JPH11303625A - Exhaust emission control device for internal combustion engine and exhaust emission control method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently purify the NOx concentration in exhaust gas by disposing a SOx absorbent absorbing NOx when the air fuel ration in the inflow exhaust gas is lean, and disposing a SOx absorbent on the upstream side thereof in an internal combustion engine for burning the lean air-fuel mixture. SOLUTION: In an internal combustion engine for burning lean air-fuel mixture, a SOx absorbent 2 is disposed in the upstream area in an exhaust passage 1, and a NOx absorbent 3 having no oxygen absorbing force is arranged in the downstream area. Further, a catalytic converter rhodium is arranged in the downstream area from the respective absorbents 2, 3. The SOx absorbent to be used absorbs SOx in exhaust gas generated from an internal combustion engine at the time of lean, and emits the same at the time of theoretical air fuel ratio or rich. On the other hand, the NOx absorbent to be used having no oxygen absorbing force takes at least one kind selected from alumina or the other groups as a carrier to support at least one kind of basic material or the others selected from alkali metal or the other groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for purifying exhaust gas discharged after fuel combustion in an internal combustion engine and an exhaust gas purifying method using the same.

[0002]

2. Description of the Related Art The main components of exhaust gas discharged after fuel combustion in an internal combustion engine are mainly carbon dioxide (CO ₂ ), carbon monoxide (CO), water (H ₂ O), oxygen (O ₂ ), and nitrogen. (N
₂ ), hydrogen (H ₂ ), etc., and nitrogen oxides (NOx), sulfur oxides (SOx), hydrocarbons (H
C) is also included.

The harmful components in the exhaust gas include carbon monoxide (CO), nitrogen oxide (NOx), and sulfur oxide (SO
x), hydrocarbons (HC), and the like.

[0004] More specifically, CO adversely affects the metabolic function of animals, and NOx directly affects animals and humans, for example, causing damage to the central nervous system and respiratory system. In addition, after being diffused into the atmosphere, NOx and HC generate various chemical reactions due to sunlight, generate photochemical smog, and stimulate skin, mucous membranes, eyes, etc., and are indirect to animals and humans. May be affected.

In view of the above-mentioned problems, in recent years, emission regulations have been tightened in various countries around the world due to avoidance of adverse effects on animals and human beings and global protection of the global environment. For example, in Europe, Asia and Australia, legislation to enhance emissions, legislation for low-mission vehicles in the United States of America, and regulations on total nitrogen oxides in Japan (applied to diesel vehicles) have been studied, approved, and introduced.

[0006] For this reason, exhaust gas research and development has been conducted since the 1960s to purify exhaust gas.
In the 970s, three-way catalysts and other catalysts and absorbents capable of simultaneously reducing HC, NOx, and CO were developed and put into practical use, and further improvements and improvements have been made thereafter.

Further, the generation of harmful components in the exhaust gas depends on the air-fuel ratio in the internal combustion engine, the influence of the ignition timing, the stroke volume,
Influence of engine specifications such as stroke / bore (S / D) ratio, compression ratio, etc., influence of fuel itself such as fuel properties and emission amount, and humidity, temperature, pressure, etc. of air sucked into the internal combustion engine Depending on conditions and other factors, recent research has shown that controlling the air-fuel ratio in an internal combustion engine can reduce harmful components in exhaust gases.

This is based on the air-fuel ratio (air / fuel, ie, A /
When F) is on the lean side (actual air-fuel ratio / stoichiometric air-fuel ratio> 1), that is, when the oxygen concentration is high, it is based on the result that HC, NOx, CO, and the fuel consumption rate are all effective.

For this reason, the internal combustion engine manufacturing and development industry has developed a lean burn system in which combustion is performed with the air-fuel ratio lean, but when the air-fuel ratio is lean, the exhaust gas becomes excessively oxygen. Since harmful components (especially NOx) in the exhaust gas generated thereby increase, how to purify and eliminate the harmful components has become a major issue.

At present, as a method for purifying harmful components in exhaust gas, NOx discharged at the time of leaning is absorbed, and the absorbed NOx is reduced and purified at a stoichiometric air-fuel ratio or at a rich time (when the oxygen concentration is low). Systems and other methods have been found.

