JPH11247654A - Exhaust emission control device using nox stored and reduced type three-way catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain deterioration of purifying performance to the minimum by sufficiently supplying HC and Co to a NOx stored and reduced type three-way catalyst, and providing a means for feedback controlling the air fuel ratio of combustion mixture to a target air fuel ratio. SOLUTION: A first air fuel ratio detecting means 4, a NOx stored and reduced type three-way catalyst 2, a three-way catalyst 3, and a second air fuel ratio detecting means 5 are sequentially arranged, a first air duel ratio feedback means 6a and a second air fuel feedback means 6b are connected to the first air fuel ratio detecting means 4 and the second air fuel ratio detecting means 5 in such a manner as to perform data communication, the first air fuel ratio feedback means 6a feedback controls the air fuel ratio of exhaust mixture to a target air fuel ratio according to the exhaust air fuel ratio detected by the first air fuel ratio detecting means 4, and the second air fuel ratio feedback means 6b feedback controls the air fuel ratio of the combustion mixture to a target air fuel ratio according to the exhaust air fuel ratio detected by the second air fuel ratio detecting means 5 immediately after the target air duel ratio of combustion mixture is swtiched from lean to storichiometry or rich.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrocarbons (hereinafter referred to as "HC") in exhaust gas discharged from internal combustion engines such as automobiles (gasoline and diesel) and boilers.
The present invention relates to an exhaust gas purifying apparatus using a NOx storage reduction type three-way catalyst for purifying carbon monoxide (hereinafter referred to as "CO") and nitrogen oxides (hereinafter referred to as "NOx"). The present invention relates to an exhaust gas purification device in which a NOx storage reduction type three-way catalyst is disposed in a passage to improve a NOx purification rate.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for fuel-efficient vehicles due to the depletion of petroleum resources and the problem of global warming, and the development of lean-burn vehicles has attracted attention for gasoline vehicles.

In such a lean-burn vehicle, during lean-burn operation, the exhaust air-fuel ratio becomes an oxygen-rich atmosphere (hereinafter, referred to as "lean atmosphere") having an oxygen concentration higher than a stoichiometric air-fuel ratio (hereinafter, referred to as "stoichiometric"). When a normal three-way catalyst is used in a lean atmosphere, the action of purifying NOx becomes insufficient. Therefore, it has been desired to develop a catalyst that can purify NOx even in a lean atmosphere.

In response to such a demand, Japanese Patent Application Laid-Open No.
No. 9397 discloses that N 2 in exhaust gas in a lean atmosphere is used.
Ox is absorbed, and the absorbed NOx is converted to stoichiometric oxygen-deficient atmosphere (hereinafter referred to as "rich atmosphere") having a lower oxygen concentration.
That. Japanese Patent Laid-Open No. 8-2 discloses an engine in which an exhaust system is provided with a NOx storage-reduction type three-way catalyst which releases and reduces the exhaust gas in the exhaust system.
Japanese Patent No. 70440 discloses an exhaust gas purifying apparatus in which three-way catalysts are arranged upstream and downstream of a NOx storage reduction three-way catalyst, respectively.

[0005]

However, if an ordinary three-way catalyst is arranged upstream of the NOx storage reduction type three-way catalyst in the exhaust system, the oxidation reaction of the three-way catalyst causes H
Since C and CO are consumed, when the air-fuel ratio of the combustion mixture changes from a lean region to a rich region, HC required when the NOx released from the NOx storage reduction type three-way catalyst is subjected to the reduction treatment. In addition, there is a problem that CO is not sufficiently supplied. In such a situation, in order to supply HC and CO required for reducing the NOx released from the NOx storage reduction type three-way catalyst to the NOx storage reduction type three-way catalyst, a means for increasing the degree of richness is required. However, in the NOx storage-reduction type three-way catalyst, the ability to absorb or release NOx changes depending on the exhaust gas temperature or the state of deterioration, so that the degree of oxygen richness may be increased more than necessary. In addition, there was a problem that the purification performance of CO deteriorated.

