JP2002166170A - Exhaust gas cleaning catalyst and method for preparing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst where sulfur stuck to a catalyst is easily removed even by a less amount of noble metals carried than that of conventional catalysts and which is excellent particularly in purging efficiency of NOx in the range of excess oxygen. SOLUTION: This catalyst is an exhaust gas cleaning catalyst containing a compound of 1A-3A groups, two or more types of aluminas different in crystallite diameter and a catalytic noble metal, which adsorbs NOx at lean time and reduces adsorbed NOx at rich time or at stoichiometric time. An alumina smaller in crystallite diameter carries catalytic noble metal and furthermore the compound of 1A-3A groups. Powders obtained by drying after mixing the two or more types of aluminas and by baking them at 500-800 deg.C are mixed with the catalytic noble metal in an aqueous solution containing the compound of 1A-3A groups, and carried by a refractory inorganic carrier, obtaining the catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrocarbons (HC) and carbon monoxide (C) 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 catalyst for purifying O) and nitrogen oxides (NOx) and a method for producing the same, and particularly to N in an oxygen-excess region.
The present invention relates to an exhaust gas purification catalyst focusing on an Ox purification method and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, the demand for fuel-efficient vehicles has been increasing due to the problem of depletion of petroleum resources and the problem of global warming, and development of lean-burn vehicles has attracted attention for gasoline vehicles. In such a lean-burn vehicle, during lean-burn operation, the exhaust gas atmosphere becomes an oxygen-excess atmosphere (lean) compared to the stoichiometric air-fuel state. However, when a normal three-way catalyst is applied in a lean region, excess oxygen is generated. There is a problem that the NOx purification action becomes insufficient due to the influence. Therefore, development of a catalyst that can purify NOx even when oxygen becomes excessive has been desired.

[0003]

SUMMARY OF THE INVENTION Conventionally, N
Various catalysts for purifying Ox have been proposed. For example, as represented by a catalyst in which platinum (Pt) and lanthanum (La) are supported on a porous carrier (JP-A-5-168860), NOx in a lean region is represented. There has been proposed a catalyst that absorbs NOx and releases and purifies NOx during stoichiometry. However, the fuel and the lubricating oil contain sulfur (S), and this sulfur is discharged as an oxide into the exhaust gas, so that NOx
The absorbent is poisoned by sulfur, and the NOx absorption capacity is reduced (this is referred to as "sulfur poisoning"). This sulfur poisoning cannot be avoided as long as the exhaust gas contains some form of sulfur, and how to remove sulfur attached to the catalyst has become an important issue.

[0004] The present invention has been made in view of such problems of the prior art, and an object of the present invention is to remove sulfur adhering to a catalyst even if the amount of noble metal carried is smaller than before. , Especially in the oxygen-excess region.
x It is to provide an exhaust gas purification catalyst having good purification efficiency.

[0005]

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 an exhaust gas purifying catalyst containing a 1A-3A group compound, two or more kinds of alumina and a catalytic noble metal is used. The present inventors have found that the above-mentioned problems can be solved by achieving both the SOx desorption performance and the NOx absorption performance, and have completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention is classified by a group 1A to 3A compound containing at least one element selected from the group consisting of alkali metals, alkaline earth metals and rare earths, and a crystallite diameter. Containing two or more types of alumina and at least one type of catalytic noble metal selected from the group consisting of platinum, rhodium and palladium, adsorbs NOx when lean, and reduces NOx adsorbed during rich or stoichiometric It is characterized by the following.

In a preferred embodiment of the exhaust gas purifying catalyst according to the present invention, the difference between the alumina crystallite diameters of the two or more types of alumina is 1 to 45 nm. It is characterized by being carried.

Further, the method for producing an exhaust gas purifying catalyst of the present invention is a method for producing the above exhaust gas purifying catalyst,
The above two or more aluminas are mixed and dried in an aqueous solution,
Baking at a temperature of 500 to 800 ° C. to form a powder, mixing the powder and the catalyst noble metal with an aqueous solution containing the 1A to 3A group compound, and supporting a slurry obtained by grinding on a refractory inorganic carrier; It is characterized by.

Still another aspect of the present invention is a method for producing an exhaust gas purifying catalyst, comprising: the alumina having a small crystallite diameter supporting the catalytic noble metal; Alumina having a large diameter is mixed in an aqueous solution, dried, and calcined at a temperature of 500 to 800 ° C. to form a powder. The powder is mixed with the aqueous solution of the above-mentioned 1A to 3A group compound, and the slurry is obtained by grinding. On a refractory inorganic carrier.