More specifically, in an internal combustion engine in which a lean air-fuel mixture is burned, when the air-fuel ratio of the inflowing exhaust gas is lean, NOx is absorbed, and when the oxygen concentration in the inflowing exhaust gas decreases, the absorbed NOx is released. By disposing the NOx absorbent in the exhaust passage of the internal combustion engine, the NOx generated when the lean mixture is burned is absorbed by the NOx absorbent, and the NOx absorbent is absorbed before the NOx absorption capacity of the NOx absorbent is saturated. An exhaust gas purification device for an internal combustion engine has been proposed in which an air-fuel ratio of exhaust gas flowing into an agent is temporarily made rich to release NOx from a NOx absorbent and reduce the released NOx. (Japanese Patent Application No. 3-284
095).

Further, since sulfur is contained in the fuel, sulfide (mainly SOx) generated after the combustion thereof is N
Since it is absorbed by the Ox absorbent, and as a result, the NOx absorption rate of the NOx absorbent decreases, the Nx in the exhaust passage of the internal combustion engine is reduced to absorb the sulfide in the exhaust gas.
An exhaust gas purifying device having a sulfur trapping device provided upstream of the Ox absorbent arrangement has been proposed by a related application by the same applicant (see Japanese Patent Application No. 4-208090).

The prior art described above has been sufficiently improved and improved in order to achieve the object of purifying exhaust gas generated by fuel combustion in an internal combustion engine while maintaining NOx absorption power. However, it is considered that it is difficult to sufficiently absorb NOx as far as the present inventors know.

That is, since the fuel and the lubricating oil for an internal combustion engine contain a sulfur-containing substance, SOx (mainly in the form of SO ₂ , which is oxidized on a catalyst in the exhaust gas of the internal combustion engine) SO ₃ ). This SOx is mainly captured by the SOx absorbent disposed upstream of the NOx absorbent.

[0015] This SOx absorbent generally comprises SOx
Before absorption capacity is saturated, the air-fuel ratio of the exhaust gas flowing into the SOx absorbent is temporarily during stoichiometric or rich, the absorbed _{SOx SO 2, H 2 S,} COS, and other sulfide It is changed into an object and released.

The released sulfide is absorbed by alumina. Then, when the air-fuel ratio is made lean, ceria or cerium oxide contained in the NOx absorbent is oxidized by oxygen absorbed by the composite oxide or other compound to generate SO ₃ .

Since the generated SO ₃ is strongly acidic, it is absorbed by a NOx absorbent composed of an oxide and / or a carbonate of a basic alkali metal, an alkaline earth metal, and a rare earth element. The absorption capacity of the absorbent decreases.

Further, when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is temporarily made rich, the SOx absorbed by the NOx absorbent is released more than the NOx absorbed by the NOx absorbent. When the NOx absorbent is used for a long period of time, the absorption amount of SOx increases, while the absorption amount of NOx gradually decreases, and finally the NOx absorption amount decreases.
There was a problem that the absorbent could hardly absorb NOx.

[0019]

SUMMARY OF THE INVENTION The present invention provides an exhaust gas purifying apparatus for an internal combustion engine which sufficiently purifies NOx concentration in exhaust gas discharged by fuel combustion in the internal combustion engine, and an exhaust gas purifying method using the same. It is. In particular, the present invention purifies a considerable amount of NOx concentration in exhaust gas discharged by arranging a NOx absorbent having no oxygen absorbing power in an exhaust passage of an internal combustion engine in an internal combustion engine burning a lean mixture. An exhaust gas purification device for an internal combustion engine and an exhaust gas purification method using the same are provided.

[0020]

[Summary of the Invention]

<Summary> An object of the present invention is to solve the above problems. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is characterized by comprising the following (1) and (2). (1) In an internal combustion engine that burns a lean air-fuel mixture, it absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the air-fuel ratio of the inflowing exhaust gas is stoichiometric or rich. The NOx absorbent having no oxygen absorbing power is disposed in the exhaust passage of the internal combustion engine, and (2) the SOx absorbent is disposed upstream from the position where the NOx absorbent is disposed.

Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a three-way catalyst for purifying CO, HC and NOx is required in a downstream portion from a portion of the NOx absorbent disposed in the exhaust passage of the internal combustion engine. It is also characterized by being arranged according to.

