JPH0819740A - Catalyst for exhaust gas purification and manufacturing method therefor - Google Patents

Abstract

PURPOSE:To provide a catalyst for high exhaust gas purification which has high NOX purifying efficiency even in oxygen excessive atmosphere. CONSTITUTION:A catalyst for exhaust gas purification consists of a catalytic element and aluminosilicate having solid acidity and molecule sieving function and the catalytic element is composed of alumina and a catalytic metal carried on the alumina. The alumina is reformed alumina whose conversion ratio R into a-type is set to be 0.1%<=R<=95%. In the case A and B are defined as the contained weight of the catalytic element and the contained weight of the aluminosilicate, respectively, the weight ratio A1={A/(A+B)}X100 is set to be a value to satisfy 11wt.%<=A1<=95wt.%. The catalytic metal is one of a metal selected from platinum-group. The weight ratio a1 of the catalytic metal in the catalytic element is set to be 0.1wt.%<a1<=5wt.%. A catalyst like this has relatively weak oxidizing function, so that CHO which is a partly oxidized product of HC and has high NOX reducing function can be produced in a wide temperature of an exhaust gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an exhaust gas purifying catalyst, in particular, a catalytic element and an aluminosilicate having solid acidity and molecular sieving property, the catalytic element being alumina and a catalytic metal supported on the alumina. And an exhaust gas purifying catalyst comprising:

[0002]

2. Description of the Related Art Conventionally, activated alumina having a γ phase and / or an η phase has been used as the alumina in the catalyst element, and Pt has been used as the catalyst metal. In this case, the aluminosilicate has a function as a support and an adsorption ability for HC and the like (see, for example, JP-B-56-27295).

[0003]

However, when Pt is supported on activated alumina, since the activated alumina is porous and has a large specific surface area, Pt is highly dispersed, so that the HC adsorption capacity by Pt is high. Although the NOx adsorption capacity is improved, the oxygen excess atmosphere (for example,
When the air-fuel ratio A / F≈24), the catalyst causes HC
Complete oxidation of (hydrocarbon), that is, HC → CO ₂ + H ₂ O
Oxidation reaction of NOx progresses, and it is a partial oxide of HC and NOx
Insufficient production of active CHO with reducing ability
There is a problem that the reduction and purification of NOx cannot be sufficiently performed and the temperature range for purification of NOx becomes narrow because the reduction inhibitory effect of oxygen adsorbed on the t surface is likely to occur.

In view of the above, the present invention uses, as the alumina, one having a smaller specific surface area than that of the activated alumina, and by supporting a specific amount of the metal for the catalyst on the exhaust gas, the partial oxidation of HC can be widely performed. The catalyst and the catalyst which can be developed in a temperature range and can be used in combination with a specific amount of aluminosilicate to adsorb and desorb active CHO, thereby improving the NOx purification rate even in an oxygen excess atmosphere. It is an object to provide a method for producing a catalyst.

[0005]

The present invention comprises a catalytic element,
Aluminosilicate with solid acidity and molecular sieving property
And the catalyst element is supported on alumina and the alumina.
Exhaust gas purification catalyst consisting of the used catalyst metal
The alumina has an α conversion rate R of 0.1% ≦ R ≦ 95%.
The modified alumina is set, and the catalyst element
The total weight is A, while the aluminosilicate is mixed
When the weight is B, the weight ratio of the catalyst element is A₁=
{A / (A + B)} × 100 is 11% by weight ≦ A₁<95
%, And the catalyst metal is from the platinum group
At least one metal selected, said catalytic element
Weight ratio a of the metal for the catalyst in₁Is 0.1% by weight
<A ₁It is characterized in that ≦ 5% by weight is set.

In the method for producing an exhaust gas purifying catalyst according to the present invention, activated alumina is heated at a heating temperature T of 800 ° C. ≦ T ≦ 1.
A step of performing a heat treatment set at 100 ° C. to obtain a modified alumina having an α conversion R of 0.1% ≦ R ≦ 95% from the activated alumina, and the modified alumina is selected from a white metal. A step of producing a catalytic element by supporting at least one catalytic metal, and setting the weight ratio a ₁ of the catalytic metal in the catalytic element to 0.1% by weight <a ₁ ≦ 5% by weight. Mixing the catalyst element and an aluminosilicate having solid acidity and molecular sieving property,
When the compounding weight of the catalyst element is A and the compounding weight of the aluminosilicate is B, the weight ratio A ₁ = {A / (A + B)} × 100 of the catalyst element is 11% by weight ≦ A ₁ < It is characterized in that the step of setting to 95% by weight is sequentially performed.

