JPH1181988A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the lean burning exhaust gas purifying performance while effectively preventing the contamination of the lean NOx catalyst with SOx by providing an SOx catching material and a lean NOx catalyst in an exhaust gas flow passage, and raising temperature of the SOx catching material in the reducing atmosphere. SOLUTION: During the operation of an engine provided with an SOx catching material 17 and a lean NOx catalyst 18 in order in an exhaust system thereof, an ECU 25 evaluates the engine operating condition and the condition of the lean NOx catalyst 18 so as to decide the air-fuel ratio, and controls an injector 5. After eliminating the SOx in the exhaust with the SOx catching material, at the time of theoretical air-fuel ratio operation, NOx, HC and CO in the exhaust gas are purified by a catalystic converter rhdium function of the lean NOx catalyst 18, and at the time of lean burning operation, NOx is purified by the NOx catching ability, and while HC and CO are oxidized for purifying by the catalyst function, and at the same time, a part of the NOx is deoxidized for purifying. When the NOx purifying ability is lowered, air-fuel ratio is shifted to a rich side so as to restore the NOx adsorbing ability of the lean NOx catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas discharged from an internal combustion engine of an automobile or the like, and more particularly to a device for purifying exhaust gas discharged from an internal combustion engine capable of lean air-fuel ratio combustion (lean burn).

[0002]

2. Description of the Related Art Carbon monoxide (CO) and hydrocarbons (HC: H) contained in exhaust gas discharged from an internal combustion engine of an automobile or the like are used.
Hydrocarbons, nitrogen oxides (NOx), and the like adversely affect the human body as air pollutants and cause problems such as hindering plant growth. So far, great efforts have been made to reduce these emissions, and in addition to reducing the amount generated by improving the combustion method of the internal combustion engine, a method of purifying the exhaust gas using a catalyst or the like has been developed. Has been promoted and has achieved steady results. For gasoline engine vehicles, Pt and Rh, which are three-way catalysts, are the main components of activity, and HC and CO
The mainstream is a method using a catalyst that renders harmless by simultaneously oxidizing NO and reducing NOx.

[0003] By the way, due to its characteristics, the three-way catalyst effectively acts only on exhaust gas generated by burning near the theoretical air-fuel ratio called a window. So conventionally,
Although the air-fuel ratio fluctuates according to the driving conditions of the vehicle, the fluctuation range is, in principle, the theoretical air fuel (A (weight of air) / F (weight of fuel) = about 14.7 in the case of gasoline; The air / twist ratio is represented by A / F = 14.7, but this value varies depending on the fuel type.) However, if the engine can be operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, fuel efficiency can be improved, and lean burn combustion technology has been developed. In recent years, combustion at an air-fuel ratio higher than the stoichiometric air-fuel ratio has been promoted. The development of lean burn vehicles and vehicles equipped with in-cylinder injection engines (Direct Injection vehicles; hereinafter referred to as DI vehicles) have been advanced and some of them have been put to practical use. However, as described above, when lean burn exhaust gas (hereinafter referred to as "lean exhaust gas") is purified by a current three-way catalyst, HC and CO can be oxidized and purified, but NOx cannot be effectively reduced and purified. Therefore, for full-fledged use of lean burn vehicles and DI vehicles, a technology for purifying exhaust gas generated by lean burn, that is, a technology for purifying HC, NO, and NOx in exhaust gas containing a large amount of oxygen (O ₂ ). Development, especially NO
It is essential to develop a technology for purifying x.

In order to solve this problem, the development of a new catalyst and a catalyst system has been promoted. One of them is to once capture NOx in lean exhaust gas by a method such as adsorption, absorption or occlusion, and to obtain the NOx in a reducing atmosphere. There is a method of reducing and purifying trapped NOx. This method is disclosed, for example, in JP-A-62-97630, JP-A-62-106826, JP-A-62-117620 and Japanese Patent No. 2600492.

[0005] One of the practical problems of this method is poisoning by sulfur compounds.

