JP2002339736A - Nitrogen oxide storage reduction type catalyst, exhaust emission control system having the catalyst, and exhaust emission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an NOx storage reduction type catalyst capable of supplying sufficient reducer when the NOx storage reduction type catalyst is regenerated, sufficiently purifying, by reduction, NOx discharged from the NOx storage reduction type catalyst, and exhibiting a high NOx purifying rate in a lean burn engine or a diesel engine, an exhaust emission control system having the catalyst, and an exhaust emission control method. SOLUTION: This NOx storage reduction type catalyst capable of purifying, by reduction, NOx in exhaust emission comprises NOx storing substance storing NOx when O2 concentration in exhaust emission is high and discharging NOx when O2 concentration in exhaust gas is low and oxidation-reduction catalyst. Reducer storing substance is carried on the NOx storage reduction type catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, in operation of the internal combustion engine, when the high O ₂ concentration in the exhaust gas is adsorbed on or occluded NOx, when the O ₂ concentration is low, releases adsorbed or occluded NOx reduction Have NOx storage substances,
The present invention relates to a nitrogen oxide storage reduction catalyst for purifying NOx in exhaust gas, an exhaust gas purification system including the same, and an exhaust gas purification method.

[0002]

2. Description of the Related Art Various studies and proposals have been made on NOx catalysts for reducing and removing NOx from exhaust gas from internal combustion engines such as diesel engines and some gasoline engines and various combustion devices.

[0003] Among these NOx catalysts, there is a NOx storage-reduction type catalyst having a NOx storage substance, which is used for purifying exhaust gas from lean-burn gasoline engines and diesel engines.

[0004] Unlike the three-way catalyst, this NOx occlusion reduction type catalyst can purify NOx even if O ₂ is present in the exhaust gas. FIG. 16 shows the NOx occlusion reduction type catalyst 30X. Fig. 1 shows the structure of the monolith catalyst provided.
7 and 18 show the arrangement of the active metal on the surface of the carrier layer,
3 shows a mechanism of NOx reduction purification.

In the monolithic catalyst 50 shown in FIG. 16, a large number of polygonal (square in FIG. 16) cells 50S are provided on a carrier 51 of a structural material made of cordierite, SiC, stainless steel or the like in order to increase the surface area. And is formed in a honeycomb shape.

Then, as shown in FIGS. 17 and 18,
The catalyst coat layer 31 is provided on the inner wall of the cell 50S having a large surface area as a whole.
Composed of catalyst metal 32 and NOx storage material 33
The storage reduction catalyst 30X is carried.

The catalyst coat layer 31 is formed of a porous coat material such as porous zeolite or alumina, and has a catalyst metal 32 such as platinum having an oxidation / reduction function and N
Potassium, sodium, lithium with Ox storage function
NOx storage substance 33 composed of one or more of alkali metals such as cesium, alkaline earth metals such as barium and calcium, and rare earths such as lanthanum and yttrium.
Are carried.

With this configuration, the NOx storage reduction catalyst 3
0X is, NOx occlusion and NO by the O ₂ concentration of the exhaust gas of
It has two functions, x release and purification.

FIG. 17 shows this NOx storage reduction type catalyst 30.
FIG. 4 shows a purification mechanism of X under an exhaust gas condition in which exhaust gas contains O ₂ , such as a normal diesel engine or a lean burn gasoline engine.

[0010] As shown in FIG. 17, O ₂ in the flue gas
As a result, NO discharged into the exhaust gas is oxidized by the catalytic metal 32 having an oxidizing function, such as platinum, to become NO ₂ . Then, the NO _2, since barium is NOx occluding substance 33 or the like is occluded in the form of such nitrates (eg Ba (NO _{3) 2),} so that the NOx in the exhaust gases are purified.

However, if this state continues, the NOx storage substances 33 having the NOx storage function all change to nitrates and saturate, losing the NOx storage function. O ₂ is not present and also to generate an exhaust gas exhaust temperature called high rich spike gas, the exhaust gas NOx storage reduction catalyst 3
Send to 0X.

When the exhaust gas eliminates O ₂ in the exhaust gas and raises the CO concentration and the exhaust temperature, as shown in FIG. 18, in the NOx storage-reduction catalyst 33 storing NOx, the nitrate returns to the original barium or the like. NO ₂ is released, and since the released NO ₂ has no O _{2 in} the exhaust gas, the NO ₂ is released on a catalytic metal 32 such as platinum having an oxidizing function.
CO in the exhaust gas, HC, and H ₂ or the like as a reducing agent, H
_It is reduced to ₂ O, CO ₂ and N ₂ and purified.

In the exhaust gas purification system provided with these conventional NOx storage reduction catalysts 30X, NO
from the NOx occlusion reduction type catalyst 33 occludes x, to release NO _2, as CO in the exhaust gas, HC, and H ₂ reducing agent, by reducing release the NO ₂ H ₂ O, the CO _2, N ₂ In order to purify the exhaust gas, the operating conditions of the engine are controlled, the operation is performed at a stoichiometric air-fuel ratio and a rich air-fuel ratio which is an air-fuel ratio close to the stoichiometric air-fuel ratio, and the exhaust gas temperature is increased.
₍₂ ) The exhaust gas whose concentration has been reduced to zero is passed through the NOx storage reduction catalyst 30
X.

[0014]

However, in this case, since the NOx stored in the NOx storage-reduction type catalyst is released at once at the same time as the operation at the rich air-fuel ratio, the NOx in the exhaust gas is reduced. Since CO and HC serving as reducing agents are rapidly consumed and run short, NOx which is not reduced and purified is directly discharged as shown in FIG. 19, and there is a problem that the NOx purification rate is greatly reduced.

In order to prevent the NOx purification rate from decreasing, NOx is reduced so that NOx can be reduced with a small amount of reducing agent.
To reduce the NOx storage amount by shortening the lean-burn time, which is the x-storage period, to increase the frequency of rich air-fuel ratio operation, or to increase the air-fuel ratio during rich air-fuel ratio operation to compensate for the reducing agent shortage If you make the conditions darker,
Increased rich air-fuel ratio operation and extreme rich air-fuel ratio operation cause extreme deterioration of fuel efficiency and extreme deterioration of CO, HC, and PM, as well as deterioration of engine oil and deterioration of engine durability. There is.

In a lean-burn gasoline engine in which the thermal efficiency is improved by lean-burn, O _{2 in} the exhaust gas
In order to make the concentration zero, it is necessary to perform a temporary but different combustion from the lean combustion, in which the proportion of fuel is higher than the stoichiometric air-fuel ratio. This hinders the improvement of thermal efficiency,
In addition, there is a problem that complicated engine control is required.

Also, in a diesel engine, the fuel is temporarily burned to reduce the O ₂ concentration in the exhaust gas to zero, but the fuel ratio is higher than the stoichiometric air-fuel ratio. Smoke, C by using low excess air fuel in diesel combustion
There is a problem that O, HC, and PM are generated, and the exhaust gas is extremely deteriorated.

[0018] Furthermore, since the engine is excessively operated temporarily but excessively, and the engine performance such as output and stability is extremely deteriorated, more complicated engine control is required. There is a problem that many difficult problems arising from proper control must be solved.