[0007]

When the α conversion rate R is set as described above, the specific surface area of the modified alumina is smaller than that of the activated alumina having the γ phase because it has the α phase. Therefore, when a specific amount of the catalyst metal is supported on the modified alumina, the dispersibility of the metal is suppressed as compared with the activated alumina, so that the catalyst exhibits a relatively weak oxidizing ability with respect to HC.

As a result, HC is partially oxidized to NOx.
Active CHO having a reducing ability is generated, and this active CHO is produced.
Is generated in a wide exhaust gas temperature range, and aluminosilicate adsorbs and stores a part of active CHO,
Further, since a part of the NOx is separated and supplied, NOx is reduced and purified by the active CHO that is in the free state from the beginning and the activated CHO that is in the free state from the beginning, and the purification temperature range is expanded.

Since the NOx purifying ability of the catalyst is high on the low temperature side of the exhaust gas, when it is combined with a catalyst which exhibits a high NOx purifying ability on the high temperature side thereof, for example, aluminosilicate supported with CeO ₂ . The purification temperature range can be further expanded.

Further, since the modified alumina has an α phase which is a stable phase, it is unlikely to cause pore clogging due to a phase change in activated alumina and burying of a metal for a catalyst due to it, and therefore has excellent heat resistance. The degree of deterioration of catalytic activity at high temperature is small.

However, in the modified alumina, the alpha conversion ratio R
However, if R <0.1%, the degree of reduction of the specific surface area is small and the intended purpose cannot be achieved. On the other hand, R> 95.
%, The specific surface area is greatly reduced by clogging the pores with excessive progress of the α conversion rate, and as a result, the dispersibility of the metal for catalyst is extremely deteriorated and the NOx adsorption capacity is drastically reduced. Further, when the weight ratio A _{1 of the} catalyst element is A ₁ <11 wt%, the NOx purification rate becomes low due to the decrease of the catalytic ability by the catalyst element, while when A ₁ ≧ 95 wt%, the absorption and desorption by the aluminosilicate is performed. Since the action is reduced, the NOx purification rate is similarly reduced.

Further, the weight ratio a _{1 of the} metal for the catalyst is a ₁
When ≦ 0.1% by weight, the NOx purification rate becomes low due to the decrease of the catalytic ability, while even if a ₁ > 5% by weight, the NOx purification effect commensurate with the increase in the carried amount of the metal for the catalyst cannot be obtained. .

According to the above manufacturing method, the catalyst having the above characteristics can be easily mass-produced. However,
When the heating temperature T in the heat treatment is T <800 ° C., the phase change from the γ phase and / or the η phase to the α phase cannot be smoothly progressed, while when T> 1100 ° C., the upper limit of the α conversion rate R is increased. It becomes difficult to control the value (R = 95%).

[0014]

EXAMPLE An exhaust gas purifying catalyst is a mixture of a catalytic element and an aluminosilicate having solid acidity and molecular sieving property, and the catalytic element comprises alumina and a catalytic metal supported on the alumina.

As the alumina, modified alumina having an α phase is used, and as the metal for the catalyst, at least one selected from white metals, Pt in this embodiment is used. Further, as the aluminosilicate, unmodified zeolite, in this example, modified ZSM-5 zeolite obtained by subjecting unmodified ZSM-5 zeolite to de-Al treatment is used.

The alpha conversion rate R of the modified alumina is 0.1% ≦ R ≦
It is set to 95%, preferably 45% ≦ R ≦ 90%.
The α-ratio R was measured by the following method. (I) Commercially available α-alumina and γ-alumina (activated alumina) were blended in a predetermined weight ratio, and the respective blends were mixed while being pulverized in a mortar for 30 minutes. Table 1 shows the composition of each formulation (1)-(5).