[0006] The present invention has been made in view of the problems of such technology, and has as its object the following.
Provided is an exhaust gas purifying apparatus capable of improving the NOx purification rate when the exhaust air-fuel ratio switches from lean to stoichiometric or rich, and minimizing deterioration of HC and CO purifying performance in a rich region. It is in.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the oxygen storage capacity in the three-way catalyst disposed downstream of the NOx storage reduction type three-way catalyst in the exhaust system is reduced. HC and C required to reduce NOx by reducing the amount of contributing components
O is sufficiently supplied to the NOx storage-reduction type three-way catalyst, and air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the combustion mixture to the target air-fuel ratio based on the exhaust air-fuel ratio is provided. The inventors have found that deterioration of the purification performance of the three-way catalyst for HC and CO is suppressed to a minimum, and have completed the present invention.

That is, the exhaust gas purifying apparatus using the NOx storage reduction type three-way catalyst of the present invention comprises:
In an exhaust gas purifying apparatus in which a NOx storage reduction type three-way catalyst and a three-way catalyst are sequentially arranged, the NOx storage reduction type three-way catalyst absorbs NOx in exhaust gas in a lean atmosphere and converts the absorbed NOx into a stoichiometric air-fuel ratio. Or a NOx occlusion reduction type three-way catalyst that performs a reduction treatment by releasing in a rich atmosphere, and a noble metal-supported powder in which at least one noble metal selected from the group consisting of platinum, palladium, and rhodium is supported on a porous carrier; LnαBOβ (where Ln is at least one selected from the group consisting of La, Ce, Nd and Sm, and B is Fe, Co, Ni
And Mn, wherein 0 <α <1 and 0 <β <4. ), And a carbonate of at least one metal selected from the group consisting of Mg, Ca, Sr, Ba, Na, K and Cs. , Palladium and rhodium, and the amount of ceria and / or ceria-containing composite oxide contained in the three-way catalyst is 5 to 3 per liter of the catalyst.
0 g.

A preferred embodiment of the exhaust gas purifying apparatus using the NOx storage-reduction type three-way catalyst of the present invention is a first air-conditioner disposed upstream of the NOx storage-reduction type three-way catalyst for detecting the exhaust air-fuel ratio. Fuel ratio detecting means, and second air-fuel ratio detecting means disposed downstream of the NOx storage reduction type three-way catalyst and detecting an exhaust air-fuel ratio. In a normal state, the first air-fuel ratio detecting means detects the exhaust air-fuel ratio. First air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the combustion mixture to the target air-fuel ratio based on the exhaust air-fuel ratio to be performed, and immediately after the target air-fuel ratio of the combustion mixture is switched from lean to the stoichiometric air-fuel ratio or rich. A second air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the combustion mixture to a target air-fuel ratio based on the exhaust air-fuel ratio detected by the second air-fuel ratio detection means. It is characterized in.

[0010]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, when the exhaust air-fuel ratio is switched from lean to stoichiometric or rich, the NOx absorbed and reduced by the three-way NOx storage reduction type catalyst is used.
Ox is released from the NOx storage-reduction type three-way catalyst and then reduced, but the amount of component that contributes to the oxygen storage capacity in the three-way catalyst disposed downstream of the NOx storage-reduction type three-way catalyst in the exhaust system Is reduced, the amount of HC and CO consumed by the oxidation reaction of the three-way catalyst is reduced, and the HC and CO required for the reduction treatment are sufficiently supplied to the NOx storage reduction type three-way catalyst. The purification rate of NOx is improved.

Further, when the exhaust air-fuel ratio is switched from a lean region to a rich region by using output signals of air-fuel ratio detecting means installed upstream and downstream of the exhaust system from the NOx storage reduction type three-way catalyst, If the time for which the fuel is kept rich is controlled, the NOx absorbed in the lean region is sufficiently released and reduced without depending on the deterioration state and the operating temperature of the NOx storage reduction type three-way catalyst. In addition to improving the efficiency, it is not necessary to supply more HC and CO than necessary, and deterioration of the purification performance of HC and CO in the rich region is minimized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An exhaust gas purifying apparatus according to the present invention will be described with reference to the drawings. The present invention is not limited to this.