Further, the present invention also provides an exhaust gas purification method, which is characterized in that the exhaust gas purification device for an internal combustion engine is used.

<Effect> The exhaust gas purifying apparatus for an internal combustion engine and the exhaust gas purifying method using the same according to the present invention purify exhaust gas (especially NOx) generated by fuel combustion of the internal combustion engine more effectively. The exhaust gas purifying apparatus of the present invention has one of its main components in that a NOx absorbent having no oxygen absorbing power is disposed in an exhaust passage of an internal combustion engine, and is included in the above-mentioned prior art. Some of the various problems can be solved.

That is, in an exhaust gas purification apparatus in which a NOx absorbent having an oxygen absorbing power (particularly, a NOx absorbent using a cerium-zirconium composite oxide and other substances) is disposed in an exhaust passage of an internal combustion engine. When the air-fuel ratio of the inflowing exhaust gas is lean, SO ₂ is absorbed by the SOx absorbent, but when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio or rich, the SOx absorbed by the SOx absorbent is released, and the NOx is absorbed. Reacts with oxygen absorbed in the agent
₃ is generated.

The generated SO ₃ is used as NO in the NOx absorbent.
Is absorbed as Ox, so that the NOx absorbent
It is often the case that the fuel cell is saturated by x and cannot absorb NOx.

However, NO having no oxygen absorbing power
In the present invention using the x absorbent, such a problem is greatly improved.

[Specific Description of the Invention] An exhaust gas purifying apparatus for an internal combustion engine according to the present invention is typically an SOx absorbent in an internal combustion engine that burns a lean air-fuel mixture. A NOx absorbent having no oxygen-absorbing power in a downstream portion thereof, and a three-way catalyst disposed in a downstream portion of a portion where they are disposed as necessary. is there.

<Exhaust Gas Purifying Apparatus—Internal Combustion Engine> The exhaust gas purifying apparatus according to the present invention can be used for any internal combustion engine.

For example, the engine may be a two-cycle or four-cycle engine classified by the stroke and operation of the piston.
It may be a spark ignition engine, a compression ignition engine classified by a fuel ignition device, and even a gasoline engine, a diesel engine, a petroleum engine, an alcohol engine, and other engines classified by a used fuel. Can be. In addition, these are listed as examples, and the present invention is not limited to these at all.

An internal combustion engine to which the present invention is applied is
The condition that "lean mixture is burned" is imposed, but this does not mean that the lean mixture is always burned, but the stoichiometric air-fuel ratio or rich state is used if necessary to This includes the case of burning.

Further, the preparation of the "lean mixture" may be performed by any of mechanical, physical, electrical, and other methods, and a mixing method thereof.

<Exhaust Purification Device-SOx Absorbent> The SOx absorbent constituting the exhaust purification device of the present invention absorbs SOx in the exhaust gas generated from the internal combustion engine when lean and releases it when the stoichiometric air-fuel ratio or rich. Any of them can be used.

In general, for example, alumina (zeolite), activated carbon, and other trapping agents, platinum (P)
t), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (O
s) and noble metals, alkali metals, alkaline earth metals, rare earth elements, nickel (Ni), manganese (M
n), copper (Cu), vanadium (V), chromium (C
An SOx absorbent carrying an active substance consisting of a base metal such as r), zinc (Zn) and the like, and other substances is used.

Typically, zinc (Zn), manganese (M
n), calcium (Ca), and at least one selected from the group consisting of others, and platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium ( An SOx absorbent carrying at least one noble metal selected from the group consisting of Os) and other noble metals is preferable.

The SOx absorbent is not limited to those exemplified above, and may be used alone or in combination of two or more (regardless of the same type or different types). Further, since the usage form of the SOx absorbent is not limited, the SOx absorbent may have a flat shape, a spherical shape, a sub-spherical shape, a granular shape, a three-dimensional network structure plate shape, a mesh shape, and other shapes.

The SOx absorbent can be arranged at any position in the exhaust passage of the internal combustion engine, but is arranged in the exhaust passage of the internal combustion engine at a position upstream of the place where the NOx absorbent and the three-way catalyst are arranged. Is preferred.