[0010] In still another aspect of the present invention, there is provided a method for producing an exhaust gas purifying catalyst, the method comprising producing the exhaust gas purifying catalyst, wherein the crystallite diameter supporting the catalytic noble metal and the 1A to 3A group compound is supported. Alumina having a small particle size and alumina having a large crystallite diameter are mixed in an aqueous solution and dried.
It is characterized in that it is fired at a temperature of from 00 to 800 ° C. to form a powder, and a slurry obtained by pulverizing the powder in an aqueous solution is supported on a refractory inorganic carrier.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The exhaust gas purifying catalyst of the present invention will be described below in detail. In this specification, “%” indicates mass percentage unless otherwise specified.

As described above, the exhaust gas purifying catalyst of the present invention comprises a 1A to 3A group compound, two or more kinds of alumina classified by crystallite diameter, and a catalytic noble metal.

Here, the above-mentioned 1A-3A group compound is
Potassium metal, alkaline earth metal or rare earth, and these
It is a compound containing elements in any combination. These sources
By containing element, NOx adsorption performance is enhanced. Ma
Further, as the alkali metal, sodium (Na),
Potassium (K), rubidium (Rb) and cesium (C
s) and the like, as the alkaline earth metal, magnesium sulfide
(Mg), calcium (Ca), strontium (S
r) and barium (Ba), such rare earths include:
Lantern (La), Praseodymium (Pr) and Neodymium
It is desirable to use (Nd) or the like. In this case, NO
x to N ₂This is effective because it can be easily reduced to Furthermore, on
The Group 1A to 3A compounds include carbonates, oxides and hydroxides.
It is desirable.

Further, the oxide equivalent weight of the above-mentioned 1A-3A group compound is preferably 1-50 g per liter of catalyst capacity. In this case, it is particularly effective because the purification effect can be improved. On the other hand, if it is less than 1 g, the action of the compound containing an alkali metal or the like may not be sufficiently obtained, and
g, it is difficult to obtain a significant effect of increasing the amount,
It only promotes thermal degradation of the catalytic noble metal.

The exhaust gas purifying catalyst of the present invention contains two or more kinds of aluminas (having different surface areas) classified by the crystallite diameter. Here, “crystallite” refers to an aggregate in which a single crystal form has the same directionality, and the crystallite diameter is obtained by the following Scherrer's formula (1) using the half-width of the XRD peak and θ. (See FIGS. 2 and 3).

(Crystallite diameter) = λ / ((half width × 3.14 / 180) × COSθ) (1)

Here, if the crystallite diameter of alumina contained in the catalyst is the same, it is difficult to achieve both SOx desorption performance and NOx absorption performance. In other words, only alumina with a small crystallite diameter (alumina with a large surface area) has excellent NOx absorption performance but insufficient SOx desorption performance, while alumina with a large crystallite diameter (alumina with a small surface area) ) Alone has excellent SOx desorption performance but insufficient NOx absorption performance. The present inventors have found that both of the above characteristics can be imparted to an exhaust gas purification catalyst by using two or more types of alumina classified by crystallite diameter. Further, as a result of further research, platinum (Pt) and rhodium (R
h) and catalyst noble metals such as palladium (Pd) were found to exhibit the above characteristics. Although the details are not necessarily clear, at this time, as shown in FIG. 1, alumina 1 having a small crystallite diameter adheres around alumina 2 having a large crystallite diameter, and the dispersibility of the catalytic noble metal 3 is maintained. Inferred.

The term "two or more types of alumina classified by crystallite diameter" means that alumina having a small crystallite diameter and alumina having a large crystallite diameter are included. Is preferably 1 to 45 nm. For example, when two kinds of alumina are contained, it is sufficient that the alumina having the largest crystallite diameter and the alumina having the smallest crystallite diameter have the above-mentioned difference in the alumina crystallite diameter when three or more kinds are contained. The content ratio of the alumina having a small crystallite diameter to the alumina having a large crystallite diameter is 1 to
It is desirable that the ratio be about 1: 5 to 1.

Further, the above two or more types of alumina include:
Alumina having a crystallite diameter of 15 nm or less and a crystallite diameter of 15 n
It is preferable to include alumina having a size larger than m and equal to or smaller than 50 nm. Alumina with a small crystallite diameter has a crystallite diameter of 15 nm
If it is larger than this, the absorption performance of NOx cannot be sufficiently exhibited. If the crystallite diameter of alumina having a large crystallite diameter exceeds 50 nm, the SOx desorption performance is good, but the absorption performance of NOx becomes insufficient. There is.

