JP2001132432A - Exhaust gas purifying method, and exhaust gas purifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for purifying exhaust gas at high efficiency. SOLUTION: In this method and device for purifying exhaust gas from an internal combustion engine, a cylinder which is actuated in a stoichiometric air-fuel ratio or fuel rich condition, and a cylinder in which the stoichiometric air-fuel ratio or fuel rich condition and lean burn are alternately conducted are provided, thereby NOx in lean burn exhaust gas is eliminated by ammonia denitration and NOx arresting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for purifying gas discharged from an internal combustion engine, and more particularly to an exhaust gas purifying method and apparatus suitable for purifying lean burn exhaust gas.

[0002]

2. Description of the Related Art In recent years, various internal combustion engines including automobiles have been required to further reduce harmful substance emissions and fuel consumption. In such a background, an internal combustion engine having at least one or more cylinders operating in a stoichiometric air-fuel ratio or a fuel-rich state and another cylinder performing lean combustion is operated in a stoichiometric air-fuel ratio or a fuel-rich state. JP-A-8-4522 describes a method of removing ammonia by generating ammonia from exhaust gas from at least one or more cylinders and bringing the ammonia and NOx in lean combustion exhaust gas into contact with an ammonia denitration catalyst. .

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to enhance the lean NOx purification performance in a method for denitrifying NOx in lean exhaust gas with ammonia. Another object of the present invention is to widen a temperature range in which NOx can be purified lean.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention combines a NOx purifying catalyst and an ammonia denitration catalyst, and overcomes the problems caused by the combination. The purpose was to enable lean operation. The gist of the present inventors is described below.

[1] An ammonia denitration catalyst and a lean NOx trapping catalyst are provided in an exhaust gas passage of an internal combustion engine. Then, the exhaust gas having a lean air-fuel ratio contains ammonia, and the ammonia is sequentially flown into the ammonia denitration catalyst and the lean NOx trapping catalyst.

[0006] In this manner, NOx that cannot be completely removed by the ammonia denitration catalyst can be removed by the lean NOx trapping catalyst.

Further, NOx trapped by a lean NOx catalyst
Since the amount is extremely small as compared with the case where the ammonia denitration catalyst is not used, the lean operation can be continued for a long time.

[0008] Here, the lean NOx trapping catalyst means that the oxygen concentration of the inflowing exhaust gas is higher than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent (hereinafter, the air-fuel ratio of the exhaust gas is referred to as lean). ) Sometimes adsorb NOx in the exhaust gas,
Refers to a catalyst having a function of capturing by absorption or the like.

An ammonia denitration catalyst is a catalyst for converting NOx to NH ₃
It refers to a catalyst having a function of reducing the N2 using the O _2.

[2] An ammonia denitration catalyst and a lean NOx reduction catalyst are provided in an exhaust gas passage of an internal combustion engine.

According to the present invention, NOx that cannot be completely removed by the ammonia denitration catalyst is reduced to nitrogen by the lean NOx reduction catalyst. Since the amount of NOx flowing into the lean NOx reduction catalyst is extremely small as compared with the case where there is no ammonia denitration catalyst, the NOx reduction purification by the lean NOx reduction catalyst is performed efficiently.

[3] An ammonia denitration catalyst and a NOx purification catalyst are provided in an exhaust gas passage of an internal combustion engine. Then, the exhaust gas having an air-fuel ratio of lean and rich or stoichiometric flows alternately flows.

The NOx purifying catalyst has a function of trapping NOx when the air-fuel ratio of the exhaust gas is lean, and reducing and purifying the trapped NOx and NOx contained in the exhaust gas when the air-fuel ratio of the exhaust gas is rich or stoichiometric. Have.

According to the present invention, NOx trapped by the NOx purification catalyst when the air-fuel ratio of the exhaust gas is lean is reduced and purified when the exhaust gas is rich or stoichiometric, and the NOx trapping function is restored.

It is preferable that the NOx purification catalyst has a NOx reduction function when the air-fuel ratio of the exhaust gas is lean.

[4] An ammonia generation catalyst is provided in a part of the exhaust gas passages of a plurality of cylinders capable of independently controlling the air-fuel ratio. An ammonia denitration catalyst and a NOx purification catalyst are sequentially provided downstream of a junction where exhaust gases from a plurality of cylinders join.
The air-fuel ratio of the exhaust gas at the junction is alternately switched between lean and rich or stoichiometric.

[5] Ammonia generating catalysts are provided in all exhaust gas passages of a plurality of cylinders capable of independently controlling the air-fuel ratio, and thereafter the configuration is the same as in the above [4].

In this case, the cycle at which the air-fuel ratio of each cylinder is switched between lean, rich, and stoichiometric is shifted.

The above [4] and [5] embody the method of the above [1].

[6] In any one of the above [1] to [5], the lean trap catalyst, the NOx purifying catalyst or the lean NOx
Means is provided for removing at least a part of the ammonia from the exhaust gas flowing into the reduction catalyst. For example, an ammonia oxidation catalyst is provided.

When no ammonia removing means is provided,
In the lean NOx trapping catalyst, the NOx purification catalyst, or the lean NOx reduction catalyst, the oxidation of ammonia occurs,
NOx purification or capture is less likely to occur.

The lean NOx trapping catalyst or NOx
In order to make it difficult for NOx purification or trapping to occur in the purification catalyst or lean NOx reduction catalyst, it is desirable that the ammonia concentration in the exhaust gas be reduced to 35 ppm or less by ammonia removing means.

It is also possible to reduce the concentration of ammonia flowing out of the ammonia denitration catalyst by increasing the amount of air flowing into the stoichiometric or rich operating cylinder.

[7] In any one of the above [1] to [6], a plurality of catalysts having different temperature ranges for purifying NOx in a lean manner are combined. For example, an ammonia denitration catalyst having high lean NOx purification performance at 400 to 600 ° C .;
Lean NOx with high NOx purification performance at ~ 500 ° C
A trapping catalyst, a lean NOx reduction catalyst, or a NOx purification catalyst is combined. Alternatively, an ammonia denitration catalyst having a high NOx purification performance in a temperature range of 100 to 300 ° C, an ammonia denitration catalyst of 300 to 400 ° C and 40
Combine with an ammonia denitration catalyst at 0-600 ° C.

When the temperature of the exhaust gas flowing into the ammonia denitration catalyst is lower than the optimum temperature range of the ammonia denitration catalyst, the air-fuel ratio of the cylinder operating in the stoichiometric or rich state is temporarily switched to the lean combustion state. Preventing NH ₃ generation in the ammonia generation catalyst, and returning the air-fuel ratio of the cylinder that has been operating in the lean burn state temporarily to the stoichiometric or rich state after the exhaust gas temperature reaches the optimum temperature range of the ammonia denitration catalyst Is desirable.

The temperature of the exhaust gas flowing into the ammonia denitration catalyst can be detected by providing a temperature sensor upstream of the ammonia denitration catalyst.