FIG. 1 is a block diagram showing an example of a basic configuration of an exhaust gas purifying apparatus using a NOx storage reduction type three-way catalyst according to the present invention. In this figure, in this purification device, a first air-fuel ratio detecting means 4, a NOx storage reduction type three-way catalyst 2, a three-way catalyst 3, and a second air-fuel ratio detecting means 5 are arranged from the upstream side of the exhaust system of the internal combustion engine 1. They are arranged sequentially. Also, the first
The first air-fuel ratio feedback unit 6a and the second air-fuel ratio feedback unit 6b are connected to the air-fuel ratio detection unit 4 and the second air-fuel ratio detection unit 5 so that data communication is possible.
The first air-fuel ratio feedback means 6a feedback-controls the air-fuel ratio of the exhaust gas mixture to the target air-fuel ratio based on the exhaust air-fuel ratio detected by the first air-fuel ratio detection means 4, and the second air-fuel ratio feedback means 6b Immediately after the target air-fuel ratio of the mixture is switched from lean to stoichiometric or rich, the air-fuel ratio of the combustion mixture is feedback-controlled to the target air-fuel ratio based on the exhaust air-fuel ratio detected by the second air-fuel ratio detection means 5.

FIG. 2 is a system configuration diagram showing an example of an exhaust gas purifying apparatus using the NOx storage reduction type three-way catalyst according to the present invention. It is to be noted that the same members as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
In FIG. 2, reference numeral 7 denotes a fuel injection valve, and reference numeral 8 denotes an exhaust pipe. A casing containing the fuel injection valve 7, the internal combustion engine 1, and the NOx storage reduction three-way catalyst 2 via the exhaust pipe 8. The casing containing the three-way catalyst 3 is in communication with the casing. In addition, a first pipe for detecting an exhaust air-fuel ratio is provided in the exhaust pipe 8.
An air-fuel ratio sensor 4a and a second air-fuel ratio sensor 5a are arranged upstream of the NOx storage reduction type three-way catalyst 2 and downstream of the three-way catalyst 3, respectively. The first air-fuel ratio sensor 4a and the second air-fuel ratio sensor 5a And the output of the fuel injection valve 7 is the first
A control unit 6 that functions as the air-fuel ratio feedback means 6a and the second air-fuel ratio feedback means 6b
It is connected to the.

Here, the NOx storage reduction type three-way catalyst 2 is
NOx in exhaust gas when the exhaust air-fuel ratio is in the lean region
Is a catalyst for reducing the absorbed NOx when the exhaust air-fuel ratio is in a stoichiometric or rich range. For example, an alumina as a supporting base material, and an alkali typified by cesium and potassium are formed on the supporting base material. At least one selected from metals and alkaline earth metals represented by barium and at least one selected from noble metals such as platinum, palladium and rhodium are supported.

In the three-way catalyst 3, the amount of ceria (CeO ₂ ), which is a component contributing to the oxygen storage capacity, is adjusted. Specifically, in a conventional three-way catalyst,
In the present invention, the amount is adjusted to 5 to 30 g per liter of the catalyst, preferably 5 to 15 g per liter of the catalyst, in contrast to 50 to 60 g per liter of the catalyst.

As the first air-fuel ratio sensor 4a and the second air-fuel ratio sensor 5a, sensors that detect the exhaust air-fuel ratio based on the oxygen concentration in the exhaust gas can be used, but a stoichiometric sensor that detects only the stoichiometric air-fuel ratio is used. Or a wide-range air-fuel ratio sensor capable of detecting the exhaust air-fuel ratio in a wide range.