[0006] Sulfur (S) is contained in fossil fuels such as gasoline, and sulfur is mainly present as SOx in combustion exhaust gas. SOx is composed of sulfur dioxide (SO ₂ ) and sulfur trioxide (S
O ₃ ), but the former is usually the majority. SOx is easily bonded to the NOx trapping material, and has a stronger binding force than NOx. Therefore, SOx is trapped by the NOx trapping material and N
When occupying the Ox trapping site, the so-called SOx poisoning phenomenon occurs, in which the NOx trapping ability is greatly reduced and eventually no longer shows the trapping ability.

In order to solve this problem, for example, Japanese Patent Application Laid-Open No. 8-281116 discloses an N-type carrier containing zirconium phosphate as a carrier.
An Ox trapping material is disclosed in JP-A-9-926, and a NOx trapping material using a composite oxide of Ti, Zr and Al as a carrier is disclosed in JP-A-6-66129.
JP-A-9-32619 proposes an apparatus for regenerating a SOx-poisoned NOx trapping material. However, these are
Although effective in reducing the problem of Ox poisoning, in addition to the limited effects, there are also problems such as the complexity of the device. In fact, studies have been continued in search of more practical methods. is there.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to reduce SOx poisoning and effectively reduce the amount of N2 from lean burn exhaust gas of an internal combustion engine.
It is an object of the present invention to provide an apparatus capable of removing and detoxifying harmful components such as Ox.

[0009]

As a solution to the above-mentioned problem, a method is conceivable in which an SOx trapping material is provided in an exhaust gas passage of an internal combustion engine and a lean NOx catalyst is provided downstream of the SOx trapping material. This method first requires that the SOx trapping material has a high SOx trapping ability. Further, in this method, SOx accumulates in the trapping material and eventually loses the SOx trapping ability, so that regeneration of the trapping material is indispensable. Therefore, it is essential that the trapping material can be easily regenerated. Further, as described later, it is necessary that the sulfur compound discharged in the regeneration operation does not cause poisoning of the lean NOx catalyst located downstream, or that the NOx catalyst can be easily regenerated with little poisoning.

The present inventor has solved the above-mentioned problems and has accomplished the present invention.

In the present invention, the above objects are solved by the following methods.

The most significant feature of the present invention is that SOx in exhaust gas is trapped in an exhaust gas passage of an internal combustion engine by a method such as adsorption or absorption, and an oxidizing agent and a reducing agent at a temperature higher than the trapped temperature and contained in the exhaust gas. In the redox stoichiometry, an SOx trapping material for desorbing or releasing trapped SOx when the amount of the reducing agent is equal to or more than that of the oxidizing agent (hereinafter referred to as a reducing atmosphere) is provided. When there is a large amount of oxidizing agent relative to the reducing agent (hereinafter referred to as oxidizing atmosphere) in the redox stoichiometric relationship between
C) and at the same time oxidize and purify carbon monoxide (CO)
x is trapped by a method such as adsorption or absorption, and the NOx trapped in a reducing atmosphere is contact-reduced to restore the NOx trapping ability, while at the same time reducing and purifying NOx in the exhaust gas and HC (hydrocarbon), CO (carbon monoxide). NOx that purifies oxidized water
A catalyst is provided, and the SOx trapping material is heated in a reducing atmosphere to increase S
An exhaust gas purification apparatus characterized by restoring Ox trapping ability.

Here, the oxidizing agent is O ₂ , nitric oxide (N
O), nitrogen dioxide (NO ₂ ), etc., which are mainly O ₂ .
The reducing agent is HC supplied to the internal combustion engine, HC (including oxygen-containing hydrocarbon) as a derivative thereof generated in the combustion process, C
O, hydrogen (H ₂ ), and other reducing substances such as HC added to exhaust gas as a reducing component described later.

[0014] SOx in the exhaust gas is generally composed of SO ₂ and part of SO ₃ voluminous. Therefore, these can be effectively trapped by converting them into sulfites and / or sulfates.

The SOx trapping material that achieves this object includes alkali metals such as lithium (Li), potassium (K) and sodium (Na), and magnesium (Mg) and calcium.
(Ca), strontium (Sr), alkaline earth metals such as barium (Ba), aluminum (Al), titanium (Ti), vanadium (V), chromium (C
r), manganese (Mn), iron (Fe), cobalt (C
o), first transition elements such as nickel (Ni), copper (Cu), zinc (Zn), lanthanum (La), cerium (C
e) a composition comprising a metal containing at least one element selected from rare earth metals such as e) and a metal oxide (or composite oxide), and a composition comprising the composition supported on a porous heat-resistant metal oxide Things can be applied.