[0017]

[Table 1] (ii) Powder X-ray diffraction was performed on each of the blends (2) to (5), and X-ray reflection on the {113} plane of α-alumina appeared at 2θ = 43.4 ± 0.2 ° in CuKα ray. The strength was measured. (iii) Assuming that the X-ray reflection intensity of the compound (5) is 100%, the X-ray reflection intensity ratios of the compounds (2) to (4) are calculated,
When the relationship between the weight ratio of α-alumina and the X-ray reflection intensity ratio was determined, the results shown in FIG. 1 were obtained.

As is apparent from FIG. 1, the weight ratio of α-alumina and the X-ray reflection intensity ratio are in direct proportion to each other. Therefore, the weight ratio of α-alumina is defined as the α conversion rate R, and the modified alumina is converted into α conversion. In determining the rate R, the X-ray reflection intensity of the {113} plane of α-alumina in the modified alumina was measured, and the X-ray reflection intensity ratio was calculated from the X-ray reflection intensity of the compound (5). The α conversion rate R is obtained from FIG. 1 based on the X-ray reflection intensity ratio.

When the α-ratio R is set as described above, the specific surface area of the modified alumina is as follows because it has an α phase.
It becomes smaller than that of activated alumina having γ phase and the like.
Therefore, when Pt is supported on this modified alumina,
Since the dispersibility of Pt is suppressed as compared with activated alumina,
The catalyst exhibits a relatively weak oxidizing ability with respect to HC.

As a result, HC is partially oxidized to NOx.
Active CHO having a reducing ability is generated, and this active CHO is produced.
Is generated in a wide exhaust gas temperature range and reformed Z
The SM-5 zeolite adsorbs and stores a part of the active CHO, and also releases a part of the active CHO to supply the active CHO.
NOx is reduced and purified by HO, and its purification temperature range is expanded.

Further, the modified alumina is a stable phase α
Since it has a phase, it does not easily cause pore closure and Pt burial due to phase change in the activated alumina, and thus has excellent heat resistance and a low degree of deterioration of catalytic activity at high temperature.

De-A for unmodified ZSM-5 zeolite
As the l treatment, at least one treatment of acid treatment, steam treatment and boiling water treatment is applied.

As the acid treatment, a 0.5 to 5N HCl solution is heated to 70 to 90 ° C., unmodified ZSM-5 zeolite is added to the HCl solution, and the mixture is stirred for 1 to 20 hours. The method is adopted.

For boiling water treatment, unmodified ZSM-
5 zeolite is treated with water, and the ambient temperature around the unmodified ZSM-5 zeolite in the water containing state is set to 550 to 60.
The temperature was raised to 0 ° C., and unmodified ZSM-5 was added to the high temperature atmosphere.
A method of holding the zeolite for about 4 hours is adopted.

Further, as steam treatment, unmodified ZS
M-5 zeolite containing 750 to 10% water content
A method of holding in an atmosphere of 900 ° C. for 10 to 20 hours is adopted.

These acid treatment, boiling water treatment and steam treatment are applied singly or in combination of two or more, and are repeated as necessary. Thus modified ZSM-5 zeolite is obtained, its SiO ₂ / Al ₂ O ₃ molar ratio of 2
5 to 800.

Such modified ZSM-5 zeolite is
The hydrophobic property is enhanced by the de-Al treatment, and the specific surface area is expanded by the removal of Al in addition to the basic skeleton structure of the unmodified ZSM-5 zeolite. Noh is improved. As a result, the modified ZSM-5 zeolite is
Exhibits good adsorption capacity for C and active CHO.

Furthermore, the modified ZSM-5 zeolite is free from Al.
Since the treatment improves the crystallinity and suppresses the generation of nuclei of thermal decomposition products, the heat resistance temperature is 100%.
It is raised to about 0 ℃.

In the above catalyst, in order to improve the NOx purification rate, when the compounding weight of the catalytic element is A and the compounding weight of the modified ZSM-5 zeolite is B, the weight ratio of the catalytic element is A ₁ = {A / (A + B)} × 100 is 1
It is set such that ₁ % by weight ≦ A ₁ <95% by weight.

In order to improve the NOx purification rate in the same manner as described above, when the Pt blending weight in the catalyst is a and the modified alumina blending weight is b, the Pt weight ratio a ₁ = {a / (A + b)} × 100 is 0.1% by weight <
It is set to a ₁ ≦ 5% by weight.

