperature of exhaust gas flowing into the exhaust gas purifying catalyst; air-fuel ratio control An exhaust gas purifying apparatus for an internal combustion engine, comprising: an air-fuel ratio control device, wherein an upper limit temperature and a lower limit temperature of the exhaust gas temperature are determined in advance, and the exhaust gas temperature detected by the exhaust gas temperature detecting means is the lower limit temperature. Above and below the upper limit temperature, the air-fuel ratio is set to operation control including lean of 18 or more, and when the exhaust gas temperature is below the lower limit temperature or above the upper limit temperature, the stoichiometric or rich air-fuel ratio is 14.7 or less. An exhaust gas purifying apparatus for an internal combustion engine, the operation of which is controlled by an engine. 11. The air-fuel ratio control device according to claim 1, wherein when the temperature detected by the exhaust gas temperature detecting means is 300 to 700 ° C., the air-fuel ratio is set to an operation control including lean combustion at an air-fuel ratio of 18 or more.
When lower or above 700 ° C., the air / fuel ratio is increased to 14.
The exhaust gas purifying apparatus for an internal combustion engine according to claim 10, wherein operation control of only stoichiometric or rich combustion of 7 or less is performed. 12. The exhaust gas purifying apparatus for an internal combustion engine according to claim 10, wherein the exhaust gas purifying catalyst has at least one selected from an alkali metal and an alkaline earth metal. 13. The exhaust gas purifying catalyst, comprising: at least one selected from an alkali metal and an alkaline earth metal;
The exhaust gas purifying apparatus for an internal combustion engine according to claim 10, further comprising at least one selected from Pt, Rh, and Pd. 14. The exhaust gas purifying catalyst, wherein a monolith structure is coated with a mixture of a porous inorganic oxide and MgO, and the coating layer is selected from at least one selected from an alkali metal and an alkaline earth metal, and selected from a noble metal. 14. The exhaust gas purifying apparatus for an internal combustion engine according to claim 10, wherein at least one selected from the group consisting of at least one selected from rare earth metals, and titanium and Mn are supported. 15. The exhaust gas purifying apparatus for an internal combustion engine according to claim 14, wherein the monolith structure uses a metal honeycomb.