JP2005262144A - NOx storage reduction catalyst - Google Patents

Abstract

A recovery process from sulfur poisoning can be easily performed, further suppressing the reduction of the NO _x purification activity during endurance.
[Solution]
On the surface of the NO _x storage-reduction type lower catalyst layer 2 using an oxide carrier that is less likely to adsorb sulfur oxides than alumina, a molar ratio of NO _x storage material other than Li and Li to alumina is Li / (other than Li _the NO _x storage material) to form the NO _x storage-and-reduction type catalyst layer 3 on the carrying such that ≧ 2.
The upper catalyst layer 3 has a much larger amount of SO _x trapped than the theoretical value, and the recovery of the NO _x storage capacity is easy, so that sulfur poisoning of the lower catalyst layer 2 is suppressed, and NO _{x in} both catalyst layers. Can be purified.
[Selection] Figure 1

Description

The present invention absorbs NO _x in lean atmosphere, relates _the NO _x storage-reduction catalyst for reducing and purifying by releasing NO _x that was stored in the stoichiometric or rich atmosphere, specifically _the NO _x storage reduction can suppress sulfur poisoning Relates to the catalyst.

Recently, occludes NO _x in lean atmosphere, NO _x storage-reduction catalyst for reducing and purifying by releasing NO _x that was stored in the stoichiometric or rich atmosphere has been developed and put into practical use. The NO _x storage reduction catalyst is formed by supporting a noble metal such as Pt and an NO _x storage material selected from alkali metals, alkaline earth metals and rare earth elements on an oxide carrier such as alumina. In the lean atmosphere, NO in the exhaust gas is oxidized by the noble metal to become NO ₂ , which is stored by reacting with the NO _x storage material to become nitrite or nitrate. In a stoichiometric or rich atmosphere, nitrite or nitrate decomposes and NO _x is released, so that the NO _x storage agent recovers the NO _x storage capacity, and the released NO _x is abundant in the atmosphere. It is reduced by reducing components such as

Further, as described in, for example, JP-A-09-173866, a continuous regeneration type in which a coating layer is formed from alumina or the like on the surface of a DPF cell partition wall and a noble metal such as platinum (Pt) is supported on the coating layer. DPF (filter catalyst) has been developed. According to this filter catalyst, the collected PM is oxidized and burned by the catalytic reaction of the noble metal, so that the filter function can be regenerated by burning the PM simultaneously with the collection or continuously with the collection. Since the catalytic reaction occurs at a relatively low temperature and PM can be burned while the amount of trapped is small, there is an advantage that the thermal stress acting on the DPF is small and damage is prevented. And for example, as disclosed in Japanese Patent Laid-Open No. 09-094434, it is also known NO _x storage-and-reduction type filter catalyst further carrying _the NO _x storage material in the coating layer.

However, since the exhaust gas contains sulfur oxides, the NO _x storage material also reacts with sulfur oxides. However, since the sulfate that is produced is more difficult to decompose than nitrate, it is difficult to restore the NO _x storage capacity of the NO _x storage material that has become sulfate in a normal atmosphere, which reduces the NO _x purification activity. There was a problem to do. This phenomenon is called sulfur poisoning of the NO _x storage material. The sulfur from poisoning recover _the NO _x storage capacity of _the NO _x storage material, it is necessary to handle the exhaust gas atmosphere as a reducing agent-rich rich atmosphere, the fuel consumption when the processing time is long is deteriorated. In particular, exhaust gas from a diesel engine contains a large amount of sulfur oxides, and in the above-mentioned NO _x storage reduction type filter catalyst, it is a big problem to suppress sulfur poisoning.

Accordingly Japanese Patent 2002-177779 discloses the use of a Li and K as _the NO _x storage material, _the NO _x storage-reduction catalyst for the diesel engine is disclosed which carries so that Li / K ≧ 1.4 in a molar ratio . According to this catalyst, even when the exhaust gas temperature is in a low temperature range of about 600 ° C., the sulfur component is efficiently desorbed from the NO _x storage material. However, with this catalyst, although the amount of sulfur desorption is large, the recovery of NO _x storage capacity is not sufficient, and further improvement is desired.