In particular, by arranging the SOx absorbent upstream of the arrangement position of the NOx absorbent, the subsequent treatment of NOx in the exhaust gas by the NOx absorbent can be performed more effectively.

<Exhaust Purification Device-NOx Absorbent> The NOx absorbent constituting the exhaust purification device of the present invention absorbs NOx in exhaust gas generated from the internal combustion engine when lean and releases it when the stoichiometric air-fuel ratio or rich. Any of them can be used.

The NOx absorbent having no oxygen-absorbing power of the present invention is typically potassium (K), sodium (Na), using at least one selected from the group consisting of alumina, titania, silica, and zirconia as a carrier. , Lithium (Li), cesium (Cs), and other alkali metals, calcium (Ca), strontium (Sr),
Barium (Ba) and other alkaline earth metals,
And at least one basic substance selected from the group consisting of scandium (Sc), yttrium (I), lanthanum (La), and other rare earth elements, and platinum (Pt);
Palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os),
And a NOx absorbent carrying at least one noble metal selected from the group of noble metals and other noble metals, which does not contain ceria or cerium-zirconium composite oxide, and an oxidizing absorbent equivalent thereto. It is a NOx absorbent.

According to the above NOx absorbent, oxygen is not absorbed even when the air-fuel ratio of the inflowing exhaust gas is lean. Therefore, even when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich, , S released from SOx absorbent
Since Ox (mainly SO ₂ ) or H ₂ S does not cause an oxidation reaction to become SO _{3 in the} NOx absorbent, SO ₃
As a result, the NOx absorbent does not absorb the NOx, and as a result, the situation where the NOx absorbent is saturated by the SOx and the NOx absorbent cannot be absorbed does not occur.

It should be noted that these NOx absorbents are not limited to those exemplified above, and may be used alone or in combination of two or more (regardless of the same type or different types). Further, since the use form of the NOx absorbent is not limited, it may be a flat shape, a spherical shape, a subspherical shape, a granular shape, a three-dimensional network structure plate shape, a mesh shape, and other shapes.

The NOx absorbent can be arranged at any position in the exhaust passage of the internal combustion engine. Is also preferably arranged in the upstream part.

In particular, by disposing the NOx absorbent downstream of the arrangement position of the SOx absorbent, the subsequent NOx
The treatment of NOx in the exhaust gas by the absorbent can be facilitated, and the three-way catalyst disposed as needed in the downstream portion from the disposition position of the NOx treating agent can be effectively used.

<Exhaust gas purifier-optional three-way catalyst> In the exhaust gas purifier of the present invention, if necessary, three types of pollutants of CO, HC and NOx can be simultaneously purified in the exhaust passage of the internal combustion engine. A source catalyst can be placed.

In the exhaust gas purifying apparatus of the present invention, the three-way catalyst used as required may be any catalyst that can efficiently treat HC, CO and NOx pollutants. Alternatively, a three-way catalyst known and commonly used in the art can be used.

For example, in general, a catalyst comprising one or a combination of two or more of platinum (Pt), palladium (Pd), rhodium (Rh), and other noble metals, and a palladium ( Pd) -based catalyst and at least one noble metal selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), and others, using cerium (Ce) and alumina, zeolite, and others as carriers Or cerium oxide, calcium (Ca), and strontium (S
r), barium (Ba), and other alkaline earth metals, calcium (Ca), strontium (Sr),
Barium (Ba) and other alkaline earth metals,
There is a catalyst that supports scandium (Sc), yttrium, and other rare earth elements.

The three-way catalyst optionally used in the present invention comprises at least one noble metal selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh) and others using alumina as a carrier, and A catalyst supporting cerium oxide or a cerium-zirconium composite oxide and having improved low-temperature activity is preferable.

These three-way catalysts are not limited to those exemplified above, and may be used alone or in combination of two or more (regardless of the same type or different types). Further, since the usage form of the three-way catalyst is not limited, the three-way catalyst may have a planar shape, a spherical shape, a subspherical shape, a granular shape, a three-dimensional network structure plate shape, a mesh shape, and other shapes.

The three-way catalyst can be arranged at any position in the exhaust passage of the internal combustion engine. However, in the exhaust passage of the internal combustion engine, the three-way catalyst is arranged downstream of the place where the SOx absorbent and the NOx absorbent are arranged. Is preferred.