In producing the catalyst, basically, γ-
For activated alumina such as alumina, the heating temperature T is 800 ° C ≤
T ≦ 1100 ° C., preferably 900 ° C. ≦ T ≦ 1050 ° C.
The heat treatment set to
A step of obtaining a modified alumina having a phase and an α-ratio R of 0.1% ≦ R ≦ 95%, a step of supporting Pt on the modified alumina to obtain a catalytic element, and the catalytic element And the step of mixing the modified ZSM-5 zeolite with each other are sequentially performed.

In this case, after Pt is loaded on the modified alumina, the same heat treatment as described above may be performed to obtain the modified alumina from the activated alumina. Further, the form of the catalyst is not limited to the above mixture, and it is also possible to have a laminated structure having an upper layer made of a catalytic element and a lower layer made of modified ZSM-5 zeolite.

The loading of Pt on the modified alumina or activated alumina is carried out by immersing the modified alumina or the like in a hexachloroplatinic acid (H ₂ PtCl ₆ ) solution. In this case, the Pt weight ratio a ₁ is 0.1% by weight <
The Pt concentration of the hexachloroplatinic acid solution is adjusted so that a ₁ ≦ 5% by weight. As a platinum compound, Pt (N
Various compounds containing Pt such as H ₃ ) ₂ (NO ₂ ) ₂ are applicable.

Specific examples will be described below. A. Production of modified alumina Commercially available activated alumina (γ-alumina, α conversion R = 0%)
Then, using an electric furnace, heat treatment was performed in the atmosphere while changing the heating temperature T and the heating time to obtain various modified aluminas having different α conversion rates.

Table 2 shows the heat treatment conditions and the α conversion R for Examples 1 to 11 of modified alumina.

[0036]

[Table 2] B. Production of Modified ZSM-5 Zeolite (a) Na ₂ SiO ₂ / Al ₂ O ₃ Molar Ratio = 33.7
Type unmodified ZSM-5 zeolite 500g at 90 ° C for 5N
It was put into an HCl solution and then stirred for 20 hours to obtain a slurry. (B) The solid content was filtered off from the slurry, and the solid content was washed with 20 times the amount of pure water. (C) The solid content is subjected to a drying treatment in the atmosphere at 100 ° C. for 5 hours, and then the solid content after drying is dried in the air at 4
Lumped modified ZSM that has been subjected to calcination at 00 ° C for 12 hours
-5 zeolite was obtained. (D) The pulverized modified ZSM-5 zeolite was pulverized to obtain a powdered modified ZSM-5 zeolite. The modified SiO ₂ / Al ₂ O ₃ molar ratio of ZSM-5 zeolite is 41.3, thus it can be seen that the de-Al is occurring. The heat resistant temperature of the modified ZSM-5 zeolite is 1
It was 000 ° C. Example I A. Preparation of catalyst (a) Example 9 in Table 2, therefore the alpha conversion R = 81
% Modified alumina 98.5 g was added to a hexachloroplatinic acid solution 21.4 g (Pt concentration 7.0%) and mixed well, then the solid content was filtered off, and then the solid content was 120 ° C.,
A drying treatment under the conditions of 1 hour, more solids, in the atmosphere, 600 ° C., the weight ratio a ₁ of Pt subjected to baking treatment under conditions of 1 hour a ₁ = 1.5% by weight of the catalyst element Obtained. (B) 90 g of catalytic element, modified ZSM-5 zeolite 9
0 g, 20% silica sol 100 g and ethanol 24
0 g and alumina balls were placed in a pot and wet-milled for 12 hours to prepare a slurry catalyst. In this case, the weight ratio A ₁ of the catalyst element is A ₁ = 50% by weight.

A cordierite honeycomb support having a diameter of 25.5 mm, a length of 60 mm, and a size of 300 cells-10.5 mil was immersed in this slurry catalyst, and then the honeycomb support was taken out from the slurry catalyst to remove excess air. The catalyst is removed by spraying, then the honeycomb support is kept under heating at 120 ° C. to dry the slurry catalyst, and the honeycomb support is further subjected to a calcination treatment in the atmosphere at 600 ° C. for 1 hour to obtain the catalyst. Were held on the honeycomb support. In this case, the amount of catalyst retained on the honeycomb support was 150 g / liter. This catalyst is referred to as Example 1.

