JP2000314311A - Exhaust gas emission control method, device and catalyst for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of a repeatedly used a device which reduces and purifies NOx in exhaust gas while bringing a lean air-fuel ratio of exhaust gas and a rich air-fuel ratio of exhaust gas into alternate contact with an NOx purifying catalyst, by using a catalyst showing an absorption spectrum in a caught condition of NO2. SOLUTION: This internal combustion engine is operated such that an exhaust gas atmosphere is alternately subjected to an oxidized atmosphere and a reduced atmosphere, and NOx in exhaust gas is purified by an NOx purifying catalyst 18. In such an exhaust gas emission control method, a catalyst for showing the absorption spectrum of a captured condition of NO2 is used, when an NOx catching condition is measured by an infrared absorption spectrum (FT-IR). The NOx is captured on an NOx catching material surface as NO2, without taking NOx in the NOx catching material as a nitric acid compound. As a catalyst for use, a noble metal and a material having an NOx capturing material including alkali metal or alkali earth metal are preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying nitrogen oxides discharged from an internal combustion engine of an automobile or the like, a purifying catalyst and a purifying apparatus, and in particular, to a lean burn of fuel (lean burn).
The present invention relates to an internal combustion engine capable of reducing pressure, a method for purifying nitrogen oxides emitted from an automobile equipped with the internal combustion engine, a purification catalyst and a purification device.

[0002]

2. Description of the Related Art Conventionally, harmful substances (HC, HC) contained in combustion exhaust gas generally discharged from a gasoline engine for automobiles have been used.
CO, NOx) are purified by an exhaust gas purification system using a three-way catalyst. The system uses a stoichiometric air-fuel ratio for the combustion state of the internal combustion engine, that is, a weight ratio of air (A) and fuel (F), which is not too much or less, (A / F: generally, 14.7) and harmful substances (HC, CO,
NOx) in a three-way catalyst (Pt, Rh, P
(a precious metal such as d) is used for purification.

However, in recent years, various internal combustion engines including automobiles have been required to further reduce harmful substances, reduce fuel consumption, and emit carbon dioxide (CO ₂ ), a kind of global warming gas. Reduction is required. Against this background, lean burn engine systems for burning fuel at a lean air-fuel ratio with respect to air have been developed for automobiles in order to reduce fuel consumption, and have been put to practical use mainly in small cars.

[0004] However, in order to expand and spread the system, it is essential to develop an exhaust gas purification technology, which is another problem. Conventional three-way catalysts emit from lean burn engines
NOx cannot be purified. In other words, the conventional three-way catalyst efficiently reduces and purifies NOx in exhaust gas (hereinafter referred to as a reducing atmosphere) operated at or below the stoichiometric air-fuel ratio to N ₂ , but when the air-fuel ratio becomes higher than the stoichiometric air-fuel ratio. O in exhaust gas
_{2 The} concentration increases (hereinafter, this state is referred to as an oxidizing atmosphere), and the oxidation reaction between HC and CO occurs preferentially.
x cannot be reduced and purified.

[0005] As means for solving this problem, WO93 / 07363 and WO93 / 08383, which have been published internationally under the Patent Cooperation Treaty, propose a method of installing a NOx absorbent in an exhaust gas passage. The NOx absorbent has the ability to absorb NOx in exhaust gas in an oxidizing atmosphere and to release the absorbed NOx when the atmosphere is switched to a reducing atmosphere and the oxygen concentration in the exhaust gas decreases.

However, since the absorption and release of NOx involves a periodic change in the crystal structure of the absorbent, careful consideration must be given to the durability during repeated use.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a method, a catalyst and a purifying apparatus for purifying nitrogen oxides having excellent NOx purifying performance in an oxidizing atmosphere.

[0008]

The present inventors have arranged a nitrogen oxide purifying catalyst in an exhaust gas passage of an internal combustion engine, and alternately repeated the operation in which the exhaust gas atmosphere becomes an oxidizing atmosphere and a reducing atmosphere, thereby reducing the nitrogen in the exhaust gas. In the method of purifying oxides, the present inventors have conducted intensive studies on a method of purifying nitrogen oxides that traps NOx on the catalyst surface in an oxidizing atmosphere, a catalyst, and a purifier.

As a result, they have found that a catalyst containing a component that traps nitrogen oxides as NO ₂ in an oxidizing atmosphere, and a method and a device for purifying nitrogen oxides using the catalyst are effective. The nitrogen oxide trapping material desirably has at least one selected from alkali metals and alkaline earth metals.

In the present invention, since the nitrogen oxide is not taken into the trapping material as a nitric acid compound, a change in the structure of the trapping material can be prevented, and the durability during repeated use is improved. The trapping forms for trapping NOx on the catalyst surface include NO and N
Although there is O ₂ , there are the following advantages by trapping as NO ₂ .

NOx trapped in an oxidizing atmosphere is
By switching the operating state below the stoichiometric air-fuel ratio, HC in the exhaust gas, CO, is reduced and purified by reacting with a reducing agent such as H _2. For example, when CO is used as a reducing agent, the reduction reaction of NO and NO ₂ is represented by Expressions (1) and (2). Since it is difficult to calculate the thermal power of the reduction reaction of trapped NOx, NO, N
It was substituted by the calculation of the thermal power during the reduction reaction of O ₂ gas. An index of the ease of the reduction reaction is obtained from the standard free energy of formation (ΔG). Generally, when ΔG is negatively large, a product is easily obtained. ΔG of NO is -343 kJ / mol-NO, NO ₂
ΔG was -566 kJ / mol-NO ₂ . Therefore, N
It is considered that the one captured as O ₂ is easily reduced.

NO + CO → 0.5N ₂ + CO ₂ ΔG: −343 kJ / mol (1) NO ₂ + 2CO → N ₂ + 2CO ₂ ΔG: −566 kJ / mol (2) When the oxidizing atmosphere and the reducing atmosphere are repeated, NOx is used in the oxidizing atmosphere. Trapping NO as NO ₂ can quickly purify trapped NOx when switching to the reducing atmosphere.

Further, reducing agents such as HC and CO exist in an oxidizing atmosphere. Therefore, in an oxidizing atmosphere, N
When Ox is captured as NO ₂ , the NOx reduction reaction performance in the same atmosphere is excellent.

Further, when the atmosphere is switched to the reducing atmosphere, the amount of NO ₂ captured by the nitrogen oxide capturing material is more likely to react with a reducing agent such as CO than in the case of capturing NO. Therefore, capture N
It is possible to shorten the time of the reducing atmosphere required to remove Ox from the nitrogen oxide trapping material.