By arranging the three-way catalyst particularly downstream of the SOx absorbent and the NOx absorbent, CO, HC, NOx
Can be efficiently processed finally.

<Exhaust gas purifier-other optional components>
The exhaust gas purifying apparatus of the present invention has an SO.
Although the x absorbent, the NOx absorbent having no oxygen absorbing power and, if necessary, the three-way catalyst are required as essential components, not only these components but also the spirit of the present invention are not deviated. Other components may be included in the scope.

Therefore, a trapping agent or a catalyst for adsorbing CO, HC, etc., a system for rapidly heating the catalyst with an external electric power or a burner, and others may be used alone or in combination of two or more.

<Exhaust Gas Purification Method Using Exhaust Gas Purifier> The exhaust gas purifier of the present invention is typically provided with an SOx absorbent and N 2 gas downstream of a manifold which is an exhaust gas outlet of an internal combustion engine.
An internal combustion engine exhaust passage is provided, which is arranged in the order of an Ox absorbent and, if necessary, a three-way catalyst.

Further, an embodiment of the exhaust gas purifying apparatus of the present invention and an exhaust gas purifying method using the exhaust gas purifying apparatus of the present invention are as follows.
Typically, it is performed by the steps (1) to (4). (1) Exhaust gas generated by combustion of the lean mixed fuel in the internal combustion engine passes through an exhaust manifold by an exhaust valve, and flows into an exhaust passage in the internal combustion engine in which the exhaust emission control device of the present invention is installed. I do. (2) The inflowing exhaust gas first passes through the SOx absorbent.
At this time, when the air-fuel ratio of the inflowing exhaust gas is finely adjusted to be lean or (theoretical air-fuel ratio or rich), SOx is adsorbed or released to the SOx absorbent by an oxidation or reduction reaction. (3) Subsequently, the inflowing exhaust gas passes through the NOx absorbent disposed downstream of the SOx absorbent. At this time, when the air-fuel ratio of the inflowing exhaust gas is finely adjusted to be lean or (theoretical air-fuel ratio or rich), NOx is adsorbed or released to the NOx absorbent by an oxidation or reduction reaction. Most of the NOx is converted into N ₂ by this step. (4) Finally, the treated exhaust gas passes through the passage of the internal combustion engine as it is and is released to the atmosphere or NOx
By passing through a three-way catalyst arranged as necessary downstream of the absorbent, NOx, HC, and CO in the exhaust gas are efficiently purified and released.

<Exhaust Gas Purification Apparatus-Utilization> The exhaust gas purification apparatus of the present invention can be used for any apparatus using an internal combustion engine. For example, transporters (automobiles, such as passenger cars, buses, trucks, and others, railcars, motorcycles, motorized bicycles, heavy equipment, and other things), agricultural and forestry and fishery machinery (tilling machines, tractors,
Combine and other things, chainsaws, minecarts, timber transporters and other things, ships, fishing boats, motorboats and other things), civil engineering machines (cranes, presses, excavators and other things), generators, And various other fields. However, the exhaust gas purification device of the present invention
It is not limited to the use of those exemplified above.

[0057]

The following embodiments and examples illustrate the present invention in more detail. Therefore, the following embodiments and examples are merely enumerated and listed for easy understanding of the contents of the present invention, and do not limit the scope of the present invention in any way.

Example 1 (1) Sample Machine Example 1 uses an engine which is an internal combustion engine shown in FIG. 1 and an exhaust gas purifying apparatus of the present invention connected to an exhaust port of the engine. Do it. In FIG. 1, reference numeral 1 denotes an exhaust manifold, reference numeral 2 denotes an SOx absorbent, and reference numeral 3 denotes N.
Ox absorbent.