For comparison, a slurry catalyst was prepared by the same method as above except that the commercially available activated alumina was used as alumina, and the slurry catalyst and the same honeycomb support were used, and the same method as above. The catalyst was held on the honeycomb support. In this case, the amount of catalyst retained on the honeycomb support was the same as that described above, and this catalyst was used in Comparative Example 1
And B. Exhaust Gas Assumption Purification Test Assuming exhaust gas corresponding to the theoretical air-fuel ratio A / F = 14.6 and the air-fuel ratio A / F = 24.3 in an oxygen excess atmosphere, two types of compositions having the compositions shown in Table 3 are provided. First and second test gases were prepared.

[0039]

[Table 3] In the purification test, first, the catalyst of Example 1 was installed in a fixed-bed flow reactor, and then the first test gas was fed into the reactor with a space velocity S.V. V. = 5 × 10 ⁴ h ⁻¹ , the temperature of the first test gas was raised from room temperature at 20 ° C./min, and the purification rates of HC, CO, and NO were measured at a predetermined gas temperature. Further, the purification rate of HC and the like was measured by the same method as described above using the second test gas. Further, the same purification test was conducted on the catalyst of Comparative Example 1.

Table 4 shows various conditions and measurement results.

[0041]

[Table 4] As is clear from Table 4, the catalyst of Example 1 has a high purification rate of HC and the like, and in particular, the NO purification rate in an oxygen excess atmosphere such as the air-fuel ratio A / F = 24.3 is about 2 that of the catalyst of Comparative Example 1.
It is twice. This is due to the difference in the physical properties between the modified alumina having the α conversion rate R = 81% and the activated alumina having the α conversion rate R = 0% as described above. Example II Various catalysts were produced in the same manner as in Example I. In this case, the total compounding weight of the catalytic element and the modified ZSM-5 zeolite was set to 180 g as in Example I.

Table 5 shows the catalysts of Examples 1 to 6 and Comparative Example 1,
2 shows the α conversion rate R of reformed alumina, the composition, the maximum NO purification rate r, and the gas temperature when the purification rate r is obtained in the catalyst of No. 2.

In these catalysts, the Pt weight ratio a
₁ is a ₁ = 1.5% by weight (constant), and the weight ratio A _{1 of the} catalytic element is A ₁ = 25% by weight (constant), and the α conversion rate R of the modified alumina changes.

The purification test was performed in the same manner as in Example I, using the test second gas (A / F = 24.3) in Example I. This also applies to other catalysts described later.

[0045]

[Table 5] Table 6 shows the α conversion rate R, composition, and maximum NO purification rate r of the modified alumina in the catalysts of Examples 7 to 14 and the catalysts of Comparative Examples 3 and 4.
And the gas temperature at which the purification rate r is obtained.

In these catalysts, the Pt weight ratio a
₁ is a ₁ = 1.5% by weight (constant), and the weight ratio A _{1 of the} catalyst element is A ₁ = 50% by weight (constant), and the α conversion rate R of the modified alumina changes.

[0047]

[Table 6] Table 7 shows the α conversion rate R, the composition, the maximum NO purification rate r and the gas temperature when the purification rate r is obtained for the modified alumina in the catalysts of Examples 15 to 19 and the catalysts of Comparative Examples 5 and 6.

In these catalysts, the Pt weight ratio a
₁ is a ₁ = 1.5% by weight (constant), and the weight ratio A _{1 of the} catalytic element is A ₁ = 75% by weight (constant), and the α conversion rate R of the modified alumina changes.

[0049]

[Table 7] FIG. 2 is based on Tables 5 to 7, and shows the α conversion rate R of the modified alumina.
2 is a graph showing the relationship between the maximum NO purification rate r and the maximum NO purification rate r. In the figure, points 1 to 19 correspond to Examples 1 to 19, respectively, and points (1) to (6) correspond to Comparative Examples 1 to 6, respectively.

