JP3871110B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

【００４５】
【表２】

【００４６】
表１より、本発明の好適範囲内である実施例１〜１２で得られた排気ガス浄化触媒は、比較例１〜３で得られた排気ガス浄化触媒に比べて、耐久後及びＳ脱離処理後の浄化性能が優れており、現時点では特に実施例１２が１１モードのＨＣ転化率、Ｓ脱離処理後のＮＯｘ転化率ともに最も良好であることがわかる。また、実施例の排気ガス浄化触媒は、特にＳ脱離処理後のＮＯｘの浄化率がよいことがわかる。
【００４７】
以上、本発明を好適実施例により詳細に説明したが、本発明はこれら実施例に限定されるものではなく、本発明の要旨の範囲内において種々の変形が可能である。
例えば、本発明の排気ガス浄化触媒は、ＨＣ吸着層の上の第２層を更に２層に分け、上層にＲｈ、Ｐｔを含む層、下層にＰｔを含む層のようにもできる。
【００４８】
【発明の効果】
以上説明してきたように、本発明によれば、ＨＣ吸着材層に、触媒貴金属と、所定の結晶子径を有するアルカリ化合物とを含むＮＯｘ浄化触媒成分層を積層し、硫黄成分の脱離性能とＮＯｘ吸収性能を両立させることとしたため、触媒に付着した硫黄の脱離処理が容易で、特に酸素過剰領域（リーン域）でのＮＯｘ浄化効率が良好な排気ガス浄化触媒を提供することができる。
【図面の簡単な説明】
【図１】排気ガス浄化触媒の積層構造の一部分を示す断面図である。
【図２】粒子径及び結晶子径の概略を示す図である。
【図３】Ｘ線回折ピークを示す図である。
【符号の説明】
１ 第１層（ＨＣ吸着材層）
２ 第２層（ＮＯｘ触媒成分層）
３ アルカリ化合物
４ ハニカム担体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst that purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in exhaust gas discharged from internal combustion engines such as automobiles (gasoline, diesel) and boilers. In particular, the present invention relates to an exhaust gas purification catalyst focused on NOx purification in an oxygen-excess region and a method for producing the same.
[0002]
[Prior art]
In recent years, demand for fuel-efficient vehicles has increased due to the problem of depletion of petroleum resources and global warming, and the development of lean burn vehicles has attracted attention for gasoline vehicles. In lean-burn vehicles, the exhaust gas atmosphere becomes leaner than the theoretical air-burning state during lean-burn driving. However, when a normal three-way catalyst is applied in the lean region, the effect of excess oxygen There has been a problem that the NOx purification action becomes insufficient. For this reason, development of a catalyst capable of purifying NOx even when oxygen is excessive has been desired.
[0003]
In recent years, attention has also been paid to a technique for removing HC discharged in a temperature range where the catalyst is not sufficiently activated when the engine is started. By mounting both a catalyst capable of purifying NOx under excess oxygen and a catalyst capable of removing HC at low temperatures, the functions of both catalysts can be exhibited, but the exhaust pressure increases and fuel consumption deteriorates. There was a case. Therefore, the need for one catalyst that satisfies these two functions has increased.
[0004]
Conventionally, various catalysts for purifying NOx in the lean region have been proposed. For example, a catalyst in which platinum (Pt) and lanthanum (La) are supported on a porous carrier (JP-A-5-168860) is representative. In addition, a catalyst that absorbs NOx in the lean region and releases NOx at the time of stoichiometric purification is proposed.
Further, as represented by a catalyst containing zeolite (Japanese Patent Laid-Open No. 11-47596), a catalyst for purifying HC at a low temperature has been proposed.
In order to satisfy the functions of these two catalysts with a single catalyst, for example, a layer containing a noble metal and an alkali as a NOx adsorbent is placed on the zeolite layer as an HC adsorbent, and NOx is purified in the upper layer. There are catalysts that allow low-temperature HC absorption in lower-layer zeolites. When making such a catalyst, first, a zeolite layer is coated on a heat-resistant inorganic carrier, followed by coating an alumina layer containing a noble metal, and finally impregnating with alkali or the like.
However, this method has a problem that alkali is absorbed by the zeolite layer as much as 60 to 80%, and the HC absorbing function of the zeolite layer cannot be sufficiently exhibited.