Before switching to lean and rich, lean N
An example of a system in consideration of the possibility that the NOx trapping amount of the Ox trapping catalyst or the NOx purification catalyst reaches saturation will be described below.

The internal combustion engine has an engine control unit and can control the air-fuel ratio for each cylinder. It is also possible to divide each cylinder into a plurality of groups and control the air-fuel ratio for each group.

Here, a part of the cylinder operates in a stoichiometric air-fuel ratio (stoichiometric) or a fuel-rich state. The remaining cylinders alternately operate between a stoichiometric air-fuel ratio or a fuel rich state and a lean burn state.

The number of cylinders operating in the stoichiometric air-fuel ratio or fuel-rich state and the number of cylinders operating in the stoichiometric air-fuel ratio or the fuel-rich state and lean-burn state alternately depend on the operating conditions such as the NOx concentration to be purified, the amount of exhaust gas, and the temperature of exhaust gas. Preferably, the state is estimated by the engine control unit in real time, and optimized and variably controlled each time according to the operating state. Further, it is also possible to operate with the number of cylinders fixed in advance without depending on the operation state.

In the downstream of the junction, an exhaust gas having an oxygen concentration higher than the oxygen concentration required for completely oxidizing hydrocarbons, carbon monoxide and H2 in the exhaust gas and an exhaust gas having an oxygen concentration lower than the oxygen concentration are obtained. Flow alternately.

At least the wake of a cylinder operating in the stoichiometric air-fuel ratio or fuel-rich state is provided with an ammonia generating catalyst. When the number of cylinders is variably controlled, an ammonia generation catalyst may be provided downstream of a cylinder that operates alternately between a stoichiometric air-fuel ratio or a fuel rich state and a lean combustion state.

Although the NOx purification mechanism according to the present invention is not always clear, it is estimated that the NOx purification mechanism is mainly based on the equations (1)-(7).

2NO + 5H2 → 2NH3 + 2H2O (1) 4NH3 + 4NO + O2 → 4N2 + 6H2O (2) 8NH3 + 6NO2 → 7N2 + 12H2O (3) NOx + NOx trapping agent → NOx (trapping) (4) (NOx (Capture): NOx is captured by the NOx capture material) NOx (Capture) + HC, CO, H2, NH3 → N2 + CO2 + H2O (5) NOx + HC, CO, H2 → N2 + CO2 + H2O ( 6) NH3 + 1.25O2 → NO + 1.5H2O (7a) NH3 + 1.75O2 → NO2 + 1.5H2O (7a)

Exhaust gas from a cylinder operating in a stoichiometric air-fuel ratio or in a fuel-rich state contains less coexisting oxygen than hydrocarbons, carbon monoxide, and H ₂ , and is therefore an ammonia-producing catalyst. An NH ₃ conversion reaction occurs.

The generated NH ₃ merges with the exhaust gas of another cylinder at the junction.

When the stoichiometric air-fuel ratio or the fuel-rich state and the lean-burn state alternately perform the stoichiometric air-fuel ratio or the fuel-rich state and the lean-burn state alternately, the ammonia denitration catalyst is used when the cylinder is the lean-burn state. NOx reduction represented by the equations (2) to (3) occurs. NOx not reacted by the ammonia denitration catalyst is captured by the NOx purification catalyst.
(Equation (4)). Alternatively, it is reduced in the NOx purification catalyst
(Equation (5)).

Unreacted NH3 is oxidized by the NOx purifying catalyst.
(Equations (7a) and (7b)), and at least a portion is purified.

Here, the state of the trapped NOx includes at least one of adsorption and absorption.

When the cylinders performing the stoichiometric air-fuel ratio or the fuel-rich state and the lean-burn state alternately have the stoichiometric air-fuel ratio or the fuel-rich state, the trapped NOx is the coexisting HC in the exhaust gas,
CO, H ₂ , and NH are reduced with a reducing agent in _three buildings (Equation (5)).
NOx in the exhaust gas is also reduced by the reducing agent (formula
(6)). According to the above method, high NOx purification performance can be obtained in a wide temperature range.

Here, if a NOx purifying catalyst is provided upstream of the ammonia denitration catalyst, the cylinder which alternately performs the stoichiometric air-fuel ratio or the fuel rich state and the lean combustion state will not react with the coexisting oxygen in the lean combustion state. Oxidation reaction of NH ₃
(Equations (7a) and (7b)) proceed on the NOx purification catalyst. result,
There is a shortage of NH ₃ required to reduce NOx (Equations (2)-(3)) with the ammonia denitration catalyst. Therefore, it is not preferable in principle that the NOx purification catalyst is provided upstream of the ammonia denitration catalyst.

Further, NOx is added downstream of the ammonia denitration catalyst.
The method of arranging the purification catalyst is NOx with ammonia denitration catalyst.
Unreacted NH ₃ not involved in the purification may flow into the NOx purification catalyst. When a large amount of NH ₃ is present in the exhaust gas, the NOx purifying catalyst inhibits the NOx trapping reaction (formula (4)). NH ₃ is suppressed adsorption to NOx scavenging reaction in the NOx purification catalyst (equation (4)), NOx purification performance is decreased. Further, NH ₃ is oxidized on the NOx purification catalyst (formula (7)
a), (7b)), the amount of NOx to be captured by the NOx purification catalyst increases, and the NOx purification performance decreases. These synergistic effects are N
It is presumed to be the cause of the decrease in Ox purification performance.

Therefore, it is desirable that NH ₃ be minimized in the exhaust gas contacting the NOx purification catalyst.

In the present invention, it is desirable to coat an ammonia denitration catalyst layer on the ammonia oxidation catalyst layer.

It is also desirable to coat an ammonia oxidation catalyst layer on the upper layer of the NOx purification catalyst and coat an ammonia denitration catalyst layer on the upper layer of the ammonia oxidation catalyst layer.

As a result, space can be saved.

Ammonia generation catalyst, ammonia denitration catalyst, ammonia oxidation catalyst, lean NOx trapping catalyst, NO
As the method for preparing the x purification catalyst and the lean NOx reduction catalyst, any of an impregnation method, a kneading method, a coprecipitation method, and a sol-gel method can be applied.

Generally, exhaust gas purifying catalysts are often used as honeycomb catalysts. When preparing a honeycomb catalyst by the impregnation method for the catalyst of the present invention, first, a porous carrier is coated on the honeycomb. Next, it is desirable that the active metal-containing solution be dipped in the porous carrier-coated honeycomb, dried and fired. When a honeycomb catalyst is prepared by a kneading method, the porous carrier and the active metal-containing solution are wet-kneaded, and then dried and calcined to obtain an active metal-containing catalyst powder. A honeycomb catalyst is obtained by coating this catalyst powder on a honeycomb.

Specific examples of the catalyst material suitable for the present invention are described below.

The ammonia producing catalyst is composed of a porous carrier, P
It is desirable to include at least one selected from t, Pd, Rh, and Ru. It is also possible to use a commercially available three-way catalyst or a precatalyst for removing hydrocarbons at the time of starting the engine.