From the above, the practical effect of trapping NOx as NO ₂ is that deterioration of fuel efficiency can be suppressed by shortening the reducing atmosphere operation time.

Whether or not the nitrogen oxide purifying catalyst captures NO ₂ is confirmed by infrared absorption spectroscopy (F
T-IR) to measure the NOx trapping form. In the case of trapping NOx as NO ₂ , the infrared absorption spectrum of the trapped NOx does not match the absorption spectrum of nitrate ions, and NO
_This is the same as the infrared absorption spectrum obtained when only ₂ is distributed. Thereby, the nitrogen oxide is not taken in the nitrogen oxide trapping material as a nitric acid compound, and NO ₂
It can be seen that they are trapped on the surface of the nitrogen oxide trapping material.

The FT-IR measurement is performed, for example, as follows. After reducing the nitrogen oxide purifying catalyst at 500 ° C., it is cooled to the reaction temperature without contacting with the atmosphere, and NO and O
While flowing the _two gases, the NOx trapping state is measured by a diffuse reflection type infrared absorption spectrum method. Further, an FT-IR spectrum obtained when only NO ₂ flows at the reaction temperature is measured. Measurement results, if the NO ₂ trapping type NO and O ₂ at a gas flow and NO ₂ at the time of gas flow FT-
Although the IR spectra agree, the FT-IR
Does not match the spectrum. The reaction temperature is desirably 300 ° C. or more and 500 ° C. or less, which is a practical operating temperature range of an automobile.

The nitrogen oxide purifying method using the nitrogen oxide purifying catalyst satisfying the above characteristics satisfies excellent NOx purifying performance and durability.

The present inventors have conducted intensive studies on a catalyst satisfying the above characteristics, and have found that a porous carrier, a nitrogen oxide trapping material containing at least one selected from a noble metal and an alkali metal or an alkaline earth metal are obtained. Has been found to be effective. Noble metals have the function of reducing NOx.

The alkali metal or alkaline earth metal of the nitrogen oxide trapping material is Na, Li, K, Rb, Cs, Mg,
It is desirable to be selected from Ca and Sr.
At least one selected from g and Sr is preferable.

In addition to the alkali metal or alkaline earth metal, the nitrogen oxide trapping material may be B, Si, Mn, G
It is desirable to include at least one selected from e, Cr, V, Ti, Mo, Sn, and Zr. In particular, alkali metals or alkaline earth metals, B, Si, Mn, Ge,
It is preferable that at least one selected from Cr, V, Ti, Mo, Sn, and Zr forms a composite oxide.

The above nitrogen oxide purifying catalyst is an excellent NOx
Has purification performance. However, when selecting a catalyst material, durability against SOx (hereinafter referred to as SOx resistance)
Also, durability against heat (hereinafter, heat resistance) should be considered.

The nitrogen oxide trapping material of the present invention traps SOx contained in exhaust gas from automobiles. The trapping of SOx causes a decrease in the trapping capacity of NOx. This is called SOx poisoning. However, the nitrogen oxide purification catalyst of the present invention can remove trapped SOx by setting it in a reducing atmosphere. The temperature at which the trapped SOx is removed is desirably 500 ° C. or higher. Further, the noble metal of the nitrogen oxide purification catalyst is
By using h, Pt, and Pd, the removal efficiency of trapped SOx at 500 ° C. can be improved. At this time, as a secondary effect, NO in an oxidizing atmosphere at 400 ° C. or higher.
The x purification rate is also improved, and the temperature range of NOx purification performance can be expanded.

From the above, it is preferable that the noble metal is Rh, Pt, and Pd in the nitrogen oxide purifying catalyst.

Further, B, Si, Mn, Ge, Cr, V,
Among Ti, Mo, and Sn, Ti is a substance that suppresses SOx poisoning. Therefore, in order to suppress SOx poisoning of the nitrogen oxide trapping material, it is preferable to include Ti and at least one selected from an alkali metal or an alkaline earth metal, and particularly to include a composite oxide thereof. preferable. As the alkali metal or alkaline earth metal which can maintain a high NOx purification rate by being combined with Ti, Na or Sr is preferable.

By supporting the rare earth metal on the noble metal and the alkali metal or alkaline earth metal as a nitrogen oxide trapping material, a three-way catalytic performance is added, and a high NOx purification performance can be obtained even in a reducing atmosphere. Rare earth metal is Ce
Is desirable.

From the above, Ce and M are added to the porous carrier.
g, at least one selected from Na and Sr, and Ti, Rh, Pt and Pd are supported, and Ti preferably forms a composite oxide with at least one selected from Na and Sr.

The temperature of exhaust gas from automobiles is 100
It may rise to around 0 ° C. Therefore, it is considered that durability against heat is also necessary. In order to enhance heat resistance, a composite oxide of Mn and an alkali metal or an alkaline earth metal is preferable.

From the above, considering heat resistance and SOx resistance, at least one selected from the group consisting of Ce, Mg, Na and Sr, Ti, Mn, Rh, Pt and Pd are supported on the porous carrier. , Mn and Ti preferably form a composite oxide with at least one selected from Na and Sr.

The function of each component of the nitrogen oxide purifying catalyst according to the present invention is considered as follows.

At least one selected from alkali metals or alkaline earth metals and B, Si, Mn, Ge, C
The composite oxide with at least one selected from the group consisting of r, V, Ti, Mo, and Sn functions as a nitrogen oxide trapping material.

The noble metal converts NO to NO ₂ in an oxidizing atmosphere.
Oxidizes to Also, NO from the gas phase in a reducing atmosphere
x and N trapped in the nitrogen oxide trapping material in an oxidizing atmosphere
Both Ox are reduced.

The rare earth metal has a function of releasing oxygen at a stoichiometric air-fuel ratio or lower and capturing oxygen at a stoichiometric air-fuel ratio or higher. Using this function, CO and HC are purified in a reducing atmosphere. The catalyst composition ratio of the nitrogen oxide purifying catalyst is such that Pd is 0.1 to 3.0 parts by weight, Pt is 1.0 to 6.0 parts by weight, based on 100 parts by weight of the porous carrier. Rh
From 0.05 to 1.0 part by weight, Na, Mg, S
at least one member selected from the group consisting of B, Ti, Si, Mn, Mo, W,
It is preferable that the total amount of at least one selected from Cr, Ge, Sn, V and Zr is 3 to 50 parts by weight, and the rare earth metal is 15 to 50 parts by weight.