[0005]
[Problems to be solved by the invention]
As a countermeasure for the above problem, for example, a solid alkali such as barium carbonate (BaCO ₃ ) is used, and this is mixed with a noble metal and alumina to form a slurry, which is then coated on the zeolite layer. By adopting this method, the absorption of alkali into the zeolite layer is surely suppressed to about 20%.
However, since a solid is used for the alkali, the crystallite diameter of the alkali is increased, and the NOx absorption performance during lean may be deteriorated.
At the same time, the alkali is poisoned by sulfur contained in the fuel and the lubricating oil, and the NOx absorption ability may be reduced (sulfur poisoning).
[0006]
The present invention has been made in view of such problems of the prior art, and its object is to facilitate the desorption treatment of sulfur adhering to the catalyst, particularly in an oxygen-excess region (lean region). It is an object of the present invention to provide an exhaust gas purification catalyst having good NOx purification efficiency.
[0007]
[Means for Solving the Problems]
As a result of intensive research in view of the above problems, the present inventors have laminated a HC adsorbent layer with a NOx purification catalyst component layer containing a catalyst noble metal and an alkali compound having a predetermined crystallite diameter, thereby removing sulfur components. The present inventors have found that the above problems can be solved by achieving both separation performance and NOx absorption performance, and have completed the present invention.
[0008]
That is, the exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst formed by laminating a second layer containing a NOx purification catalyst component on a first layer containing an HC adsorbent,
The second layer contains at least one catalytic noble metal selected from the group consisting of rhodium, palladium and platinum, and an alkali compound containing an alkali metal and / or an alkaline earth metal;
The crystallite size of the alkali compound is 250 mm or less.
[0009]
Moreover, a preferred form of the exhaust gas purifying catalyst of the present invention, the alkaline compound has the following general formula _{Ba x Mg y (CO 3)} 2
(Wherein x and y are atomic ratios of the respective elements, and x = 0.5 to 1.999, y = 0.001 to 1.5, and x + y = 2.0) It is a salt.
[0010]
Furthermore, another preferred embodiment of the exhaust gas purification catalyst of the present invention is characterized in that the oxide-converted weight of the alkali compound is 1 to 50 g per liter of catalyst capacity.
[0011]
Furthermore, the method for producing an exhaust gas purification catalyst of the present invention is a method for producing the above exhaust gas purification catalyst,
A powder in which at least one catalyst noble metal selected from the group consisting of rhodium, palladium and platinum is supported on alumina is mixed with an aqueous solution of a water-soluble salt containing the alkali metal and / or alkaline earth metal to form a slurry, After adjusting the pH of the slurry to be in the range of 7.0 to 12.0, the average particle size of the particles in the slurry was set to 0.1 to 5 μm and laminated on the first layer, and 100 to 300 ° C. And the second layer is formed by baking at 400 to 700 ° C.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the exhaust gas purification catalyst of the present invention will be described in detail. In the present specification, “%” indicates a mass percentage unless otherwise specified.
[0013]
The exhaust gas purification catalyst of the present invention is formed by laminating a second layer containing a NOx purification catalyst component on a first layer containing an HC adsorbent. Typically, as shown in FIG. 1, a catalyst in which a NOx catalyst component layer 2 containing an alkali compound 3 is laminated on an HC adsorbent layer 1 formed on a honeycomb carrier 4 can be exemplified. An exhaust gas purification catalyst that achieves both HC purification and NOx purification under an oxygen-excess atmosphere.
The second layer contains rhodium (Rh), palladium (Pd) or platinum (Pt), and a catalyst noble metal according to any combination thereof, and an alkali compound containing an alkali metal and / or an alkaline earth metal. It consists of Here, the alkali compound indicates an alkali metal compound, an alkaline earth metal compound, or a composite compound thereof, and is preferably dispersed from the surface of the second layer without being biased from the viewpoint of improving the NOx purification ability. .
In addition, as the alkali compound, a compound containing an element related to sodium (Na), potassium (K), cesium (Cs), magnesium (Mg), calcium (Ca) or barium (Ba), and any combination thereof. For example, it is preferable to use Na ₂ CO ₃ , Cs ₂ CO ₃ , MgCO ₃ , CaCO _3, BaCO _3, etc., and the NOx absorption capacity can be further improved.
As the HC adsorbent contained in the first layer, typically, FAU type zeolite, MFI type zeolite, MOR type zeolite and β zeolite can be used, and these show excellent HC adsorbing ability even at low temperatures. So it is effective.