Japanese Patent Application Laid-Open No. 2002-126453 discloses an exhaust gas purification device in which a sulfur trapping layer capable of physically adsorbing SO _x is formed on the surface of a NO _x storage reduction catalyst layer. According to this exhaust gas purifying apparatus, since SO _x is trapped in the sulfur scavenging layer in a high temperature lean atmosphere, it is possible to suppress the sulfur poisoning of the NO _x storage material is supported on _the NO _x storage reduction catalyst layer. However, in this technique, never sulfur trapping layer contributes to the purification of exhaust gases, to a thickness of the coating layer is thickened by a sulfur trapping layer, NO _x storage-reduction catalyst layer to the exhaust gas pressure loss as the conventional equivalent The thickness of the must be reduced. Therefore, when trying to maintain the NO _x purification capacity at the same level as before, the NO _x occlusion reduction catalyst layer is loaded with the noble metal and NO _x occlusion material at a high density, and the activity tends to decrease due to the growth of noble metal grains. There is a problem that.
JP 09-094434 JP 2002-177779 JP 2002-126453

The present invention has been made in view of the above-described circumstances, can be easily recovered from sulfur poisoning, and the problem to be solved is to further suppress the decrease in NO _x purification activity during durability. To do.

The feature of the NO _x storage-reduction catalyst of the present invention that solves the above problems is that a support base material is formed by supporting a noble metal and a NO _x storage material on an oxide support that is less likely to adsorb sulfur oxide than alumina. a lower catalyst layer formed on the surface of the catalyst layer after being formed on the surface under it carries the noble metal and _the NO _x storage material catalyst layer in an alumina made, _the NO _x storage material of the upper catalyst layer Includes at least an element other than Li and Li, and is included so as to satisfy a molar ratio of Li / (element other than Li) ≧ 2.

  An inflow side cell clogged on the exhaust gas downstream side, an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and a porous material that partitions the inflow side cell and the outflow side cell and has a large number of pores It is preferable that the filter catalyst has a lower catalyst layer and an upper catalyst layer formed on the surface of the cell partition wall and the inner surface of the pores.

  In the case of a filter catalyst, the average particle size of the lower catalyst layer is preferably 0.5 to 1.2 μm, and the average particle size of the upper catalyst layer is preferably 1.5 μm or more.

According to the NO _x storage reduction catalyst of the present invention, a large amount of SO _x can be trapped in the upper catalyst layer, so that sulfur poisoning of the NO _x storage material in the lower catalyst layer is suppressed. Moreover, since the upper catalyst layer easily desorbs SO _x , the NO _x storage capacity is easily recovered. Therefore, sulfur poisoning can be suppressed and a recovery process can be easily performed. In normal conditions, NO _x is purified by the upper catalyst layer and the lower catalyst layer, and in the situation where SO _x is trapped by the upper catalyst layer, NO _x is mainly purified by the lower catalyst layer, so that the NO _x purification activity is reduced. Further suppression is possible, and high NO _x purification performance is exhibited.

And it is possible to recover _the NO _x storage capacity of the catalyst layer on the sulfur poisoning by the rich processing of short, fuel economy is improved.

As a result of intensive research on the sulfur poisoning phenomenon of the NO _x storage reduction catalyst, the present inventors have found that a larger amount of SO _x may be captured than the theoretical sulfur poisoning amount calculated as a chemical reaction. That is, in the NO _x storage reduction catalyst using alumina as a support, the total amount of the trapped amount due to the reaction between the NO _x storage material and SO _x and the trap amount due to the reaction between the alumina and SO _x is the theoretical sulfur poisoning amount. However, the actual amount of sulfur poisoning was found to be more than twice that amount. Moreover, this phenomenon and Li as _the NO _x storage material, the _the NO _x storage material other than Li, _(the NO _x storage material other than Li) Li / In molar ratio is also apparent that occurs when carrying such that ≧ 2 next, in this way, _the NO _x storage-reduction catalyst carrying _the NO _x storage material, also become clear that sulfur components from a relatively low temperature range of about 600 ° C. is easy easy recovery of the desorbed _the NO _x storage capacity It was. Furthermore, this phenomenon occurs specifically when alumina is used as a support, and it has also been clarified that such a phenomenon does not occur in other oxide supports such as zirconia and titania.

Therefore, the catalyst described in Japanese Patent Application Laid-Open No. 2002-177779 was insufficient in recovery of NO _x storage capacity despite the large amount of desorbed sulfur component during the recovery treatment. /K≧1.4 is supported so that a large amount of specifically trapped SO _x is mainly desorbed, and most of the SO _{x that} has reacted with the NO _x storage material remains as it is and is recovered. It seems that it was insufficient.