In order to obtain the above-mentioned composite oxide, catalyst preparation conditions are important. It is desirable to perform a heat treatment at 600 ° C. or higher.

The shape of the nitrogen oxide purifying catalyst according to the present invention can be applied in various shapes depending on the application. A honeycomb structure made of various materials such as cordierite, stainless steel, etc. is coated with a catalyst powder carrying various components.
It can be applied as a powder or the like. When it is arranged in an exhaust gas passage of an automobile, a honeycomb shape is preferable.

As a method for preparing the nitrogen oxide purifying catalyst, any of a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, a vapor deposition method, and a preparation method utilizing a chemical reaction can be applied. It is possible.

As starting materials for the nitrogen oxide purifying catalyst,
Various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonate compounds, organic compounds, and the like, and metals and metal oxides can be used.

As the porous carrier, metal oxides or composite oxides such as alumina, titania, silica, silica-alumina, and magnesia can be used. Alumina is preferable in consideration of heat resistance, and titania is preferable in consideration of SOx resistance. It is preferable to use a mixture of alumina and titania as the carrier.

The exhaust gas purifying method of the present invention is suitable for a stratified or homogeneous lean burn vehicle capable of operating in an oxidizing atmosphere. The following is preferable as an exhaust gas purifying apparatus when the exhaust gas purifying method of the present invention is applied to an automobile.

In a device for purifying nitrogen oxides in exhaust gas by arranging a nitrogen oxide purifying catalyst in an exhaust gas passage of an internal combustion engine operated at an air-fuel ratio higher than the stoichiometric air-fuel ratio, a nitrogen oxide purifying catalyst and operating condition determination Means and air-fuel ratio (A / F) control means. The operating state determining means includes NOx trapping quantity estimating means, NOx removing quantity estimating means, SOx trapping quantity estimating means, SO
It has x emission amount estimation means. The NOx trapping amount at an air-fuel ratio higher than the stoichiometric air-fuel ratio is estimated by the NOx trapping amount estimating means, and the SOx trapping amount is estimated by the SOx trapping amount estimating means. If the NOx trapping amount estimating means or SOx trapping amount estimating means determines that the predetermined NOx trapping amount or SOx trapping amount is exceeded, the NOx removal amount estimating means and the SOx trapping amount are determined.
The x emission amount estimating means issues a command to the air-fuel ratio controlling means to execute an operation at a stoichiometric air-fuel ratio or less.

As a method of detecting the trapped amount of nitrogen oxides and the trapped amount of SOx, for example, a NOx sensor, an oxygen sensor, an exhaust gas temperature sensor, an air flow sensor, a boost pressure gauge and an engine speed meter can be used.

[0042]

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.

Example 1 A slurry made of alumina powder and an alumina precursor and adjusted to be nitric acid was coated on a cordierite honeycomb (400 cells / inc ² ), dried and fired, and the honeycomb had an apparent volume 1. An alumina-coated honeycomb coated with 150 g of alumina per liter in terms of Al ₂ O ₃ was obtained. Hereinafter, unless otherwise specified, the amount of alumina coating is expressed as Al ₂ O ₃ . The alumina-coated honeycomb was impregnated with an aqueous solution of Ce nitrate, dried at 200 ° C, and then fired at 600 ° C. Next, a mixed solution of dinilotodiamine Pt nitric acid solution and Rh nitrate, a nitric titania sol, and an aqueous solution containing Na nitrate and Mg nitrate were impregnated. Then, drying at 200 ° C., followed by 600
And then fired at 700 ° C. for 1 hour. Hereinafter, the firing time is 1 hour unless otherwise specified. As described above, 150 parts by weight of alumina were converted to N in metal conversion.
a 18 parts by weight, Ti 4 parts by weight, Mg 1.8 parts by weight, Rh
Example catalyst 1 was obtained containing 0.23 parts by weight, 2.7 parts by weight of Pt, and 27 parts by weight of Ce. Further, Example Catalyst 2 was obtained in which 450 ° C. was used in place of the firing temperature of 600 ° C. in Example Catalyst 1 and the final firing temperature was also 450 ° C.

Table 1 shows the compositions of the catalysts of Examples 1 and 2 and the final calcination temperature. In addition, the number described before the element in a table | surface shows the carrying amount [g / L] in terms of metal per liter of apparent honeycomb volume.

[0045]

[Table 1]

Test Example 1 The structure of the NOx trapping material of each of the catalysts 1 and 2 was measured by the powder X-ray diffraction method.
Measurement is not possible due to the small amount of loading.

Therefore, the mixed solution of Na nitrate and nitric titania sol was dried and calcined at 450 ° C. or 700 ° C., and the structure of the powder obtained was examined by powder X-ray diffraction. as a result,
At 450 ° C., no composite oxide of Na and Ti was detected. On the other hand, the one baked at 700 ° C. is Na ₂ Ti
O ₃ was detected.

From the above, it was found that the catalyst 1 of the present embodiment had Na and T
It is clear that i forms a composite oxide.

Test Example 2 The trapping state of NOx in the catalysts 1 and 2 was examined by a diffuse reflection type Fourier transform infrared absorption (FT-IR) method.

The test method is shown below.

Example catalyst 1 or example catalyst 2 was placed on the sample stage.
Put the crushed powder. To prevent contact with the outside air, a container was placed on the sample stage. This container has a KBr window through which infrared light can pass. First, 500 ° C. in a He gas stream
, And the pretreatment gas was allowed to flow for 10 minutes while maintaining the temperature at 500 ° C. The composition of the pretreatment gas was 1 vol% of CO and the balance of He. After the completion of the pretreatment, the catalyst was cooled in a He gas stream, kept at a predetermined temperature from room temperature to 500 ° C., and the infrared absorption spectrum of the catalyst before the reaction was measured. Subsequently, the reaction gas is circulated,
An average infrared absorption spectrum was measured for 2 to 3 minutes after the start of the reaction. From the infrared absorption spectrum after the reaction gas flow, the infrared absorption spectrum before the reaction gas flow was swept (hereinafter, difference spectrum). The reaction gas is NO600volppm,
O _{2 5} vol%, He balance (hereinafter, NO-O ₂ gas), or NO ₂ 600 volppm, He balance (hereinafter, NO ₂ gas) was used.

