JPH0871427A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE: To obtain a catalyst having superior high-temp. durability. CONSTITUTION: A catalyst 11 made of a mixture of a crystalline aluminosilicate with a catalytic element is carried on a honeycomb body 2. The crystalline aluminosilicate has an irregular crystal structure formed by lacking part of the constituent elements of a crystalline aluminosilicate having a regular crystal structure and the single lattice volume (V1 ) of the irregular crystal structure calculated from the crystal lattice constant by an X-dry diffraction method is made smaller than the single lattice volume (V1 ) of the regular crystal structure calculated from the crystal lattice constant by an X-ray diffraction method (V1 <V2 ). The crystalline aluminosilicate of the catalyst 11 withstands 1,000 deg.C and has function to adsorb hydrocarbons at low temp. as well as superior heat resistance. The catalytic element consists of Al2 O3 particles and Pd carried on the particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst, and more particularly to a catalyst composed of a crystalline aluminosilicate and a catalytic element.

[0002]

2. Description of the Related Art Conventionally, in order to improve the purification rate of HC existing in low-temperature exhaust gas immediately after the engine is started, HC containing zeolite is provided upstream of the exhaust gas purification catalyst of the exhaust system.
There is known an exhaust gas purifying device provided with a suction adsorber (see Japanese Patent Laid-Open No. 2-75327). Further, a zeolite catalyst in which a metal such as Cu is supported on a zeolite by an ion exchange method is also known in order to improve the purification rate of NOx associated with the combustion of a lean air-fuel mixture in an oxygen excess state (JP-A-63).
(See Japanese Patent Publication No. 283727).

[0003]

Although the components of the exhaust gas purifying catalyst in the engine are required to have a heat resistance of 900 to 1000 ° C., the zeolite in the conventional apparatus and catalyst has a heat resistant temperature of about 700 ° C. Therefore, there is a problem that the high temperature durability of the adsorber and the catalyst is poor, and the performance is deteriorated in a short time. Further, since the conventional device requires an exhaust gas purifying catalyst and an adsorber,
There is also a problem that the configuration of the device becomes complicated.

In view of the above, the present invention has a function of adsorbing HC in the low temperature exhaust gas immediately after the engine is started, and H adsorbed as the temperature of the catalytic element rises due to the exhaust gas.
C and fresh HC can be immediately purified, and moreover, NOx accompanying combustion of a lean air-fuel mixture in an excess oxygen state.
It is an object of the present invention to provide an exhaust gas purifying catalyst which is capable of purifying exhaust gas, has excellent high-temperature durability, and has a simplified structure.

[0005]

An exhaust gas purifying catalyst according to the present invention comprises a mixture of a crystalline aluminosilicate and a catalytic element, and the crystalline aluminosilicate is a crystal having a regular crystal structure. In addition to having an anomalous crystal structure lacking some of the constituent elements of the basic aluminosilicate,
The single lattice volume V ₁ obtained from the crystal lattice constant of the irregular crystal structure by the X-ray diffraction method is smaller than the single lattice volume V ₂ obtained from the crystal lattice constant of the regular crystal structure by the X-ray diffraction method. The catalyst element is set to a small value (V ₁ <V ₂ ), and the catalyst element comprises a ceramic carrier and at least one of a catalyst metal and a catalyst metal oxide supported on the carrier. The metals forming the oxides are group Ib of the periodic table and group VIIa of the periodic table.
It is characterized in that it is at least one metal selected from at least one group selected from the group consisting of iron, iron and platinum.

The exhaust gas purifying catalyst according to the present invention is a crystal.
At least one layer of a hydrophobic aluminosilicate, and
A multilayer structure composed of at least one layer of a medium element.
And said crystalline aluminosilicate has a regular crystal structure
Of the constituent elements in crystalline aluminosilicates with
It has an anomalous crystal structure lacking parts, and its anomalous consequences.
Obtained from the crystal lattice constant by the X-ray diffraction method in the crystal structure
Single lattice volume V ₁In the regular crystal structure
Single lattice obtained from crystal lattice constant by X-ray diffraction method
Volume V₂Less than (V₁<V₂) Set to the catalyst
The element is a carrier made of ceramics and supported on the carrier.
At least one of a catalyst metal and a catalyst metal oxide
And constitutes the catalyst metal and metal oxide.
The metals are group Ib, group VIIa, iron and
At least selected from at least one group of the platinum group
It is a kind of metal.