(2) Absorbent used The SOx absorbent and the NOx absorbent used in Example 1 were prepared as follows. SOx Absorbent Acetic acid and water were added to commercially available alumina (BET specific surface area: 200 m ² / g) powder, and the mixture was pulverized for 1 hour with a ball mill to form a slurry. A commercially available 400-cell cordierite honeycomb (outer diameter: 106 mm, length: 114 mm) is immersed in this slurry, pulled up, and after removing excess slurry with an air gun, dried at 105 ° C. for 30 minutes, and further dried at 500 ° C.
For 1 hour. The amount of the attached slurry is 120 g /
L. Based on the water absorption of the honeycomb, Pt is 1 g
A [Pt (NH ₃ ) ₄ ] Cl ₂ solution is prepared so that / L can be supported. After the honeycomb with the slurry attached is immersed in this solution, it is dried at 105 ° C. for 30 minutes, and further dried at 500 ° C.
Calcination was carried out at ℃ for 1 hour. Thereafter, Ca was loaded using a Ca (NO ₃ ) ₂ solution so that 6.5 g / L of Ca could be loaded in the same manner as Pt, to obtain an SOx absorbent.

[0060] Oxygen absorbers the NOx absorbent commercial TiO ₂ (BET specific surface area 120 m ² / g) powder in acetic acid and free water was added and the slurry was milled with a ball mill for 1 hour. A commercially available 400-cell cordierite honeycomb (outer diameter: 106 mm, length: 114 mm) is immersed in this slurry, pulled up, and after removing excess slurry with an air gun, dried at 105 ° C. for 30 minutes, and further dried at 500 ° C. for 1 minute.
Bake for hours. The amount of the attached slurry is 150 g / L. Based on the amount of water absorbed by this honeycomb, Pt is 3.5 g
/ L, Rh is 0.35 g / L, so that [Pt
(NH ₃ ) ₄ ] A mixed solution of Cl ₂ and Rh (NO ₃ ) ₃ was prepared. After dipping the honeycomb with the slurry attached to this solution, the excess solution was removed with an air gun, dried at 105 ° C. for 30 minutes, and fired at 500 ° C. for 1 hour. Then, Pt
And using a barium acetate solution so as to support 28 g / L of Ba in the same manner as in the case of Rh to obtain a NOx absorbent containing no oxygen absorbent.

(3) Implementation Details In the engine shown in FIG. 1, fuel in a lean mixture is burned. The exhaust gas generated by the combustion flows through the exhaust valve and the exhaust manifold into the exhaust passage of the internal combustion engine in which the exhaust gas purification device of the present invention is disposed.

The exhaust gas that has flowed in is first treated with a SOx absorbent. At this time, when the air-fuel ratio of the inflowing exhaust gas is lean, SOx is reduced by the metal carried on the SOx absorbent.
(The main component is SO ₂ ) is oxidized to SO ₃ and absorbed by the SOx absorbent.

When the air-fuel ratio of the exhaust gas flowing into the SOx absorbent becomes a stoichiometric air-fuel ratio or rich, the SO ₃ absorbed by the SOx absorbent becomes a reducing component (CO, H) in the exhaust gas.
C, H ₂ ), and is released from the SOx absorbent as a chemical substance of SO ₂ or H ₂ S.

Next, the exhaust gas is treated with the NOx absorbent disposed downstream of the SOx absorbent. At this time, NO
x When the air-fuel ratio of the exhaust gas flowing into the absorbent is lean,
NOx (main component is NO) is oxidized to NO ₂ by the metal supported on the NOx absorbent and absorbed by the NOx absorbent.
At this time, since SOx is completely absorbed by the SOx absorbent,
It is not absorbed at all by the NOx absorbent.

When the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is set at the stoichiometric air-fuel ratio or rich, most of the NOx absorbed by the NOx absorbent is exhausted as NO and the metal carried on the NOx absorbent is discharged. reducing substances in the exhaust gas above (CO, HC, H ₂₎ is reduced by the majority of the NOx is reduced to harmless N _2.

At this time, the SO released from the SOx absorbent is
₂ and H ₂ S, without being oxidized to S0 ₃ in the NOx absorbent (when the air-fuel ratio is lean, the NOx absorbent is because oxygen is not absorbed), i.e., the NOx absorbent Released as is without absorption.

As described above, it is up to the present inventors to consider that the exhaust gas purifying apparatus of the present invention has the above-described chemical and physical reactions acting in the exhaust gas purifying system of the internal combustion engine.

Example 2 (1) Sample Machine Example 2 uses an engine which is an internal combustion engine shown in FIG. 2 and an exhaust gas purifying apparatus of the present invention connected to an exhaust port of the engine. Do it. 2, reference numeral 4 denotes an exhaust manifold, reference numeral 5 denotes an SOx absorbent, and reference numeral 6 denotes N.
The Ox absorbent and the symbol 7 indicate a three-way catalyst.