FIG. 1 shows the difference spectrum between Example Catalyst 1 and Example Catalyst 2 when NO-NO ₂ gas was passed at 300 ° C. The positive direction of the vertical axis (infrared absorption intensity) in the figure indicates generation. In Example Catalyst 1, the infrared absorption intensity showed a maximum value at about 1410 / cm. On the other hand, in the case of Example Catalyst 2, the maximum values were shown at about 1410 / cm and about 1257 / cm.

Here, if NOx trapping is due to absorption, an infrared absorption spectrum of NaNO ₃ should be observed. The NO ₃ ion of NaNO ₃ is reported to be 1381 / cm (K. Buijs, CJH Schutte, Spectroch
imica Acta, 18 (1962) 307-313). The infrared absorption spectrum of NaNO ₃ at room temperature measured using this apparatus showed a maximum value at 1380 / cm. Also, 30
When heated to 0 ° C., the infrared absorption spectrum of NaNO ₃ was about 1350 / cm.

On the other hand, the infrared absorption spectrum of "M-ONO (M: metal)" is reported to have a maximum value at 1470 to 1400 / cm (Guido Busca, Vincenzo Lorenzell).
i, J. Catal., 72 (1981) 303-313).

Therefore, NO ₂ gas was passed through the catalyst 1 of the embodiment at room temperature and 300 ° C. FIG. 2 shows the results.
At both room temperature and 300 ° C., the infrared absorption spectrum showed a maximum value at about 1410 / cm.

Next, NO gas was added to the catalyst 2 of the embodiment at 300 ° C.
Was distributed. FIG. 3 shows the results. About 1257
/ Cm, the infrared absorption spectrum showed a maximum value. Therefore,
It is clear that the catalyst of Example 2 is mainly composed of NO chemisorption.

From the above, neither of the catalysts 1 and 2 of the embodiment captures NOx as a nitric acid compound, but the catalyst of the embodiment 1 mainly captures NO _{2 by} chemical adsorption of NO _2. The mode of trapping NOx in the catalyst 2 is mainly chemical adsorption of NO. FIG. 4 shows the results when the NO-O ₂ gas flow temperature was 300, 400, and 500 ° C. in Example Catalyst 1. The maximum value of the infrared absorption intensity was shown at about 1410 / cm at all temperatures of 300, 400 and 500 ° C.

From the above, it was found that the catalyst of Example 1 was 300 to
It can be seen that NO in an oxygen-excess atmosphere at 500 ° C. is trapped as NO ₂ on the nitrogen oxide trapping material.

Example 2 Test Example 3 After installing Example Catalyst 1 or Example Catalyst 2 in a reaction tube, the catalyst 5 was passed while flowing a reducing atmosphere model gas.
The temperature was raised to 00 ° C. at a rate of 10 ° C./min, and subsequently cooled to 400 ° C. under a N ₂ atmosphere. At 400 ° C., a reducing atmosphere model gas and an oxidizing atmosphere model gas were alternately circulated. As test conditions, the flow time of each model gas was 3 minutes, the catalyst volume was 6 ml, and the SV was 30,000 / h. Also,
The equation for defining the NOx purification rate is shown in equation (2). The NOx purification rate is defined as the rate of decrease in the NOx concentration before and after circulation in the catalyst layer.

[0060]

(Equation 1)

The composition of the oxidizing atmosphere model gas is NOx:
_{600volppm, C 3 H 6: 500volppm} , CO: 0.1vol
%, CO ₂ : 10 vol%, O ₂ : 5 vol%, H ₂ O: 10 vol
%, N ₂ : Residual.

The composition of the reducing atmosphere model gas is NOx:
_{1000volppm, C 3 H 6: 600volppm} , CO: 0.5v
ol%, CO ₂ : 5 vol%, O ₂ : 0.5 vol%, H ₂ : 0.3
_{vol%, H 2 O: 10vol} %, N 2: was the remainder.

(Test Results) Table 2 shows the NOx purification rate 3 minutes after the oxidizing atmosphere model gas flow and the NOx purification rate 1 and 2 minutes after switching from the oxidizing atmosphere to the reducing atmosphere model gas. When switching from the oxidizing atmosphere model gas to the reducing atmosphere model gas, the NOx purification rate of the example catalyst 1 reaches 100% faster than that of the example catalyst 2.

Therefore, the catalyst 1 of the embodiment can quickly reduce and purify trapped NOx in a reducing atmosphere.

[0065]

[Table 2]

Test Example 4 After installing the catalyst of Example 1 or Catalyst 2 of Example in a reaction tube, the temperature was raised to 500 ° C. at a rate of 10 ° C./min while flowing a reducing atmosphere model gas, and then N ₂ atmosphere Cooled down to 300 ° C. An oxidizing atmosphere model gas was passed at 300 ° C. As test conditions, the flow time of each model gas was 3 minutes, the catalyst volume was 6 ml,
V was set to 30,000 / h.

(Test Results) Table 3 shows N in an oxidizing atmosphere.
The steady value of the Ox purification rate was shown. The NOx concentration of the oxidizing atmosphere model gas was of two types, 600 ppm and 1000 ppm. The steady value indicates that NOx has been reduced and purified. The steady value of Example Catalyst 1 was superior to Example Catalyst 2. Therefore, the example catalyst 1 in which a monomolecular layer is formed on the surface of the NOx trapping material has excellent reduction and purification performance of trapped NOx even in an oxidizing atmosphere.

[0068]

[Table 3]

[Example 3] The catalyst 1 of the example was used to
The x property was examined.

Test Example 5 After the catalyst 1 of the example was set in a reaction tube, 500 ° C. while flowing a model gas in a reducing atmosphere.
Temperature at 10 ° C / min until 30 ° C under N ₂ atmosphere.
Cooled to 0 ° C. At 300 ° C., an oxidizing atmosphere model gas and an oxidizing atmosphere model gas were alternately circulated. The NOx purification rate at this time was defined as the initial performance.

Next, the NOx purification rate after SOx poisoning was measured. The measuring method is described below. The temperature was maintained at 300 ° C., and the SOx poisoning model gas was passed for one hour. Oxidizing atmosphere model gas with 150 volppm SO ₂ added to S
Ox poisoning model gas was used.

After completion of SOx poisoning, the temperature was raised to 400 ° C. at a rate of 10 ° C./min while flowing a reducing atmosphere model gas, and then cooled to 300 ° C. in an N ₂ atmosphere. At 300 ° C., a reducing atmosphere model gas and an oxidizing atmosphere model gas were alternately circulated.