In the above SOx trapping material, SO ₂ in the exhaust gas becomes a sulfite and SO ₃ becomes a sulfate. The sulfite is oxidized by O ₂ contained in the exhaust gas and partly changes to sulfate. As a matter of course, when the exhaust gas is a lean burn exhaust gas in an oxidizing atmosphere, the oxidation of the sulfite easily proceeds. SO ₃ is captured as a sulfate as described above. Some of the SO ₃ is combined with the water vapor in the exhaust gas to form sulfuric acid, which is attached to the SOx trapping material or scattered as a sulfuric acid mist. In any case, SOx trapped by the SOx trapping agent exists mainly as sulfite and sulfate.

Further, the SOx trapping material of the present invention includes:
Lithium (Li), potassium (K), sodium (N
a) and alkaline earth metals such as magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba), and titanium (Ti);
And aluminum (Al), and vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Z
n) and at least one element selected from rare earth metals such as lanthanum (La) and cerium (Ce), and noble metals such as platinum (Pt), rhodium (Rh) and palladium (Pd). A composition comprising a metal containing at least one element selected from the group consisting of a metal and a metal oxide (or a composite oxide), and a composition comprising the composition supported on a porous heat-resistant metal oxide can be used.

The present composition is characterized in that a precious metal such as platinum (Pt), rhodium (Rh), palladium (Pd) or the like is added to the above composition. In the present SOx trapping material, SO
When capturing x, SO ₂ is converted to S
The ability to capture as O ₃ is enhanced. As a result, SOx
Capture ability is enhanced.

Further, as the SOx trapping material in the present invention, aluminum (Al), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Z
n) and at least one element selected from rare earth metals such as lanthanum (La) and cerium (Ce), and noble metals such as platinum (Pt), rhodium (Rh) and palladium (Pd). A composition comprising a metal containing at least one element selected from the group consisting of a metal and a metal oxide (or a composite oxide), and a composition comprising the composition supported on a porous heat-resistant metal oxide can be used.

In the present SOx trapping material, SOx is converted into SO _{3 by} the catalytic action of the noble metal and trapped as a transition metal sulfate. For example, a stable oxide A of the first transition element Al
l ₂ O ₃ becomes aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) to capture SOx. In addition, CeO _2, a stable oxide of Ce, which is a rare earth metal, becomes Ce (SO ₄ ) ₂ and captures SOx. These sulfates are more easily regenerated in reducing atmospheres than alkali metal and alkaline earth metal sulfates.

Therefore, there is a feature that the degree of temperature increase performed in the regeneration is reduced.

In the above-mentioned SOx trapping material, the SOx trapping ability reduced by trapping SOx is restored by placing the SOx trapping material at a higher temperature than in the SOx trapping and in a reducing atmosphere. In the method of the present invention, placing the SOx trapping material upstream of the NOx trapping material facilitates achieving this temperature condition.

Recovery of the SOx trapping ability releases SO ₂ and proceeds as follows. In the following, the SOx trapping component is represented by alkali metal M, and the reducing agent is represented by hydrocarbon (HC). [Sulfite sulfation]

[0024]

## STR1 ## M ₂ SO ₄ + HC → M ₂ SO ₃ + CO ₂ M: SOx trapping metal component HC: Reducing agent component [Recovery of SOx trapping ability of sulfite]

[0025]

## STR2 ## M ₂ SO ₃ + HC → M ₂ O + SO ₂

[0026]

Embedded image M ₂ O + CO ₂ → M ₂ CO ₃ (SOx trapping component) The released SO ₂ is contained in the gas of the reducing atmosphere and reaches the lean NOx catalyst located downstream. The present invention prevents the SOx poisoning of the lean NOx catalyst according to the release SO ₂ in the following materials and methods.