Further, examples of the above-mentioned two or more types of alumina include boehmite and γ-alumina, and it is particularly preferable to use boehmite because the catalytic performance is enhanced.

The catalyst noble metal contained in the exhaust gas purifying catalyst of the present invention includes platinum, rhodium or palladium,
And a catalytic noble metal according to any combination of these.
Such a catalytic noble metal is preferably supported on the alumina having a small crystallite diameter. In other words, sufficient NO is supported only on alumina having a small crystallite diameter.
x can be absorbed and desorbed. Further, it is preferable that the alumina having a small crystallite diameter further supports the above-mentioned 1A to 3A group compound. By improving the degree of dispersion of the catalytic noble metal and the 1A to 3A group compounds, sintering is less likely to occur, and a small amount (support amount) of N
This is effective because Ox can be efficiently absorbed and desorbed.

Cerium oxide (CeO ₂ ) can be supported on the alumina having a small crystallite diameter.
At this time, desorption of SOx attached to the alumina can be further promoted. This is presumed to be related to the generation of hydrogen by Pt / CeO ₂ or the like.

The exhaust gas purifying catalyst of the present invention has an air / fuel ratio A /
NO is adsorbed when F is in excess of oxygen (lean), and is reduced when it is at the stoichiometric air-fuel ratio (rich) or when the fuel is excessive (stoichiometric).
The working air-fuel ratio in an internal combustion engine or the like using such an exhaust gas purifying catalyst is 20 to 50 and 10.0 to 14.6.
It is preferable that NOx is within this range, so that NOx can be efficiently purified.

The exhaust gas purifying catalyst of the present invention 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 by supporting it on a monolithic carrier such as a honeycomb structure made of ceramic such as cordierite or a metal such as ferrite stainless steel.

Further, it is desirable that such an exhaust gas purifying catalyst has high heat resistance in view of a situation where it is exposed to a high temperature. Therefore, a material for improving the heat resistance of zirconia or alumina conventionally used in a three-way catalyst may be appropriately added.

Next, the method for producing the exhaust gas purifying catalyst of the present invention will be described in detail. A first method for producing an exhaust gas purifying catalyst comprises mixing two or more types of alumina in an aqueous solution, drying the mixture, and calcining the mixture at a temperature of 500 to 800 ° C. to obtain a powder. A slurry obtained by mixing with an aqueous solution containing a group 1A to 3A compound and pulverizing the slurry is supported on a refractory inorganic carrier. That is, in this manufacturing method, an alumina powder in which two or more types of alumina classified by the crystallite diameter are adhered to each other is formed, and the catalyst noble metal and the 1
An exhaust gas purifying catalyst can be obtained by carrying the Group A to Group 3A compounds.

In a second method for producing an exhaust gas purifying catalyst, the alumina having a small crystallite diameter supporting the catalyst noble metal and the alumina having a large crystallite diameter are mixed in an aqueous solution and dried. It is characterized in that it is calcined at a temperature of up to 800 ° C. to form a powder, and this powder is mixed with an aqueous solution of the above-mentioned group 1A to 3A compound, and the resulting slurry is supported on a refractory inorganic carrier. That is, in this manufacturing method, the catalyst noble metal is supported on the alumina having a small crystallite diameter, and the alumina having a small crystallite diameter and the alumina having a large crystallite diameter are brought into close contact with each other to form an alumina powder. The exhaust gas purifying catalyst is obtained by carrying the above-mentioned 1A to 3A group compound on the substrate.

Further, a third method for producing an exhaust gas purifying catalyst is characterized in that the above-mentioned alumina having a small crystallite diameter and the alumina having a large crystallite diameter carrying the catalyst noble metal and the above-mentioned Group 1A to 3A compound are dissolved in an aqueous solution. Mix and dry at 500
It is characterized in that it is fired at a temperature of up to 800 ° C. to form a powder, and a slurry obtained by pulverizing this powder in an aqueous solution is supported on a refractory inorganic carrier. That is, in this manufacturing method, the catalyst noble metal and the 1
An exhaust gas purifying catalyst can be obtained as an alumina powder which carries a group A to group 3A compound and adheres it to alumina having a large crystallite diameter.