Finally, the NOx purification rate after the regeneration treatment was measured. The measuring method is described below. 60 the temperature under N ₂ atmosphere
The temperature was raised to 0 ° C., maintained at 600 ° C., and subjected to a regeneration treatment in which a reducing atmosphere model gas was passed for 10 minutes. After the completion of the regeneration treatment, the mixture was cooled to 300 ° C. in a N ₂ atmosphere. 300 ℃
, A reducing atmosphere model gas and an oxidizing atmosphere model gas were alternately circulated.

(Test Results) Table 4 shows the oxidizing atmosphere switching 1
The NOx purification rate after one minute was shown. The NOx purification performance of the example catalyst 1 deteriorated by SOx poisoning was recovered by the regeneration process.

[0075]

[Table 4]

Example 4 Example catalyst 3-5 was prepared according to the catalyst preparation method for example catalyst 1. In addition, an alumina-coated honeycomb coated with 190 g of alumina per liter of apparent honeycomb volume was used. Table 5
Table 2 shows the catalyst composition and final firing temperature.

[0077]

[Table 5]

Test Example 6 As in Test Example 2 of Example 1, NO-O ₂ gas was passed at 300 ° C.

(Test Results) At about 1410 / cm, the infrared absorption spectrum intensity showed a maximum value.

[Test Example 7] The NOx purification rate in an oxidizing atmosphere was measured in accordance with Test Example 3 of Example 2. However, the test temperature was 300 to 500 ° C.

(Test Results) Table 6 shows the oxidizing atmosphere switching 1
The NOx purification rate after one minute was shown. The catalysts of Examples 4 and 5 supporting Pd exhibited excellent NOx purification performance at 400 ° C. or higher compared to Example Catalyst 3.

[0082]

[Table 6]

[Test Example 8] SOx resistance was examined in the same manner as in Test Example 5 of Example 4. However, the temperature at the time of the regeneration process is 50
0 ° C.

(Test Results) Table 7 shows the NOx purification rates one minute after switching the oxidizing atmosphere at 300 ° C. The NOx purification rates of the example catalysts 4 and 5 supporting Pd were recovered by the regeneration treatment at 500 ° C.

[0085]

[Table 7]

[Example 5] Based on the catalyst preparation method of Example 1, B, Si, Mn, G
Example Catalyst 6-12 supporting e, Cr, V, Ti, Mo, and Sn was prepared. Table 8 shows the catalyst composition. In any of the example catalysts 6-12, when the FT-IR measurement was performed using NO-O ₂ gas, the infrared absorption spectrum of the nitric acid compound was different from the infrared absorption spectrum of the nitric acid compound, and almost the same infrared absorption spectrum as that when the NO ₂ gas was flowing was obtained. Was done.

[0087]

[Table 8]

Example 6 Based on the catalyst preparation method of Example 1, Example Catalysts 13 to 15 in which Sr was carried instead of Na of Example Catalyst 1 were prepared. Alumina coat amount is 19
0 g / L, and the final calcination temperature of the catalyst was 700 ° C. Table 9 shows the catalyst composition. When the FT-IR was measured using NO-O ₂ gas, the infrared absorption spectrum was almost the same as that when the NO ₂ gas was flowing, different from the infrared absorption spectrum of the nitrate compound.

[0089]

[Table 9]

[Embodiment 7] FIG. 5 is an overall configuration diagram showing an embodiment of a nitrogen oxide purifying apparatus according to the present invention.

This is a system equipped with an in-cylinder injection engine 99 that can be operated in an oxidizing atmosphere, and includes a combustion system, an intake system, a fuel supply system, an exhaust system, and a control unit 25. The combustion system includes an injector 5, a spark plug 6, a piston 9, and the like. The intake system has an air cleaner 1, an air flow sensor 2, a throttle valve 3, and the like. The fuel supply system has a fuel tank 13, a fuel pump 12, and the like. The exhaust system is an oxygen concentration sensor (or air-fuel ratio sensor) 1
9, an exhaust gas temperature sensor 22, a nitrogen oxide purifying catalyst 18 according to the present invention, a catalyst outlet gas temperature sensor 21, and the like. The control unit (ECU) 25 includes an I / O LSI as an interface, an arithmetic processing unit MPU, a storage device ROM and RAM storing a control program group, a timer counter, and the like. ECU2
5 includes a load sensor 8 for detecting the depression amount of the accelerator pedal 7, a crank angle sensor 29, a knock sensor 26, an air flow sensor 2, a water temperature sensor 28, an oxygen concentration sensor (or air-fuel ratio sensor) 19, and an exhaust gas temperature sensor 22. , A detection signal from the catalyst outlet gas temperature sensor 21 and the like are input via an input interface.

The above exhaust gas purifying apparatus functions as follows.

The in-cylinder injection engine 99 creates a mixture of intake air and fuel and burns this mixture at the top dead center of the piston 9 to operate the engine. Here, the intake air to the in-cylinder injection engine 99 is filtered by the air cleaner 1, measured by the air flow sensor 2, passes through the throttle valve 3, and passes through the in-cylinder injection engine 99.
Is supplied to the combustion chamber. Further, fuel is injected into the combustion chamber from the fuel tank 13 via the fuel pump 12 by the injector 5.
Is injected at high pressure.

The ECU 25 evaluates the operating state of the internal combustion engine and the state of the nitrogen oxide purifying catalyst 18 according to the present invention based on the sensor signals and a control program group stored in advance to determine the air-fuel ratio (air-fuel ratio). The operating state is determined, and the air-fuel mixture is burned under predetermined conditions by controlling the injector 5 and the amount of intake air.

The combustion exhaust gas is led to the exhaust system. A nitrogen oxide purification catalyst 18 is provided in the exhaust system. When the air-fuel ratio is lean, NOx in the exhaust gas of the oxidizing atmosphere is purified by the nitrogen oxide purifying catalyst 18 by trapping and reduction.
Next, before the NOx trapping amount of the nitrogen oxide purifying catalyst 18 reaches saturation, the air-fuel ratio is shifted to fuel rich, and the trapped NOx
x is reduced and purified. Also, during fuel-rich operation,
Since the nitrogen oxide purifying catalyst 18 has a three-way catalytic function, it purifies NOx, HC, and CO in exhaust gas. On the other hand, the NOx trapping performance of the nitrogen oxide purification catalyst 18 gradually decreases due to the absorption of SOx contained in the exhaust gas. Therefore, N
Before the Ox purification performance does not satisfy the desired performance, S
The regeneration of the nitrogen oxide purification catalyst poisoned by Ox is performed. The regeneration is performed by operating the combustion system according to a control program in the ECU 25 such that the exhaust gas has a reducing atmosphere and a set temperature (for example, 600 ° C.). By the above operation, NOx in exhaust gas is effectively purified while preventing or suppressing SOx poisoning of the nitrogen oxide purification catalyst 18 under all engine combustion conditions.