(2) Absorbent Used, Three- Way Catalyst SOx Absorber, NOx Absorber The same absorbent as in the first embodiment is used. Three-way catalyst The three-way catalyst comprises alumina as a carrier, at least one noble metal selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh) and others, and cerium oxide or cerium-zirconium composite oxide. A catalyst that supports the substance and has improved low-temperature activity is used.

(3) Implementation Details The operation is performed in the same manner as in the first embodiment. It can be seen that the exhaust gas can be further purified because the three-way catalyst is arranged downstream of the NOx absorbent.

<Comparative Example 1> (1) Sample Machine In Comparative Example 1, an engine which is an internal combustion engine shown in FIG. 3 and an exhaust gas purifying device (conventional type) connected to an exhaust port of the engine were used. Perform using Note that reference numeral 8 in FIG.
Is an exhaust manifold, 9 is an SOx absorbent, 10 is
Indicates a NOx absorbent.

(2) Absorbent used SOx absorbent The same absorbent as in Example 1 is used.

NOx Absorbent Containing Oxygen Absorber The NOx absorbent used in Comparative Example 1 was prepared as follows. Commercially available Al ₂ O ₃ (BET specific surface area 200 m ² /
g) Cerium oxide powder is added to and mixed with the powder so that the proportion of cerium oxide in the total mixture is 25% by weight. Further, acetic acid and water were added to the mixed powder, and the mixture was pulverized for 1 hour with a ball mill to form a slurry. A commercially available 400 cell cordierite honeycomb (outer diameter: 106 m) was added to this slurry.
m, 114 mm in length) and then pulled up, and after removing excess slurry with an air gun, drying at 105 ° C. for 30 minutes and baking at 500 ° C. for 1 hour. The amount of the attached slurry is 150 g / L. Based on the water absorption of the honeycomb, Pt was 3.5 g / T and Rh was 0.35 g / T.
L, [Pt (NH ₃ ) ₄ ] Cl ₂ and Rh
A mixed solution of (NO ₃ ) ₃ was prepared. After immersing the honeycomb with the slurry attached to this solution, the excess solution was removed with an air gun, dried at 105 ° C for 30 minutes, and dried at 500 ° C for 1 minute.
Fired for hours. After that, Ba was loaded using a barium acetate solution so that 28 g / L of Ba could be loaded by the same method as in the case of Pt and Rh to obtain a NOx absorbent containing an oxygen absorbent.

(2) Implementation Details As in the first embodiment, in the engine shown in FIG. 3, fuel in a lean mixture state is burned. Exhaust gas generated by combustion passes through exhaust valves and exhaust manifolds.
The exhaust gas flows into an exhaust passage of an internal combustion engine in which an exhaust purification device (conventional product) is arranged.

The inflowing exhaust gas is first treated with a SOx absorbent. At this time, when the air-fuel ratio of the exhaust gas flowing into the SOx absorbent is lean, SOx (the main component is SO ₂ ) is oxidized to SO ₃ by the metal supported on the SOx absorbent, and S
Absorbed by Ox absorbent.

When the air-fuel ratio of the exhaust gas flowing into the SOx absorbent fluctuates at the time of the stoichiometric air-fuel ratio or rich, the SO ₃ absorbed by the SOx absorbent becomes a reducing component (C) in the exhaust gas.
O, HC, and H ₂ ), and are released from the SOx absorbent as SO ₂ or H ₂ S chemicals.

Next, the exhaust gas is treated with the NOx absorbent disposed downstream of the SOx absorbent. At this time, NOx
NO when the air-fuel ratio of the exhaust gas flowing into the absorbent is lean
NOx (main component is N
O) is oxidized to NO ₂ and absorbed by the NOx absorbent. Also, since the air-fuel ratio of the exhaust gas is lean,
Absorbed by Ox absorbent. Furthermore, SOx is not absorbed at all by the NOx absorbent because SOx is absorbed in its entirety by the SOx absorbent.