The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to supply a sufficient reducing agent at the time of regeneration of a NOx storage reduction type catalyst in a lean burn engine or a diesel engine. NOx
An object of the present invention is to provide a NOx occlusion reduction type catalyst capable of sufficiently reducing and purifying NOx released from an occlusion reduction type catalyst and exhibiting a high NOx purification rate, an exhaust gas purification system including the same, and an exhaust gas purification method.

A further object is to make the air-fuel ratio in the exhaust gas extremely low by eliminating the need to perform combustion in which the proportion of fuel is higher than the stoichiometric air-fuel ratio in which the O ₂ concentration becomes almost zero in a lean burn engine or a diesel engine. It is possible to avoid excessively enriched operation and operation in which an extremely large amount of NOx reducing agent is supplied, thereby preventing extreme deterioration of engine performance such as output and stability due to excessive excessive fuel operation and improving thermal efficiency. In addition, a NOx storage reduction catalyst capable of avoiding an increase in smoke, CO, HC, and PM generated by low excess air combustion in a diesel engine and preventing extreme deterioration of exhaust gas, and a NOx storage reduction catalyst An object of the present invention is to provide an exhaust gas purification system and an exhaust gas purification method.

[0021]

Means for Solving the Problems A nitrogen oxide occlusion reduction catalyst for achieving the above object, an exhaust gas purification system provided with the catalyst, and an exhaust gas purification method are configured as follows.

1) This nitrogen oxide storage-reduction catalyst stores a nitrogen oxide storage material that stores nitrogen oxide when the oxygen concentration in the gas is high and releases nitrogen oxide when the oxygen concentration in the gas is low. A nitrogen oxide storage-reduction catalyst having an oxidation-reduction catalyst for reducing and purifying nitrogen oxides in a gas, wherein the nitrogen oxide storage-reduction catalyst carries a reducing agent storage substance. Oxide storage reduction catalyst.

This carrier is formed of a porous coating material such as porous zeolite or alumina, and the oxidation-reduction catalyst is formed of a catalytic metal such as platinum having an oxidation / reduction function. The NOx storage material having the NOx storage function is formed of an alkali metal such as potassium, sodium, lithium, and cesium, an alkaline earth metal such as barium and calcium, and a rare earth such as lanthanum and yttrium.

As the reducing agent occluding material, for example, there is a reducing agent occluding material of Y-type zeolite having a temperature characteristic shown in FIG. The boundary between the low temperature and the high temperature differs depending on the substance forming the reducing agent storage material, but in practice, 100
C. to 400.degree.

Then, as reducing agents, unburned HC and CO
Can be used. In addition, other reducing agents such as ammonia and urea can be used.

According to this configuration, HC, CO in the exhaust gas
Reducing agent like can be occluded by a reducing agent occluding substance during normal O ₂ concentration is high engine operating conditions in exhaust gas, such as lean-burn engines and diesel engines, also the O ₂ concentration in the exhaust gas to almost zero During the regeneration of the NOx storage-reduction type catalyst that performs an operation in which the air-fuel ratio state in the exhaust gas becomes rich, the NOx storage-reduction type catalyst is released from the reducing agent storage material in a short time. NOx released from the catalyst in a short time can be reduced.

Therefore, NOx can be sufficiently purified even during regeneration by avoiding a shortage of the reducing agent, and can reduce HC and CO.
Such reducing substances are absorbed by the reducing agent-absorbing substance during normal operation, and are consumed as the reducing agent of NOx during regeneration of the NOx storage reduction catalyst, so that the emission to the outside is suppressed.

Further, since NOx during regeneration is reduced by the reducing agent absorbed during normal operation, the supply amount of the reducing agent during regeneration can be reduced, and an excessive fuel operation can be avoided.

2) In the nitrogen oxide storage-reduction catalyst, at least one of a concave portion or a convex portion that causes local stagnation in a gas flow is provided on the carrier supporting the nitrogen oxide storage material. It is provided and configured.

According to this configuration, the NOx occlusion is carried out in a normal N
It operates in the same manner as the Ox storage reduction catalyst, but the release of NOx and the regeneration of the reduction are performed as follows.

In this regeneration, the temperature of the exhaust gas is lowered, and the reducing agent adsorbed or occluded by the reducing agent storage material is released into a recess provided in the wall surface of the catalyst carrier, and the catalyst is oxidized and burned by the catalytic action of the oxidation-reduction catalyst. Let it.

Since the exhaust gas stagnates in this concave portion, O ₂ is consumed by the combustion of the released reducing agent, so that O ₂ is temporarily lost, and a reducing atmosphere is formed locally. With this Kyokusho occurrences of oxygen deficiency, NOx occlusion material releases NO _2, NO _2, which is the release, reducing agent HC in the exhaust gas, CO, by H _2, H ₂ O, CO
_It is reduced to N ₂ and purified.

3) In the nitrogen oxide storage reduction catalyst described above, the concave portion or the convex portion has a width of 0.01 μm to 100 μm and a depth of 0.01 μm with respect to a cross section in the gas flow direction.
It is formed and formed to have a size within the range of μm to 100 μm.

The concave or convex portion having a width of 0.01 μm to 100 μm and a depth of 0.01 μm to 100 μm indicates the size of the concave or convex portion. The shape of the section is not limited. Therefore, the cross-sectional shape of the concave portion or the convex portion includes various cross-sectional shapes such as a rectangle, a semicircle, a polygon, and an irregular shape. In addition, “0.01 μm to 100 μm
The phrase “fit within the range of m” does not necessarily mean that the shape completely falls within this rectangle, but it is sufficient that 90% of the cross section of the concave portion or the convex portion falls within this range.

4) In the above nitrogen oxide storage reduction catalyst, the reducing agent storage material is formed of a reducing agent storage material that adsorbs or stores the reducing agent at a low temperature and releases the reducing agent at a high temperature.

5) Alternatively, in the nitrogen oxide storage-reduction catalyst, instead of having the reducing agent storage material supported on a carrier of the nitrogen oxide storage-reduction catalyst, the nitrogen oxide To form a carrier that carries the substance occluding substance.

6) In the above nitrogen oxide storage reduction catalyst, the reducing agent storage material is formed of zeolite.

Next, the exhaust gas purification system according to the present invention is configured as follows.

7) The exhaust gas purification system provided with the above-mentioned nitrogen oxide storage-reduction type catalyst is provided with a catalyst device provided with the above-mentioned nitrogen oxide storage-reduction type catalyst in an exhaust passage of an engine, Regeneration timing detection means for detecting the regeneration timing of the material occlusion reduction type catalyst, rich operation control means for performing an operation in which the air-fuel ratio state in the exhaust gas becomes rich,
Reducing agent supply means for supplying a reducing agent to exhaust gas supplied to the nitrogen oxide storage reduction catalyst.

As the regeneration timing detecting means, a NOx concentration sensor or a NOx emission integrated value obtained by estimating the NOx generation amount in each operation state from the operation state of the engine and cumulatively calculating the NOx generation amount is used. There are things to do.

The operation in which the air-fuel ratio state in the exhaust gas becomes rich does not necessarily mean that rich combustion is performed in the cylinder bore as in post-injection, and the amount of air in the exhaust gas flowing into the NOx occlusion reduction type catalyst is not necessarily required. The operation may be performed in a rich state in which the ratio between the fuel and the fuel amount is close to the stoichiometric air-fuel ratio or the fuel amount is larger than the stoichiometric air-fuel ratio.