The ammonia denitration catalyst is made of TiO2 as a material whose optimal temperature range for NOx purification is 100 to 300 ° C.
-Cr2O3, TiO2-MnOx, TiO2-CoO and the like. In addition, TiO2-WO3, TiO2-SnO2, TiO2-Ni are used as materials whose optimum temperature range for NOx purification is 300 to 500C.
O, TiO2-CeO2, TiO2-Fe2O3, TiO2-Fe2O3-MoO3, T
iO2-MoO3 and others.

The ammonia oxidation catalyst comprises a porous carrier, A
It is desirable to have at least one selected from g, Fe, Ni, Cu, and Co.

The NOx purification catalyst comprises a porous carrier, an alkali metal (Li, Na, K, Rb, Cs) and an alkaline earth metal (Mg, C
It is desirable to have at least one selected from a, Sr, and Ba) and a noble metal. Preferably, at least one selected from Ti, Zr and Si, and Ce or La as a rare earth metal
At least one selected from the group consisting of: NOx is composed of alkali metals (Li, Na, K, Rb, Cs) and alkaline earth metals (Mg, C
a, Sr, Ba) selected from at least one or alkali metals (Li, Na, K, Rb, Cs) and alkaline earth metals (Mg, Ca,
It is captured by a composite oxide of at least one selected from Sr and Ba) and at least one selected from Ti, Zr and Si.

When the present invention is applied to an internal combustion engine that can perform only lean operation but cannot perform rich operation, a reducing agent is added to the exhaust gas flowing into the ammonia generation catalyst from the outside to make the air-fuel ratio of the exhaust gas rich or stoichiometric. Is desirable.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.

[0056]

Embodiment 1 FIG. 1 shows an example of a schematic configuration diagram of a combination of an ammonia generation catalyst, an ammonia denitration catalyst, and a NOx purification catalyst. The opening degree of the throttle valves 1 and 2 is determined by the amount of depression of the accelerator pedal by the driver, and also determines the amount of air that enters the cylinder 5-8 of the internal combustion engine. Each cylinder and throttle valve are controlled by an engine control unit 19. Although not shown in the cylinders 5-8, an injector that injects fuel having an air-fuel ratio of a fixed value with respect to the air amount for each cylinder, an ignition plug that ignites an air-fuel mixture and explodes. Is provided. The cylinder 5-8
The exhaust manifold 9 between the gas and the exhaust gas merging section 10 is provided with ammonia generation catalysts 11, 20-22. Also, the junction
In the wake of 10, ammonia denitration catalyst 12 and NOx purification catalyst
13 are provided.

In such a configuration, the cylinder 5 operates steadily with the air-fuel ratio at the stoichiometric air-fuel ratio (stoichiometric) or the rich state, and the cylinder 6-8 alternately operates the stoichiometric air-fuel ratio or the fuel-rich state and the lean combustion. It is possible to do.

NOx in the exhaust gas from the stoichiometric or rich operating cylinder is converted to NH ₃ by the ammonia generation catalyst. The generated NH ₃ is mixed with other exhaust gas at the junction.

When the cylinders 6-8 are operating in lean combustion and the air-fuel ratio of the exhaust gas at the junction is lean, part of the NOx in the mixed gas is reduced and purified by the ammonia denitration catalyst 12. NOx unreacted by the ammonia denitration catalyst 12 is NO
It is captured by the x purification catalyst 13.

When the cylinder 6-8 switches to the stoichiometric air-fuel ratio or the fuel rich state, the NOx trapped by the NOx purifying catalyst 13
x is reduced and purified hydrocarbon in the exhaust gas, carbon monoxide, by a reducing agent such as H2, NH _3.

Incidentally, an ammonia denitration catalyst layer may be coated on the NOx purification catalyst layer to be integrated.

[0062]

Second Embodiment FIG. 2 shows an example of a configuration in which an ammonia oxidation catalyst 15 is provided between an ammonia denitration catalyst 12 and a NOx purification catalyst 13.

The NH ₃ discharged without being used for NOx reduction in the ammonia denitration catalyst 12 is oxidized by the ammonia oxidation catalyst 15.

It is to be noted that a multi-layer coated catalyst in which an ammonia denitration catalyst layer is coated on the ammonia oxidation catalyst layer may be used.

Alternatively, a multi-layer catalyst may be used in which an ammonia oxidation catalyst layer is coated on the NOx purification catalyst layer and an ammonia denitration catalyst layer is further coated on the ammonia oxidation catalyst layer.

[0066]

Third Embodiment FIG. 3 shows an example of a system in which a catalyst temperature sensor 18 is installed in front of an ammonia denitration catalyst 12. The cylinder 5 is constantly operated in a fuel-rich state. The cylinders 6-8 are operated in the fuel rich state and the lean burn state at the same cycle for each cylinder. A map of the NOx purification rate of the ammonia denitration catalyst 12 with respect to the exhaust gas temperature is input to the engine control unit 19. Figure 4 shows the ammonia denitration catalyst and N
It is an example of each NOx purification rate with respect to exhaust gas temperature of an Ox purification catalyst. Below the temperature T1 [° C.], the NOx purification rate of the ammonia denitration catalyst becomes less than X1 [%].

The exhaust gas temperature T is measured by the catalyst temperature sensor 18, and the NOx purification rate X of the ammonia denitration catalyst 12 is estimated by the engine control unit 19. When the engine control unit 19 determines that the estimated value is less than X1, the throttle valve 1 is throttled to reduce the amount of air flowing into the cylinder 5. The flow rate of the exhaust gas flowing into the ammonia generation catalyst 11 decreases, and the NH ₃ concentration at the junction 10 decreases.
As a result, unreacted NH discharged from the ammonia denitration catalyst 12
₃ is reduced, and a decrease in the NOx purification rate of the NOx purification catalyst 13 is suppressed.

[0068]

Embodiment 4 FIG. 5 is a schematic diagram showing a system configuration for controlling the air-fuel ratio and the air amount of all cylinders. FIG. 6 shows an example of a map of the NOx purification rate X with respect to the exhaust gas temperature T of the ammonia denitration catalyst and the number N of cylinders operated with fuel rich. When the NOx purification rate X is less than X1, the number N of cylinders that perform steady operation with fuel rich is N0
Becomes On the other hand, when the NOx purification rate X is equal to or more than X1, the number N of cylinders that perform steady operation with fuel rich becomes N1. Where N0 <N1
And N1 is 1 or more. Here, suppose N0 is 0, N1
Is set to 1. The map of FIG. 6 is programmed in the engine control unit 19 in advance.

The exhaust gas temperature T at the junction 10 is measured by the catalyst temperature sensor 18. Engine control unit 19
Then, the NOx purification rate X of the ammonia denitration catalyst 12 is estimated.
When the engine control unit 19 determines that the estimated value is equal to or more than X1, the number N of cylinders operating in fuel rich is set to 1
Is determined. At this time, the cylinder 5 operates only with fuel rich. On the other hand, the cylinders 6-8 perform control capable of switching between a fuel rich state and a lean burn state.