As is clear from FIG. 2 and Tables 5-7,
Alumina in the catalysts of Comparative Examples 1, 3 and 5 was activated alumina, and the α conversion rate R was R = 0%. Alumina in the catalysts of Comparative Examples 2, 4 and 6 was α-alumina, and the α conversion rate R was R = 100%. The maximum value of the maximum NO purification rate r in this case is 22% in the catalysts of Comparative Examples 1 and 3, and therefore, like the catalysts of Examples 1 to 19, the weight ratio A ₁ of the catalyst element is 11% by weight ≦ A. ₁ <
95% by weight, and the Pt weight ratio a ₁ is 0.1% by weight <
When a ₁ ≦ 5% by weight, the maximum NO is set by setting the α conversion ratio R of the modified alumina to 0.1% ≦ R ≦ 95%.
The purification rate r can be improved to r> 22% in an oxygen excess atmosphere. From Fig. 2, the alpha conversion rate R of the modified alumina
Is set to 45% ≦ R ≦ 90%, the maximum NO purification rate r
Can be further improved to 32% ≦ r ≦ 55%. From this, it is understood that the preferable range of the α conversion rate R of the modified alumina is 45% ≦ R ≦ 90%.

Table 8 shows the α conversion ratio R, composition of the modified alumina in the catalysts of Examples 20 to 25 and the catalysts of Comparative Examples 7 and 8.
The maximum NO purification rate r and the gas temperature when the purification rate r is obtained are shown.

In these catalysts, α of modified alumina is used.
The conversion rate R is R = 81% (constant), and the Pt weight ratio a ₁
Is a ₁ = 1.5% by weight (constant), and the weight ratio A ₁ of the catalyst element changes.

[0053]

[Table 8] FIG. 3 is based on Tables 5-8, and the alpha conversion rate R = 8 of the modified alumina.
2 is a graph showing the relationship between the weight ratio A ₁ of the catalytic element and the maximum NO purification rate r at 1% and Pt weight ratio a ₁ = 1.5 wt%. In the figure, points 6, 12, 1
9, 20 to 25 correspond to Examples 6, 12, 19, 20 to 25, respectively, and points (7) and (8) are Comparative Examples 7 and 8.
Respectively correspond to.

As is clear from FIG. 3 and Table 8, the weight ratio A ₁ of the catalyst element in the catalyst of Comparative Example 7 was A ₁ = 10.
% By weight, and that in the catalyst of Comparative Example 8 is A ₁
= 95% by weight. The maximum value of the maximum NO purification rate r in this case is 22% in the catalyst of Comparative Example 8, and therefore, like the catalysts of Examples 6, 12, 19, 20 to 25,
When the α conversion ratio R of the modified alumina is 0.1% ≦ R ≦ 95% and the Pt weight ratio a ₁ is 0.1% by weight <a ₁ ≦ 5% by weight, the weight ratio A ₁ of the catalytic element is 11%. Weight% ≤ A ₁ <
Maximum NO purification rate r by setting to 95% by weight
Can be improved to r> 22% in an oxygen excess atmosphere. From FIG. 3, the weight ratio A ₁ of the catalytic element is 1
By setting 2% by weight ≦ A ₁ ≦ 80% by weight, it is possible to improve the maximum NO purification rate r to r ≧ 36%. From this, the preferable range of the weight ratio A ₁ of the catalyst element is 12
It can be seen that weight% ≦ A ₁ ≦ 80% by weight.

Table 9 shows the catalysts of Examples 26 and 27 and Comparative Example 9
Ratio of modified alumina, composition, maximum N
The O purification rate r and the gas temperature when the purification rate r is obtained are shown.

In these catalysts, α of modified alumina is used.
The conversion rate R is R = 81% (constant), the weight ratio A _{1 of the} catalyst element is A ₁ = 50% by weight (constant), and the Pt weight ratio a ₁ changes.

[0057]

[Table 9] As is clear from Table 9, the Pt weight ratio a ₁ in the catalyst of Comparative Example 9 is a ₁ = 0.1% by weight. The maximum value of the maximum NO purification rate r in this case is 22%. Therefore, as in the catalysts of Examples 26 and 27, the α conversion rate of the modified alumina is 0.1% ≦ R ≦ 95%, and the catalytic element Weight ratio A
_{When 1} is 11% by weight ≦ A ₁ <95% by weight, the Pt weight ratio a _{1 is set} to 0.1% by weight <a ₁ ≦ 5% by weight to obtain the maximum NO purification rate r in the oxygen excess atmosphere. It can be improved to r> 22%.