According to the exhaust gas purifying system having this configuration, the air-fuel ratio in the exhaust gas is made rich to generate an oxygen-deficient state, and a reducing agent is supplied to regenerate the NOx storage reduction catalyst. It is possible to sufficiently purify NOx in exhaust gas by relatively simple control and with a small supply amount of the reducing agent.

8) Alternatively, in the exhaust gas purification system provided with the nitrogen oxide storage-reduction catalyst, the nitrogen gas may be provided with at least one of a concave portion or a convex portion that causes local stagnation in the gas flow. A catalyst device having an oxide storage-reduction catalyst is provided in an exhaust passage of an engine, a regeneration timing detecting means for detecting a regeneration timing of the nitrogen oxide storage-reduction catalyst, and a low exhaust temperature operation for lowering exhaust gas temperature. An exhaust gas temperature control unit for performing a high exhaust gas temperature operation for raising the exhaust gas temperature, and a reducing agent supply unit for supplying a reducing agent to the exhaust gas supplied to the nitrogen oxide storage reduction catalyst are provided.

Even with the exhaust gas purifying system having this configuration, it is possible to purify NOx in exhaust gas by relatively simple control.

The exhaust gas purifying method according to the present invention is as follows.

9) The exhaust gas purifying method in the exhaust gas purifying system provided with the nitrogen oxide occlusion reduction type catalyst is the exhaust gas purifying system provided with the rich operation control means. At the time of regeneration of the reduction catalyst, the air-fuel ratio state in the exhaust gas is operated to be rich, and a reducing agent is supplied to the exhaust gas supplied to the nitrogen oxide storage reduction catalyst.

10) Further, in the exhaust gas purifying method described above, the operation in which the air-fuel ratio state in the exhaust gas becomes rich is performed by the post-injection in the fuel injection into the cylinder of the engine.

According to these configurations, the operation for making the air-fuel ratio state in the exhaust gas rich during regeneration is performed by means of relatively simple post-injection, and NOx is released from the NOx storage-reduction type catalyst. NOx released
Can be simultaneously released from the reducing agent storage substance or reduced and purified by reducing substances such as HC and CO contained in the exhaust gas.

Further, by performing the post-injection, the fuel having a function as a reducing agent is contained in the exhaust gas, and can play a part in the supply of the reducing agent.

Furthermore, since a nitrogen oxide storage-reduction type catalyst having a reducing agent storage material that stores reducing substances such as HC and CO in exhaust gas during normal engine operation and releases during regeneration is used, Emissions of HC, CO, etc. during operation can be reduced, and reducing substances, such as HC, CO, supplied during regeneration can be reduced. Therefore, the supply amount of the reducing substance is reduced, and the fuel efficiency is improved. Further, the capacity of the reducing agent supply device can be small, and the capacity and size can be reduced.

11) Alternatively, in the exhaust gas purifying method in the exhaust gas purifying system provided with the nitrogen oxide occlusion reduction type catalyst, the exhaust gas purifying system may include an exhaust gas purifying method when the nitrogen oxide occlusion reduction type catalyst is regenerated. A low exhaust temperature operation for lowering the temperature is performed, and when the catalyst temperature decreases in the low exhaust temperature operation, a reducing agent increasing operation for increasing the amount of the reducing agent supplied to the nitrogen oxide storage reduction catalyst is performed to increase the reducing agent. After the operation is continued for a predetermined time, a high exhaust gas temperature operation for increasing the exhaust gas temperature is performed.

The predetermined time during which the reducing agent increasing operation is continued is a time stored in the control device, and is obtained in advance by experiments, measurements, calculations, and the like. Further, it is not always necessary to be a fixed value, and it may be changed depending on the operating state or history of the engine.

12) In the exhaust gas purification method described above, the low exhaust gas temperature operation is performed by advancing the injection timing and the ignition timing of the fuel injection into the combustion chamber of the engine cylinder, and the high exhaust gas temperature operation is performed. The fuel injection into the combustion chamber of the cylinder of the engine is performed by retarding the injection timing and the ignition timing.

13) Alternatively, in the exhaust gas purifying method described above, the low exhaust temperature operation may be performed by reducing one or both of the engine speed and the engine load, and the high exhaust temperature operation may be performed. Either increase the engine speed or increase the engine load,
Or both.

14) Alternatively, in the exhaust gas purifying method described above, the exhaust gas temperature is reduced by injecting air into the exhaust passage.

According to these configurations, since the NOx storage reduction type catalyst capable of locally generating an oxygen deficiency state is used, it is not necessary to perform an excessive fuel operation for reducing the O ₂ concentration in the exhaust gas. In addition, deterioration of engine performance such as output and stability due to the excessive fuel operation is avoided.

Therefore, in a lean burn engine or a diesel engine, NOx in the exhaust gas can be purified without lowering the thermal efficiency of the engine. In the diesel engine, the exhaust gas is used for regeneration of the NOx storage reduction catalyst. Since it is not necessary to perform low excess air combustion to reduce the O ₂ concentration in the smoke, smoke, CO, H
Extreme deterioration of C and PM can be prevented.

15) In the exhaust gas purification method described above, in the regeneration of the nitrogen oxide storage reduction catalyst,
NOx disposed downstream of the nitrogen oxide storage reduction catalyst
When the detection value of the density sensor exceeds a predetermined determination value, the reproduction operation is started.

16) Alternatively, in the above exhaust gas purifying method, in the regeneration of the nitrogen oxide storage reduction catalyst, the regeneration operation is started when the estimated integrated value of the NOx emission exceeds a predetermined judgment value. It is configured as follows.

With the above-described configurations, it is possible to appropriately determine when the regeneration operation is necessary.

[0061]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a NOx storage reduction catalyst according to the present invention, an exhaust gas purification system including the same, and an exhaust gas purification method will be described with reference to the drawings.

[NOx Storage Reduction Catalyst of First Embodiment] First, the NOx storage reduction catalyst of the first embodiment according to the present invention will be described.

FIG. 1 shows the wall structure of the NOx storage reduction catalyst 30 according to the first embodiment. The NOx storage reduction catalyst 30 is formed of a monolith honeycomb catalyst 3 and is provided in a cell 3S of the monolith honeycomb. This cell 3
S is formed of the carrier 3A, and the catalyst coat layer 31 is formed on this surface.
Is provided.

Then, the catalyst coat layer 31 of the carrier 3A
, An oxidation-reduction catalyst 32, a NOx storage material 33, and a reducing agent storage material 34 are supported.

The catalyst coating layer 31 is formed of a porous coating material such as porous zeolite or alumina, and the oxidation-reduction catalyst 32 is formed of a catalyst metal such as platinum having an oxidation / reduction function. The catalytic metal 32 has an oxidizing activity in a temperature range higher than the activation start temperature. In the case of platinum, the activation start temperature is in a range of about 150 ° C. to 200 ° C.

The NOx storage substance 33 having a NOx storage function stores NOx when the O ₂ concentration in the gas is high, and releases NOx when the O ₂ concentration in the gas is low. , An alkali metal such as lithium and cesium, an alkaline earth metal such as barium and calcium, and a rare earth such as lanthanum and yttrium. When barium is employed, the NOx release start temperature is 200 ° C. or higher when the excess air ratio is 1 or less.