Here, among the functions of the ECU 25, the control device of the nitrogen oxide purifying catalyst 18 according to the present invention will be described.

As shown in FIG. 6, NOx is stored in the ECU 25.
Captured amount estimating means 101 and trapped NOx removal amount estimating means 10
2, an SOx trap amount estimating unit 103, an SOx removal amount estimating unit 104, an exhaust gas flow amount estimating unit 105, and an air-fuel ratio control unit 106. First, the NOx purification control of the nitrogen oxide purification catalyst 18 will be described.

The NOx trapping amount estimating means 101 is a function for estimating the integrated value of the NOx trapping amount (NOx trapping amount estimating unit) 10.
1A and a function (NOx trapping amount determining unit) 101B for determining whether or not this integrated value has reached a preset value. The air-fuel ratio control means 106 includes a fuel-lean combustion operation control unit 106A and a fuel-rich combustion operation control unit 106B.

The NOx trapping amount estimating section 101A estimates the NOx trapping amount at each time, integrates the NOx trapping amount with the operation time, and accumulates N
Estimate the amount of captured Ox.

The NOx trapping amount at each time is determined from the exhaust gas temperature, the NOx amount in the exhaust gas, and the NOx trapping ability of the nitrogen oxide purifying catalyst 18. The exhaust gas temperature is obtained from the catalyst outlet gas temperature sensor 21. The NOx amount in the exhaust gas is determined from the exhaust gas flow rate and the A / F. The exhaust gas flow rate is obtained from the exhaust gas flow rate estimation means 105, and the A / F is obtained from the air-fuel ratio control means 106. NO of the nitrogen oxide purification catalyst 18
Regarding the x trapping ability, the NOx when the exhaust gas temperature, the amount of NOx in the exhaust gas, and the amount of exhaust gas were used as parameters in preliminary experiments
A map of the x capture amount is determined and obtained. This map is N
It is installed in the Ox capture amount estimation unit 101A.

The accumulated NOx trapping amount is obtained by accumulating the NOx trapping amount for each fuel-lean combustion operation time.

The NOx trapping amount determining section 101B determines whether or not the accumulated NOx trapping amount obtained by the NOx trapping amount estimating section 101A exceeds a predetermined amount. If the amount exceeds a certain amount, it will be captured
The control is shifted to the NOx removal amount estimating means 102. The predetermined amount is determined in advance by a designer, for example, to be an amount of 80% of the maximum NOx trapping amount of the nitrogen oxide purification catalyst 18.

The trapped NOx removal amount estimating means 102 issues a command for switching from the lean fuel combustion to the fuel rich combustion to the air-fuel ratio control means 106. The setting conditions of the fuel-rich combustion, that is, the A / F and the operation time are set by preliminary experiments. The operation according to the set conditions is performed by the air-fuel ratio control unit 106.
It is carried out in. The trapped NOx removal amount estimating means 102 monitors the fuel-rich combustion operation time and A / F, and when it is determined that the set conditions are satisfied, issues an instruction to the air-fuel ratio control means 106 to return from fuel-rich combustion to fuel-lean combustion. , NOx
The control is passed to the capture amount estimating means 101.

Next, the regeneration control of the nitrogen oxide purifying catalyst 18 that has absorbed SOx will be described.

The SOx trapping amount estimating means 103 has a function (SOx trapping amount estimating unit) 103A for estimating the amount of SOx absorbed into the SOx trapping material, and the integrated value of the SOx trapping amount has reached a predetermined amount from the estimated value. Function (SOx
(A capture amount determination unit) 103B. The SOx removal amount estimating means 104 estimates operating conditions such as the time required for SOx release from the SOx trapping material and the air-fuel ratio (SOx removal condition setting unit) 104A, and reports that the operating condition has reached the estimated value. A determination (SOx removal condition determination unit) 104B is provided.

That is, when the amount of SOx absorbed by the nitrogen oxide purifying catalyst 18 increases, the NOx trapping performance decreases.
Therefore, when the SOx trapping amount estimating unit 103A estimates the SOx trapping amount of the nitrogen oxide purification catalyst 18, and the SOx trapping amount determining unit 103B determines that the integrated value of the SOx trapping amount has reached a predetermined amount, the air-fuel ratio control unit The air-fuel ratio is set by the fuel-rich combustion operation control unit 106B so as to generate the exhaust gas in the reducing atmosphere, and the fuel injection amount control of the injector 5 is started. At this time, the SOx removal amount estimating means 104
The SOx removal condition setting unit 104A estimates a control value (time, air-fuel ratio, etc.) required for releasing trapped SOx from the nitrogen oxide purification catalyst 18, and based on the estimated value, a fuel-rich combustion operation control unit 106B Performs the control. The information of the fuel-rich combustion operation control unit 106B is monitored by the SOx removal condition determination unit 104B. When it is determined that the control value has reached the estimated value, the oxidizing atmosphere is controlled by the fuel-lean combustion operation control unit 106A of the air-fuel ratio control unit 106. Then, the air-fuel ratio is set so as to generate the exhaust gas, and the fuel injection amount control of the injector 5 is started.

Here, the amount of trapped SOx in the oxidizing atmosphere of the nitrogen oxide purifying catalyst 18 and the amount of SOx in the reducing atmosphere
The Ox emission amount is estimated from the exhaust gas flow rate, the fuel consumption amount, the exhaust gas temperature, and the operation time. Therefore, maps of the SOx trapping amount and the SOx emission amount of the nitrogen oxide purification catalyst 18 with respect to the exhaust gas flow rate, the fuel consumption amount, the exhaust gas temperature, and the operation time are prepared by preliminary experiments. Then, map each map to SO
The x capture amount estimating means 103 and the SOx removal amount estimating means 104 are provided to perform control based on a map. The exhaust gas flow rate is estimated by the exhaust gas flow rate estimating means 105 from the intake air amount, the fuel injection amount, and the exhaust gas temperature. Information on the fuel consumption is obtained from the air-fuel ratio control means 106. The exhaust gas temperature is obtained from the catalyst outlet gas temperature sensor 21, and the intake air amount is obtained from the air flow sensor 2. The operating time can be measured by measuring the driving time of the injector 5 or operating the timer 30 during the fuel-lean combustion operation.

