JP2013024230A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system which uses a base metal-supported NOelimination catalyst and enables deterioration in the NOelimination performance of the system caused by particle growth of base metal particles to be efficiently suppressed.SOLUTION: The exhaust emission control system includes: a base metal-supported NOelimination catalyst (12); an oxygen sensor (14) disposed downstream from the NOelimination catalyst; and an air-fuel ratio controller (15) for controlling an air-fuel ratio. In the exhaust emission control system, the oxygen storage amount of the NOelimination catalyst is measured by the oxygen sensor. When the oxygen storage amount is greater than a predetermined value, the air-fuel ratio of exhaust is controlled to a fuel enriched side by the air-fuel ratio controller and NOin the exhaust is eliminated by reduction. When the oxygen storage amount is less than the predetermined value, the air-fuel ratio of the exhaust is controlled to a fuel leaned side by the air-fuel controller, and regeneration processing of the NOelimination catalyst is performed.

Description

  The present invention relates to an exhaust purification device, and more particularly to an exhaust purification device for an internal combustion engine such as a gasoline engine or a diesel engine.

In order to reduce and purify nitrogen oxides (NO _x ) contained in exhaust gas from internal combustion engines such as gasoline engines and diesel engines, it is known to use NO _x purification catalysts. However, noble metals generally used as catalyst components of such NO _x purification catalysts, such as platinum group elements such as rhodium (Rh), have been used in tandem with the tightening of automobile exhaust regulations, and therefore resources There is concern about the depletion of For this reason, while reducing the usage-amount of a platinum group element, it is required in the future to substitute the role of a platinum group element with another metal.

Much research has been conducted on catalyst components for reducing the amount of platinum group elements used or alternative catalyst components. One of such catalyst components is a base metal such as copper (Cu), a base metal-supported NO _x purification catalyst in which base metal particles are supported on a metal oxide support, and such a base metal-supported NO _x purification catalyst. Several proposals have been made on an exhaust gas purification apparatus for an internal combustion engine equipped with the above (Patent Document 1).

In Patent Document 2, when the activity of the vanadium bearing _the NO _x purification catalyst vanadium, which are supported drops on a metal oxide support, to reproduce the catalyst is contacted with 0.99 ° C. or more oxygen gas is suggesting. Further, in Patent Document 3, in the catalyst / absorber for absorbing nitrogen oxide having an oxidation catalyst component such as platinum and copper and an absorber such as hydroxide, the catalyst / absorption is obtained by absorbing the nitrogen oxide. It has been proposed to regenerate the catalyst / absorber absorber using a regeneration gas containing hydrocarbon and inert carrier gas when the body activity is reduced. Moreover, in patent document 4, in the deodorizing agent which deodorizes using the oxidation-reduction reaction between copper or copper oxides of different valences, the used copper or copper oxide is regenerated with an oxidizing substance or a reducing substance. is suggesting.

JP 2001-003733 A JP-A-52-026393 JP 2002-502691 A JP-A-5-228339

In general, when the air-fuel ratio of the exhaust is near the fuel lean or the stoichiometric air-fuel ratio, the base metal such as copper has a lower reducing ability for NO _{x in} the exhaust than the noble metal such as rhodium. That is, base metals such as copper cannot sufficiently reduce and purify NO _x contained in the exhaust if the air-fuel ratio of the exhaust is near the fuel lean or stoichiometric air-fuel ratio. Therefore, when a base metal such as copper is used as the catalyst metal of the NO _x purification catalyst, it is generally preferable to control the air-fuel ratio of the exhaust to be rich in fuel.

However, base metals such as copper have a lower thermal stability than noble metals, and therefore, even when used in a fuel-rich atmosphere, the exhaust temperature during acceleration or high-speed driving becomes high. When used over a long period of time in conditions caused grain growth of the base metal particles, reduces the contact area with the exhaust, it is thereby _the NO _x purification performance tends to be lowered.