On the other hand, when the exhaust gas temperature T becomes lower than T1, N
The estimated value of the Ox purification rate is X1, and the number N of cylinders operating in fuel rich is determined to be zero. At this time, the engine control unit 19 switches the control of the cylinder 5 to the same control as that of the cylinder 6-8. As a result, all cylinders are controlled to be able to switch between the fuel rich state and the lean combustion state.

In the lean combustion state, NH ₃ is not generated by the ammonia generation catalyst 11, and no NH ₃ is present at the junction 10. As a result, a decrease in the NOx purification rate of the NOx purification catalyst 13 due to NH ₃ is prevented.

The following is an example of a method for switching the cylinder 5-8 between the fuel rich state and the lean combustion state.

When the NOx purifying catalyst 13 has a NOx trapping function, the engine control unit 19 estimates the trapped NOx amount in the lean burn state, and the NOx purifier estimates the purifying amount of the trapped NOx in the rich state. It has a quantity estimator.

The NOx trapping amount estimating unit is configured to convert the NOx amount in the merging unit 10 estimated from the exhaust gas temperature T, the intake air amount of each cylinder and the air-fuel ratio into NOx to be purified by the ammonia catalyst 12.
By subtracting the amount, the amount of NOx flowing into the NOx purification catalyst 13 is estimated, and the time change of the amount of NOx captured by the NOx purification catalyst 13 is estimated.

When the NOx trapping amount estimating section determines that the NOx trapping amount exceeds the allowable NOx trapping amount of the NOx purifying catalyst 13 (set to be equal to or less than the maximum value of the NOx trapping amount), the air-fuel ratio of the cylinder 5-8 is switched to rich.

Next, the NOx purification amount estimating unit estimates a time required for purifying trapped NOx (hereinafter, rich time) from the rich air-fuel ratio, the air amount, and the exhaust gas temperature.

Then, the engine control unit 19
Determines that cylinders 5-8 have been operated during the rich time,
Return the air-fuel ratio of cylinders 5-8 to lean burn.

With the above-described system, high NOx purification performance can be maintained in a wide temperature range by the synergistic effect of the ammonia denitration catalyst 12 and the NOx purification catalyst 13.

[0079]

Example 5 The generation of NH ₃ from NOx in fuel-rich exhaust gas was confirmed using a Pd / Al 2 O 3 catalyst as an ammonia generation catalyst.

The method for preparing the catalyst is as follows.

A slurry made of alumina powder and an alumina precursor and adjusted to be nitric acid was coated on a cordierite honeycomb (400 cells / inc2), dried and fired, and the honeycomb had an apparent volume of 190 g per liter.
To obtain an alumina-coated honeycomb coated with alumina. The alumina coated honeycomb was impregnated with an aqueous solution of Pd nitrate, dried at 200 ° C.,
Baking at 0 ° C.

As described above, for 190 g of alumina,
Example catalyst 1 containing 2 g of Pd in terms of metal was obtained.

Test Example 1 Using a model gas simulating a rich or stoichiometric exhaust gas, the ammonia production rate of Example Catalyst 1 was evaluated.

The composition of the model gas of the stoichiometric exhaust gas is N
Ox: 1000ppm, C3H6: 600ppm, CO: 0.5%, CO2: 5%, O2:
0.5%, H2: 0.3%, H2O: 10%, N2: balance.

The composition of the model gas of the rich exhaust gas is NO
x: 750ppm, C3H6: 580ppm, CO: 3.5%, CO2: 5%, O2: 0.
3%, H2: 0.5%, H2O: 10%, N2: balance.

The catalyst volume was 6 cc and the SV was 30,000 /
h. Reduce the reaction temperature stepwise from 500 ° C to NO
The NH ₃ conversion of x was measured.

The NH ₃ generation rate was defined as a point at which the NH ₃ generation rate became stable after flowing the model gas composition at a predetermined temperature. Here, the NH ₃ generation rate follows equation (8).

[0088]

(Test Results) The test results are shown in Table 1. It was confirmed that most of the NOx was NH _{3 in the} stoichiometric and rich states.

[0090]

[Table 1]

[0091]

Example 6 (1) An ammonia denitration catalyst was obtained by the following preparation method.

The ammonium metatungstate solution was added to the titania powder at a W-Ti molar ratio of 1/9 and kneaded. The kneaded material is dried at 150 ° C.
Calcination at 0 ° C. yielded a W—Ti catalyst powder. A titania sol was added to the catalyst powder to obtain a coating slurry. Using this coating slurry, a cordierite honeycomb (400 cells / inc2) was coated with 360 g of catalyst powder per liter of apparent honeycomb volume. The firing temperature during coating was 600 ° C.

The catalyst thus obtained is referred to as Example Catalyst 2.

(2) A NOx purification catalyst was obtained by the following preparation method.

A slurry made of alumina powder and alumina precursor and adjusted to be nitric acid was coated on a cordierite honeycomb (400 cells / inc2), dried and fired, and the honeycomb had an apparent volume of 190 g per liter.
To obtain an alumina-coated honeycomb coated with alumina. The alumina coated honeycomb was impregnated with Ce nitrate dissolved in water, dried at 200 ° C., and then fired at 600 ° C.

Next, a dinitrodiammine Pt nitric acid solution,
After impregnating with a nitric acid Rh solution, an aqueous solution containing Na nitrate, Mg nitrate and titania sol, drying at 200 ° C.
Fired at ℃.

As described above, for 190 g of alumina,
18.5 g of Na, 4 g of Ti, 1.8 g of Mg, R
Example catalyst 3 was obtained, which contained 0.14 g of Pt, 2.8 g of Pt, 2.1 g of Mg, and 27 g of Ce.

(3) An ammonia oxidation catalyst was prepared by the following method.

After impregnating the alumina-coated honeycomb prepared in the same manner as (2) with an aqueous solution in which Ag nitrate was dissolved,
Drying at 0 ° C. followed by firing at 600 ° C. From the above,
Example Catalyst 4 was obtained, containing 190 g of alumina and 30 g of Ag in terms of metal.

(Test Example 2) Regarding the ammonia denitration catalyst,
The NOx purification performance when NH ₃ was added to the lean combustion exhaust gas was examined.

For the test, a model gas obtained by adding 0 to 705 ppm of NH ₃ to a model gas simulating a lean combustion exhaust gas was used.

The composition of the gas used in the test was NH3: 705-0 pp
m, NOx: 600ppm, C3H6: 500ppm, CO: 0.1%, CO2: 10%,
O2: 5%, H2O: 10%, N2: balance.

The catalyst volume was 6 cc and the SV was 30,000 /
H. Reduce the reaction temperature stepwise from 550 ° C to NO
x The purification performance was measured.

The NOx purification rate was defined as a point at which the NOx purification rate became stable after flowing the oxidizing atmosphere model gas composition at a predetermined temperature. Here, the NOx purification rate follows equation (9).