As described above, in the production of the exhaust gas purifying catalyst of the present invention, it is presumed that bonding (adhesion) of the above two or more types of alumina occurs and the structure shown in FIG. 1 is easily formed. If the sintering temperature is lower than 500 ° C., such bonding is unlikely to occur. If the firing temperature is higher than 800 ° C., the decrease in the surface area of alumina proceeds. In the second and third production methods, the catalyst noble metal and the 1A to 3A
This is effective because the degree of dispersion of the group compound can be further improved and the amount used can be saved.

[0030]

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

(Example 1) Boehmite having a crystallite diameter of 5 nm and boehmite having a crystallite diameter of 40 nm were mixed in water at a ratio of 1: 1. After drying at 130 ° C., it was baked at 600 ° C. for 1 hour to obtain powder A. This powder A was impregnated with an aqueous solution of dinitrodiammine Pt and an aqueous solution of Rh nitrate, dried and calcined at 400 ° C. for 1 hour in air to obtain an alumina powder carrying Pt and Rh (powder B). The Pt concentration of this powder was 1.
It was 0%. The Rh concentration was 1.0%. Powder B,
Alumina, Ba acetate solution and water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry solution was adhered to a cordierite-based monolithic carrier (1.7 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. An exhaust gas purification catalyst carrying 200 g / L of the layer was obtained. This catalyst has Pt = 2.0 g / L, Rh = 0.5
g / L, Ba = 30 g / L in terms of oxides were supported.

Example 2 Boehmite having a crystallite size of 5 nm was impregnated with an aqueous solution of dinitrodiammine Pt and an aqueous solution of Rh nitrate, dried and calcined at 400 ° C. for 1 hour in air to obtain Pt,
A Rh-supported alumina powder (powder A) was obtained. P of this powder
The t concentration was 1.0%. The Rh concentration was 1.0%. Powder A and boehmite having a crystallite diameter of 40 nm were mixed in water at a ratio of 1: 1. After drying this at 130 ° C,
The powder was fired at 600 ° C. for 1 hour to obtain powder B. Powder B, alumina, Ba acetate solution and water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry solution was attached to a cordierite-based monolithic carrier (1.7 L, 400 cells), and the excess slurry in the cells was removed by an air flow to remove the slurry.
After drying at 0 ° C., it was baked at 400 ° C. for 1 hour to obtain an exhaust gas purifying catalyst supporting a coat layer of 200 g / L. This catalyst has Pt = 2.0 g / L, Rh = 0.5 g / L,
Ba = 30 g / L in terms of oxide was carried.

Example 3 Boehmite having a crystallite diameter of 5 nm was impregnated with an aqueous solution of dinitrodiammine Pt and an aqueous solution of Rh nitrate, dried and calcined at 400 ° C. for 1 hour in air to obtain Pt,
A Rh-supported alumina powder (powder A) was obtained. P of this powder
The t concentration was 1.0%. The Rh concentration was 1.0%. Powder A is impregnated with Ba acetate solution, dried and dried in air.
It was calcined at 0 ° C. for 1 hour to obtain an alumina powder carrying Pt, Rh and Ba (powder B). Powder B and boehmite having a crystallite diameter of 40 nm were mixed in water at a ratio of 1: 1. This one
After drying at 30 ° C, baking for 1 hour at 600 ° C, powder C
I got Powder C, alumina and water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry solution was adhered to a cordierite-based monolithic carrier (1.7 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. An exhaust gas purification catalyst carrying 200 g / L of the layer was obtained. This catalyst has Pt = 2.0 g / L, Rh = 0.5
g / L, Ba = 30 g / L in terms of oxides were supported.

Example 4 A boehmite having a crystallite diameter of 5 nm was impregnated with an aqueous solution of Ce nitrate, dried and then dried at 400 ° C. in air.
After calcining for an hour, Ce-supported alumina powder (powder A) was obtained. The Ce concentration of this powder was 3.0%. Powder A and boehmite having a crystallite diameter of 40 nm were mixed in water at a ratio of 1: 1. After drying at 130 ° C.,
After sintering for a time, powder B was obtained. Powder B was impregnated with an aqueous solution of dinitrodiammine Pt and an aqueous solution of Rh nitrate, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt, Rh-supported alumina powder (powder C). The Pt concentration of this powder is 1.0%
Met. The Rh concentration was 1.0%. Powder C, alumina, Ba acetate solution and water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry solution was attached to a cordierite-based monolithic carrier (1.7 L, 400 cells), and the excess slurry in the cells was removed by an air flow to remove the slurry.
After drying at 0 ° C., it was baked at 400 ° C. for 1 hour to obtain an exhaust gas purifying catalyst supporting a coat layer of 200 g / L. This catalyst has Pt = 2.0 g / L, Rh = 0.5 g / L,
Ba = 30 g / L in terms of oxide was carried.