The control unit 6 determines a target air-fuel ratio in accordance with operating conditions, calculates a fuel injection amount (injection pulse width) so as to form an air-fuel mixture of the target air-fuel ratio. A fuel injection signal is determined.
In addition, as the target air-fuel ratio, not only stoichiometric and rich but also lean can be set.

The control unit 6 normally corrects the fuel injection amount by, for example, proportional integral control so that the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 4a approaches the target air-fuel ratio. For example, setting of an air-fuel ratio feedback correction coefficient (operating amount) is performed (this function corresponds to the first air-fuel ratio feedback means 6a). The switching of the target air-fuel ratio from lean to stoichiometric or rich is performed according to operating conditions (acceleration, changes in load / rotation), and even under conditions where a lean air-fuel ratio is originally set as the target air-fuel ratio. When it is estimated that the NOx absorption amount in the NOx storage reduction type three-way catalyst 2 has reached the limit value, the setting is such that the rich control can be temporarily performed, and the temporary control for the NOx reduction processing is performed. Switching to the rich range is also included.

Further, immediately after the target air-fuel ratio is switched from lean to stoichiometric or rich, the control unit 6 executes the air-fuel ratio feedback control according to a change in the output of the second air-fuel ratio sensor 5a. ing. (This function corresponds to the second air-fuel ratio feedback means 6b.) FIG. 3 shows an example of feedback control by the second air-fuel ratio feedback means 6b.

In FIG. 3, first, in step 11 (hereinafter abbreviated as "S11"), it is determined whether or not air-fuel ratio control for reducing NOx is necessary. And S
If it is determined in step 11 that air-fuel ratio control for reducing NOx is necessary, the target air-fuel ratio is switched from a lean region to a rich region (S12).

Next, the outputs of the first air-fuel ratio sensor 4a and the second air-fuel ratio sensor 5a are detected (S13), and the output of the second air-fuel ratio sensor 5a is richer than the output of the first air-fuel ratio sensor 4a. It is determined whether or not (S14). If the output of the second air-fuel ratio sensor 5a is not richer than the output of the first air-fuel ratio sensor 4a, the air-fuel ratio is increased until the output of the second air-fuel ratio sensor 5a becomes richer than the output of the first air-fuel ratio sensor 4a. Become If the output of the second air-fuel ratio sensor 5a becomes richer than the predetermined value SLr (see FIG. 4), step S
Proceed to 15 to invert the air-fuel ratio lean.

Here, the reduction process is performed by the NOx storage reduction type three-way catalyst, and while NOx is desorbed from the NOx storage reduction type three-way catalyst, HC and CO supplied to enrich the air-fuel ratio are supplied. As a result, oxidation and reduction are performed, respectively, and the output of the second air-fuel ratio sensor 5a is maintained near the stoichiometric state. Thereafter, when the amount of NOx desorbed from the NOx storage reduction type three-way catalyst decreases, the balance is lost, the output of the second air-fuel ratio sensor 5a moves in a rich direction, and the first air-fuel ratio sensor 4a and the second air-fuel ratio sensor It is considered that the desorption of NOx has ended when the outputs of 5a become equal (FIG. 4). Thereafter, the output of the second air-fuel ratio sensor becomes richer than the output of the first air-fuel ratio sensor, so that it is sufficient to perform the inversion to lean as described above.

As described above, the first air-fuel ratio sensor 4a and the second air-fuel ratio
When the target air-fuel ratio is reversed from rich to lean based on the output of the air-fuel ratio sensor 5a, the NOx absorbed by the NOx storage reduction type three-way catalyst during lean operation can be sufficiently desorbed, and HC and CO emissions can be reduced. Emission can be suppressed (FIG. 5). At this time, it is possible to effectively desorb NOx in a short period of time rather than reducing ceria, which is an oxygen storage component contained in the three-way catalyst 3 disposed downstream. In addition, by inverting the target air-fuel ratio from rich to lean based on the outputs of the first air-fuel ratio sensor 4a and the second air-fuel ratio sensor 5a, the NOx absorption amount changes with temperature or the like, Even if there is a change in the NOx absorption amount or the oxygen storage amount, the NOx that matches the NOx absorption amount
Can be set.