[0105]

(Test Results) Table 2 shows the measurement results of the NOx purification rates from 550 ° C. to 300 ° C. The catalyst 2 of the present invention was used in an automobile exhaust gas in an oxidizing atmosphere of 350 ° C. or more in NH 4
It is clear that the addition of ₃ has high NOx steady reduction performance.

Further, in order to obtain a NOx purification rate of 50% or more in the region of 400 to 550 ° C., the NH ₃ / NO ratio is preferably set to 0.9 or more.

[0108]

[Table 2]

(Test Example 3) Regarding the ammonia denitration catalyst,
The stoichiometric air-fuel ratio or the NOx purification performance when NH ₃ coexists in the exhaust gas when fuel-rich combustion and lean combustion are alternately repeated was studied.

(Test method) In Example 2, NH _{3 was used.}
The purification performance of NOx was studied using lean exhaust gas and rich exhaust gas to which NO was added.

The composition of the lean model gas is NH3: 705 ppm,
NOx: 600ppm, C3H6: 500ppm, CO: 0.1%, CO2: 10%, O
2: 5%, H2O: 10%, N2: balance.

The composition of the rich model gas is NH3: 705 ppm
, NOx: 1000ppm, C3H6: 600ppm, CO: 0.5%, CO2: 5%, O
2: 0.5%, H2: 0.3%, H2O: 10%, N2: balance.

The NOx purification rate was measured by performing a test in which a rich model gas and a lean model gas alternately flow through the catalyst layer every three minutes (hereinafter, a repeated test). The catalyst volume was 6 cc and the SV was 30,000 / h. The NOx purification performance was measured at a reaction temperature of 500 ° C. NO
x The purification rate follows equation (9).

(Test Results) Table 3 shows the test results. The catalyst 2 of the embodiment has a lean model gas NOx purification rate of 1 to 3.
85% in minutes. The NOx purification rate with the rich model gas was 65% in 1 to 3 minutes. These NOx purification rates repeat lean and rich 10 times.
It did not change even if I went there.

[0115]

[Table 3]

Test Example 4 According to Test Example 2, the catalyst of Example 2 was used.
NH _{3 in} the gas after the circulation was measured.

(Test Results) The results are shown in Table 4. NH ₃ was not completely consumed in Example Catalyst 2.

[0118]

[Table 4]

Test Example 5 Example Catalyst 2
4 was installed. The catalyst volume of the example catalyst was 6 cc.
In the same manner as in Test Example 4, Example Catalyst 4, and Example Catalyst
The NOx purification rate, HC purification rate, CO purification rate, and NH ₃ concentration of the combination of Example 2 and Example Catalyst 4 were measured. The NH ₃ concentration in the model gas was 705 ppm.

(Test Results) The results are shown in Table 5. NOx, H by the combination of Example Catalyst 2 and Example Catalyst 4
C and CO purification and suppression of unreacted NH ₃ release can be prevented.

[0121]

[Table 5]

[0122]

Example 7 Example catalyst 2 was installed upstream, and example catalyst 3 was installed downstream. Each catalyst volume was 6 cc.
In the same manner as in Test Example 3, the NOx purification rate, the HC purification rate, the CO purification rate, and the NH ₃ concentration of the combination of Example Catalyst 2 and Example Catalyst 3 were measured. The NH ₃ in the model gas
The concentration was 705 ppm. Further, each purification rate was one minute after the lean switching. The results are shown in Table 6. By combining the example catalyst 2 and the example catalyst 3, higher NOx, HC, and CO purification performance can be obtained in a lean state than when the example catalyst 2 or the example catalyst 3 is used alone. Further, even in the rich case, the catalysts of Example 2 and Example 3 were used.
The NOx purification rate of the combination of the above was 95% or more.
Further, by combining Example Catalyst 2 and Example Catalyst 3, unreacted NH ₃ could be removed. From the above, it is clear that high NOx purification performance and HC and CO purification performance can be obtained by combining the example catalyst 2 and the example catalyst 3.

[0123]

[Table 6]

[0124]

Example 8 (Test Example 6) Catalyst 3 (catalyst volume: 6 cc) was fired at 800 ° C. for 5 hours, and the NOx purification rate was measured in the same manner as in Test Example 3. However, the NH ₃ concentration and the NOx concentration in the lean model gas were changed. Each purification rate was one minute after the oxidizing atmosphere was switched.

(Test Results) The results are shown in Table 7. If NH ₃ concentration is higher than 35 ppm, compared to the case of adding the same amount of NOx and NH3, NOx purification rate was lower. On the other hand, when the NH ₃ addition concentration was 35 ppm or less, the NOx purification rate was almost equal to the case where the same amount of NOx as NH ₃ was added. Therefore, in order to increase the NOx purification performance by the combination of the example catalyst 3 and the example catalyst 2, it is necessary to reduce the amount of unreacted NH ₃ from the example catalyst 2 to 35 ppm or less.

[0126]

[Table 7]

[0127]

Example 9 A method was described in which Example Catalyst 4 was installed downstream of Example Catalyst 2, and Example Catalyst 3 was installed downstream of Example Catalyst 4.

(Test Example 7) Example catalyst 4 was installed, and
The NOx, HC, and CO purification rates were measured in the same manner as described above.

(Test Results) Table 8 shows the purification rates after three minutes of switching each reaction gas at a reaction temperature of 500 ° C. The catalyst of Example 4 did not completely purify HC and CO in a rich condition. The example catalyst 3 serving as the NOx purification catalyst richly reduces and removes NOx trapped in the lean state. Therefore,
When HC and CO are completely removed by the example catalyst 4 in the rich condition, it is impossible to reduce and remove the trapped NOx of the example catalyst 3. However, from the results of this test, it is clear that even if the example catalyst 4 is provided before the example catalyst 3, the NOx trapped by the example catalyst 3 in a rich state can be reduced and removed.

[0130]

[Table 8]

Test Example 8 Example Catalyst 2
4 and the example catalyst 3 was further installed downstream of the example catalyst 4. The volume of each example catalyst was 6 cc. Test example
In the same manner as in 3, the NOx, HC, and CO purification rates were measured. The reaction temperature was 300, 400, 500 ° C.

(Test Results) The results are shown in Table 9. 500 of the combination of Example Catalyst 2, Example Catalyst 4 and Example Catalyst 3
The NOx purification rate at 75 ° C. was 75%.
The NOx purification performance was improved by the combination of (Example 65) and Example Catalyst 3 (65%). The cause of the improvement of the NOx purification rate is that unreacted NH ₃ does not exist after the catalyst 4 of the embodiment (Example 14 test example)
It is thought to be due to 1).

Further, the NOx purification rate in a reducing atmosphere was 95% or more. Furthermore, in all the combinations of the catalysts, unreacted NH ₃ was not detected from the gas after the second-stage flow. This performance was reproduced no matter how many times the oxidizing atmosphere and the reducing atmosphere were repeated.