  The present invention has been made based on such findings.

That _the NO _x storage reduction catalyst of the present invention is made by carrying the noble metal and _the NO _x storage material in alumina, _the NO _x storage material comprises at least an element other than Li and Li, in a molar ratio Li / (other than Li The upper catalyst layer is included so that (element) ≧ 2. Since the upper catalyst layer can capture SO _x more than twice the theoretical sulfur poisoning amount, sulfur poisoning of the NO _x storage material of the lower catalyst layer is suppressed, and mainly after sulfur poisoning of the upper catalyst layer. NO _x can be purified by the lower catalyst layer. Also from _the NO _x storage material of the catalyst layer on the sulfur poisoning, 600 _the NO _x storage capacity is relatively sulfur components from a low temperature region is easily desorbed of about ℃ easily recovered, the lower catalyst layer and the upper catalyst The layer can sufficiently purify NO _x .

The lower catalyst layer is formed by supporting a noble metal and a NO _x storage material on an oxide carrier that is less likely to adsorb sulfur oxides than alumina. Examples of the oxide carrier that hardly adsorbs sulfur oxide include zirconia, titania, or a composite oxide containing at least titania. It is preferable to use an oxide having a higher acidity than alumina, but alumina or an oxide having a lower acidity than alumina may be mixed as long as the properties are not affected.

As the noble metal and the NO _x storage material supported on the lower catalyst layer, the same materials as those of the conventional NO _x storage reduction catalyst can be used. Examples of the noble metal include platinum group noble metals such as Pt, Rh, Pd, and Ir, and the NO _x storage material may be at least one selected from alkali metals, alkaline earth metals, and rare earth elements. The supported amount may be the same as that of the conventional NO _x storage reduction catalyst.

The upper catalyst layer formed on the surface of the lower catalyst layer, alumina becomes carries the noble metal and _the NO _x storage material, _the NO _x storage material comprises at least an element other than Li and Li, Li / molar ratio ( Elements other than Li) are included so that ≧ 2. As the alumina, γ type, θ type, α type and the like can be used, and γ type having a large specific surface area is particularly preferable.

As the NO _x storage material other than Li, at least one selected from alkali metals other than Li, alkaline earth metals, and rare earth elements, including K and Ba, can be used. Here, it is important that the molar ratio is Li / (NO _x storage material other than Li) ≧ 2. If this molar ratio is less than 2, the amount of SO _x trapped in the upper catalyst layer becomes small, and it becomes difficult to suppress sulfur poisoning of the lower catalyst layer. In addition, when reclaimed at temperatures exceeding 600 ° C, the NO _x storage capacity may not be restored.

The noble metal supported on the upper catalyst layer is not particularly limited, and platinum group noble metals such as Pt, Rh, Pd, and Ir can be used. Further, the loading amounts of the NO _x storage material and the noble metal may be the same as those of the conventional NO _x storage reduction catalyst.

The ratio of the lower catalyst layer to the upper catalyst layer is preferably in the range of upper catalyst layer / lower catalyst layer = 7/3 to 3/7 in weight ratio. If it is out of this range, sulfur poisoning of the lower catalyst layer may occur, or the NO _x purification performance may deteriorate.

The carrier substrate can be a monolith substrate having a straight flow structure. Also, an inflow side cell clogged on the exhaust gas downstream side, an outflow cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and a perforation having a large number of pores dividing the inflow side cell and the outflow side cell It is also possible to provide a filter base material having a quality cell partition wall. In the case of a monolith substrate, a lower catalyst layer and an upper catalyst layer are formed on the surface of the cell partition wall. In this case, it is preferable to form 100 to 300 g in total of the lower catalyst layer and the upper catalyst layer with respect to 1 L of the monolith substrate. If the formation amount is less than this range, the NO _x purification performance is lowered, and if it is more than this range, the cell passage is narrowed and the exhaust pressure loss is increased, which is not preferable.