Accordingly, an object of the present invention is to provide an exhaust purification device that uses a base metal-supported NO _x purification catalyst, and that can efficiently suppress a reduction in NO _x purification performance due to grain growth of base metal particles. And

The present invention for solving the above problems is as follows.
(1) a base metal-supported NO _x purification catalyst, which is disposed in the exhaust passage and has base metal particles supported on a metal oxide support;
An oxygen sensor disposed in the exhaust passage downstream of the NO _x purification catalyst, and an air-fuel ratio control unit for controlling the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst, and The air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is switched between fuel rich and fuel lean by the air-fuel ratio control unit, and the oxygen concentration of the exhaust gas flowing out from the NO _x purification catalyst is changed by the oxygen sensor. By measuring, the oxygen storage amount of the NO _x purification catalyst is measured, and when the oxygen storage amount is larger than a predetermined value, the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is determined as the air-fuel ratio. by controlling the fuel-rich by-fuel ratio control unit, and reduce and purify NO _x in the exhaust, and when the oxygen storage amount is below a predetermined value, an empty exhaust gas flowing into the _the NO _x purification catalyst Burning The ratio is controlled to be lean by the air-fuel ratio control unit, and the regeneration processing of the NO _x purification catalyst is performed.
Exhaust purification device.
(2) The exhaust emission control device according to (1), wherein the oxygen storage amount is measured with an interval of 1 minute or more.
(3) The exhaust emission control device according to (1) or (2), wherein the base metal is a transition metal.
(4) The exhaust emission control device according to (3), wherein the base metal is copper.
(5) The exhaust gas purification according to any one of (1) to (4), wherein the metal oxide support is selected from the group consisting of alumina, zirconia, ceria, ceria-zirconia, silica, and titania. apparatus.
(6) The exhaust emission control device according to any one of (1) to (5), wherein the exhaust gas has a temperature of 500 ° C. or higher when the regeneration process is performed.
(7) The exhaust emission control device according to any one of (1) to (6), wherein the exhaust gas has an oxygen concentration of 3 mol% or more when performing the regeneration process.
(8) The exhaust purification device includes at least two NO _x purification catalysts,
Said at least two of the NO _x purification catalyst is disposed in parallel in the exhaust passage, and while performing the regeneration process of the at least one of said _the NO _x purification catalyst, at least one other of said _the NO _x purification NO _x is reduced and purified in the catalyst,
The exhaust emission control device according to any one of (1) to (7) above.

According to the exhaust purification system of the present invention, the oxygen storage amount of the base metal carrying _the NO _x purification catalyst, used as an indicator of the degree of deterioration of the catalyst, when the oxygen storage amount is equal to or less than a predetermined value, a base metal bearing By performing the regeneration treatment of the NO _x purification catalyst, it is possible to efficiently suppress the decrease in the NO _x purification performance due to the growth of the base metal particles.

FIG. 1 is a diagram schematically showing grain growth and redispersion of base metal particles in a base metal-supported NO _x purification catalyst. FIG. 2 is a diagram schematically showing a first embodiment of the exhaust emission control device of the present invention. FIG. 3 is a diagram schematically showing a second embodiment of the exhaust emission control device of the present invention. FIG. 4 is a flowchart of the operation in the second embodiment of the exhaust emission control device of the present invention. FIG. 5 is a transmission electron microscope (TEM) photograph of a copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst). FIG. 6 is a graph showing the NO _x purification rate of the copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst) that was regenerated at temperatures of 300 ° C. to 600 ° C. FIG. 7 is a graph showing the relationship between the oxygen storage amount of the copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst) and the NO _x purification rate.