The lean NOx catalyst which achieves the object is composed of lithium (Li), sodium (Na), potassium (K),
At least one selected from magnesium (Mg), strontium (Sr), barium (Ba) and calcium (Ca), at least one selected from rare earths such as cerium (Ce), platinum (Pt), rhodium (Rh) ,
Metals and metal oxides containing at least one element selected from noble metals such as palladium (Pd) and, if necessary, at least one element selected from silica (Si), titanium (Ti) and zirconium (Zr) (Or a composite oxide) and a composition obtained by supporting the composition on a porous heat-resistant metal oxide.

Exhaust gas containing SO ₂ generated by regeneration comes into contact with the lean NOx catalyst, but the amount of SO ₂ captured is small for the following reasons. That is, SOx poisoning is not much received.

First, the bonding force of SO ₂ is weaker than that of SO ₃ . Also, SO ₂ is in a reducing atmosphere and is not converted to SO ₃ and captured. Furthermore, the contact time and concentration of SO ₂ are shorter and higher concentration than when exhaust gas passes directly. Further, SOx trapping agent Upon regeneration of the SOx trapping agent are heated, the temperature of the exhaust gas containing SO ₂ is increasing.

Further, SO ₂ poisoning can be completely prevented by raising the temperature of the SOx trapping material as required. In this case, it is necessary to raise the temperature, but since SO ₂ is adsorbed as SO ₂ or trapped as sulfite,
A temperature lower than the temperature required for regeneration of the SOx trapping material is sufficient.

In the method of the present invention, the state in which the amount of the reducing agent is equal to or larger than the amount of the oxidizing agent in the combustion exhaust gas (oxidizing atmosphere) can be prepared by the following method.

The combustion conditions in the internal combustion engine are set to the stoichiometric air-fuel ratio or excess fuel (rich). It is also possible to add a reducing agent to lean burn exhaust gas generated by lean combustion.

The former can be achieved by the following method.

A method of controlling the fuel injection amount according to the output of an oxygen concentration sensor provided in an exhaust duct, the output of an intake air flow sensor, and the like. In this method, a part of the plurality of cylinders is made excessive and the remaining fuel is made insufficient, and the components in the mixed exhaust gas from all the cylinders have the same amount or larger amount of the reducing agent than the oxidizing agent in the oxidation-reduction stoichiometry relationship. Includes methods for creating states.

The latter can be achieved by the following methods.

A method of introducing a reducing agent upstream of the SOx trapping agent in the exhaust gas stream. Gasoline, light oil, kerosene, natural gas, their reformed products, hydrogen,
Alcohols, ammonia, etc. can be applied. It is also effective to guide the blow-by gas and the canister purge gas upstream of the SOx trapping material, and to introduce a reducing agent such as a hydrocarbon contained therein. In a fuel direct injection type internal combustion engine, it is effective to inject fuel during an exhaust stroke and to input fuel as a reducing agent.

In the present invention, alumina (Al ₂ O ₃ ), titania (TiO ₂ ) and zirconia (Z) are used as the porous heat-resistant metal oxide of the SOx trapping material and the lean NOx catalyst.
Various metal oxides and composite metal oxides including metal oxides such as rO ₂ ), mutual metal oxides thereof, and the like can be applied.

In the present invention, the SOx trapping material and the lean NOx catalyst can be applied in various shapes. The present invention can be applied as a pellet, plate, granule, or powder, including a honeycomb shape obtained by coating a honeycomb-like structure made of a metal material such as cordierite or stainless steel with an adsorption catalyst component.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to specific embodiments of the present invention. The present invention is not limited to the following embodiments and examples, and it goes without saying that there are various embodiments within the scope of the idea.

[Exhaust Gas Purification Apparatus] FIG. 1 is an overall configuration diagram of an apparatus showing one embodiment of an exhaust gas purification apparatus of the present invention.
The apparatus of the present invention includes an engine 99 capable of lean burn, an intake system having an air flow sensor 2, a throttle valve 3, etc., an oxygen concentration sensor (or A / F sensor) 19, an SOx trapping material 17 provided in an exhaust gas flow path, Lean NOx
Exhaust system and control unit (ECU) having catalyst 18 etc.
And so on.

The above exhaust gas purifying device functions as follows. The intake air to the engine is filtered by an air cleaner 1 and then measured by an air flow sensor 2, passes through a throttle valve 3, receives a fuel injection from an injector 5, and is supplied to the engine 99 as a mixture.
The airflow sensor signal and other sensor signals are
ngine Control Unit).