From the above, the ammonia denitration catalyst (Example catalyst 2), the ammonia oxidation catalyst (Example catalyst 4) and the NO
By using a combination of x purification catalyst (Example catalyst 3),
It is clear that excellent NOx, HC and CO purification performances are compatible.

[0135]

[Table 9]

(Test Example 9) In the same manner as in Test Example 2, the steady-state value of the lean NOx purification rate was measured.

(Test Results) The results are shown in Table 10. The combination of Example Catalyst 2, Example Catalyst 4, and Example Catalyst 3 was superior to Example Catalyst 3 in the steady-state NOx purification rate.

[0138]

[Table 10]

From the above, it was found that Example Catalyst 2 and Example Catalyst 2
The combination of 4 and Example Catalyst 3 is an ammonia denitration catalyst
The functions of the (Example catalyst 2) and the NOx purification catalyst (Example catalyst 3) are not simply added, but the ammonia oxidation catalyst
It is clear that the combination with (Example Catalyst 4) has excellent NOx purification performance.

[0140]

Example 10 An ammonium metatungstate solution was added to and mixed with titania powder at a molar ratio of W / Ti of 1/9. The kneaded material is dried at 150 ° C.
Calcination at 00 ° C. gave a W-Ti catalyst powder. This WT
Example catalyst 5 was obtained by coating Example catalyst 3 with i catalyst powder at 100 g / L. The NH ₃ concentration was 705 ppm.

In the same manner as in Test Example 3, the N
The Ox purification rate was measured. NOx purification rate at 500 ° C is 70
%.

[0142]

Example 11 An ammonium metatungstate solution was added to titania powder at a W / Ti molar ratio of 1/9 and kneaded. The kneaded material is dried at 150 ° C.
Calcination at 00 ° C. gave a W-Ti catalyst powder.

This W—Ti catalyst powder was added to Example Catalyst 4 as 1
Example catalyst 6 coated with 00 g / L was obtained.

Example catalyst 3 (catalyst volume 6 cc) was installed downstream of example catalyst 6 (catalyst volume 6 cc), and the NOx purification rate was measured in the same manner as in Test Example 3. NH ₃ concentration 705pp
m.

The NOx purification rate at 500 ° C. by the combination of Example Catalyst 6 and Example Catalyst 3 was 73%.

[0146]

Example 12 An ammonium metatungstate solution was added to titania powder at a molar ratio of W / Ti of 1/9 and kneaded. The kneaded material is dried at 150 ° C.
Calcination at 00 ° C. gave a W-Ti catalyst powder.

A Ag nitrate solution was added to the alumina powder and kneaded. The kneaded product was dried at 150 ° C. and subsequently calcined at 600 ° C. to obtain an Ag catalyst powder having 30 parts by weight of Ag supported on both parts of 100 parts of alumina.

In the same manner as in Example 5, a cordierite honeycomb was coated with 150 g of alumina / L, and 18.5 g of Na, 8.5 g of Ti, 4 g of M
g 1.8 g, Rh 0.14 g, Pt 2.8 g, Mg 2.1 g, Ce27
Example catalyst 7 containing g was prepared.

This Ag catalyst powder was added to Example Catalyst 7 in an amount of 50 g /
L coated. Further, Example Catalyst 8 was obtained in which W-Ti catalyst powder was coated at 100 g / L on the Ag catalyst powder coating layer.

In the same manner as in Test Example 3, the N
The Ox purification rate was measured. The NH ₃ concentration was 705 ppm.

The NOx purification rate at 500 ° C. of Example Catalyst 8 was 72%.

[0152]

[Embodiment 13] FIG. 7 shows an embodiment in which an ammonia generation catalyst 20 is provided downstream of the junction 101 of the cylinders 6-7 in the first embodiment. At the downstream side of the ammonia generation catalyst 20, there is provided a merging section 10 which merges with the exhaust gas of the cylinder 5.

By managing the cylinders 6-8 as one group, the number of ammonia producing catalysts can be reduced.

[0154]

Embodiment 14 FIG. 8 shows an example in which an ammonia generation catalyst is not provided downstream of the junction 101 of the cylinders 6-8, and an oxygen concentration sensor 23 is provided upstream of the NOx purification catalyst 13. Note that cylinders 6-8
The merged exhaust gas and the exhaust gas of the cylinder 5 merge at the merge section 10.

The oxygen concentration sensor 23 measures the oxygen concentration of the exhaust gas after the ammonia denitration, and the air-fuel ratio of the exhaust gas is estimated by the engine control unit 19.

The air-fuel ratio of cylinders 5-8 and the amount of intake air are controlled by the engine control unit so that the air-fuel ratio at the junction 10 alternates between lean and rich or stoichiometric.
Controlled at 19.

As a modification of FIG. 8, the NOx purifying catalyst 13 can be replaced with a lean NOx trapping catalyst or a lean NOx reducing catalyst, and the air-fuel ratio of the exhaust gas flowing into these catalysts can be made lean.

Since most of NOx in the lean exhaust gas is purified by the ammonia denitration catalyst, the concentration of NOx flowing into the lean NOx trapping catalyst or the lean NOx reduction catalyst is low. Therefore, NOx can be sufficiently captured or purified by the lean NOx trapping catalyst or the lean NOx reduction catalyst.

[0159]

According to the present invention, high lean NOx purification performance can be obtained. Further, high NOx purification performance can be obtained in a wide temperature range.

[Brief description of the drawings]

FIG. 1 shows an ammonia generation catalyst, an ammonia denitration catalyst, and N
FIG. 1 is a system diagram using an Ox purification catalyst.

FIG. 2 is a system diagram using an ammonia generation catalyst, an ammonia denitration catalyst, an ammonia oxidation catalyst, and a NOx purification catalyst.

FIG. 3 is a system diagram using control by a temperature sensor.

FIG. 4 is a schematic diagram of a NOx purification rate depending on the temperature of an ammonia oxidation catalyst.

FIG. 5 is a system diagram for controlling the air-fuel ratio and the air amount of all cylinders.

FIG. 6 is a schematic diagram showing the NOx purification rate depending on the temperature of the ammonia oxidation catalyst and the number of cylinders operated in a fuel-rich state.

FIG. 7 is a system diagram in which an ammonia generation catalyst is provided at a junction of cylinders 6-7 in FIG. 1;

FIG. 8 shows an oxygen concentration sensor 23 upstream of the NOx purification catalyst 13.
System diagram provided with.