The catalyst of the present invention is particularly useful because there are many particulate matter (PM) in the exhaust gas from the diesel engine. In this case, the carrier substrate is a filter substrate, and a lower catalyst layer and an upper catalyst layer are formed on the surface of the cell partition wall and the inner surface of the pores. This makes it possible to purify NO _x and PM. In this case, it is preferable to form 75 to 200 g in total of the lower catalyst layer and the upper catalyst layer with respect to 1 L of the filter base material. If the formation amount is less than this range, the NO _x purification performance is lowered, and _{if the} formation amount is more than this range, the exhaust pressure loss increases due to blockage of the pores, which is not preferable.

The pore distribution in the cell partition walls of the filter substrate can be in the range of 40 to 80% porosity and 10 to 50 μm average pore diameter, similar to the conventional DPF. If the porosity or the average pore diameter is out of this range, the PM collection efficiency may decrease or the exhaust pressure loss may increase. When such a filter substrate is used, it is desirable that the average particle diameter of the lower catalyst layer is 0.5 to 1.2 μm and the average particle diameter of the upper catalyst layer is 1.5 μm or more. By setting the average particle size of the lower catalyst layer to 0.5 to 1.2 μm, it is possible to prevent the pores of the cell partition walls from being blocked, and to suppress an increase in exhaust pressure loss. On the other hand, if the average particle size of the upper catalyst layer is less than 1.5 μm, the diffusion of NO _x is rate-limiting and the NO _x storage performance of the lower catalyst layer is lowered.

  Hereinafter, the present invention will be specifically described with reference to test examples, examples and comparative examples.

(Test example)
Various NO _x storage reduction catalysts shown in Table 1 were prepared, and a model gas containing SO ₂ at a predetermined concentration was circulated at 400 ° C. Then go out with SO ₂ concentration in the gas was measured SO ₂ concentration in the gas, the SO ₂ amount trapped catalyst was determined as the S trapping amount. The results are shown in Table 1.

From Table 1, it is clear that a catalyst in which predetermined amounts of Pt, Li and Ba are supported on γ-Al ₂ O ₃ powder captures SO ₂ more than twice the theoretical value. It is also clear that the amount of SO ₂ trapped is less than the theoretical value when the Li / Ba ratio is less than ₂ or when ZrO ₂ or TiO ₂ is used as a carrier.

（実施例１）
図１に、本実施例のフィルタ型NO_x 吸蔵還元触媒を示す。フィルタ基材１は、排ガス下流側で目詰めされた流入側セル10と、流入側セル10に隣接し排ガス上流側で目詰めされた流出側セル11と、流入側セル10と流出側セル11を区画し多数の細孔を有する多孔質のセル隔壁12と、を有している。セル隔壁12の細孔表面には、下触媒層２が形成され、下触媒層２の表面には上触媒層３が形成されている。以下、この触媒の製造方法を説明し、構成の詳細な説明に代える。

(Example 1)
FIG. 1 shows a filter-type NO _x storage reduction catalyst of this example. The filter base 1 includes an inflow side cell 10 clogged on the exhaust gas downstream side, an outflow side cell 11 adjacent to the inflow side cell 10 and clogged on the exhaust gas upstream side, an inflow side cell 10 and an outflow side cell 11. And a porous cell partition wall 12 having a large number of pores. A lower catalyst layer 2 is formed on the pore surfaces of the cell partition walls 12, and an upper catalyst layer 3 is formed on the surface of the lower catalyst layer 2. Hereinafter, the method for producing the catalyst will be described, and the detailed description of the configuration will be substituted.

  A filter base material 1 (porosity 60%, average pore diameter 30 μm) made of cordierite having a diameter of 30 mm and a length of 50 mm was prepared. Next, a slurry in which 25 parts by weight of titania powder, 25 parts by weight of zirconia powder, 50 parts by weight of alumina powder, and a binder were dispersed in ion-exchanged water was prepared, and the average particle size was adjusted to 0.5 μm by an attritor and a ball mill.

  Using this slurry, a coat layer of 80 g / L was formed on the surface of the cell partition wall 12 and the pore surface inside the cell partition wall 12 of the filter substrate by a wash coat method. Thereafter, 2 g / L of Pt was supported and baked by the water absorption support method, and 0.1 mol / L of Ba was supported by the water absorption support method and then baked at 500 ° C. to form the lower catalyst layer 2.