FIG. 7 shows a flowchart of an embodiment of the present invention. First, when the fuel-lean combustion operation (step 1001) is started, the SOx trapping amount estimating unit 103A performs SOx trapping based on the intake air amount, exhaust gas temperature and air-fuel ratio or fuel consumption and operation time information (step 1002). The quantity is calculated (step 1003). next,
Proceeding to step 1004, the SOx trap amount estimating unit 103
It is determined whether the integrated value of the calculated value of the SOx trapping amount in B has reached a preset value.

If the integrated value of the calculated value of the SOx trapping amount does not exceed the preset value, the NOx trapping amount is calculated by the NOx trapping amount estimating unit 101A (step 1008).
In step 1009, the NOx trapping amount is accumulated (NOx trapping amount determining unit 101B). If the NOx trapping amount determining unit 101B determines that the accumulated NOx trapping amount has exceeded a preset value, the process proceeds to step 1010. Step 101
In the case of 0, the fuel-rich combustion operation time and A / F are determined based on the information of the NOx removal amount estimating means 102, and the air-fuel ratio control means 106 performs the fuel-rich combustion operation. After step 1010, the process returns to step 1001. If it is determined in step 1009 that the accumulated NOx trapping amount does not exceed the preset value, the process returns to step 1001.

If it is determined that the integrated value of the calculated value of the SOx trapping amount exceeds a preset value, the air-fuel ratio control means 1
At 06, the control of the fuel-rich combustion operation is started. First, the fuel-rich combustion operation time is calculated by the SOx removal condition estimation unit 104B based on the information on the exhaust gas temperature and the intake air amount (step 1005). This calculation requires the air-fuel ratio during the fuel-rich combustion operation, but here, for example, A / F: about 13 can be fixed. And
The fuel-rich combustion operation is started by the air-fuel ratio control means 106 (step 1006). The operation time is monitored in step 1007, and when the SOx removal condition determination unit 104B determines that the measured value exceeds the calculated value, the flow returns to step 1001 to start the fuel-lean combustion operation.

With the exhaust gas purifying apparatus, NOx poisoning of the nitrogen oxide purifying catalyst 18 is prevented or suppressed while SOx poisoning is prevented.
Can be purified.

[0112]

According to the present invention, nitrogen oxides contained in lean burn exhaust gas can be efficiently purified.

[Brief description of the drawings]

FIG. 1 is a difference spectrum of FT-IR when NO-O ₂ gas flows.

FIG. 2 is a difference spectrum of FT-IR when NO ₂ gas flows.

FIG. 3 is a difference spectrum of FT-IR when NO gas flows.

FIG. 4 is an FT-IR difference spectrum when a NO—O ₂ gas flows at 300 to 500 ° C.

FIG. 5 is a schematic diagram showing the entire configuration of the exhaust gas purifying apparatus of the present invention.

FIG. 6 is a control block diagram schematically showing an element configuration of a control system in the exhaust gas purifying apparatus of the present invention.

FIG. 7 is a flowchart showing an embodiment of performing NOx purification while preventing or suppressing SOx poisoning of the nitrogen oxide purification catalyst using the exhaust gas purification device of the present invention.

[Explanation of symbols]

1 ... Air cleaner, 2 ... Air flow sensor, 3 ...
Throttle valve, 5 injector, 6 spark plug, 7 accelerator pedal, 8 load sensor, 9 piston, 12 fuel pump, 13 fuel tank, 18 nitrogen oxide purification catalyst, 19 oxygen concentration sensor ( Or air-fuel ratio sensor), 21 ... catalyst outlet gas temperature sensor, 2
2: Exhaust gas temperature sensor, 25: Control unit (EC
U), 26: knock sensor, 28: water temperature sensor, 2
9 ... Crank angle sensor, 99 ... In-cylinder injection engine.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 23/64 F01N 3/08 A F01N 3/08 3/10 A 3/10 3/24 R 3/24 3/28 301C 3/28 301 B01D 53/36 104B (72) Inventor Masato Kaneda 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hisao Yamashita Hitachi, Ibaraki Prefecture 7-1-1, Omika-cho, Hitachi, Ltd.Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Ryota Doi 2520 Ojitakaba, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.Automotive Equipment Division, Hitachi, Ltd. 2520 Oita Takaba, Hitachinaka-shi, Japan Inside the Automotive Equipment Division, Hitachi, Ltd. (72) Inventor Yuichi Kitahara 2520 Oaza-Kita, Hitachinaka-shi, Ibaraki 3G091 AA02 AA12 AB06 BA14 BA32 EA35 FB10 FB12 FC04 GB02W GB05W GB06W GB07W GB10W 4D048 AA06 AA13 AA18 AB01 AB02 AB05 AB07 BA01X BA08BAX BA07X BA23X BA25X BA26X BA28X BA30X BA31X BA33X BA41X BA42X BB02 BB20 BC01 BD01 DA01 DA02 DA03 DA06 DA08 DA13 EA04 4G069 AA03 BA01A BA01B BA02A BA04A BA04B BC05A BA13B BB01A BB02A BB02BBC10B BC12BC BC59A BC59B BC62A BC62B BC71A BC71B BC72A BC72B BC75A BC75B BD02A BD02B BD03A BD03B BD05A CA03 CA07 CA08 CA13 CA14 CA15 EA19 EB12Y EC27 ED06 FC08

Claims (11)