The reducing agents include unburned HC and C
Using O or the like, this reducing agent is adsorbed or stored at low temperature,
Zeolite,
It is formed of SiC or the like. The reducing agent storage substance 34 exhibits HC and CO adsorption and storage activities from a low temperature range equal to or lower than the activation temperature of the oxidation active metal 32, and the NOx storage substance 33
HC and CO are released in the release temperature range.

When zeolite is used as the reducing agent storage material 34, the temperature at the boundary between the adsorption or occlusion of the reducing agent and the release is in the range of 100 ° C. to 400 ° C.

FIG. 3 shows a relationship (temperature characteristic) between adsorption, storage and release of HC and CO with respect to the catalyst temperature of the reducing agent storage substance 34. As can be seen from FIG. 3, the reducing agent storage substance 34 exhibits HC and CO adsorption and storage activities in a low temperature range, and releases HC and CO in a high temperature range.

[NOx Storage-Reduction Catalyst of Second Embodiment] Next, FIG. 2 shows the wall structure of the NOx storage-reduction catalyst 30A of the second embodiment. This NOx storage reduction catalyst 30A is formed of a monolith honeycomb catalyst 3 shown in the drawing, and is provided in a cell 3AS of the monolith honeycomb. The cell 3AS is formed of a carrier 3AA, and a catalyst coating layer 31A is provided on the surface thereof.
In the surface of A, as shown in the sectional view below the drawing, a local concave portion 3
Ah is provided. The recesses 3Ah can be provided by forming a large number of large recesses during sintering of cordierite.

The purpose of providing the concave portion 3Ah is to generate a stagnation portion in the flow of the gas to be treated. Therefore, not only the concave portion 3Ah but also a convex portion may be provided, and the concave and convex portions may be combined. Good. Since the size of the concave portion or the convex portion may be such that a stagnation portion of the flow can be generated, the oxidation-reduction catalyst 32 carried by the carrier 3AA, the NOx storage material 3
3. The reducing agent occlusion material 34 is included at the same time, and the size is not less than the size at which the chemical reaction easily progresses and not more than the limit size at which an appropriate stagnation can be obtained.

Regarding the size of the concave portion 3Ah or the convex portion, 90% of the area of the cross section with respect to the cross section in the gas flow direction is equal to the width of 0.
01 μm to 100 μm, depth 0.01 μm to 100
It is formed in such a size as to fit in the range of μm.

According to this structure, as shown in the lower part of FIG. 2, the gas flows in the cell 3AS. In this case, the flow near the center of the cell 3AS is fast, but the boundary layer near the wall surface is fast. Then, as you approach the wall, the flow velocity becomes slower,
On the wall, the flow velocity is zero. Depression 3 below this boundary layer
Since the gas flow is stagnant in the portion Ah, the flow of gas from the main flow at the center of the cell 3AS is extremely reduced. However, gas exchange by the flow hardly occurs, but replacement of gas component molecules by molecular diffusion occurs.

Then, the catalyst coat layer 3 of the carrier 3AA
1A carries an oxidation-reduction catalyst 32, a NOx storage material 33, and a reducing agent storage material 34, which are formed in the same manner as the NOx storage-reduction catalyst 30 of the first embodiment.
Similar reducing agents can be used.

[NOx Purification Mechanism in the First Embodiment] Next, the NOx purification mechanism in the case of the NOx storage reduction catalyst 30 having the reducing agent storage material 34 according to the first embodiment of the present invention. Will be described with reference to FIG. 4 and FIG.

When the NOx storage substance 33 has not reached saturation with respect to the adsorption and storage of NOx, NOx can be stored, and as shown in FIG. 4, in the lean burn operation in which exhaust gas with a normal lean air-fuel ratio is emitted, , O ₂ concentration is high, NOx in the exhaust gas is adsorbed and stored in the NOx storage substance 33, and the exhaust gas is purified. HC and CO are also used as catalysts 32.
Is oxidized and purified by the catalytic action of the catalyst, and the exhaust gas temperature is low and the catalyst temperature Tc is low.
The amounts of HC and CO determined by c and the concentrations of HC and CO in the exhaust gas are adsorbed and stored in the reducing agent storage substance 34.

As shown in FIG. 5, in the rich combustion operation at a low air-fuel ratio λ where the O ₂ concentration in the exhaust gas is low during regeneration, the O ₂ concentration is low and the HC and CO concentrations increase.
The NOx stored in the NOx storage reduction catalyst 30 becomes N
Released as O ₂ . At the same time, the amount of fuel combustion increases and the exhaust gas temperature increases, so that the catalyst temperature Tc also becomes higher than the temperature at which the reducing agent storage substance 34 releases HC and CO.
Therefore, the reducing agent storage substance 34 emits HC and CO.

Then, the released NO ₂ is reduced by the reducing agents such as HC and CO released in the same manner as the reducing agents HC and CO in the exhaust gas.
With CO and H ₂ , H ₂ O, C
O ₂ and N _{2 are} purified. Therefore, a sufficient reducing agent is supplied to NO ₂ released in a short time, so that NOx can be sufficiently reduced and purified, and high purification efficiency can be maintained even during regeneration.

[NOx Purification Mechanism in Second Embodiment] A NOx storage reduction catalyst 30A having a reducing agent storage material 34 according to a second embodiment of the present invention 30A.
The mechanism of NOx purification in the case of will be described with reference to FIGS.

As shown in FIG. 6, the NOx storage substance 33 is
When NOx adsorption and occlusion has not reached saturation
Means that NOx can be stored, and in normal lean burn operation
Is O _TwoBecause of the high concentration, NOx in exhaust gas
It is adsorbed and occluded by the storage substance 33 and purified. Also, H
C and CO are also oxidized and purified by the catalytic action of the catalyst 32.
And the catalyst temperature Tc at that time and HC and C in the exhaust gas.
The amounts of HC and CO determined by the O concentration are absorbed by the reducing agent storage material 34.
Dressed and occluded.

At this time, NOx, HC, CO, and other gas molecules diffuse into the stagnation portion in the concave portion 3Ah provided on the wall surface of the carrier 3AA.

Next, as shown in FIG. 7, when the exhaust gas temperature is low and the catalyst temperature Tc is lower than the temperature Tcl at which the reducing agent storage material 34 can store HC and CO, NOx, HC,
CO and other gas molecules diffuse into the stagnation portion in the concave portion 3Ah provided on the wall surface of the carrier 3AA, and the reducing agent storage material 34 stores HC and CO. Then, as shown in FIG. 8, when the exhaust gas temperature is high and the catalyst temperature Tc is equal to or higher than the temperature at which the reducing agent storage substance 34 emits HC and CO, the reducing agent storage substance 34 emits HC and CO. HC, C
Since O is oxidized by the catalytic action of the catalyst 32,
O ₂ in the stagnant portion in Ah is consumed, and extremely low O 2
_{A two-} concentration reducing atmosphere is formed.

With the occurrence of this extreme oxygen deficiency,
NO ₂ is released from the NOx storage substance 33, and the released NO ₂ is reduced to H ₂ O, CO ₂ , and N ₂ by the reducing agents HC, CO, and H ₂ in the exhaust gas to be purified.