Next, a slurry in which Pt / Al ₂ O ₃ powder in which 2.5% by weight of Pt is supported on γ-type alumina powder and a binder is dispersed in ion-exchanged water is prepared, and the average particle size is measured by an attritor and a ball mill. Was adjusted to 1.5 μm. Using this slurry, 40 g / L of the second coat layer was formed on the surface of the lower catalyst layer 2 of the filter substrate 1 on which the lower catalyst layer 2 was formed by the wash coat method. Thereafter, 0.1 mol / L of K was supported by a water absorption supporting method, 0.2 mol / L of Li was supported, and then calcined at 500 ° C. to form the upper catalyst layer 3. The molar ratio (Li / K) is 2.0, and the supported amount of Pt is 1 g / L.

(Example 2)
The same as Example 1, except that the average particle size of the slurry used in forming the lower catalyst layer 2 was 0.8 μm, and the amount of K supported by the upper catalyst layer 3 was 0.05 mol / L. The molar ratio (Li / K) of the upper catalyst layer 3 is 4.0.

(Example 3)
The average particle diameter of the slurry used when forming the lower catalyst layer 2 is 1.0 μm, the average particle diameter of the slurry used when forming the upper catalyst layer 3 is 2 μm, and 0.1 mol of Ba is substituted for K in the upper catalyst layer 3. The same as Example 1 except that / L is supported. The molar ratio (Li / Ba) of the upper catalyst layer 3 is 2.0.

Example 4
The average particle size of the slurry used when forming the lower catalyst layer 2 is 1.2 μm, and 0.1 mol / L of K is supported on the lower catalyst layer 2 instead of Ba. The average particle size of the slurry used when forming the upper catalyst layer 3 Example 1 is the same as Example 1 except that the diameter is 3 μm. The molar ratio (Li / K) of the upper catalyst layer 3 is 2.0.

(Example 5)
The lower catalyst layer 2 is loaded with 0.1 mol / L of Sr instead of Ba, the average particle diameter of the slurry used in forming the upper catalyst layer 3 is 5 μm, and the upper catalyst layer 3 is replaced with K with 0.1 mol / L of Ba. Example 1 is the same as Example 1 except that L is supported. The molar ratio (Li / Ba) of the upper catalyst layer 3 is 2.0.

(Example 6)
The lower catalyst layer 2 has a supported amount of Ba of 0.05 mol / L, the lower catalyst layer 2 further supports 0.05 mol / L, the upper catalyst layer 3 has a supported amount of K of 0.05 mol / L, and the upper catalyst layer 2 Example 3 was the same as Example 1 except that the amount of Li 3 supported was 0.3 mol / L. The molar ratio (Li / K) of the upper catalyst layer 3 is 6.0.

(Example 7)
The same as Example 1, except that the average particle size of the slurry used for forming the upper catalyst layer 3 was 0.8 μm. The molar ratio (Li / K) of the upper catalyst layer 3 is 2.0.

(Comparative Example 1)
The same procedure as in Example 1 was carried out except that the lower catalyst layer 2 was further loaded with 0.1 mol / L of K and 0.2 mol / L of Li and the upper catalyst layer 3 was not formed.

(Comparative Example 2)
The same as Example 1, except that the amount of K supported on the upper catalyst layer 3 was 0.2 mol / L and the amount of Li supported was 0.1 mol / L. The molar ratio (Li / K) of the upper catalyst layer 3 is 0.5.

(Comparative Example 3)
The average particle diameter of the slurry used when forming the lower catalyst layer 2 is 1.2 μm, and 0.1 mol / L of K is supported on the lower catalyst layer 2 instead of Ba. When the upper catalyst layer 3 is formed, Pt / Al ₂ O ₃ Example 1 except that Pt / ZrO ₂ powder in which 2.5% by weight of Pt was supported on zirconia in advance was used instead of the powder, and that the average particle diameter of the slurry used when forming the upper catalyst layer 3 was 3 μm. It is. The molar ratio (Li / K) of the upper catalyst layer 3 is 2.0.

<Test and evaluation>
The composition of each catalyst is summarized in Table 2.

上記した各触媒を電気炉に入れ、大気中にて 700℃で５時間保持する耐熱処理を行った。

Each catalyst described above was put in an electric furnace and subjected to a heat treatment which was held in the atmosphere at 700 ° C. for 5 hours.

Apart from this, S poisoning treatment in which a model gas whose SO ₂ concentration is adjusted with 1.5 times the amount of NO _x occlusion material supported by each catalyst as a guide is circulated through each catalyst at 400 ° C for 5 hours. Went.