Exhaust purification system of the present invention is disposed in the exhaust passage, and a base metal bearing _the NO _x purification catalyst base metal particles are carried on a metal oxide support, the exhaust passage downstream of the NO _x purification catalyst and oxygen (O ₂₎ sensor disposed in, and a air-fuel ratio control unit for controlling the air-fuel ratio (a / F) of the exhaust gas flowing into the _the NO _x purification catalyst. Here, in this exhaust purification device, the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is switched between the fuel rich and the fuel lean by the air-fuel ratio control unit, and the oxygen of the exhaust gas flowing out from the NO _x purification catalyst By measuring the concentration with an oxygen sensor, the oxygen storage amount of the NO _x purification catalyst is measured. When the oxygen storage amount is larger than a predetermined value, the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is When the air-fuel ratio is controlled to be rich by the air-fuel ratio control unit to reduce and purify NO _x in the exhaust gas and the oxygen storage amount is not more than a predetermined value, the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is reduced. Then, the regeneration of the NO _x purification catalyst is performed under the control of the fuel lean by the air-fuel ratio control unit.

In the present invention, the fact that the exhaust gas is “theoretical air-fuel ratio” means that the exhaust gas composition corresponds to the exhaust gas composition obtained by combustion of the air-fuel mixture having the stoichiometric air-fuel ratio (also referred to as “stoichiometric”). doing. Further, the fact that the exhaust is “fuel rich” means that the exhaust composition corresponds to the exhaust composition obtained by the combustion of the air-fuel mixture having an air-fuel ratio smaller than the stoichiometric air-fuel ratio. Still further, the fact that the exhaust is “fuel lean” means that the exhaust composition corresponds to an exhaust composition obtained by combustion of an air / fuel mixture having a larger air / fuel ratio than the stoichiometric air / fuel ratio. When the fuel is gasoline, the theoretical air fuel ratio (A / F) is 14.6, and the fuel rich air fuel ratio is, for example, 14.5 or less, 14.4 or less, 14.3 or less, NO _x purification is preferable, and 13.4 or higher, 13.6 or higher, or 13.8 or higher is preferable for fuel efficiency.

(Oxygen storage amount)
In the exhaust purification apparatus of the present invention, the oxygen storage amount of the base metal-supported NO _x purification catalyst is used as an indicator of the degree of deterioration of the catalyst. That is, in the exhaust purification system of the present invention, the oxygen storage amount of base metal carrying _the NO _x purification catalyst is equal to or less than a predetermined value, it is determined that _the NO _x purification performance of the base metal carrying _the NO _x purification catalyst is deteriorated The playback process is performed. Therefore, according to the exhaust gas purification apparatus of the present invention, it is possible to determine the degree of deterioration of the base metal-supported NO _x purification catalyst using an oxygen sensor that is generally used and has proven high reliability. it can.

Here, although not limited to theory, the reason why the oxygen storage amount of the base metal-supported NO _x purification catalyst correlates with the degree of deterioration of the catalyst may be as follows. That is, when the air-fuel ratio of the exhaust gas flowing into the base metal-supported NO _x purification catalyst is switched between fuel rich and fuel lean, the base metal-supported NO _x purification catalyst in which base metal particles are supported in a fine state is fine. It is considered that the base metal particles are reduced and oxidized, and this reduction and oxidation appear as an oxygen storage function of the catalyst. In contrast, in the base metal-supported NO _x purification catalyst in which the base metal particles are sintered and become coarse particles, the reduction of the base metal particles is similarly performed when the air-fuel ratio is switched between fuel rich and fuel lean. It is considered that oxidation is difficult to occur, or the volume to be reduced and oxidized is reduced, which appears as a decrease in the oxygen storage amount of the catalyst.

The “predetermined value” of the oxygen storage amount as a criterion for determining whether or not to perform the regeneration process is, for example, 80% or less, 90% or less, or 95% at an exhaust temperature of 500 ° C. and an air-fuel ratio of 14.0. The oxygen storage amount corresponding to the following NO _x purification rate can be set. Further, in the exhaust purification apparatus of the present invention, the measurement and evaluation of the degradation due to its oxygen storage amount of the base metal carrying _the NO _x purification catalyst is performed periodically, for example, 1 minute or more, more than three minutes, or more than 5 minutes Can be done at intervals. Also, this interval can be, for example, 24 hours or less, 10 hours or less, 5 hours or less, 1 hour or less, or 30 minutes or less.