When the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is set at the stoichiometric air-fuel ratio or rich, the NOx absorbed by the NOx absorbent is mostly discharged as NO, and is also carried by the NOx absorbent on the metal. It is reduced by reducing substances (CO, HC, H ₂ ) in the exhaust gas and reduced to mostly harmless N ₂ .

At this time, SO ₂ released from the SOx absorbent
In addition, H ₂ S is oxidized to SO ₃ by the NOx absorbent by the oxygen absorbed by the NOx absorbent, and is adsorbed by the NOx absorbent.

The SOx absorbed by the NOx absorbent is NOx
Since it is less likely to be released, SOx is absorbed and accumulated in the NOx absorbent with the passage of time, and the NOx absorption capacity is reduced.

As described above, the exhaust gas purifying apparatus of Comparative Example 1
It is up to the present inventors to consider that the chemical and physical reactions are acting in the exhaust gas purification system of the internal combustion engine as described above.

<Evaluation> The exhaust gas purification apparatus described in Examples 1 and 2 and Comparative Example 1 was mounted on a vehicle equipped with a 2L lean burn engine according to FIG. 1, FIG. 2 or FIG. I ran 1,000 km. The fuel used contained 50 ppm of sulfur.
After traveling, a vehicle test was performed in the same state as in the Japanese exhaust gas measurement mode 10-15 mode.
And the performance of the catalyst.

The measurement results are as shown in Table 1 below.

[0084]

[Table 1] As can be seen from Table 1, it can be seen that Examples 1 and 2 have a higher NOx conversion rate than Comparative Example 1.

[0085]

As can be understood from the above embodiments, the exhaust gas purifying apparatus for an internal combustion engine and the exhaust gas purifying method using the same according to the present invention provide a NOx absorbent having no oxygen absorbing power in the exhaust passage of the internal combustion engine. The NOx absorbing ability can be maintained even if the NOx absorbent is used for a long time. Further, exhaust gas (particularly, NOx) generated by fuel combustion of the internal combustion engine can be more effectively purified. This point is as described in the section of [Summary of the Invention].

[Brief description of the drawings]

FIG. 1 shows an engine in which an exhaust gas purification device according to the present invention is attached to an internal combustion engine.

FIG. 2 shows an engine in which an exhaust gas purification device according to the present invention is attached to an internal combustion engine.

FIG. 3 shows an engine in which a conventional exhaust gas purification device is attached to an internal combustion engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust manifold 2 SOx absorbent 3 NOx absorbent 4 Exhaust manifold 5 SOx absorbent 6 NOx absorbent 7 Three-way catalyst 8 Exhaust manifold 9 SOx absorbent 10 NOx absorbent

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 B01J 23/56 301A (72) Inventor Tomotaka Hirota Johnson Massey Japan K.K. Inside the Kitsuregawa Technical Center (72) Inventor Hideaki Muraki Inside the Kitsuregawa Industrial Park, Kitsuregawa-cho, Shioya-gun, Tochigi Prefecture Johnson Massey Japan Co., Ltd. Inside the Kitsuregawa Technical Center

Claims (4)

[Claims] An exhaust gas purifying apparatus for an internal combustion engine, comprising: (1) and (2): (1) In an internal combustion engine that burns a lean mixture, NOx is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean, and the absorbed NOx is released when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio or rich. The NOx absorbent having no oxygen absorbing power is disposed in the exhaust passage of the internal combustion engine, and (2) the SOx absorbent is disposed upstream from the position where the NOx absorbent is disposed. 2. The NOx absorbent having no oxygen absorbing power is selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements, using at least one selected from the group consisting of alumina, titania, silica, and zirconia as a carrier. At least one basic substance, and platinum (Pt), palladium (Pd), rhodium (Rh),
At least one noble metal selected from the group consisting of ruthenium (Ru), iridium (Ir), osmium (Os), and other noble metals, comprising ceria or cerium.
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the NOx absorbent is a zirconium composite oxide and a NOx absorbent that does not contain an oxidation absorbent equivalent thereto. 3. A three-way catalyst for purifying CO, HC and NOx is disposed downstream from a location of a NOx absorbent disposed in an exhaust passage of an internal combustion engine. 2. The exhaust gas purification device according to item 2. 4. An exhaust gas purification method for an internal combustion engine, comprising using the exhaust gas purification device according to claim 1.