FIG. 6 shows another example of the system of the exhaust gas purifying apparatus of the present invention. In FIG. 2, the first air-fuel ratio sensor 4a is arranged on the exhaust gas upstream side of the NOx storage reduction type three-way catalyst 2. Although the second air-fuel ratio sensor 5a is disposed on the exhaust downstream side of the three-way catalyst 3, the second air-fuel ratio sensor 5a is connected to the NOx storage reduction type three-way catalyst 2 and the three-way catalyst as shown in FIG. 3, the same result as in the example shown in FIG. 2 can be obtained.

In the example shown in FIG. 3 described above, the shape of the rich spike is a rectangular wave as shown in FIG. 7. However, as shown in FIG. Is obtained.

[0027]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples, Comparative Examples, and Test Examples, but the present invention is not limited to these Examples.

[Production of NOx storage-reduction type three-way catalyst] (Catalyst 1) Activated alumina powder was impregnated with an aqueous solution of palladium nitrate, dried and calcined at 400 ° C. for 1 hour in air to obtain palladium-supported alumina powder (powder A). ) Got. The palladium concentration of this powder was 5.6% by weight. Further, citric acid was added to a mixture of lanthanum carbonate and cobalt carbonate, dried, and calcined at 700 ° C. to obtain a powder (powder B). This powder contains lanthanum / cobalt at a ratio of 0.8 / 1 in a metal atomic ratio. Powder A60 obtained as described above
0 g, powder B (300 g) and water (900 g) were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid is adhered to a cordierite monolithic carrier (1.3 L, 400 cells), excess slurry in the cells is removed by an air stream, dried at 130 ° C., and then dried at 400 ° C. in air. Bake for 1 hour, coat layer weight 1
A monolith carrier of 50 g / L was obtained. The obtained 150 g /
The monolithic carrier L was impregnated with an aqueous barium acetate solution,
After drying at 0 ° C, it is baked for 1 hour at 400 ° C in air,
Catalyst 1 supporting barium carbonate was obtained. The barium content of the catalyst thus obtained was 20 g / L in terms of oxide.
Met.

(Catalyst 2) The same operation as in the case of the catalyst 1 was repeated except that Ba was changed to Cs, to obtain the present catalyst.

(Catalyst 3) Activated alumina was impregnated with an aqueous solution of rhodium nitrate, dried and calcined at 400 ° C. for 1 hour in air to obtain a rhodium-supported powder (powder C). The rhodium concentration of this powder was 2.0% by weight. Activated alumina was impregnated with an aqueous solution of dinitrodiammine platinum, dried, and calcined in air at 400 ° C. for 1 hour to obtain a platinum-supported powder (powder D). The platinum concentration of this powder was 4.0% by weight. 106 g of powder C obtained as described above, powder D265
g, powder B 300 g, activated alumina powder 229 g, water 9
00g was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid was attached to a cordierite type monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried at 130 ° C., and then at 400 ° C. for 1 hour. Baking, coat layer weight 150g
/ L of the monolith carrier was obtained. The obtained 150 g / L monolithic carrier was impregnated with a barium acetate aqueous solution, dried at 130 ° C., and calcined at 400 ° C. for 1 hour in the air to obtain a catalyst 3 supporting barium carbonate. The barium content of the catalyst thus obtained was 30 g / L in terms of oxide.

(Catalyst 4) The same operation as in Catalyst 3 was repeated, except that barium was replaced by cesium, to obtain the present catalyst.

[Production of Three-Way Catalyst] (Catalyst 5) First, an aqueous palladium nitrate solution was sprayed on activated alumina powder, and then calcined to obtain 1.19% by weight of palladium-supported alumina powder supporting 1.19% by weight of palladium. Obtained. Separately, an aqueous ammonia solution was added to an aqueous solution containing zirconium nitrate and cerium nitrate, and the resulting precipitate was fired to obtain a zirconia-cerium composite oxide. The thus obtained palladium 1.19 wt% supported alumina powder 772 g, zirconia / cerium composite oxide 428 g, and acetic acid 10 wt% aqueous solution 1200
g was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid is applied to a cordierite type monolithic carrier, the excess slurry in the cell is removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a monolithic carrier having a coat layer weight of 140 g / L. Obtained.