The ECU evaluates the operating state of various internal combustion engines and the state of the lean NOx catalyst to determine the operating air-fuel ratio, and controls the injection time of the injector 5 to set the fuel concentration of the mixture to a predetermined value. . The air-fuel mixture sucked into the cylinder is a spark plug 1 controlled by a signal from the ECU 25.
It is ignited by 0 and burns. The combustion exhaust gas is led to an exhaust system. The exhaust system is provided with a SOx trapping material 17 first, and a lean NOx catalyst 18 provided downstream thereof. Exhaust gas is S
After the SOx is removed by the Ox trapping material, the catalyst reaches the lean NOx catalyst, and purifies NOx, HC, and CO in the exhaust gas by the three-way catalytic function during the stoichiometric air-fuel ratio (stoichiometric) operation. Atmospheric exhaust gas is generated) by purifying NOx with NOx trapping ability and simultaneously oxidizing and purifying HC and CO by a catalytic function which is combined with NOx, and at the same time, reducing and purifying a part of NOx. Further, the NOx purification performance of the lean NOx catalyst is constantly evaluated during the lean burn operation based on the various sensor signals and the determination by the ECU based on the various sensor signals. If the NOx purification performance decreases, the air-fuel ratio of the combustion is shifted to the rich side ( (Reducing atmosphere exhaust gas) to recover the NOx adsorption capacity of the lean NOx catalyst. Through the above operation, the present apparatus effectively purifies exhaust gas under all engine combustion conditions of lean operation and stoichiometric (including rich) operation. Further, when it is evaluated that the NOx purification performance does not sufficiently recover even after the rich operation based on various sensor signals and the determination of the ECU based on the various sensor signals, or at a predetermined timing determined in consideration of fuel consumption and the like, the SOx Regenerate the trapping material. The regeneration is performed by shifting the air-fuel ratio or the like to the rich side to make the exhaust gas a reducing atmosphere, and simultaneously raising the temperature of the SOx trapping material. S
The temperature rise of the Ox trapping material can be achieved by increasing the engine speed. Further, NO is maintained even after the SOx trapping material is regenerated.
If the x purification ability does not sufficiently recover, the lean NOx catalyst is regenerated. The regeneration is performed by shifting the air-fuel ratio and the like to the rich side to produce a reducing atmosphere exhaust gas, and simultaneously raising the temperature of the SOx trapping material. The temperature rise of the lean NOx catalyst can be achieved by increasing the engine speed.

[SOx trapping material]
An example of preparing an x-capture material will be described.

<< SOx Capture Material Example 1 >> SOx Capture Material T-1
Was obtained in the following manner.

An alumina sol as a binder obtained by mixing alumina powder and boehmite in nitric acid was mixed to obtain a nitric acid acidic alumina slurry. 4 cells in the coating liquid
A 00 cell / in ² honeycomb made of cordierite was immersed and then immediately pulled up, and the liquid clogged in the cells was removed by air blowing, dried, and subsequently fired at 450 ° C. This operation was repeated to coat 150 g of alumina per 1 L of apparent volume of the honeycomb. The alumina-coated honeycomb was impregnated with a cerium nitrate (Ce nitrate) solution, dried, and fired at 600 ° C. for 1 hour. Subsequently, a mixed solution of a sodium nitrate (Na nitrate) solution, a titania sol solution, and a magnesium nitrate (Mg nitrate) solution was impregnated, and dried and fired similarly. As described above, Ce, Mg, and alumina are added to alumina (Al ₂ O ₃ ).
Honeycomb SOx trapping material supporting Na and Ti, (18
To give Na, 4Ti, the _{2Mg) -27Ce / Al 2 O 3} .
Here, / Al ₂ O ₃ indicates that each component was supported on Al ₂ O ₃ , and the numerical value before the element symbol indicates the honeycomb apparent volume 1
It is the weight (g) of the indicated metal component carried per L.
The notation order indicates the order in which the components are carried, and the components separated from the components near Al ₂ O ₃ are carried in order, and the components enclosed in parentheses are carried simultaneously. Hereinafter, the composition and configuration of the SOx trapping material and the lean NOx catalyst followed this notation.