Therefore, in the NOx storage reduction catalyst 30A of the second embodiment, it is not necessary to extremely reduce the O ₂ concentration in the exhaust gas during regeneration of the catalyst.

[Exhaust Gas Purification System of First Embodiment] Next, an exhaust gas purification system 1 having a NOx storage reduction catalyst 30 according to a first embodiment of the present invention will be described with reference to FIG. I will explain while.

FIG. 9 shows a configuration diagram of an engine 2 and an engine exhaust system of an exhaust gas purification system 1 provided with a NOx storage reduction catalyst 30 by way of an example of a diesel engine. The exhaust gas purification system 1 includes, in order from an upstream side of an exhaust passage 2A of the engine 2, an HC-adding injection valve 6,
The catalyst device 3 including the NOx storage reduction catalyst 30 having the reducing agent storage material 34 according to the present invention, and a catalyst temperature sensor 41 for measuring the catalyst temperature Tc of the NOx storage reduction catalyst 30
And an electronically controlled fuel injection device (injection pump system) 4 and a control device (electronic control box) 5 called an engine control unit (ECU) for controlling the fuel injection device 4.

In a system equipped with an electronic control injection device such as a common rail having a high degree of freedom in injection control, a reducing agent can be supplied to the exhaust gas in the exhaust passage 2A by controlling the fuel injection. The injection valve 6 for fuel addition as shown in FIG. 9 becomes unnecessary.

The exhaust gas purification system 1 according to the first embodiment performs a regeneration timing detecting means for detecting a regeneration timing of the NOx storage reduction catalyst 30 and an operation for enriching the air-fuel ratio state in the exhaust gas. Rich operation control means and NOx
A reducing agent supply means for supplying a reducing agent to exhaust gas supplied to the storage reduction catalyst;

The regeneration timing detecting means is provided with a NOx concentration sensor 42 on the downstream side of the catalytic converter 3, and a time when the detected value of the NOx concentration sensor 42 exceeds a predetermined judgment value is defined as a regeneration operation start timing. The NOx generation amount in each operation state is estimated from the means and the operation state of the engine 2, and this NOx
Means for cumulatively calculating the x generation amount and determining that the time when the integrated value of NOx emission exceeds a predetermined determination value as the regeneration time can be adopted. In addition, by combining these, the time when one of them exceeds a predetermined determination value may be regarded as the time for starting the regeneration operation.

This rich operation control means switches the normal engine operation state for regeneration of the NOx storage reduction catalyst 30 and performs post-injection and the like in fuel injection to the cylinder. O _{2 in} exhaust gas
To make the air-fuel ratio state in the exhaust gas a rich state.
When the post injection is adopted, CO serving as a reducing agent can be generated together with the consumption of O ₂ , so that it can also serve as one end of the reducing agent supply means.

As shown in FIG. 9, the reducing agent supply means includes a reducing agent injection valve 6 provided in the exhaust passage 2A of the engine 2 and the like, and performs post-injection by fuel injection control of the engine 2. In this way, it comprises means for supplying fuel as a reducing agent into the exhaust gas.

[Exhaust Gas Purification System According to Second Embodiment] [Exhaust Gas Purification System] Next, an exhaust gas purification system 1A having a NOx storage reduction catalyst 30A according to a second embodiment of the present invention. The configuration shown in FIG. 9 is the same as that of the exhaust gas purification system 1 including the NOx storage reduction catalyst 30 of the first embodiment,
In place of the Ox storage reduction catalyst 30, a NOx storage reduction catalyst 30A is provided.

In the exhaust gas purifying system 1A of the second embodiment, a regeneration timing detecting means for detecting the regeneration timing of the NOx storage reduction catalyst 30A, a low exhaust gas temperature operation for lowering the exhaust gas temperature, and Exhaust temperature control means for performing a high exhaust temperature operation for raising the temperature and a reducing agent supply means for supplying a reducing agent to exhaust gas supplied to the NOx storage reduction catalyst 30 are provided.

As the exhaust gas temperature control means, means for advancing or retarding the injection timing and ignition timing of the fuel injection into the combustion chamber of the cylinder of the engine 2, means for changing the rotation speed and load of the engine 2 and the like It consists of.

The regeneration timing detecting means and the reducing agent supply means are configured in the same manner as the regeneration timing detecting means and the reducing agent supply means of the exhaust gas purification system 1 of the first embodiment.

[Exhaust Gas Purification Method of First Embodiment]
In the exhaust gas purifying method in the exhaust gas purifying system 1 of the first embodiment, the O ₂ in the exhaust gas is reduced by the rich operation control means for the regeneration of the NOx storage reduction catalyst 30 by reducing the O ₂ in the exhaust gas. The regenerating operation for supplying the reducing agent by the reducing agent supply means is performed while the air-fuel ratio state of the fuel cell is set to the rich state, the regenerating operation is continued for a predetermined period of time, and the normal operation is performed. The regeneration operation is repeated when the NOx storage capacity of the type catalyst 30 approaches saturation, and is performed according to the regeneration control flow of the NOx storage reduction type catalyst as shown in FIG.

The regeneration control flow shown in FIG. 10 is schematically shown as being executed in parallel with other control flows of the engine while the engine 2 is operating. Is stopped, the reproduction control flow is not executed.

When this control flow starts, in step S11, the regeneration timing detection means determines whether the NOx storage capacity of the NOx storage reduction catalyst 30 is approaching saturation, that is, whether the regeneration operation is about to start. Determine whether or not.

If it is determined in step S11 that the NOx storage capacity has a margin and it is not time to start the regeneration operation, the regeneration operation of the NOx storage reduction catalyst 30 is not performed, and the process proceeds to step S30. The normal operation is performed for a predetermined time, and the process returns. In the normal operation, calculation of an integrated NOx emission value used by the regeneration timing detecting means is performed.

If it is determined in step S11 that the NOx storage capacity is approaching saturation and it is time to start the regeneration operation, the process proceeds to step S20, and the process proceeds to step S20.
The regeneration operation of the storage reduction catalyst 30 is performed, and after the regeneration operation is completed, the process returns, and is called again and returns from the start to step S11.

[0102] reproduction operation of this step S20 is due to the rich operation control means in the step S21, O ₂ in the exhaust gas
A rich combustion operation for reducing the air-fuel ratio state in the exhaust gas to a rich state and a reducing agent increasing operation for increasing the reducing agent by the reducing agent supply means in step S22, and counting the elapsed time in step S23, This state is maintained for a predetermined time t.
c0 is maintained, and this predetermined time t is determined in step S24.
If c0 has elapsed, the process proceeds to step S25, and the regeneration operation ends. In step S25, numerical values such as the integrated NOx emission value used by the regeneration timing detecting means are reset to zero.

By a series of operations in steps S21 to S25, the regeneration operation is completed and the process returns. And
This control flow is called until the operation of the engine is stopped, and the steps from start to return are repeatedly executed.

[NOx in Exhaust Gas of First Embodiment]
Purification Mechanism] A description will be given of a purification mechanism of NOx in exhaust gas in the exhaust gas purification system 1 and the exhaust gas purification method of the first embodiment with reference to FIGS.