Next, an aqueous rhodium nitrate solution was sprayed on the activated alumina powder, and then calcined to obtain rhodium-supported alumina carrying 1.0% by weight of rhodium. Aside from this,
An aqueous solution of palladium nitrate was sprayed on the activated alumina powder and then calcined to obtain an alumina powder carrying 1.07% by weight of palladium carrying 1.07% by weight of palladium. 114 g of the rhodium-supported alumina powder thus obtained,
306 g of alumina powder supported on 1.07% by weight of palladium, 0 g of the zirconia / cerium composite oxide, and acetic acid 10
A 900% by weight aqueous solution was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid was applied to the coating layer having a weight of 140.
g / L of a monolithic carrier, the excess slurry in the cell was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour to obtain a catalyst 5 carrying a total weight of 210 g / L of the coat layer. .

(Catalyst 6) First, 8% by weight of cerium, 4% by weight of zirconium, and 4% by weight of lanthanum are supported on activated alumina powder, and then calcined to obtain cerium, zirconium,
A lanthanum-alumina powder was obtained. An aqueous palladium nitrate solution was sprayed on the powder while stirring, and then calcined to obtain a palladium-supported alumina powder supporting 1.16% by weight of palladium. 900 g of the thus-obtained palladium-supported alumina powder and 900 g of the nitric acid acidic alumina sol were obtained.
g and a 10% by weight aqueous solution of acetic acid (1200 g) were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid was applied to a cordierite type monolithic carrier, excess slurry in the cell was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a monolithic carrier having a coat layer weight of 142 g / L. Obtained.

Next, an aqueous rhodium nitrate solution was sprayed on the activated alumina powder, and then calcined to obtain rhodium-supported alumina carrying 1.0% by weight of rhodium. 114 g of the rhodium-supported alumina powder thus obtained, 279 g of the palladium-supported alumina powder, 400 g of nitric acid acidic alumina sol and 900 g of a 10% by weight aqueous solution of acetic acid were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid was coated with the above-mentioned coat layer weight 142.
g / L of a monolithic carrier, the excess slurry in the cell was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour to obtain a catalyst 6 supporting a coat layer weight of 213 g / L.
I got

(Catalyst 7) 8% by weight of cerium was added to cerium 4
The same operation as in the case of the catalyst 6 was repeated, except that the amount was changed to% by weight, to obtain the present catalyst.

(Catalyst 8) First, 8% by weight of cerium, 4% by weight of zirconium, and 4% by weight of lanthanum are supported on activated alumina powder, and then calcined to obtain cerium, zirconium.
A lanthanum-alumina powder was obtained. An aqueous solution of palladium nitrate was sprayed while stirring the cerium-zirconium-lanthanum-alumina powder, and then calcined to obtain an alumina powder carrying 2.0% by weight of palladium carrying 2.0% by weight of palladium. Separately, a cerium-zirconium-lanthanum-alumina powder is sprayed with an aqueous solution of dinitrodiamine platinum while being stirred, and then calcined to form a 2.0% by weight platinum-supported alumina powder supporting 2.0% by weight of platinum. Obtained. 1. Palladium thus obtained
386 g of 0 wt% supported alumina powder and 386 g of platinum 2.0 wt% supported alumina powder and 10 wt% acetic acid aqueous solution 1
200 g was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.

This slurry liquid was applied to a cordierite-based monolithic carrier, excess slurry in the cell was removed with an air stream, dried, and calcined at 400 ° C. for 1 hour to obtain a monolithic carrier having a coat layer weight of 140 g / L. Obtained.