[0014]
Further, examples of the alkali compound, the general formula _{Ba x Mg y (CO 3)} 2
(Wherein x and y are atomic ratios of the respective elements, and x = 0.5 to 1.999, y = 0.001 to 1.5, and x + y = 2.0) It is preferable to use a salt. In this case, the stability as an alkali compound is improved, the crystallite diameter of the compound can be prevented from being increased by heat, and the desired crystallite diameter (250 mm or less) can be maintained. This can be confirmed by XRD.
[0015]
Furthermore, when an alkali metal or alkaline earth metal is used as the NOx absorbent, there is a big problem that the NOx absorbent is subjected to S poisoning and the NOx absorbent capacity is lowered.
In the present invention, by reducing the crystallite diameter of the alkali compound (mainly carbonate or the like), the S poisoning can be easily released. That is, by setting the crystallite diameter of the alkali compound to 250 mm or less, the alkali metal or alkaline earth metal sulfate produced by S poisoning can be easily decomposed, and S poisoning can be easily released.
On the other hand, when the crystallite diameter of the alkali compound exceeds 250 mm, the S elimination performance becomes insufficient. In addition, although the crystallite diameter of the alkali compound obtained by the normal impregnation method is 280 to 300 mm, in the exhaust gas purification catalyst obtained by the production method of the present invention described later, the crystallite diameter of the alkali compound is 250 mm or less. This is confirmed by XRD.
[0016]
Here, “crystallite” refers to an aggregate in which a single crystal form has the same directionality, and the crystallite diameter uses the full width at half maximum of the XRD peak and θ, and the following Scherrer equation (1): It is required (see FIG. 2 and FIG. 3).
(Crystallite diameter) = λ / ((half width × 3.14 / 180) × COSθ) (1)
[0017]
Further, the oxide equivalent weight of the alkali compound is preferably 1 to 50 g per liter of the catalyst capacity, and in this case, the purification effect tends to be particularly large. If it is less than 1 g, the action of the alkali compound may not be sufficiently obtained, and even if it is added in excess of 50 g, it is difficult to obtain a significant effect of increasing the amount and the thermal deterioration of the catalyst noble metal is promoted.
[0018]
The exhaust gas purification catalyst of the present invention described above can be used in various shapes, and can be used by being supported on a refractory inorganic carrier. For example, it is desirable to use it supported on a monolithic carrier (monolith carrier) such as a honeycomb structure made of a ceramic such as cordierite or a metal such as ferritic stainless steel.
[0019]
Moreover, it is desirable that the first layer, the second layer, and the carrier have high heat resistance in view of use at a high temperature. Therefore, materials that improve heat resistance such as ceria, zirconia, lanthanum, barium, and the like conventionally used in three-way catalysts, such as noble metals and alumina, may be added as appropriate.
[0020]
Next, the manufacturing method of the exhaust gas purification catalyst of the present invention will be described in detail.
In such an exhaust gas purification catalyst manufacturing method, first, a first layer containing an HC adsorbent is formed on a carrier, and then a powder in which a catalyst noble metal according to Rh, Pd or Pt, and any combination thereof is supported on alumina is used. Then, it is mixed with an aqueous solution of a water-soluble salt containing the alkali metal and / or alkaline earth metal to obtain a slurry which is a constituent material of the second layer.
Thus, by mixing the alkali metal and / or alkaline earth metal into the slurry constituting the second layer, the entry of the alkali metal and / or alkaline earth metal into the HC adsorbent is reduced, and the HC adsorption. Suppress capacity decline. Specifically, the entry of alkali metal and / or alkaline earth metal into the HC adsorbent is about 60 to 80% in the impregnation method, but can be suppressed to about 20% in the present production method.
In addition, the crystallite diameter of the alkali compound (mainly carbonate or the like) can be reduced as described later, and the decomposition of the alkali metal or alkaline earth metal sulfate formed by S poisoning is facilitated.
[0021]
Next, after adjusting the pH of the slurry to be in the range of 7.0 to 12.0, the average particle size of the particles in the slurry is set to 0.1 to 5 μm and laminated on the first layer. The exhaust gas purification catalyst described above is obtained by drying at 300 ° C. and firing at 400 to 700 ° C. to form the second layer.