[Claims] A nitrogen oxide purifying catalyst is disposed in an exhaust gas passage of an internal combustion engine, and an exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an exhaust gas having an air-fuel ratio less than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst. In the exhaust gas purifying method for an internal combustion engine, wherein the nitrogen oxides in the exhaust gas are reduced and purified, NO ₂ is trapped when the trapped state of the nitrogen oxides is measured by an infrared absorption spectrum method as the nitrogen oxide purifying catalyst. A method for purifying exhaust gas of an internal combustion engine, comprising: providing a catalyst exhibiting an absorption spectrum in a decompressed state, capturing nitrogen oxides of exhaust gas in the form of NO _{2 on} the surface of the catalyst, and reducing the nitrogen oxides. 2. The exhaust gas purifying method according to claim 1, wherein the catalyst comprises 1 vol% of CO and the balance of He.
After flowing the reducing gas heated to a temperature of 0 ° C.,
Diffuse reflection Fourier transform infrared absorption spectrum while maintaining a predetermined temperature of not less than 300 ° C. and not more than 500 ° C. in a He gas flow, and then flowing a mixed gas of NO-O ₂ consisting of 600 vol ppm of NO, ₅ vol% of O ₂ and the balance of He. NO by law
An absorption spectrum obtained when measuring the trapped state of x, and an absorption spectrum obtained when the trapped state of NOx is also measured while flowing a gas composed of 600 ppm of NO ₂ and the balance of He instead of the NO-O ₂ mixed gas. An exhaust gas purifying method for an internal combustion engine, characterized in that the absorption spectrum matches the absorption spectrum. 3. An exhaust gas passage of an internal combustion engine is provided with a nitrogen oxide purifying catalyst, and an exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio alternately flow into the exhaust gas passage. An exhaust gas purifying apparatus for an internal combustion engine provided with an air-fuel ratio control means for controlling an air-fuel ratio of exhaust gas in such a manner as to perform the above-mentioned method. _2. An exhaust gas purifying apparatus for an internal combustion engine, comprising: a catalyst exhibiting an absorption spectrum in a state where ₂ is captured, wherein nitrogen oxides of exhaust gas are captured in the form of NO _{2 on} the surface of the catalyst. 4. The exhaust gas purifying apparatus according to claim 3, wherein the catalyst comprises 1 vol% of CO and the balance of He.
After flowing the reducing gas heated to a temperature of 0 ° C.,
Diffuse reflection Fourier transform infrared absorption spectrum while maintaining a predetermined temperature of 300 ° C. or more and 500 ° C. or less in a He gas flow, and then flowing a mixed gas of 600 vol ppm of NO, ₅ vol% of O _2, and the balance of He—NO ₂ NO by law
and the absorption spectrum obtained when measuring the capture state of the x, instead of the NO-O ₂ mixed gas NO ₂ 600 ppm and H
e. An exhaust gas purifying apparatus for an internal combustion engine, wherein an absorption spectrum obtained when the state of trapping NOx is measured while flowing the gas comprising the remaining part is the same. 5. An exhaust gas purifying catalyst for trapping nitrogen oxides contained in exhaust gas of an internal combustion engine on the surface and converting hydrocarbons and carbon monoxide contained in the exhaust gas into nitrogen as a reducing agent, the method comprising the steps of: An exhaust gas purifying catalyst for an internal combustion engine, comprising: a catalyst whose absorption spectrum matches the absorption spectrum of a state in which NO ₂ is captured when the state of capturing nitrogen oxides is measured. 6. The exhaust gas purifying catalyst according to claim 5, wherein the catalyst comprises 1 vol% of CO and the balance of He.
After flowing the reducing gas heated to a temperature of 0 ° C.,
Diffuse reflection Fourier transform infrared absorption spectrum while maintaining a predetermined temperature of 300 ° C. or more and 500 ° C. or less in a He gas flow, and thereafter flowing a mixed gas of 600 vol ppm of NO, ₅ vol% of O _2, and the balance of He—NO ₂ NO by law
and the absorption spectrum obtained when measuring the capture state of the x, instead of the NO-O ₂ mixed gas NO ₂ 600 ppm and H
e. An exhaust gas purifying catalyst for an internal combustion engine, wherein the absorption spectrum obtained when the trapped state of NOx is measured while the gas consisting of the remaining part is passed also matches. 7. The exhaust gas purifying catalyst according to claim 5, wherein the porous carrier, the noble metal, at least one selected from Na, Mg, and Sr and Ti, Si, Sn, Mo, V,
An exhaust gas purifying catalyst for an internal combustion engine comprising at least one selected from Cr, B, Mn, and Zr. 8. The exhaust gas purifying catalyst according to claim 5, wherein Ce, Mg, Na and Ti, Si,
At least one selected from Sn, Mo, V, Cr, B, Mn, and Zr and at least one selected from Rh, Pt, and Pd are supported, and Ti, Si, Sn, Mo, V, and C are supported.
at least one selected from r, B, Mn, and Zr and Na
Is an exhaust gas purifying catalyst for an internal combustion engine, wherein the catalyst forms a composite oxide. 9. The exhaust gas purifying catalyst according to claim 5, wherein the porous carrier contains Ce, Mg, Na, Ti, and R.
An exhaust gas purifying catalyst for an internal combustion engine, wherein at least one selected from h, Pt, and Pd is supported, and Ti and Na form a composite oxide. 10. The exhaust gas purifying catalyst according to claim 5, wherein Pd is from 0.1 to 3.0 parts by weight and Pt is from 1.0 to 6.0 parts by weight based on 100 parts by weight of the porous carrier. 0
Not more than 0.05 parts by weight, not more than 1.0 parts by weight of Rh, 20 to 50 parts by weight in total of at least one selected from Na, Mg, and Sr; Ti, Si, S
n, Mo, V, Cr, B, Mn, and Zr in a total amount of 3 parts by weight or more and 50 parts by weight or less;
An exhaust gas purifying catalyst for an internal combustion engine, wherein the catalyst is supported in an amount of 0 part by weight or less. 11. An exhaust gas purifying apparatus according to claim 3, wherein said operating condition determining means and said air-fuel ratio control means for performing a fuel-lean combustion operation higher than the stoichiometric air-fuel ratio and a fuel-rich combustion operation lower than the stoichiometric air-fuel ratio. Wherein the operating state determining means estimates the NOx trapping amount at an air-fuel ratio higher than the stoichiometric air-fuel ratio, and determines whether the NOx trapping amount has exceeded a predetermined NOx trapping amount. NOx removal amount estimating means for issuing a command to the air-fuel ratio control means and estimating the removal amount of trapped NOx so that the air-fuel ratio operation becomes equal to or less than the stoichiometric air-fuel ratio when the captured NOx trap amount is exceeded,
SOx trapping amount estimating means for estimating the SOx trapping amount at an air-fuel ratio higher than the stoichiometric air-fuel ratio and determining whether or not the predetermined SOx trapping amount has been exceeded, and the predetermined SOx trapping amount
When the trapping amount is exceeded, a command is issued to the air-fuel ratio control means so that the air-fuel ratio operation becomes equal to or lower than the stoichiometric air-fuel ratio.
an exhaust gas purifying apparatus for an internal combustion engine, comprising: an SOx release amount estimating unit for estimating an x release amount.