If it is determined by the regeneration timing detecting means that the NOx storage substance 33 has not reached saturation with respect to the adsorption and occlusion of NOx, the normal lean combustion operation, that is, the lean combustion operation of the gasoline engine is performed. The diesel engine performs a normal combustion operation, and as shown in FIG. 4, purifies NOx in the exhaust gas by adsorbing and occluding it in the NOx occluding substance 33.

Further, HC and CO are oxidized and purified by the catalytic action of the oxidation-reduction catalyst 32, and HC and CO which cannot be oxidized are reduced in the lean burn operation because the exhaust gas temperature is low and the catalyst temperature Tc is low. It is adsorbed and stored by the storage material 34 and purified.

Then, when the reproduction timing detecting means determines that the
When it is detected that the x-occluding substance 33 is close to saturation with respect to the adsorption and occlusion of NOx, the engine operating conditions are changed, and the rich air-fuel ratio operation and the reducing agent increasing operation are performed simultaneously by post-injection, etc. The medium air-fuel ratio state is made rich, and the amount of the reducing agent in the exhaust gas is increased.

In the rich air-fuel ratio operation and the reducing agent increasing operation, O ₂ in the exhaust gas is consumed and CO is also generated. Therefore, as shown in FIG. 5, the O ₂ concentration in the exhaust gas is low and the CO concentration is high. Therefore, the N stored from the NOx storage substance 33
O ₂ is released. Further, the exhaust gas temperature is increased by the rich air-fuel ratio operation, and the catalyst temperature Tc is increased.
As shown in FIG. 5, HC and CO adsorbed or occluded by the reducing agent occlusion substance 34 are released.

Then, NO ₂ released from the NOx storage substance 33 is converted into HC,
CO and HC and CO in the exhaust gas are reduced by the catalytic action of the oxidation / reduction catalyst 32 to H ₂ O, CO ₂ , and N ₂ for purification.

The NOx from the NOx storage substance 33
When the release of NOx is completed and the NOx storage performance of the NOx storage substance 33 recovers, the operation returns to the normal operation, and this series of operations is repeated to repeatedly store, release, and purify NOx.
Purifies C, CO and NOx.

Therefore, according to the exhaust gas purification system 1 and the exhaust gas purification method provided with the NOx storage reduction catalyst 30, the HC and CO adsorbed or occluded by the reducing agent storage material 34 during normal operation are released during regeneration. Since it is used for reducing NOx, NOx can be sufficiently purified even during regeneration.

This is shown in time series in FIG. This FIG.
According to FIG. 19, it can be seen that the concentration of NOx at the catalyst outlet is significantly reduced during the rich air-fuel ratio operation as compared with the case where the NOx reduction catalyst not carrying the reducing agent storage material 34 of FIG. 19 is used.

Since the HC and CO adsorbed or occluded by the reducing agent storage material 34 during the normal operation are used at the time of regeneration, the amount of the reducing agent supplied at the time of the regeneration operation can be reduced.

[Exhaust Gas Purification Method of Second Embodiment]
In the exhaust gas purifying method in the exhaust gas purifying system 1A of the second embodiment, the regeneration operation of the NOx storage reduction catalyst 30A is performed by first performing a low exhaust gas temperature operation for lowering the exhaust gas temperature. When the catalyst temperature Tc decreases in the low exhaust temperature operation, a reducing agent increasing operation for increasing the reducing agent supplied to the NOx storage reduction catalyst 30A is performed, and after continuing the reducing agent increasing operation for a predetermined time, the exhaust gas temperature is increased. The high exhaust gas temperature operation is performed, and the high exhaust gas temperature operation is continued for a predetermined time tc1 to terminate the regeneration operation. Thereafter, the normal operation is performed and the Nx of the NOx storage reduction catalyst 30A
When the Ox storage capacity approaches saturation, the regeneration operation is repeated, and is performed according to the regeneration control flow of the NOx storage reduction type catalyst as shown in FIG.

The regeneration control flow of FIG. 12 is schematically shown as being executed in parallel with other control flows of the engine while the engine 2 is operating. Is stopped, the reproduction control flow is not executed.

When this control flow starts, in step S11A, the regeneration timing detecting means determines whether the NOx storage capacity of the NOx storage-reduction catalyst 30A is approaching saturation, that is, whether the regeneration operation has started. Determine whether or not.

If it is determined in this Steady state S11A that the NOx storage capacity has a margin and it is not time to start the regeneration operation, the regeneration operation of the NOx storage reduction type catalyst 30A is not performed, and the process goes to step S30A. Perform normal operation and return. In this normal operation,
It calculates the NOx emission integrated value used by the regeneration timing detecting means.

If it is determined in step S11A that the NOx storage capacity is approaching saturation and it is time to start the regeneration operation, the process proceeds to step S20A, where N
The regeneration operation of the Ox storage reduction catalyst 30A is performed, and the process returns. The control flow is called again, and the process returns from the start to step S11A.

In this regeneration operation, a low exhaust gas temperature operation is performed by the exhaust gas temperature control means in step S21A.
The catalyst temperature Tc of 22A is checked, and the catalyst temperature Tc is checked.
If the temperature is lower than the temperature Tc1 at which the reducing agent storage material 34 stores the reducing agent, the process proceeds to step S23A, and if not, the process returns to step S21A to continue the low exhaust temperature operation.

In step S23A, the reducing agent increasing operation in which the reducing agent is increased by the reducing agent supply means is performed for a predetermined time (for example, about 0.1 s to 5 s), and the next step S24A
The high exhaust temperature operation is performed by the exhaust temperature control means. Then, when the catalyst temperature Tc becomes higher than the temperature Tc2 at which the reducing agent storage substance 34 releases the reducing agent in the next step S25A, the elapsed time is counted in step S26A, and this state is set to a predetermined time tc1 (for example, 0. (Approximately 1 s to 5 s), and the predetermined time tc1 is determined in step S27A.
Has elapsed, the process proceeds to step S28A, and the regeneration operation ends. In step S28A, the numerical values such as the integrated NOx emission value used by the regeneration timing detecting means are reset to zero.

Further, the temperature T released in step S25A
If not higher than c2, step S24A
And repeat the high exhaust temperature operation.

This step S21A to step S28A
Through a series of operations, the regeneration operation is completed and the routine returns. This control flow is repeatedly executed until the operation of the engine is stopped.

[NOx in Exhaust Gas of Second Embodiment]
Purification Mechanism of NOx in Exhaust Gas in Exhaust Gas Purification System 1A and Exhaust Gas Purification Method of Second Embodiment Above FIG.
This will be described with reference to FIGS.

If it is determined by the regeneration timing detecting means that the NOx storage substance 33 has not reached saturation with respect to the adsorption and occlusion of NOx, as shown in FIG. The gasoline engine performs a lean combustion operation, and the diesel engine performs a normal combustion operation. NOx in exhaust gas is adsorbed and stored in the NOx storage substance 33 and purified.

Further, HC and CO are oxidized and purified by the catalytic action of the oxidation-reduction catalyst 32, and HC and CO which cannot be oxidized are adsorbed and occluded by the reducing agent storage material 34 and purified. At this time, NOx, HC, CO, and other gas molecules diffuse into the stagnation portion in the concave portion 3Ah provided on the wall surface of the carrier 3A.