Thus, by setting the pH of the slurry to 7.0 to 12.0, the alkali metal and / or alkaline earth metal is precipitated in the slurry, and the crystallite diameter of the alkali compound is increased. Is prevented.
Further, the exhaust gas purification catalyst contains an alkali compound having a desired crystallite diameter (250 mm or less) by pulverizing until the average particle diameter of the particles in the slurry becomes 0.1 to 5 μm.
Furthermore, if the drying temperature is less than 100 ° C., a sufficient drying effect cannot be obtained, and if it exceeds 300 ° C., the coating layer is cracked and peeled off because of a high temperature.
Furthermore, when the firing temperature is less than 400 ° C., the noble metal or alkali salt is not decomposed, so that the desired purification performance does not appear. When it exceeds 700 ° C., the crystallite diameter of the noble metal or alkali increases because the temperature is too high. Does not develop.
[0022]
Moreover, as a form of the alkali compound containing the alkali metal and / or alkaline earth metal, it is desirable to use a carbonate, an oxide, a hydroxide, or the like.
Furthermore, it is preferable to use barium (Ba) and / or magnesium (Mg) as the alkaline earth metal.
Furthermore, the exhaust gas purification catalyst of the present invention adsorbs NOx when the air-fuel ratio A / F is excessive in oxygen (during lean), and when it is at the stoichiometric air-fuel ratio (during rich) or when fuel is excessive ( NOx adsorbed at the time of stoichiometry can be reduced, but the working air-fuel ratio in the internal combustion engine or the like at this time is preferably 20 to 50 and 10.0 to 14.6, and if it is within this range, NOx Can be efficiently purified.
[0023]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
[0024]
Example 1
<First layer>
Using β zeolite as the HC adsorbent, the HC adsorbent, silica sol and water were charged into a magnetic ball mill, mixed and ground to obtain a slurry liquid. The median diameter of this slurry was 3 μm. This slurry liquid is attached to a cordierite monolith carrier (1.7 L, 400 cells), excess slurry in the cells is removed by air flow, dried at 130 ° C., and then baked at 400 ° C. for 1 hour. A first layer was formed by supporting 200 g / L of layer.
[0025]
<Second layer>
An aqueous solution of dinitrodiammine Pt was impregnated into alumina, dried, and then fired in air at 400 ° C. for 1 hour to obtain Pt-supported alumina powder (powder A). The Pt concentration of this powder was 1.5%.
An aqueous Rh nitrate solution was impregnated into alumina, dried, and then fired in air at 400 ° C. for 1 hour to obtain an Rh-supported alumina powder (powder B). The Rh concentration of this powder was 2.0%.
Powder A, powder B, alumina, Ba acetate solution and water were added to a magnetic ball mill to adjust the pH to 9, and then mixed and ground to obtain a slurry liquid. The median diameter of this slurry was 3 μm. This slurry liquid is deposited on the first layer, excess slurry in the cell is removed with an air stream, dried at 130 ° C., and then fired at 400 ° C. for 1 hour to carry a coat layer of 150 g / L. Two layers were formed to obtain the exhaust gas purification catalyst of this example. At this time, the crystallite diameter of the carbonic acid Ba was 240 mm. Table 2 shows the compositions of the first layer and the second layer.
[0026]
(Example 2)
Except that the HC adsorbent β-zeolite was changed to MFI-type zeolite, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0027]
(Example 3)
Except that the HC adsorbent β zeolite was MOR type zeolite, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0028]
Example 4
Except that β zeolite of HC adsorbent was changed to FAU type zeolite, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0029]
(Example 5)
An exhaust gas purification catalyst of this example was obtained by repeating the same operation as in Example 1 except that Ba acetate in the slurry forming the second layer was changed to Na acetate. Table 2 shows the compositions of the first layer and the second layer.
[0030]
(Example 6)
Except that the acetic acid Ba in the slurry forming the second layer was changed to Ca acetate, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0031]
(Example 7)
Except for changing acetic acid Ba in the slurry forming the second layer to acetic acid K, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0032]
(Example 8)
Except for changing acetic acid Ba in the slurry forming the second layer to carbonic acid Cs, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0033]
Example 9
An exhaust gas purification catalyst of this example was obtained by repeating the same operation as in Example 1 except that Ba acetate in the slurry forming the second layer was changed to Mg acetate. Table 2 shows the compositions of the first layer and the second layer.