(Reproduction processing)
In the exhaust purifying apparatus of the present invention, the oxygen storage amount of base metal carrying _the NO _x purification catalyst is larger than the predetermined value, it is determined that _the NO _x purification catalyst is not deteriorated, flows into the _the NO _x purification catalyst The air-fuel ratio of the exhaust gas to be exhausted is controlled to be rich in fuel by the air-fuel ratio control unit to reduce and purify NO _x in the exhaust gas. Further, in the exhaust purification device of the present invention, when the oxygen storage amount of the base metal-supported NO _x purification catalyst is equal to or less than a predetermined value, it is determined that the NO _x purification catalyst has deteriorated, and this NO _x purification catalyst The air-fuel ratio of the exhaust gas flowing into the exhaust gas is controlled to be lean by the air-fuel ratio control unit, and the regeneration process of the NO _x purification catalyst is performed.

In the apparatus of the present invention, grain growth of the base metal particles of base metal carrying _the NO _x purification catalyst, and regeneration of the base metal carrying _the NO _x purification catalyst having thus the grain growth and base metal particles, as shown by the schematic diagram of FIG. 1 It is thought to happen.

That is, as shown in FIG. 1, when a base metal-supported NO _x purification catalyst 6 in which fine base metal particles 1 are supported on a carrier 2 is used for reduction purification of NO _x in a fuel-rich atmosphere, The fine base metal particles 1 grow and thereby become a base metal-supported NO _x purification catalyst 7 having coarse base metal particles 3, thereby reducing the NO _x purification rate. However, such coarse base metal particles 3, when exposed to the fuel-lean atmosphere is oxidized and redispersed, become fine fine base metal particles 1 when exposed again fuel-rich atmosphere, whereby _the NO _x purification The catalyst is regenerated. The regenerated NO _x purification catalyst 6 can be preferably used again for NO _x reduction purification in a fuel-rich atmosphere.

In order to accelerate the regeneration process, it may be preferable to perform the regeneration process at a predetermined temperature, for example, a temperature of about 500 ° C. or higher, about 600 ° C. or higher, or about 700 ° C. or higher. Moreover, this regeneration process can be performed at a temperature of 900 ° C. or lower or 800 ° C. or lower, for example. To achieve the temperature of such regeneration processing time is to adjust the operating conditions of the internal combustion engine or the like, to increase the temperature of the exhaust, that like to heat the _the NO _x purification catalyst by the heating unit such as an electric heater Can do.

Further, this regeneration treatment can be performed for any time during which the NO _x purification catalyst can be at least partially regenerated, for example, 1 second or more, 3 seconds or more, 5 seconds or more, 10 seconds or more, 1 minute or more. And can be carried out over a period of 60 minutes or less, 30 minutes or less, 10 minutes or less, or 5 minutes or less.

  Furthermore, this regeneration treatment can be performed so that the oxygen concentration in the exhaust gas is 3 mol% or more, 5 mol% or more, and 10 mol% or more. The oxygen concentration during the regeneration process may be, for example, 50 mol% or less, 30% or less, or 25% or less. Such oxygen concentration can be achieved by control by the air-fuel ratio control unit. Specifically, for example, such an oxygen concentration can be achieved by adjusting the amount of oxygen and / or fuel supplied to a combustion apparatus such as an internal combustion engine by an air-fuel ratio control unit.

(Use)
Exhaust purification system of the present invention can be used for the reduction and purification of the NO _x in the exhaust from the combustion device such as an internal combustion engine. Such internal combustion engines can in particular include automotive engines, such as automotive gasoline and diesel engines.

(Base metal-supported NO _x purification catalyst)
The context of the present invention, a base metal bearing _the NO _x purification catalyst is _the NO _x purification catalyst base metal particles are supported on a metal oxide support.

Here, as the base metal, transition metals, particularly titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and silver, and more particularly copper can be used. The support may be any metal oxide generally used as a metal oxide support, such as alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), ceria (CeO ₂ ), ceria-zirconia (CeO ₂ —ZrO _2). ), Silica (SiO ₂ ), and titania (TiO ₂ ).