Then, when the reproduction timing detecting means determines that the
When it is detected that the x-occluding substance 33 is close to saturation with respect to the adsorption and occlusion of NOx, the engine operating conditions are changed and a low exhaust gas temperature operation for lowering the exhaust gas temperature is performed to lower the catalyst temperature Tc. Thus, when the catalyst temperature Tc decreases, the amount of the reducing agent in the exhaust gas is increased by the reducing agent supply means.

In the low exhaust temperature operation and the reducing agent increasing operation, the increased amounts of HC and CO in the exhaust gas are adsorbed or occluded by the reducing agent storage material 34 as shown in FIG.
Then, during a predetermined time, the reducing agent occlusion substance 34 causes HC,
When CO is adsorbed or occluded, a high exhaust gas temperature operation for increasing the exhaust gas temperature is performed.

By performing this high exhaust temperature operation, the catalyst temperature T
c, and as shown in FIG.
4 to release HC and CO adsorbed or occluded, thereby consuming O ₂ in the stagnation of the recess 3Ah on the wall surface of the carrier 3A.
₂ Temporarily reduce the concentration to zero%.

Due to the decrease in the O ₂ concentration, the stored NO ₂ is released from the NOx storage substance 33,
₂ is reduced with reducing agents HC, CO, and H ₂ by the catalytic action of the oxidation / reduction catalyst to be purified to H ₂ O, CO ₂ , and N ₂ .

After this purification, O ₂ also diffuses into the stagnation of the concave portion and the O ₂ concentration rises. However, since NO x is released and purified, the NO x storage performance of the NO x storage substance 33 recovers, and NOx is absorbed and purified.

Then, NOx from the NOx storage substance 33
When the release of NOx is completed and the NOx storage performance of the NOx storage substance 33 recovers, the operation returns to the normal operation, and this series of operations is repeated to repeatedly store, release, and purify NOx.
Purifies C, CO and NOx.

Therefore, the NOx storage reduction type catalyst 30A
According to the exhaust gas purifying system 1A and the exhaust gas purifying method provided with the above, it is possible to avoid an excessive excess fuel operation, so that the extreme deterioration of the engine performance such as the output and the stability caused by the excessive excessive fuel operation is prevented. Can be prevented.

[0132]

As described above, the N according to the present invention is
According to the Ox storage reduction catalyst, the exhaust gas purification system and the exhaust gas purification method including the same, the following effects can be obtained.

First, according to the first embodiment, the following effects can be obtained.

According to the exhaust gas purification system and the exhaust gas purification method provided with the NOx storage reduction catalyst and the NOx storage reduction catalyst of the first embodiment, HC, C
A reducing agent such as O is stored by the reducing agent storage substance in a normal engine operating state and is released in a short time when the NOx storage reduction catalyst is regenerated. Therefore, NOx released from the NOx storage reduction catalyst in a short time can be sufficiently reduced by the reducing agent released during the regeneration.

[0135] Therefore, regarding the NOx, even during the regeneration, the NOx purification efficiency can be maintained high by sufficiently purifying the NOx and reducing the amount of the exhausted NOx. Also, H
C and CO are absorbed by the reducing agent storage material during normal operation, and are consumed as a NOx reducing agent during regeneration, so that the amount of emission can be reduced.

Since the supply amount of the reducing agent at the time of regeneration can be reduced, the capacity and the size of the reducing agent supply means can be reduced.

In the case where fuel is supplied as a reducing agent in post-injection or the like, an excessive excess fuel supply for supplying the reducing agent during regeneration can be avoided. Extreme deterioration of engine performance such as stability and deterioration of fuel efficiency can be prevented.

In particular, in diesel combustion, since the combustion with a low excess air can be avoided, the smoke, CO, HC, and PM generated by this combustion can be prevented from being extremely deteriorated.

Next, according to the second embodiment, the following effects can be obtained.

According to the exhaust gas purifying system and the exhaust gas purifying method provided with the NOx occlusion reduction type catalyst and the NOx occlusion reduction type catalyst according to the second embodiment, the local oxygen deficiency state can be used. Sometimes it is not necessary to extremely reduce the O ₂ concentration in the exhaust gas.

Accordingly, the NOx storage-reduction type catalyst
It is possible to avoid an extreme excess fuel operation for discharging the fuel, thereby preventing an extreme deterioration of the engine performance such as the output and the stability and a deterioration of the fuel efficiency due to the extreme excess fuel operation.

In a lean fuel gasoline engine,
Since NOx emission does not require rich combustion, which is a low excess air ratio combustion in which the proportion of fuel is higher than the stoichiometric air-fuel ratio, which is not a lean combustion, the thermal efficiency of the engine can be improved. In addition, since it is not necessary to perform rich combustion even in a diesel engine, it is possible to avoid an excessive increase in smoke, CO, HC, and PM due to rich combustion in diesel combustion.

[Brief description of the drawings]

FIG. 1 is a diagram showing a wall structure of a NOx storage reduction catalyst according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a wall structure of a NOx storage reduction catalyst according to a second embodiment of the present invention.

FIG. 3 is a diagram showing temperature characteristics of HC and CO adsorption and occlusion substances according to the present invention.

FIG. 4 is a schematic diagram showing a mechanism for purifying NOx of the NOx storage reduction catalyst according to the first embodiment of the present invention, and shows a case of lean combustion gas.

FIG. 5 is a schematic view showing a mechanism for purifying NOx of the NOx storage-reduction type catalyst according to the first embodiment of the present invention, and shows a case of rich combustion gas.

FIG. 6 is a schematic diagram showing a mechanism for purifying NOx of a NOx storage reduction catalyst according to a second embodiment of the present invention, and shows a case of lean combustion gas.

FIG. 7 is a schematic diagram showing a mechanism for purifying NOx of a NOx storage reduction catalyst according to a second embodiment of the present invention, and shows a case of low-temperature exhaust gas.

FIG. 8 is a schematic diagram showing a mechanism for purifying NOx of a NOx storage reduction catalyst according to a second embodiment of the present invention, and shows a case of high-temperature exhaust gas.

FIG. 9 is a configuration diagram illustrating an exhaust gas purification system including the NOx storage reduction catalyst according to the present invention.

FIG. 10 is a regeneration control flow of the NOx storage reduction type catalyst showing the exhaust gas purification method of the first embodiment according to the present invention.

FIG. 11 is a time series diagram showing states of exhaust gas when the exhaust gas purification system and the exhaust gas purification method according to the first embodiment of the present invention are used.

FIG. 12 is a regeneration control flow of a NOx storage reduction catalyst showing an exhaust gas purification method according to a second embodiment of the present invention.

FIG. 13 is a schematic view showing a mechanism of exhaust gas purification and catalyst regeneration in an exhaust gas purification system according to a second embodiment of the present invention, showing a case of a normal lean burn operation.

FIG. 14 is a schematic view showing a mechanism of exhaust gas purification and catalyst regeneration in an exhaust gas purification system according to a second embodiment of the present invention, showing a case of low exhaust temperature and reducing agent increasing operation.

FIG. 15 is a schematic view showing a mechanism of exhaust gas purification and catalyst regeneration in an exhaust gas purification system according to a second embodiment of the present invention, showing a case of high exhaust gas temperature operation.