[0034]
(Example 10)
Except that the particle size of the slurry forming the second layer was 4.5 μm, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0035]
(Example 11)
Except that the particle size of the slurry forming the second layer was 1.5 μm, the same operation as in Example 1 was repeated to obtain the exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0036]
(Example 12)
<First layer>
Β zeolite was used as the HC adsorbent, and the HC adsorbent, silica sol, and water were charged into a magnetic ball mill, mixed and ground to obtain a slurry liquid. The median diameter of this slurry was 3 μm. This slurry liquid is attached to a cordierite monolith carrier (1.7 L, 400 cells), excess slurry in the cells is removed by air flow, dried at 130 ° C., and then baked at 400 ° C. for 1 hour. A first layer was formed by supporting 200 g / L of layer.
[0037]
<Second layer>
An aqueous solution of dinitrodiammine Pt was impregnated into alumina, dried, and then fired in air at 400 ° C. for 1 hour to obtain a Pt-supported alumina powder (powder A). The Pt concentration of this powder was 1.5%.
An aqueous Rh nitrate solution was impregnated into alumina, dried, and then fired in air at 400 ° C. for 1 hour to obtain an Rh-supported alumina powder (powder B). The Rh concentration of this powder was 2.0%.
Powder A, powder B, alumina, Ba acetate solution, Mg acetate solution, and water were added to a magnetic ball mill to adjust the pH to 9, and then mixed and ground to obtain a slurry solution. The median diameter of this slurry was 3 μm. This slurry liquid is deposited on the first layer, excess slurry in the cell is removed with an air stream, dried at 130 ° C., and then fired at 400 ° C. for 1 hour to carry a coat layer of 150 g / L. Two layers were formed to obtain the exhaust gas purification catalyst of this example. At this time, the crystallite diameter of the carbonic acid Ba was 230 mm. Table 2 shows the compositions of the first layer and the second layer.
[0038]
(Comparative Example 1)
<First layer>
Using β zeolite as the HC adsorbent, the HC adsorbent, silica sol and water were charged into a magnetic ball mill, mixed and ground to obtain a slurry liquid. The median diameter of this slurry was 3 μm. This slurry liquid is attached to a cordierite monolith carrier (1.7 L, 400 cells), excess slurry in the cells is removed by air flow, dried at 130 ° C., and then baked at 400 ° C. for 1 hour. A first layer was formed by supporting 200 g / L of layer.
[0039]
<Second layer>
An aqueous solution of dinitrodiammine Pt was impregnated into alumina, dried, and then fired in air at 400 ° C. for 1 hour to obtain Pt-supported alumina powder (powder A). The Pt concentration of this powder was 1.5%.
An aqueous Rh nitrate solution was impregnated into alumina, dried, and then fired in air at 400 ° C. for 1 hour to obtain an Rh-supported alumina powder (powder B). The Rh concentration of this powder was 2.0%.
Powder A, powder B, alumina and water were put into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid. The median diameter of this slurry was 3 μm. The slurry was adhered onto the first layer, excess slurry in the cell was removed by air flow, dried at 130 ° C., and then fired at 400 ° C. for 1 hour to carry a coating layer of 150 g / L.
The catalyst was impregnated with Ba acetate, dried at 130 ° C., calcined at 400 ° C. for 1 hour, and loaded with 30 g / L to form a second layer, whereby an exhaust gas purification catalyst of this example was obtained. Table 2 shows the compositions of the first layer and the second layer.
[0040]
(Comparative Example 2)
Except that the particle diameter of the slurry forming the second layer was 7 μm, the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0041]
(Comparative Example 3)
Except that the firing temperature for forming the second layer was 800 ° C., the same operation as in Example 1 was repeated to obtain an exhaust gas purification catalyst of this example. Table 2 shows the compositions of the first layer and the second layer.
[0042]
(Test Example 1: Conversion after endurance)
Endurance method The exhaust gas purification catalyst obtained in each of the above examples was installed in the exhaust system of an engine with a displacement of 4400 cc, domestic regular gasoline was used, the catalyst inlet temperature was 650 ° C., and the engine was operated for 50 hours.
Evaluation Method The catalyst was mounted on the exhaust system of an engine with a displacement of 2000 cc, and the vehicle was run in 11 mode to obtain the exhaust purification rate. The evaluation results are shown in Table 1.