(Oxygen sensor)
In the context of the present invention, the oxygen sensor may be any sensor capable of measuring the oxygen concentration in the exhaust. Examples of such an oxygen sensor include an oxygen sensor used for measuring the oxygen concentration in exhaust from an automobile, particularly an oxygen sensor using zirconia as an oxygen ion conductor.

(Air-fuel ratio control unit)
With respect to the present invention, the air-fuel ratio control unit may be an electronic control unit (ECU), for example, an electronic control unit that adjusts the air-fuel ratio of the exhaust gas by adjusting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine. Here, such adjustment of the air-fuel ratio of the air-fuel mixture can be achieved by adjusting the amount of fuel injected from the fuel injection valve, adjusting the amount of air contained in the air-fuel mixture, and the like.

(Embodiment)
The preferred embodiments of the exhaust emission control device of the present invention will be described in more detail below with reference to the drawings. However, the following description is merely intended to illustrate preferred embodiments of the present invention, and It is not intended to be limited to such specific embodiments.

(First embodiment)
FIG. 2 is a diagram schematically showing a first embodiment of the exhaust gas purification apparatus of the present invention relating to purification of exhaust gas from an internal combustion engine.

2, the exhaust side of the internal combustion engine 10 is coupled to the base metal carrying _the NO _x purification catalyst 12 through the exhaust passage 11, further outlet of the _the NO _x purification catalyst 12 is connected to an exhaust passage 13 Yes. Note that arrows 10 _in and 10 _out indicate the flow direction of the air-fuel mixture supplied to the internal combustion engine 10 and the exhaust gas exiting from the internal combustion engine 10, respectively.

In this embodiment, an oxygen (O ₂ ) sensor 14 for detecting the oxygen concentration in the exhaust gas flowing out from the NO _x purification catalyst 12 is attached to the exhaust flow path 13. Further, the air-fuel ratio of the exhaust is controlled by an electronic control unit (ECU) 15 as an air-fuel ratio control unit.

(First embodiment-operation)
In this embodiment, the oxygen storage amount of the base metal-supported NO _x purification catalyst 12 is measured by the oxygen sensor 14. When the oxygen storage amount measured in this way is larger than a predetermined value, it is determined that the NO _x purification catalyst has not deteriorated, and the electronic control unit 15 controls the air-fuel ratio of the exhaust to be rich in fuel. Te, reduces and purifies NO _x in the exhaust by _the NO _x purification catalyst 12. Further, when the oxygen storage amount measured in this way is equal to or less than a predetermined value, it is determined that the NO _x purification catalyst 12 has deteriorated, and the electronic control unit 15 sets the air-fuel ratio of the exhaust to the fuel lean. And the regeneration process of the NO _x purification catalyst 12 is performed.

(Second Embodiment)
FIG. 3 is a view schematically showing a second embodiment of the exhaust emission control device of the present invention relating to the purification of exhaust gas from the internal combustion engine.

3, the internal combustion engine 20 has first to fourth cylinders 21 to 24, and fuel injection valves 21a to 24a are provided in the cylinders 21 to 24, respectively. The first and fourth cylinders 21 and 24, through the exhaust passage 25, the first base metal supported NO _x in purification catalyst 27 are connected, also the second and third cylinders 22 and 23, the exhaust passage 26 is connected to the second base metal-supported NO _x purification catalyst 28. Further, the outlet portions of the first and second NO _x purification catalysts 27 and 28 are respectively connected to the exhaust passages 29 and 30, and these exhaust passages 29 and 30 are further connected to a single exhaust on the downstream side. It merges with the flow path 31. Note that arrows 20 _in and 20 _out indicate the flow direction of the air-fuel mixture supplied to the internal combustion engine 20 and the exhaust gas exiting from the internal combustion engine 20, respectively.

In this embodiment, oxygen sensors 32 and 33 for detecting the oxygen concentration in the exhaust gas flowing out from the first and second NO _x purification catalysts 27 and 28 are attached to the exhaust passages 29 and 30, respectively. .