[Explanation of symbols]

1, 2, 23, 24 ... throttle valve, 3, 4, 2
5, 26 ... intake manifold, 5-8 ... cylinder, 9 ...
Exhaust manifold, 10, 101 ... junction, 11, 2
0 to 22: ammonia generating catalyst, 12: ammonia denitration catalyst, 13: NOx purification catalyst, 14: catalyst in which an ammonia denitration catalyst and a lean NOx trapping catalyst are integrated,
15: Ammonia oxidation catalyst, 16: Catalyst integrating ammonia denitration catalyst and ammonia oxidation catalyst, 17: Ammonia denitration catalyst, ammonia oxidation catalyst, lean NOx
Catalyst integrated with trapping catalyst, 18… Temperature sensor, 1
9 ... Engine control unit.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02D 41/04 305 F02D 41/04 305Z 43/00 301 43/00 301E 301T (72) Inventor Masato Kaneda Hitachi City, Ibaraki Prefecture 7-2-1 Omikacho, Hitachi, Ltd. Power and Electricity Development Laboratory (72) Inventor Shosei Nagayama 7-2-1, Omikamachi, Hitachi, Ibaraki Pref., Hitachi Electric Power and Electricity Development Laboratory (72) Inventor Toshio Yamashita 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Electric Power & Electric Research Laboratory, Hitachi, Ltd. (72) Inventor Osamu Kuroda Hitachi, Ltd. 2520 Odaiba, Hitachinaka City, Ibaraki Prefecture Hitachi, Ltd. (72) Inventor Yuichi Kitahara 2520 Oji Takaba, Hitachinaka-shi, Ibaraki F-term in Hitachi Automotive Equipment Group (reference) 3G084 AA03 AA04 BA05 BA09 BA13 BA24 DA10 DA27 EA11 EB01 FA10 FA27 3G091 AA0 2 AA12 AA13 AA17 AA24 AA28 AB01 AB02 AB03 AB04 AB05 BA14 BA31 BA33 CA17 CB02 CB06 CB07 DA01 DA02 DB06 DB10 DB13 EA07 EA17 EA18 EA30 FB10 FB11 FB12 FC02 GA06 GA16 GB01 HA GB HA GB HA HA GB GBW GB03 GB10 GB03 HA37 3G301 HA01 HA04 HA06 HA07 HA15 HA18 JA15 JA25 JA33 JB09 LA03 LB04 MA01 MA11 NA06 NA08 NA09 NC01 NC02 NE01 NE06 NE13 NE14 NE15 PD11B PD11Z PD12B PD12Z PF03B PF03Z

Claims (20)