<< SOx Capture Material Example 2 >> SOx Capture Material T-2
Was obtained in the following manner.

In the same manner as in T-1, (18Na, 4Ti,
2 mg) was obtained -27Ce / Al ₂ O _3. This was impregnated with a mixed solution of a dinitodiamine Pt nitric acid solution and a rhodium nitrate (Rh nitrate) solution, dried, and baked at 450 ° C. for 1 hour. Further, it was impregnated with a Mg nitrate solution and fired at 450 ° C. for 1 hour. By the above, Ce, Mg, N is added to alumina (Al ₂ O ₃ ).
SOx trapping material supporting a, Ti, Rh, Pt, 2Mg
-(0.2Rh, 2.7Pt)-(18Na, 4Ti, 2M
It was obtained _{g) -27Ce / Al 2 O 3} .

<< SOx Capture Material Example 3 >> SOx Capture Material T-3
Was obtained in the following manner.

First, an alumina-coated honeycomb was obtained by the method shown for the SOx trap T-1. The alumina coated honeycomb is impregnated with a cerium nitrate (Ce nitrate) solution and dried.
It was baked at 00 ° C. for 1 hour. This was impregnated with a palladium nitrate (Pd nitrate) solution, dried and calcined at 450 ° C. for 1 hour. Further, it was impregnated with a Mg nitrate solution and fired at 450 ° C. for 1 hour. Thus, Ce, Pd, and alumina (Al ₂ O ₃ )
SOx trapping material supporting Mg, 2Mg-3Pd-27C
e / Al ₂ O ₃ was obtained.

[Lean NOx Catalyst] An example of preparing a lean NOx catalyst N-1 according to the method of the present invention will be described.

An alumina-coated honeycomb was obtained in the same manner as in the case of the SOx trapping material. The alumina coated honeycomb is impregnated with a cerium nitrate (Ce nitrate) solution, dried and dried.
It was baked at 0 ° C. for 1 hour. Subsequently, sodium nitrate (nitrate N
a) A mixed solution of a solution, a titania sol solution, and a magnesium nitrate (Mg nitrate) solution was impregnated, and dried and fired similarly. Further, it is impregnated with a mixed solution of a dinitodiamine Pt nitric acid solution and a rhodium nitrate (Rh nitrate) solution, dried, and dried.
Calcination was carried out at ℃ for 1 hour. Finally, impregnate with Mg nitrate solution 45
It was baked at 0 ° C. for 1 hour. As described above, alumina (Al
₂ O ₃₎ to Ce, Mg, Na, Ti, Rh, honeycomb lean NOx catalyst carrying Pt, 2Mg- (0.2Rh,
2.7Pt)-(18Na, 4Ti, 2Mg) -27Ce /
Al ₂ O ₃ was obtained.

Test Example 1 The effects of the present invention will be described below with reference to specific test examples.

The exhaust gas purification performance of the adsorption catalyst and the device of the present invention was evaluated.

<< Test Method >> The performance of the exhaust gas purifying apparatus using the SOx trapping material and the lean NOx catalyst obtained by the above method was evaluated by the following method.

A 1.0-liter honeycomb (400 cell / in ² ) SOx trapping material prepared by the method of the present invention immediately below an engine in an exhaust passage of a passenger car equipped with a 1.8-liter lean-burn gasoline engine. Was placed under the floor of the flow, and then a honeycomb-shaped honeycomb having a volume of 1.7 L (400 cells / in
² ) A lean NOx catalyst was placed. The SOx trapping material and the lean NOx catalyst were previously heat-treated in an oxidizing atmosphere at 700 ° C. for 5 hours to be stabilized. The above car, sulfur (S) content 400
The vehicle was driven at a constant speed of 40 km / h on a chassis dynamometer using gasoline containing ppm as fuel. During this time, the air-fuel ratio is A /
F (weight of air A and fuel F) is 22 (exhaust gas is an oxidizing atmosphere), and every 55 seconds, a rich state of A / F = 13 (exhaust gas is a reducing atmosphere) for 0.2 seconds is inserted and lean NOx catalyst The NOx trapping ability was restored. During traveling, the NOx concentration in the exhaust gas was measured by direct analysis using an automobile exhaust gas measuring device. The NOx purification rates listed below were represented by the values of the exhaust gas composition obtained by direct analysis immediately before the insertion of the rich operation. Further, a rich operation was performed in which exhaust gas for regenerating the SOx trapping material described later was used as a reducing atmosphere according to the purpose of the test.