(Second Embodiment-Operation)
FIG. 4 is a flowchart of the operation of the second embodiment of the exhaust emission control device of the present invention.

As shown in FIG. 4, first, in step 101, the oxygen storage amount C ₁ of the first base metal-supported NO _x purification catalyst 27 is measured by the oxygen sensor 32. Thereafter, in step 201, the measured oxygen storage amount C ₁ in the first of the NO _x purification catalyst 27, it is determined whether less than a predetermined value C _p, the measured value C _1, predetermined If it is equal to or less than the value C _p (C ₁ ≦ C _p ), that is, if it is determined that the first NO _x purification catalyst 27 has deteriorated, the routine proceeds to step 301.

On the other hand, when the measured oxygen storage amount C _{1 of} the first NO _x purification catalyst 27 is larger than the predetermined value C _p in step 201 (C ₁ > C _p ), that is, the first NO _x purification. If it is determined that the catalyst 27 has sufficient catalytic activity, the routine proceeds to step 102 where the operation for the second base metal-supported NO _x purification catalyst 28 is started.

Next, in step 301, the first and fourth cylinders 21 and 24 are closed by closing the fuel injection valves 21a and 24a, reducing the amount of fuel injected from these fuel injection valves 21a and 24a, etc. the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst 27, by controlling the fuel-lean, starts reproduction processing. Thereafter, in step 401, it is determined whether or not the reproduction process is completed. If the reproduction process is completed, the process proceeds to step 501. Regarding the determination of the completion of the reproduction process, for example, the elapsed time from the start of the reproduction process is measured by a timer, and the reproduction process is completed when the elapsed time measured by the timer exceeds a predetermined time. It can be judged.

After the regeneration process is completed, the first NO _x purification catalyst is opened by opening the fuel injection valves 21a and 24a in step 501 and increasing the amount of fuel injected from these fuel injection valves 21a and 24a. The air-fuel ratio of the exhaust gas flowing into the engine 27 is controlled to be rich in fuel, and the regeneration process is completed.

On the other hand, as described above, when it is determined in step 201 that the first NO _x purification catalyst 27 exhibits sufficient catalytic activity, the process proceeds to step 102 and the second NO _x purification catalyst 28 is inspected. The operation is performed in the same manner as in the case of the first NO _x purification catalyst 27.

As described above, according to this embodiment, it is possible to reduce and purify NO _x in the exhaust gas at both the first and second NO _x purification catalysts 27 and 28 at all times. When either one of the NO _x purification catalyst of the first and second of the NO _x purification catalyst 27 and 28 is deteriorated to a predetermined degree, the fuel only atmosphere of the exhaust gas flowing into the _the NO _x purification catalyst while switching to a lean atmosphere performed regeneration process of _the NO _x purification catalyst, it is possible to reduce and purify NO _x in the exhaust at the other of the NO _x purification catalyst.

<Example 1>
In this example, the effect of heat treatment in a fuel-rich and fuel-lean atmosphere on the particle size of the copper particles of the copper-supported alumina catalyst was evaluated.

5 mass% copper (Cu) was supported on an alumina (Al ₂ O ₃ ) support by an impregnation method, dried at 120 ° C., and calcined at 600 ° C. for 5 hours to obtain a copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst) was obtained.

This copper-supported alumina catalyst was heat-treated at 700 ° C. for 10 minutes in an atmosphere containing 1 mol% of hydrogen (H ₂ ) and the balance of nitrogen (N ₂ ), that is, a fuel-rich atmosphere. A transmission electron microscope (TEM) photograph of the copper-supported alumina catalyst thus heat-treated is shown in FIG. In FIG. 5A, copper particles having a particle size of about several nm were observed.

  The copper-supported alumina catalyst thus heat-treated in the fuel-rich atmosphere was heat-treated at 500 ° C. for 10 minutes in an air atmosphere, that is, a fuel-lean atmosphere. A transmission electron microscope (TEM) photograph of the copper-supported alumina catalyst thus heat-treated is shown in FIG. In FIG.5 (b), it was observed that the copper particle confirmed in Fig.5 (a) has lose | disappeared. This indicates that the copper particles are dispersed into very fine particles at the atomic level by heat treatment in a fuel-lean atmosphere.