Next, an aqueous rhodium nitrate solution was sprayed on the activated alumina powder, and then calcined to obtain rhodium-supported alumina carrying 1.0% by weight of rhodium. 114 g of the rhodium-supported alumina powder thus obtained, 306 g of the above-described palladium 2.0% by weight supported alumina powder, and 900 g of a 10% by weight aqueous solution of acetic acid were charged into a magnetic ball mill,
The mixture was pulverized to obtain a slurry liquid.

This slurry liquid was applied to the coating layer having a weight of 140.
g / L of a monolithic carrier, the excess slurry in the cells was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour to obtain a catalyst 8 supporting a coat layer weight of 210 g / L.
I got

(Comparative catalyst 1) The same operation as in catalyst 5 was repeated, except that 0 g of the zirconia / cerium composite oxide was replaced with 95 g of the zirconia / cerium composite oxide, to obtain the present catalyst.

(Durability method) The catalyst of each example was attached to the exhaust system of an engine with a displacement of 4400 cc, and the inlet temperature was set to 700 ° C.
And operated for 50 hours. [Equipment Performance Test] Using the various catalysts obtained as described above and the catalyst configurations shown in Table 1, Examples 1 to 7 were used.
And the exhaust gas purifying apparatus of Comparative Example 1 was assembled. These devices were tested by the following method, and the obtained results are shown in Table 1. (Evaluation method) A catalyst was mounted as shown in Table 1 in the same flow path of an engine exhaust system with a displacement of 2000 cc, and the Air /
Fuel = 11.0 and Air / Fuel = 22.0 were alternately operated, and the catalyst inlet temperature was raised to the upstream 45 ° C.
At 0 ° C. and 350 ° C. on the downstream side, the total conversion in one cycle of this switching operation was determined.

[0049]

[Table 1]

From the results shown in Table 1, the amount of ceria and / or the complex oxide containing ceria was 5 to 30 per liter of the catalyst.
g (Examples 1 to 7)
While the HC conversion and the NOx conversion were both good, a three-way catalyst containing more than 30 g of the complex oxide containing ceria CeO ₂ and ceria per liter of the catalyst was used (Comparative Example 1). ) Shows that the conversion of HC is good, but the conversion of NOx is lower than in Examples 1 to 7.

[0051]

As described above, according to the present invention, the amount of components contributing to the oxygen storage capacity in the three-way catalyst disposed downstream of the NOx storage reduction three-way catalyst can be reduced. For this reason, when the exhaust air-fuel ratio switches from lean to stoichiometric or rich, sufficient HC and CO can be supplied to the NOx storage reduction type three-way catalyst,
An exhaust gas purification device with an improved NOx purification rate can be provided.

Further, according to the present invention, air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the combustion mixture to the target air-fuel ratio based on the exhaust air-fuel ratio is provided. It is also possible to provide an exhaust gas purification device that can be minimized.

[0053]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a tombstone configuration of an exhaust gas purifying apparatus using a NOx storage reduction type three-way catalyst according to the present invention.

FIG. 2 is a configuration diagram illustrating an example of a system of an exhaust gas purification device using a NOx storage reduction type three-way catalyst according to the present invention.

FIG. 3 is a flowchart illustrating an example of control by a second air-fuel ratio feedback unit of the exhaust gas purifying apparatus according to the present invention.

FIG. 4 is a diagram illustrating an output of an air-fuel ratio sensor and a desorption state of NOx.

FIG. 5 is a diagram showing an example of control of an air-fuel ratio sensor output and NOx and HC emission states when FIG. 3 is implemented.

FIG. 6 is a configuration diagram showing another example of the system of the exhaust gas purifying apparatus using the NOx storage reduction type three-way catalyst according to the present invention.