Test Example 1 T-1 was applied to the SOx trap and N-1 was applied to the lean NOx catalyst.

During traveling at 40 km / h, the temperature of the exhaust gas at the inlet of the SOx trapping material was about 450 ° C. In addition, traveling 10h
Each time, the engine speed was increased for 10 minutes in the rich condition of A / F = 14.5 and the exhaust gas temperature at the inlet of the SOx trapping material was reduced to about 6
50 ° C. When the operation was performed by the above method, a NOx purification rate of 90% was obtained at the start of the operation, and this value was substantially maintained until 100 hours.

Test Example 2 T-2 was applied to the SOx trap and N-1 was applied to the lean NOx catalyst.

When the same operation as in Test Example 1 was performed, a NOx purification rate of 90% was obtained at the start of the operation, and this value was almost maintained until 100 hours.

Test Example 3 T-3 was applied to the SOx trapping material, and N-1 was applied to the lean NOx catalyst.

The same operation as in Test Example 1 was performed, except that SOx
In regenerating the trapping material, A / F = 1 every 10 hours of running
The engine speed was increased for 10 minutes in the 4.5 rich state, and the exhaust gas temperature at the inlet of the SOx trapping material was set to about 600 ° C.
When the operation was performed by the above method, a NOx purification rate of 90% was obtained at the start of the operation, and this value was almost maintained until 100 hours.

Test Example 4 T-1 was applied to the SOx trap and N-1 was applied to the lean NOx catalyst.

When the operation was carried out in the same manner as in Test Example 3, a NOx purification rate of 90% was obtained at the start of the operation.
After 00h, it decreased to 80%. At this point, A / F
= 14.5, the engine speed was further increased for 10 minutes, and the exhaust gas temperature at the inlet of the lean NOx catalyst was reduced to about 5
70 ° C. As a result, the performance with a NOx purification rate of 90% was restored.

Comparative Example 1 Only the lean NOx catalyst N-1 was placed under the floor without providing any SOx trapping material. The same operation as in Test Example 1 and a regeneration operation in the case where the SOx trapping material was present were performed.
At the start of operation, a NOx purification rate of 90% was obtained, but 20h
Later it dropped to 60%.

[0065]

As is apparent from the above, according to the apparatus of the present invention, the SOx trapping material is provided in the exhaust gas flow path, and the lean NOx catalyst is provided downstream of the exhaust gas flow path, thereby preventing SOx poisoning of the lean NOx catalyst. In addition, NOx and the like in the lean burn exhaust gas can be effectively purified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an exhaust gas purifying apparatus showing a typical embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Air cleaner, 2 ... Air flow sensor, 3 ... Throttle valve, 5 ... Injector, 6 ... Spark plug, 7
... Accelerator pedal, 8 ... Load sensor, 9 ... Intake air temperature sensor, 12 ... Fuel pump, 13 ... Fuel tank, 17 ...
SOx trapping material, 18 lean NOx catalyst, 19 oxygen sensor, 20 SOx trapping temperature sensor, 21 lean NOx catalyst temperature sensor, 25 ECU, 26 knock sensor, 28 water temperature sensor, 29 crank angle sensor , 99 ... Engine.

Continuing on the front page (72) Inventor Kojiro Okude 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Toshio Ogawa 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Morio Fujitani 1-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi Research Laboratories (72) Inventor Hisao Yamashita, Omikamachi, Hitachi City, Ibaraki Prefecture Hitachi 1-1, Hitachi, Ltd., Hitachi Research Laboratories (72) Inventor Shigeru Azuhata 7-1-1, Omika-cho, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Yuichi Kitahara Hitachinaka, Ibaraki 2520 Address, Takahiro-shi, Hitachi, Ltd.Automotive Equipment Division of Hitachi, Ltd. (72) Inventor Toshifumi Hiratsuka 2520 Address, Ojitaka-Oita, Hitachinaka-shi, Ibaraki Automotive Equipment Division of Hitachi, Ltd. (72) Norihiro Shinozuka, Inventor Hitachinaka If 2520 address Co., Ltd. Hitachi automotive equipment business unit