  Further, the copper-supported alumina catalyst heated in the air in this way was heat-treated at 700 ° C. for 10 minutes and 50 hours, respectively, in an atmosphere containing 1 mol% hydrogen and the balance nitrogen, that is, a fuel-rich atmosphere. Transmission electron microscope (TEM) photographs of the copper-supported alumina catalyst thus heat-treated are shown in FIGS. 5 (c) and 5 (d), respectively. In FIG.5 (c), the copper particle which has a particle diameter of about several nanometer was observed similarly to the case of Fig.5 (a). Further, in FIG. 5 (d) (TEM photograph shown as an inverted image), as is clear from the above, there are many large copper particles (white lumps in FIG. 5 (d)) exceeding several tens of nm, particularly about 50 nm. Observed.

<Example 2>
In this example, the effect of regeneration treatment conditions in a fuel-lean atmosphere on the particle size of copper particles of a copper-supported alumina catalyst was evaluated.

In the same manner as in Example 1, a copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst) was obtained. Moreover, this copper carrying | support alumina catalyst was shape | molded in the pellet form for evaluation.

The pellet-shaped copper-supported alumina catalyst thus obtained was heat-treated at 700 ° C. for 30 minutes in an atmosphere containing 1 mol% of hydrogen (H ₂ ) and the balance of nitrogen (N ₂ ), that is, a fuel-rich atmosphere. And deteriorated. Thereafter, the copper-supported alumina catalyst thus deteriorated was regenerated by heat treatment at 300 ° C., 400 ° C., 500 ° C., and 600 ° C. for 10 minutes in an air atmosphere, that is, a fuel lean atmosphere.

Thus fuel-lean atmosphere copper supported alumina catalyst was deteriorated in, and the copper on alumina catalyst was regenerated in fuel-lean atmosphere to evaluate _the NO _x purification rate. Specifically, the evaluation of the NO _x purification rate was carried out by applying a model gas for evaluation having the composition shown in Table 1 below to a temperature of 500 ° C. and 15 L / 15 to 3.0 g of the copper-supported alumina catalyst thus heat-treated. was circulated at a flow rate were measured _the NO _x purification rate when steady state was reached. Note that the model gas for evaluation shown in Table 1 below is prepared so as to correspond to an exhaust having an air-fuel ratio (A / F) of about 14.0.

The evaluation result of the NO _x purification rate is shown in FIG. As is apparent from the results of FIG. 6, the regeneration treatment at a temperature of 500 ° C. or higher in a fuel lean atmosphere makes the copper-supported alumina catalyst significant in about 1 to 5 minutes, particularly about 3 to 5 minutes. Was able to play.

<Example 3>
In this embodiment, an atmosphere of using copper on alumina catalyst was evaluated for impact on _the NO _x purification performance of copper on alumina catalysts.

In the same manner as in Example 1, a copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst) was obtained. Moreover, this copper carrying | support alumina catalyst was shape | molded in the pellet form for evaluation.

Exhaust gas from the internal combustion engine was supplied at 600 ° C. and 500 ° C. to the pellet-like copper-carrying alumina catalyst thus obtained, and the NO _x purification rate was evaluated. The results of this evaluation are shown in Table 2 below.

As shown in Table 2, when using the copper used as the catalyst metal, the air-fuel ratio of the exhaust gas, by the rich atmosphere, it is possible to promote _the NO _x purification.

<Example 4>
In this example, the correlation between the oxygen storage amount of the NO _x purification catalyst and the NO _x purification performance was examined.

In the same manner as in Example 1, a copper-supported alumina catalyst (Cu / Al ₂ O ₃ catalyst) was obtained. For evaluation, the copper-supported alumina catalyst was coated on a 1.3 liter honeycomb substrate (diameter 103 mm, length 155 mm, 400 cells, 4 mil). The coat weight of the copper supported alumina catalyst was 150 g / substrate-liter, so the copper weight was 7.5 g / substrate-liter.