[Claims] In the method for purifying exhaust gas of an internal combustion engine, when the oxygen concentration of the ammonia denitration catalyst and the exhaust gas flowing into the exhaust gas passage is higher than the oxygen concentration required for completely oxidizing the coexisting reducing agent. A lean NOx trapping catalyst for trapping NOx in the exhaust gas is provided, and ammonia is contained in the exhaust gas in a state where the oxygen concentration is higher than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent, and the ammonia flows into the ammonia denitration catalyst. Exhaust gas, after purifying at least a part of NOx in exhaust gas, and then flowing the lean NOx into a lean NOx trapping catalyst. 2. An exhaust gas purifying method for an internal combustion engine, comprising the steps of: providing an ammonia denitration catalyst in an exhaust gas passage and an oxygen concentration of an inflowing exhaust gas higher than an oxygen concentration required for completely oxidizing a coexisting reducing agent; A lean NOx reduction catalyst that reduces NOx in the exhaust gas is provided, and ammonia is contained in the exhaust gas in a state where the oxygen concentration is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, and the ammonia flows into the ammonia denitration catalyst. An exhaust gas purifying method comprising: purifying at least a part of NOx in exhaust gas, flowing the lean NOx into a lean NOx reduction catalyst, and purifying at least a part of the remaining NOx. 3. An exhaust gas purifying method for an internal combustion engine, wherein the ammonia concentration in the exhaust gas passage is higher than the oxygen concentration required for completely oxidizing the coexisting reducing agent. NOx in the exhaust gas is trapped, and when the oxygen concentration of the inflowing exhaust gas is lower than the oxygen concentration required to completely oxidize the coexisting reducing agent, the NO in the exhaust gas is reduced.
x and a NOx purifying catalyst for reducing the trapped NOx are provided, and the exhaust gas having an oxygen concentration higher than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent contains ammonia and flows into the ammonia denitration catalyst. After purifying at least a portion of the NOx in the exhaust gas, the NOx is flown into the NOx purification catalyst to capture at least a portion of the NOx present in the exhaust gas, and then the oxygen concentration of the exhaust gas flowing at least into the NOx purification catalyst is reduced. An exhaust gas purifying method comprising reducing the trapped NOx and NOx in exhaust gas to an oxygen concentration required to completely oxidize a coexisting reducing agent. 4. A method for purifying exhaust gas discharged from an internal combustion engine having a plurality of cylinders capable of independently controlling the air-fuel ratio, wherein an ammonia generation catalyst is provided in an exhaust gas passage of some of the cylinders. An air-fuel ratio rich or stoichiometric exhaust gas flows into the ammonia generating catalyst to generate ammonia, and a merging section is provided for merging exhaust gases of a plurality of cylinders downstream of the ammonia generating catalyst, and ammonia denitration is provided downstream of the merging section. When the oxygen concentration of the catalyst and the inflowing exhaust gas is higher than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent, the catalyst traps NOx in the exhaust gas and the reducing agent in which the oxygen concentration of the inflowing exhaust gas coexists NOx in the exhaust gas and the trapped NOx when the oxygen concentration is lower than the oxygen concentration necessary to completely oxidize
After providing a NOx purification catalyst for reducing NOx, making the air-fuel ratio of the exhaust gas at the confluence part lean, and flowing it into the ammonia denitration catalyst to purify at least a part of NOx in the exhaust gas,
At least a part of the NOx is trapped by flowing into the NOx purification catalyst, and then the air-fuel ratio of the exhaust gas at the junction is made rich or stoichiometric, and the NOx in the trapped NOx and the exhaust gas is reduced.
A method for purifying exhaust gas of an internal combustion engine, comprising purifying exhaust gas. 5. A method for purifying exhaust gas discharged from an internal combustion engine having a plurality of cylinders capable of independently controlling the air-fuel ratio. When the air-fuel ratio of a cylinder is rich or stoichiometric, the air-fuel ratio of the other cylinders is made lean, and a merging section is provided for merging exhaust gases of a plurality of cylinders with the downstream of the ammonia generation catalyst. When the oxygen concentration of the ammonia denitration catalyst and the inflowing exhaust gas is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, the NOx in the exhaust gas is captured, and the oxygen concentration of the inflowing exhaust gas coexists. A NOx purification catalyst for reducing the NOx in the exhaust gas and the trapped NOx when the oxygen concentration is lower than the oxygen concentration necessary to completely oxidize the reducing agent to be exhausted. After flowing into the near denitration catalyst and purifying at least a part of NOx in the exhaust gas, it flows into the NOx purifying catalyst to capture at least a part of the NOx, and thereafter, the air-fuel ratio of the exhaust gas at the junction is rich or stoichiometric. And purifying the trapped NOx and NOx in the exhaust gas. 6. The exhaust gas purifying method for an internal combustion engine according to claim 5, wherein the air-fuel ratio of each cylinder is alternately switched between lean and rich or stoichiometric. 7. The lean NOx trapping catalyst, the NOx purifying catalyst, or the lean NOx according to claim 1,
An exhaust gas purifying method for an internal combustion engine, comprising removing at least a part of ammonia contained in the exhaust gas before the exhaust gas flows into the x reduction catalyst. 8. An ammonia oxidation catalyst is provided between an ammonia denitration catalyst and a lean NOx trapping catalyst, a NOx purification catalyst or a lean NOx reduction catalyst, and when exhaust gas flowing into the ammonia oxidation catalyst is lean,
A method for purifying exhaust gas of an internal combustion engine, comprising oxidizing ammonia contained in the exhaust gas. 9. The internal combustion engine according to claim 7, wherein the ammonia concentration in the exhaust gas before the exhaust gas flows into the lean NOx trapping catalyst, the NOx purification catalyst, or the lean NOx reduction catalyst is 35 ppm or less. Exhaust gas purification method. 10. The internal combustion engine according to claim 9, wherein the concentration of unreacted ammonia in the ammonia denitration catalyst is controlled by changing the stoichiometric air-fuel ratio or the amount of air flowing into a cylinder operating in a fuel-rich state. Exhaust gas purification method. 11. An ammonia denitration catalyst, a lean NOx trapping catalyst, a NOx purification catalyst, or a lean NOx reduction catalyst according to any one of claims 1 to 6, wherein the exhaust gas has an air-fuel ratio different in a temperature range capable of purifying lean NOx. An exhaust gas purifying method for an internal combustion engine, comprising: 12. An exhaust gas purifying apparatus for an internal combustion engine, wherein the concentration of oxygen in the exhaust gas passage is higher than the oxygen concentration required for completely oxidizing the coexisting reducing agent, and the NOx in the exhaust gas containing ammonia. An ammonia denitration catalyst for purifying at least a portion is provided, and when the oxygen concentration of the inflowing exhaust gas is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, the NOx in the exhaust gas is captured in the subsequent stream. An exhaust gas purifying apparatus for an internal combustion engine, comprising a lean NOx trapping catalyst. 13. An exhaust gas purifying apparatus for an internal combustion engine, wherein the oxygen concentration in the exhaust gas passage is higher than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent and the NOx in the exhaust gas containing ammonia. An ammonia denitration catalyst for purifying at least a portion is provided, and when the oxygen concentration of the inflowing exhaust gas is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, NOx in the exhaust gas is reduced. An exhaust gas purifying apparatus for an internal combustion engine, comprising a lean NOx reduction catalyst. 14. An exhaust gas purifying apparatus for an internal combustion engine, wherein the oxygen concentration in the exhaust gas passage is higher than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent, and the NOx concentration in the exhaust gas containing ammonia is reduced. An ammonia denitration catalyst for purifying at least a portion is provided, and when the oxygen concentration of the inflowing exhaust gas is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, the NOx in the exhaust gas is captured in the subsequent stream. And a NOx purification catalyst for reducing NOx in the exhaust gas and the trapped NOx when the oxygen concentration of the inflowing exhaust gas is equal to or lower than the oxygen concentration necessary for completely oxidizing the coexisting reducing agent. Exhaust gas purification device for an internal combustion engine. 15. An exhaust gas purifying apparatus for exhaust gas discharged from an internal combustion engine having a plurality of cylinders capable of independently controlling the air-fuel ratio, wherein the air-fuel ratio of the exhaust gas flowing into the exhaust gas passage of some of the cylinders is adjusted. An ammonia-generating catalyst for generating ammonia when rich or stoichiometric is provided, and a merging section for merging exhaust gases from a plurality of cylinders is provided downstream of the ammonia-generating catalyst. An ammonia denitration catalyst that is higher than the oxygen concentration necessary to completely oxidize the agent and that purifies at least a part of NOx in the exhaust gas containing ammonia; When the oxygen concentration of the exhaust gas is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, NOx in the exhaust gas is trapped, and the oxygen concentration of the inflowing exhaust gas coexists. That NOx and the capture N of the exhaust gas when the oxygen concentration below that required to completely oxidize the reducing agent
A NOx purification catalyst for reducing Ox is provided, and control means for controlling the air-fuel ratio of each cylinder is provided so that the air-fuel ratio of the exhaust gas at the junction can be alternately switched between lean and rich or stoichiometric. Exhaust gas purification device for an internal combustion engine. 16. An exhaust gas purifying apparatus for exhaust gas discharged from an internal combustion engine having a plurality of cylinders capable of independently controlling the air-fuel ratio, wherein the air-fuel ratio of the exhaust gas flowing into the exhaust gas passage of each cylinder is rich or An ammonia generating catalyst for generating ammonia at the time of stoichiometry is provided, and a merging section for merging exhaust gases of a plurality of cylinders is provided downstream of the ammonia generating catalyst, and a reducing agent having an oxygen concentration coexisting is provided downstream of the merging section. An ammonia denitration catalyst that is higher than the oxygen concentration necessary for complete oxidation and that purifies at least a portion of NOx in the exhaust gas containing ammonia is provided. When the concentration is higher than the oxygen concentration required to completely oxidize the coexisting reducing agent, NOx in the exhaust gas is trapped, and the oxygen concentration of the inflowing exhaust gas coexists. NOx and the trapped NOx of the exhaust gas when Motozai oxygen concentration below that required to completely oxidize the
When the air-fuel ratio of some cylinders is rich or stoichiometric, the air-fuel ratio of the other cylinders is lean, and the air-fuel ratio of the exhaust gas at the junction is lean and rich or stoichiometric. An exhaust gas purifying apparatus for an internal combustion engine, further comprising control means for controlling the air-fuel ratio of each cylinder so as to be alternated. 17. An exhaust gas purifying apparatus for an internal combustion engine according to claim 16, wherein said control means has a function of alternately switching the air-fuel ratio of each cylinder between lean and rich or stoichiometric. 18. The method according to claim 12, wherein
An exhaust gas purifying apparatus for an internal combustion engine, comprising: means for removing at least a part of ammonia contained in the exhaust gas before the exhaust gas flows into the lean NOx trapping catalyst, the NOx purification catalyst, or the lean NOx reduction catalyst. . 19. An ammonia gas for oxidizing ammonia contained in exhaust gas between an ammonia denitration catalyst and a lean NOx trapping catalyst, a NOx purifying catalyst, or a lean NOx reduction catalyst when the exhaust gas flows lean. An exhaust gas purifying apparatus for an internal combustion engine, comprising an oxidation catalyst. 20. The method according to claim 18, wherein the lean N
Ox trapping catalyst or NOx purification catalyst or lean NOx
Operate at least rich or stoichiometric based on the ammonia concentration measurement value of the exhaust gas flowing into the lean NOx trapping catalyst or NOx purification catalyst so that the ammonia concentration in the exhaust gas before the exhaust gas flows into the reduction catalyst becomes 35 ppm or less. An exhaust gas purifying apparatus for an internal combustion engine, comprising: control means for controlling the number of cylinders to be operated, the air-fuel ratio, or the amount of air.