Comparative Example 1 The same operation as in Example 1 was performed except that boehmite having a crystallite diameter of 5 nm was used instead of boehmite having a crystallite diameter of 40 nm, that is, the crystallite diameter of all alumina was changed to 5 nm. Was repeated to obtain an exhaust gas purifying catalyst of this example.

Comparative Example 2 The same operation as in Example 1 was carried out except that boehmite having a crystallite diameter of 40 nm was used instead of boehmite having a crystallite diameter of 5 nm, that is, the crystallite diameter of all alumina was changed to 40 nm. Was repeated to obtain an exhaust gas purifying catalyst of this example.

Comparative Example 3 The same operation as in Example 1 was repeated, except that boehmite having a crystallite diameter of 5 nm was used instead of boehmite having a crystallite diameter of 5 nm, to obtain an exhaust gas purifying catalyst of this example.

Example 5 The same operation as in Example 1 was repeated, except that boehmite having a crystallite diameter of 40 nm was used instead of boehmite having a crystallite diameter of 40 nm, to obtain an exhaust gas purifying catalyst of this example.

Example 6 An exhaust gas purifying catalyst of this example was obtained by repeating the same operation as in Example 1 except that the weight in terms of oxide of Ba in the catalyst was changed to 60 g / L.

<Evaluation Test> The following durability method and sulfur desorption treatment method were performed, and HC and C after durability and S desorption treatment with the exhaust gas purifying catalysts obtained in the above Examples and Comparative Examples.
The conversions of O and NOx were measured. The recovery rate was determined using the following equation (2): recovery rate = (NOx conversion rate after desorption treatment) / (NOx conversion rate after endurance) (2)

(Durability method) The exhaust gas purifying catalysts obtained in the above Examples and Comparative Examples were mounted on the exhaust system of an engine having a displacement of 4400 cc, and domestic regular gasoline was used.
The catalyst inlet temperature was set to 650 ° C., and the operation was performed for 50 hours. Then, after performing S poisoning treatment (using S concentration of 300 ppm gasoline, catalyst inlet temperature at 350 ° C. and operating for 5 hours), S desorption treatment (using domestic regular gasoline,
The catalyst inlet temperature was set to 650 ° C., and the operation was performed for 30 minutes.

(Sulfur desorption method) Displacement 2000cc
The exhaust gas purifying catalysts obtained in the above Examples and Comparative Examples were mounted on the exhaust system of the engine of Example 1, and lean (A / F = 20)
The operation was performed for 10 sec → rich (A / F = 11.0) 2 sec → stoichiometric (A / F = 14.7) 5 sec, and the exhaust gas purification rate in this section was determined. Inlet temperature 350
° C.

[0043]

[Table 1]

As shown in Table 1, the exhaust gas purifying catalysts obtained in Examples 1 to 6 which are within the preferred range of the present invention are Comparative Examples 1 to 3.
It can be seen that the catalyst has excellent performance as compared with the exhaust gas purification catalyst obtained in (1). That is, for example, Example 1 and Comparative Example 1
In comparison, the NOx performance after durability was better in Comparative Example 1, but in Example 1, the decrease in performance after the S desorption treatment was smaller,
Good recovery rate. This is because of the large S
It can be estimated that the desorption effect is large. Further, comparing Example 1 and Comparative Example 2, it is understood that Example 1 has a better balance between the recovery rate and the NOx conversion performance. Further, Example 1
Compared with Comparative Example 3, there is no difference in the recovery rate, but Example 1
The NOx conversion performance is much better, and the total purification rate is improved when mounted on a vehicle. This can be presumed to be because in Comparative Example 3, the size of alumina having a small crystallite diameter was too large at 20 nm. Furthermore, when comparing Example 1 and Example 5, there is no difference in the recovery rate, but the NOx conversion performance of Example 1 is excellent. This can be presumed to be because in Example 5, the size of alumina having a large crystallite diameter was too large at 20 nm. Further, when comparing Example 1 with Example 6, the NOx performance after durability is better in Example 6, but the recovery rate is higher in Example 1 because the performance decline after S desorption is large. . It can be estimated that this is because the amount of Ba is in a preferable range. As described above, with the catalyst shown in the embodiment, even if S is present in the fuel, it is possible to obtain the effect that the catalyst is less susceptible to deterioration (S poisoning) and the catalyst activity is hardly reduced.