[0058]

According to the present invention, by specifying the alpha conversion rate R of the modified alumina, the weight ratio A ₁ of the catalytic element and the weight ratio a _{1 of the} metal for the catalyst as described above, it is possible to achieve Can provide an exhaust gas purification catalyst having a high NOx purification rate.

Further, according to the present invention, it is possible to provide a manufacturing method capable of easily mass-producing the catalyst having the above characteristics.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the weight ratio of α-alumina and the X-ray reflection intensity ratio.

FIG. 2 is a graph showing the relationship between the alpha conversion rate of modified alumina and the maximum NO purification rate.

FIG. 3 is a graph showing the relationship between the weight ratio of catalyst elements and the maximum NO purification rate.

[Procedure amendment]

[Submission date] April 13, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

[0003]

However, when Pt is supported on activated alumina, since the activated alumina is porous and has a large specific surface area, Pt is highly dispersed, so that the HC adsorption capacity by Pt is high. Although the NOx adsorption capacity is improved, the oxygen excess atmosphere (for example,
When the air-fuel ratio A / F≈24), the catalyst causes HC
Complete oxidation of (hydrocarbon), that is, HC → CO ₂ + H ₂ O
Oxidation reaction of NOx progresses, and it is a partial oxide of HC and NOx
Insufficient production of active CHO with reducing ability
There is a problem that the reduction inhibitory action of oxygen adsorbed on the t surface is likely to occur, so that reduction and purification of NOx cannot be sufficiently performed , and the purification temperature range of the catalyst for NOx becomes narrow.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

In this case, after Pt is supported on the activated alumina, the same heat treatment as described above may be performed to obtain the modified alumina from the activated alumina. Further, the form of the catalyst is not limited to the above mixture, and it is also possible to have a laminated structure having an upper layer made of a catalytic element and a lower layer made of modified ZSM-5 zeolite.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 20/18 ZAB D B01D 53/36 104 A (72) Inventor Yoshiyuki Nakanishi Central 1 Wako, Saitama Prefecture 4-1-1 Stock Company Honda Technical Research Institute

Claims (4)

[Claims] 1. An exhaust gas purifying catalyst comprising a catalyst element and an aluminosilicate having solid acidity and molecular sieving property, wherein the catalyst element is an exhaust gas purifying catalyst comprising alumina and a catalyst metal supported on the alumina. Assuming that the modified alumina has an alpha conversion rate R set to 0.1% ≦ R ≦ 95%, the compounding weight of the catalyst element is A, and the compounding weight of the aluminosilicate is B, Weight ratio of catalyst element A ₁ = {A / (A + B)} × 100
Is set to 11% by weight ≦ A ₁ <95% by weight, the metal for catalyst is at least one metal selected from the platinum group, and the weight ratio a _{1 of the} metal for catalyst in the catalyst element is 0. An exhaust gas purifying catalyst, characterized in that 1 wt% <a ₁ ≤ 5 wt%. 2. The exhaust gas purifying catalyst according to claim 1, wherein the aluminosilicate is a modified zeolite obtained by subjecting an unmodified zeolite to a de-Al treatment. 3. The catalyst metal is Pt.
Or the exhaust gas purifying catalyst according to 2. 4. A heating temperature T of 800 ° C. is applied to activated alumina.
A step of performing a heat treatment set to ≦ T ≦ 1100 ° C. to obtain a modified alumina having an α conversion R of 0.1% ≦ R ≦ 95% from the activated alumina; A catalyst element is manufactured by supporting at least one selected catalyst metal, and the weight ratio a ₁ of the catalyst metal in the catalyst element is 0.1% by weight <a ₁ ≦ 5.
Mixing the step of setting to the weight%, the catalyst element, and aluminosilicate having solid acidity and molecular sieving property,
At that time, when the compounding weight of the catalyst element is A and the compounding weight of the aluminosilicate is B, the weight ratio A ₁ = {A / (A + B)} × 100 of the catalyst element is 11% by weight ≦ A method for producing an exhaust gas purifying catalyst, which comprises sequentially performing the step of setting A ₁ <95% by weight.