FIG. 7 is a diagram showing a waveform of air-fuel ratio control in FIG. 3;

FIG. 8 is a diagram showing another example of the waveform of the air-fuel ratio control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 NOx storage reduction type three-way catalyst 3 Three-way catalyst 4 1st air-fuel ratio detection means 4a 1st air-fuel ratio sensor 5 2nd air-fuel ratio detection means 5a 2nd air-fuel ratio sensor 6 Control unit 6a 1st air-fuel ratio feedback Means 6b Second air-fuel ratio feedback means 7 Fuel injection valve 8 Exhaust pipe

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 ZAB F01N 3/28 ZAB 3/28 ZAB 301C 301 F02D 41/14 ZAB F02D 41/14 ZAB 310A 310 310F B01D 53 / 36 102B

Claims (7)

[Claims] 1. An exhaust gas purifying apparatus in which a NOx storage-reduction type three-way catalyst and a three-way catalyst are sequentially arranged from an upstream side of an exhaust system. A NOx storage-reduction type three-way catalyst that absorbs NOx and releases the absorbed NOx at a stoichiometric air-fuel ratio or in a rich atmosphere for reduction treatment, wherein at least one noble metal selected from the group consisting of platinum, palladium and rhodium And a noble metal-supported powder having the following formula: LnαBOβ (where Ln is at least one selected from the group consisting of La, Ce, Nd and Sm, and B is Fe, Co, Ni
And Mn, wherein 0 <α <1 and 0 <β <4. And a carbonate of at least one metal selected from the group consisting of Mg, Ca, Sr, Ba, Na, K and Cs. And at least one selected from the group consisting of palladium and rhodium, and the amount of ceria and / or ceria-containing composite oxide contained in the three-way catalyst is 5 to 30 g per liter of the catalyst. An exhaust gas purifying apparatus using a NOx storage reduction type three-way catalyst, characterized in that: 2. The composite oxide powder according to the following formula (Ln ₁ -δCδ) αBOβ (where Ln is at least one selected from the group consisting of La, Ce, Nd and Sm; Is at least one selected from Ba and K, and B is Fe, Co, Ni and M
n at least one selected from the group consisting of
δ <1, 0.8 <α <1, β are oxygen amounts that satisfy the valence of each element. 2. The exhaust gas purifying apparatus according to claim 1, wherein: 3. The exhaust gas purifying apparatus according to claim 1, wherein the noble metal-supported powder is formed by supporting palladium and / or rhodium on a porous carrier. 4. The exhaust gas purifying apparatus according to claim 1, wherein the noble metal-supported powder has palladium supported on a porous carrier. 5. Immediately after the target air-fuel ratio of the combustion mixture is switched from lean to the stoichiometric air-fuel ratio or rich,
Feedback control of the air-fuel ratio of the combustion air-fuel mixture
The exhaust gas purifying apparatus according to any one of claims 1 to 4, wherein an exhaust air-fuel ratio downstream of the x storage reduction three-way catalyst is inverted from lean to a stoichiometric air-fuel ratio or rich. 6. A first air-fuel ratio detecting means disposed upstream of the NOx occlusion reduction type three-way catalyst to detect an exhaust air-fuel ratio, and an exhaust gas disposed downstream of the NOx occlusion reduction type three-way catalyst. A second air-fuel ratio detecting means for detecting an air-fuel ratio is provided. In a normal state, the air-fuel ratio of the combustion mixture is feedback-controlled to a target air-fuel ratio based on the exhaust air-fuel ratio detected by the first air-fuel ratio detecting means. Immediately after the first air-fuel ratio feedback means and the target air-fuel ratio of the combustion air-fuel mixture are switched from lean to the stoichiometric air-fuel ratio or rich, the combustion air-fuel ratio is determined based on the exhaust air-fuel ratio detected by the second air-fuel ratio detection means. The exhaust gas purifying apparatus according to any one of claims 1 to 5, further comprising second air-fuel ratio feedback means for performing feedback control of the air-fuel ratio to a target air-fuel ratio. 7. The second air-fuel ratio feedback means,
The feedback control is performed until the output of the second air-fuel ratio detection means reaches a predetermined value immediately after the target air-fuel ratio of the combustion mixture is switched from lean to the stoichiometric air-fuel ratio or rich. An exhaust gas purifying apparatus as described in the above.