[0043]
(Test Example 2: Conversion after S desorption treatment)
Endurance method The exhaust gas purification catalyst obtained in each of the above examples was installed in the exhaust system of an engine with a displacement of 4400 cc, domestic regular gasoline was used, the catalyst inlet temperature was 650 ° C., and the engine was operated for 50 hours.
Then, after S poisoning treatment (using gasoline with S concentration of 300 ppm, the catalyst inlet temperature is 350 ° C. and operating for 5 hours), S desorption treatment (using domestic regular gasoline, catalyst inlet temperature being 650 ° C.) For 30 minutes).
Evaluation method The catalyst is mounted on the exhaust system of a 2000 cc engine, lean (A / F = 20) 10 sec → rich (A / F = 11.0) 2 sec → stoichiometric (A / F = 14.7) ) Operation for 5 seconds was performed, and the exhaust gas purification rate in this section was obtained. The inlet temperature was 350 ° C. The evaluation results are shown in Table 1.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
From Table 1, the exhaust gas purification catalysts obtained in Examples 1 to 12 which are within the preferred range of the present invention are more durable and S desorbed than the exhaust gas purification catalysts obtained in Comparative Examples 1 to 3. The purification performance after the treatment is excellent, and it can be seen that Example 12 shows the best HC conversion rate in 11 mode and NOx conversion rate after S desorption treatment at present. It can also be seen that the exhaust gas purification catalyst of the example has a particularly good NOx purification rate after the S desorption treatment.
[0047]
As mentioned above, although this invention was demonstrated in detail by the suitable Example, this invention is not limited to these Examples, A various deformation | transformation is possible within the range of the summary of this invention.
For example, the exhaust gas purification catalyst of the present invention can be divided into two layers, the second layer on the HC adsorption layer, and the upper layer may include Rh and Pt, and the lower layer may include Pt.
[0048]
【The invention's effect】
As described above, according to the present invention, the NOx purification catalyst component layer containing the catalyst noble metal and the alkali compound having a predetermined crystallite diameter is laminated on the HC adsorbent layer, and the sulfur component desorption performance is achieved. Therefore, it is possible to provide an exhaust gas purification catalyst that facilitates the desorption treatment of sulfur adhering to the catalyst and has good NOx purification efficiency particularly in an oxygen-excess region (lean region). .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a part of a laminated structure of an exhaust gas purification catalyst.
FIG. 2 is a diagram showing an outline of particle diameter and crystallite diameter.
FIG. 3 is a diagram showing X-ray diffraction peaks.
[Explanation of symbols]
1 First layer (HC adsorbent layer)
2 Second layer (NOx catalyst component layer)
3 Alkali compound 4 Honeycomb carrier

Claims (6)

An exhaust gas purification catalyst formed by laminating a second layer containing a NOx purification catalyst component on a first layer containing an HC adsorbent,
The second layer contains at least one catalytic noble metal selected from the group consisting of rhodium, palladium and platinum, and an alkali compound containing an alkali metal and / or an alkaline earth metal;
An exhaust gas purification catalyst, wherein the crystallite size of the alkali compound is 250 mm or less. The exhaust gas purification catalyst according to claim 1, wherein the alkali compound is a compound containing at least one element selected from the group consisting of sodium, potassium, cesium, magnesium, calcium and barium. The alkali compound has the following general formula Ba _x Mg _y (CO ₃ ) ₂
(Wherein x and y are atomic ratios of the respective elements, and x = 0.5 to 1.999, y = 0.001 to 1.5, and x + y = 2.0) The exhaust gas purifying catalyst according to claim 1 or 2, wherein the exhaust gas purifying catalyst is a salt. The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein an oxide-converted weight of the alkali compound is 1 to 50 g per liter of catalyst capacity. A method for producing the exhaust gas purification catalyst according to any one of claims 1 to 4,
A powder in which at least one catalyst noble metal selected from the group consisting of rhodium, palladium and platinum is supported on alumina is mixed with an aqueous solution of a water-soluble salt containing the alkali metal and / or alkaline earth metal to form a slurry, After adjusting the pH of the slurry to be in the range of 7.0 to 12.0, the average particle size of the particles in the slurry was set to 0.1 to 5 μm and laminated on the first layer, and 100 to 300 ° C. The method for producing an exhaust gas purifying catalyst is characterized in that the second layer is formed by baking at 400 to 700 ° C.   6. The method for producing an exhaust gas purification catalyst according to claim 5, wherein the alkaline earth metal is barium and / or magnesium.

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