Claims (6)

[Claims] An SOx in an exhaust gas is supplied to an exhaust gas passage of an internal combustion engine.
Is trapped by a method such as adsorption or absorption, and at a temperature higher than the trapped temperature and in the redox stoichiometry of the oxidizing agent and the reducing agent contained in the exhaust gas, the reducing agent is equal to or more than the oxidizing agent (reducing atmosphere) In the case of (1), an SOx trapping material for desorbing or releasing the trapped SOx is provided, and in the subsequent stream, the amount of the oxidizing agent is larger than that of the reducing agent in the oxidation-reduction stoichiometry of the oxidizing agent and the reducing agent contained in the exhaust gas (oxidizing atmosphere ) In this case, hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas are oxidized and purified, and at the same time, NOx is captured by a method such as adsorption and absorption.
NOx trapped in a reducing atmosphere is catalytically reduced to NO
At the same time as recovering the x trapping ability, a lean NOx catalyst for reducing and purifying NOx in exhaust gas and oxidizing and purifying HC (hydrocarbon) and CO (carbon monoxide) is provided.
An exhaust gas purifying apparatus characterized in that the temperature of the trapping material is raised to recover the SOx trapping ability. 2. The method according to claim 1, wherein the SOx
In recovering the SOx trapping ability by raising the temperature of the trapping material,
At the same time, the lean NOx catalyst is heated in a reducing atmosphere to prevent SO ₂ poisoning of the lean NOx catalyst and / or
₍₂₎ An exhaust gas purifying apparatus characterized by regenerating the NOx trapping ability of a poisoned lean NOx catalyst. 3. The method according to claim 1, wherein the SOx trapping material comprises lithium (Li), potassium (K), sodium (N
a) and alkaline earth metals such as magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba), and titanium (Ti);
And aluminum (Al), and vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Z
a composition comprising a metal oxide (or composite oxide) containing a first transition element such as n) and at least one element selected from rare earth metals such as lanthanum (La) and cerium (Ce); An exhaust gas purifying apparatus, which is a composition supported on a porous heat-resistant metal oxide. 4. The SOx trap according to claim 1, wherein the SOx trapping material is lithium (Li), potassium (K), sodium (N
a) and alkaline earth metals such as magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba), and titanium (Ti);
And aluminum (Al), and vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Z
n) and at least one element selected from rare earth metals such as lanthanum (La) and cerium (Ce), and a platinum group such as platinum (Pt), rhodium (Rh) and palladium (Pd). Composition comprising metal and metal oxide (or composite oxide) containing at least one element selected from metals (so-called noble metals), composition comprising the composition supported on porous heat-resistant metal oxide , Which is an exhaust gas purification device. 5. The method according to claim 4, wherein the SOx trapping material is aluminum (Al), vanadium (V), chromium (C
r), manganese (Mn), iron (Fe), cobalt (C
o), first transition elements such as nickel (Ni), copper (Cu), zinc (Zn), lanthanum (La), cerium (C
and metal oxides containing at least one element selected from rare earth metals such as e) and at least one element selected from noble metals such as platinum (Pt), rhodium (Rh) and palladium (Pd). Or a composite oxide), or a composition obtained by supporting the composition on a porous heat-resistant metal oxide. 6. The method according to claim 1, wherein the lean NOx catalyst comprises lithium (Li), sodium (Na), potassium (K), magnesium (Mg), strontium (S).
r), at least one selected from barium (Ba) and calcium (Ca), at least one selected from rare earths such as cerium (Ce), and platinum (Pt),
Contains at least one element selected from noble metals such as rhodium (Rh) and palladium (Pd), and contains silica (Si), titanium (Ti), and zirconium (Zr) as required.
An exhaust gas purifying apparatus comprising: a composition comprising a metal and a metal oxide (or a composite oxide) containing at least one element selected from the group consisting of: and a composition comprising the composition supported on a porous heat-resistant metal oxide. .