The exhaust gas from the internal combustion engine was supplied at 500 ° C. to the copper-supported alumina catalyst thus obtained, and the NO _x purification rate by the copper-supported alumina catalyst was evaluated. Further, in the internal combustion engine, the fuel was cut intermittently for 5 seconds to make the exhaust gas into a fuel lean atmosphere, thereby regenerating the copper-carrying alumina catalyst.

The _the NO _x purification rate in conjunction with assessing the evaluation, an evaluation of the oxygen storage amount of the copper on alumina catalysts. Specifically, the composition of the exhaust gas supplied to the copper-supported alumina catalyst is switched between a fuel-rich atmosphere and a fuel-lean atmosphere, the oxygen concentration of the input gas and the output gas is evaluated, and From the oxygen concentration and the model gas flow rate, the oxygen storage amount of the copper-supported alumina catalyst was determined.

The relationship between the oxygen storage amount and _the NO _x purification rate of the copper on alumina catalyst, is shown in FIG. From FIG. 7, it is understood that the oxygen storage amount of the NO _x purification catalyst correlates with the NO _x purification performance, and that the decrease in the oxygen storage amount corresponds to the decrease in the NO _x purification rate.

Base metal carrying _the NO _x purification catalyst 10 an internal combustion engine 11, 13 exhaust passage 12 base metal carrying _the NO _x purification catalyst having a base metal bearing _the NO _x purification catalyst 7 coarse base metal particles having a fine base metal particles 2 carrier 3 coarse base metal particles 6 fine base metal particles 14 Oxygen sensor 15 Electronic control unit as air-fuel ratio controller

Claims (8)

A base metal-supported NO _x purification catalyst, which is disposed in the exhaust passage and has base metal particles supported on a metal oxide carrier;
An oxygen sensor disposed in the exhaust flow path downstream of the NO _x purification catalyst, and an air-fuel ratio control unit for controlling the air-fuel ratio of the exhaust flowing into the NO _x purification catalyst, and The air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is switched between fuel rich and fuel lean by the air-fuel ratio control unit, and the oxygen concentration of the exhaust gas flowing out from the NO _x purification catalyst is changed by the oxygen sensor. By measuring, the oxygen storage amount of the NO _x purification catalyst is measured, and when the oxygen storage amount is larger than a predetermined value, the air-fuel ratio of the exhaust gas flowing into the NO _x purification catalyst is determined as the air-fuel ratio. When the fuel ratio is controlled by the fuel ratio control unit to reduce and purify NO _x in the exhaust gas and the oxygen storage amount is equal to or less than a predetermined value, the exhaust air flowing into the NO _x purification catalyst is emptied. Burning The ratio is controlled to be lean by the air-fuel ratio control unit, and the regeneration processing of the NO _x purification catalyst is performed.
Exhaust purification device.   The exhaust emission control device according to claim 1, wherein the oxygen storage amount is measured with an interval of 1 minute or more.   The exhaust emission control device according to claim 1 or 2, wherein the base metal is a transition metal.   The exhaust emission control device according to claim 3, wherein the base metal is copper.   The exhaust emission control device according to any one of claims 1 to 4, wherein the metal oxide support is selected from the group consisting of alumina, zirconia, ceria, ceria-zirconia, silica, and titania.   The exhaust emission control device according to any one of claims 1 to 5, wherein when performing the regeneration process, the exhaust gas has a temperature of 500 ° C or higher.   The exhaust emission control device according to any one of claims 1 to 6, wherein when performing the regeneration process, the exhaust gas has an oxygen concentration of 3 mol% or more. The exhaust purification device has at least two NO _x purification catalysts;
Wherein at least two of the NO _x purification catalyst is disposed in parallel in the exhaust passage, and while performing the regeneration process of the at least one of said _the NO _x purification catalyst, at least one other of said _the NO _x purification NO _x is reduced and purified in the catalyst,
The exhaust emission control device according to any one of claims 1 to 7.