FIG. 16 is a view showing the structure of a monolithic honeycomb catalyst.

FIG. 17 is a schematic diagram showing a mechanism for purifying NOx of a conventional NOx storage reduction catalyst, and shows a case of exhaust gas having a lean air-fuel ratio.

FIG. 18 is a schematic view showing a mechanism for purifying NOx of a conventional NOx storage reduction catalyst, and shows a case of exhaust gas having a rich air-fuel ratio.

FIG. 19 is a time-series diagram showing the state of exhaust gas when an exhaust gas purification system and an exhaust gas purification method of the related art are used.

[Explanation of symbols]

 1, 1A Exhaust gas purification system 2 Engine 2A Exhaust passage 3 Catalyst device 3A, 3AA Carrier 3Ah Depression 30, 30A NOx storage reduction type catalyst 32 Redox catalyst 33 NOx storage substance 34 Reducing agent storage substance 42 NOx concentration sensor Tc Catalyst temperature

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/20 F01N 3/24 R 4G069 3/24 3/28 301C 3/28 301 301P F02D 41/04 305A F02D 41 / 04 305 335A 335 43/00 301B 43/00 301 301J 45/00 314Z 45/00 314 B01D 53/36 102B F02P 5/15 F02P 5/15 B F term (reference) 3G022 AA06 EA01 GA05 GA09 3G084 AA01 AA04 BA05 BA09 BA15 BA17 DA10 DA22 EA11 EB24 EC01 EC02 FA18 FA28 FA33 3G091 AA12 AA18 AB06 BA07 BA14 CA08 CA18 CB00 CB03 CB05 CB07 DA01 DA02 DB06 DB10 EA18 EA30 EA33 FB12 FC02 GA06 GA16 GB02Y GB03Y GB04 HA03 GB01 HA03 GB01 GB03 GB01 MA18 NA04 NA08 NC08 NE01 NE06 NE13 NE23 PA17Z PD01Z PD12Z PE01Z 4D048 AA06 AB02 BA02X BA06X BA11X BA14X BA15X BA18X BA30X BA41X BA45X BB02 DA02 DA08 4G069 AA03 AA11 BA01B BA07B BC01B BC08BCA38 CA75 BC13BCA8 9 EA25 EB01 EE06 ZA04B

Claims (16)

[Claims] 1. A gas containing a nitrogen oxide occluding substance which occludes nitrogen oxide when the oxygen concentration in the gas is high, and releases nitrogen oxide when the oxygen concentration in the gas is low, and a redox catalyst. A nitrogen oxide storage reduction catalyst for reducing and purifying nitrogen oxides, wherein the nitrogen oxide storage reduction catalyst carries a reducing agent storage substance. 2. The method according to claim 1, wherein the carrier supporting the nitrogen oxide occluding substance is provided with at least one of a concave portion and a convex portion which cause local stagnation in the gas flow.
The nitrogen oxide storage-reduction catalyst according to the above. 3. The method according to claim 1, wherein the concave portion or the convex portion is formed to have a size in a range of 0.01 μm to 100 μm in width and 0.01 μm to 100 μm in depth with respect to a cross section in a gas flow direction. The nitrogen oxide storage reduction catalyst according to claim 2, wherein 4. The reducing agent storing substance according to claim 1, wherein the reducing agent storing substance absorbs or stores the reducing agent at a low temperature and releases the reducing agent at a high temperature. 6. The nitrogen oxide storage reduction catalyst according to 5. above. 5. The carrier for supporting the nitrogen oxide storage material with the reducing agent storage material instead of supporting the reducing agent storage material on the carrier for the nitrogen oxide storage reduction catalyst. The nitrogen oxide occlusion reduction type catalyst according to any one of claims 1 to 4. 6. The nitrogen oxide storage reduction catalyst according to claim 1, wherein the reducing agent storage substance is zeolite. 7. A regeneration timing detecting means for providing a catalyst device provided with the nitrogen oxide storage reduction catalyst according to claim 1 in an exhaust passage of an engine, and detecting a regeneration timing of the nitrogen oxide storage reduction catalyst. And an exhaust gas comprising rich operation control means for performing an operation that makes the air-fuel ratio state in the exhaust gas rich, and reducing agent supply means for supplying a reducing agent to the exhaust gas supplied to the nitrogen oxide storage reduction catalyst. Gas purification system. 8. A catalyst device provided with the nitrogen oxide storage reduction catalyst according to any one of claims 2 to 6 is provided in an exhaust passage of an engine, and regeneration of the nitrogen oxide storage reduction catalyst is performed. Regeneration time detecting means for detecting the timing, exhaust temperature control means for performing a low exhaust temperature operation for lowering the exhaust gas temperature and a high exhaust temperature operation for increasing the exhaust gas temperature, and exhaust gas supplied to the nitrogen oxide storage reduction catalyst An exhaust gas purification system comprising: a reducing agent supply unit that supplies a reducing agent therein. 9. The exhaust gas purification system according to claim 7, wherein when the catalyst for storing and reducing nitrogen oxides is regenerated, an operation for enriching the air-fuel ratio state in exhaust gas is performed, and the storage and reduction for nitrogen oxides is performed. Exhaust gas purification method, characterized in that a reducing agent is supplied in exhaust gas supplied to a catalyst. 10. The exhaust gas purifying method according to claim 8, wherein the operation in which the air-fuel ratio state in the exhaust gas becomes rich is performed by post-injection in fuel injection into a cylinder of the engine. 11. The exhaust gas purification system according to claim 8, wherein a low exhaust gas temperature operation for lowering exhaust gas temperature is performed during regeneration of the nitrogen oxide storage reduction catalyst,
When the catalyst temperature decreases in the low exhaust temperature operation, a reducing agent increasing operation for increasing the amount of the reducing agent supplied to the nitrogen oxide storage reduction catalyst is performed, and after continuing the reducing agent increasing operation for a predetermined time, the exhaust gas temperature is reduced. An exhaust gas purification method comprising performing a high exhaust temperature operation to raise the temperature. 12. The low exhaust temperature operation is performed by advancing an injection timing and an ignition timing of fuel injection into a combustion chamber of an engine cylinder, and the high exhaust temperature operation is performed by fuel injection into a combustion chamber of an engine cylinder. 12. The exhaust gas purifying method according to claim 11, wherein the injection timing and the ignition timing are retarded. 13. The method according to claim 1, wherein the low exhaust temperature operation is performed by reducing one of an engine speed and an engine load.
The exhaust gas purifying method according to claim 11, wherein the high exhaust gas temperature operation is performed by increasing one or both of the engine speed and the engine load. 14. The exhaust gas purifying method according to claim 11, wherein the exhaust gas temperature is lowered by injecting air into an exhaust passage. 15. In the regeneration of the nitrogen oxide storage reduction catalyst, a regeneration operation is performed when a detection value of a NOx concentration sensor disposed downstream of the nitrogen oxide storage reduction catalyst exceeds a predetermined determination value. 10. The start of the process is performed.
15. The exhaust gas purification method according to any one of items 14 to 14. 16. The regeneration operation of the nitrogen oxide storage-reduction catalyst, wherein a regeneration operation is started when an estimated integrated value of NOx emissions exceeds a predetermined determination value. The exhaust gas purifying method according to any one of the above.