  Further, an S desorption treatment in which the rich model gas shown in Table 3 was circulated at 600 ° C. for 10 minutes was performed on each catalyst after the S poisoning treatment.

耐熱処理後、Ｓ被毒処理後、及びＳ脱離処理後の各触媒を評価装置にそれぞれ配置し、表３に示すリーンガスの定常状態から４秒間リッチガスを導入し、再びリーンガスに切り換えた際のNO_x 吸蔵量をそれぞれ測定した。測定温度は 300℃である。結果を表４に示す。

Each catalyst after heat-resistant treatment, after S poisoning treatment, and after S desorption treatment is placed in the evaluation device, and when the rich gas is introduced for 4 seconds from the steady state of the lean gas shown in Table 3, it is switched to the lean gas again. _the NO _x storage amount was measured. The measurement temperature is 300 ℃. The results are shown in Table 4.

表４より、各実施例の触媒は各比較例の触媒に比べて耐熱処理後とＳ被毒処理後のNO_x 吸蔵量の差が小さいことがわかる。このことから、各実施例の触媒ではNO_x 吸蔵材の硫黄被毒が生じにくいことが示唆される。

From Table 4, it can be seen that the catalyst of each example has a smaller difference in the NO _x storage amount after the heat-resistant treatment and after the S poisoning treatment than the catalyst of each comparative example. This suggests that sulfur poisoning of the NO _x storage material is unlikely to occur in the catalyst of each example.

Further, in the catalysts of Examples 1 to 6, the NO _x occlusion amount after the S poisoning treatment and after the S desorption treatment is significantly improved as compared with the catalysts of Comparative Examples 1 and 2. This is an effect due to the formation of the upper catalyst layer 3, that the sulfur poisoning of the lower catalyst layer 2 is suppressed by capturing SO _{x in} the upper catalyst layer 3, and NO is removed by the S desorption treatment. _This is considered to be due to the fact that the NO _x storage capacity of the _x storage material was sufficiently recovered. The catalyst of Comparative Example 2 has the same configuration as Example 1 except that the molar ratio (Li / K) is different. However, when the molar ratio (Li / K) is 0.5, the amount of SO _x trapped is not so large. , sulfur poisoning occurs in the lower catalyst layer 2, yet believed recovery of the NO _x storage capacity is insufficient.

Further, the catalyst of Comparative Example 3, especially lower _the NO _x storage amount after the S-poisoning treatment and after S desorption process, which is due for the use of zirconia as a carrier for the upper catalyst layer 3, the upper catalyst This is because the amount of sulfur trapped in the layer 3 is small.

Note that in Example 7, because it is small _the NO _x storage amount after the S-poisoning treatment and after S desorption process than the other embodiments, this is the average particle size of the upper catalyst layer 3 is too small, NO _{This is probably} because _x did not sufficiently diffuse to the lower catalyst layer 2.

It is sectional drawing which shows the structure of the exhaust gas purification apparatus of one Example of this invention.

Explanation of symbols

1: Filter base material 2: Lower catalyst layer 3: Upper catalyst layer
10: Inflow side cell 11: Outflow side cell 12: Cell bulkhead

Claims (3)

A carrier substrate, a lower catalyst layer of the sulfur oxides formed on the surface of the carries the noble metal and _the NO _x storage material becomes carrier substrate adsorption hardly oxide support of alumina,
An upper catalyst layer formed by supporting a noble metal and a NO _x storage material on alumina and formed on the surface of the lower catalyst layer;
The _the NO _x storage material of the upper catalyst layer contains at least an element other than Li and Li, _the NO _x storage-reduction catalyst, characterized in that contained as the Li / (elements other than Li) ≧ 2 in a molar ratio . An inflow side cell clogged on the exhaust gas downstream side, an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, the inflow side cell and the outflow side cell are partitioned, and a large number of pores are formed. 2. The NO _x storage-reduction catalyst according to claim 1, further comprising: a porous cell partition wall, wherein the lower catalyst layer and the upper catalyst layer are formed on a surface of the cell partition wall and a surface in the pores. The NO _x storage-reduction catalyst according to claim 2, wherein the lower catalyst layer has an average particle size of 0.5 to 1.2 µm, and the upper catalyst layer has an average particle size of 1.5 µm or more.

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