[0045]

As described above, according to the present invention, an SOx catalyst using an exhaust gas purifying catalyst containing a Group 1A to 3A compound, two or more kinds of alumina classified by crystallite diameter and a catalytic noble metal is used. Since the desorption performance and the NOx absorption performance are both compatible, even if the amount of noble metal carried is smaller than before, the desorption treatment of the sulfur adhering to the catalyst is easy, and the exhaust gas with good NOx purification efficiency especially in the oxygen excess region. A gas purification catalyst can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the structure of an exhaust gas purifying catalyst (alumina and catalytic noble metal).

FIG. 2 is a diagram schematically showing a particle diameter and a crystallite diameter.

FIG. 3 is a view showing an X-ray diffraction peak.

[Explanation of symbols]

 1 Alumina with small crystallite diameter 2 Alumina with large crystallite diameter 3 Catalyst noble metal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/28 301 B01D 53/36 104A F-term (Reference) 3G091 AA12 AA17 AA18 AB06 AB09 BA11 BA14 BA15 BA19 BA39 CB02 DA01 DA02 DB10 FB10 FB11 FB12 GA06 GB01X GB02W GB02Y GB03W GB03Y GB04W GB04Y GB05W GB06W GB07W GB10X GB16X GB17X HA18 4D048 AA06 AA13 AA18 BA10X BA10Y BA14Y BA15Y BA19Y BA30X BA30A BAAA BCABAA BC12 BC BC75B CA03 CA09 CA13 DA06 FA02 FA03 FB15 FB30

Claims (9)

[Claims] 1. A group 1A-3A compound containing at least one element selected from the group consisting of alkali metals, alkaline earth metals and rare earths, two or more kinds of alumina classified by crystallite diameter, and platinum. And at least one catalytic noble metal selected from the group consisting of rhodium and palladium, and adsorbs NOx during lean operation and reduces NOx adsorbed during rich or stoichiometric operation. . 2. The method according to claim 1, wherein a difference between alumina crystallite diameters of the two or more aluminas is 1 to 45 nm, and alumina having a small crystallite diameter supports the catalyst noble metal. 2. The exhaust gas purification catalyst according to 1. 3. The exhaust gas purifying catalyst according to claim 2, wherein the alumina having a small crystallite diameter further supports the group 1A to 3A compound. 4. The exhaust gas purifying catalyst according to claim 1, comprising alumina having a crystallite diameter of 15 nm or less and alumina having a crystallite diameter of more than 15 nm and 50 nm or less. . 5. The exhaust gas purifying catalyst according to claim 1, wherein the weight of the group 1A to 3A compound in terms of oxide is 1 to 50 g per liter of the catalyst capacity. . 6. A method according to claim 2, wherein said alumina having a small crystallite diameter supports cerium oxide.
The exhaust gas purifying catalyst according to any one of the above items. 7. A method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein the two or more aluminas are mixed in an aqueous solution and dried.
Baking at a temperature of 500 to 800 ° C. to form a powder, mixing the powder and the catalyst noble metal with an aqueous solution containing the 1A to 3A group compound, and supporting a slurry obtained by grinding on a refractory inorganic carrier. A method for producing an exhaust gas purifying catalyst, comprising: 8. The method for producing an exhaust gas purifying catalyst according to claim 2, wherein the alumina having a small crystallite diameter supporting the catalytic noble metal and the alumina having a large crystallite diameter are mixed in an aqueous solution. The powder is dried and calcined at a temperature of 500 to 800 ° C. to obtain a powder.
A method for producing an exhaust gas purifying catalyst, comprising supporting a slurry obtained by pulverization on a refractory inorganic carrier. 9. The method for producing an exhaust gas purifying catalyst according to claim 3, wherein the alumina having a small crystallite diameter supports the catalyst noble metal and the 1A to 3A group compound, and the alumina having a large crystallite diameter. Alumina is mixed in an aqueous solution and dried, and 500 to 8
A method for producing an exhaust gas purifying catalyst, comprising sintering at a temperature of 00 ° C. to form a powder, and supporting a slurry obtained by crushing the powder in an aqueous solution on a refractory inorganic carrier.