[0007]

When the crystalline aluminosilicate is provided with the irregular crystal structure as described above, the heat resistance temperature is 900 to 10
The temperature rises to 00 ° C, and the catalyst using the same exhibits excellent high temperature durability.

Further, since the crystalline aluminosilicate is highly activated, it has a function of adsorbing HC in the low temperature exhaust gas at a high collection rate immediately after the engine is started.
Then, as the temperature of the exhaust gas rises, the adsorbed HC is released, so that the HC and new HC are immediately purified by the heated catalyst element. In addition, the catalyst using the crystalline aluminosilicate also exhibits a purifying ability for NOx accompanying the combustion of a lean air-fuel mixture in an oxygen excess state.

In this case, when the catalyst metal or the like is directly supported on the crystalline aluminosilicate, most of the catalyst metal or the like will be present in the fine pores, so that the catalyst is activated in the activated atmosphere in the fine pores. There is a risk that the metal for use in sintering will cause thermal deterioration of the catalyst, but as described above, the metal for catalyst is supported on the ceramic carrier and mixed with the crystalline aluminosilicate, or in a laminated structure with it. Then, the problem of thermal deterioration can be avoided.

Further, since the crystalline aluminosilicate and the catalyst element exist in a mixed or laminated state, the structure is simplified as compared with the conventional device.

[0011]

EXAMPLE FIG. 1 shows an example of a regular ZSM-5 type crystal structure possessed by a low activity ZSM-5 zeolite as a low activity aluminosilicate. In this crystal structure, Si and an element E (for example, B, which belongs to Group IIIa and / or Group IIIb of the periodic table) are included in an oxygen ring composed of 10 oxygens.
Al, Sc, Ga, Y, In, etc.) are bonded.

Low activity ZSM having such a crystal structure
When the -5 zeolite is activated to remove the element E, the silicon ring existing around the oxygen ring shrinks to fill the void lacking the element E, as shown in FIG. Along with this, the Si—O—Si bond angle expands from α in FIG. 1 to β (β> α), and as a result, the oxygen ring also contracts.

Since such a phenomenon occurs, the highly active ZSM which is the crystalline aluminosilicate according to the present invention.
-5 zeolite has an anomalous ZSM-5 type crystal structure (Fig. 2), and is determined as the product axbxc of lattice constants a, b, and c by X-ray diffraction due to contraction of oxygen ring and silicon ring. The single lattice volume V ₁ is reduced compared to a similar single lattice volume V ₂ in the regular ZSM-5 type crystal structure (ie, V ₁ <V ₂ ).

Since the contraction of the oxygen ring increases the surface energy inside the ring, the ZSM-5 zeolite after the activation treatment is highly activated and the heat resistance is also improved.

The single lattice volume V ₁ in the anomalous ZSM-5 type crystal structure is preferably V ₁ ≤5373Å ³ . When V ₁ > 5373Å ³ , the activity of the highly active ZSM-5 zeolite tends to decrease.

The low activity ZSM-5 zeolite is, due to its synthetic raw material, one or more metals selected from alkali metals, such as one or more metals selected from Na, K, or alkaline earth metals, such as, for example, It contains at least one metal of Ca and Mg. In the highly active ZSM-5 zeolite, the metal content C ₁ is preferably C ₁ ≦ 450 ppm in order to improve the activity.

Further, the low activity ZSM-5 zeolite may contain impurities which are at least one of Fe, Cu, Ni or Cr, which adversely affects the heat resistance thereof. In this case, the content ratio C _{2 of the} impurities is C _2. In order to improve heat resistance, it is desirable that C ₂ ≦ 200 ppm.

As the activation treatment, low activity ZSM-
The method of applying at least one treatment of acid treatment, steam treatment or boiling water treatment to 5 zeolite is adopted. During this activation treatment, alkali metals such as Na, Ca
Alkaline earth metals such as Fe, impurities such as Fe, etc.
It can be removed so that it fits in ₁ , C ₂ . Further, since the removal of alkali metal and alkaline earth metal is due to the replacement with hydrogen, the number of adsorption active sites in the pores of the highly active ZSM-5 zeolite increases, and the increase is evenly distributed throughout the pores. As a result, the adsorption capacity of the highly active ZSM-5 zeolite is improved.

As the acid treatment, a method of raising the temperature of a 0.5 to 5 N HCl solution to 70 to 90 ° C. and immersing the low activity ZSM-5 zeolite in the HCl solution for 5 to 20 hours is adopted. It

For boiling water treatment, low activity ZSM-
5 zeolite is treated with water, and the ambient temperature around the low activity ZSM-5 zeolite in the water containing state is 550 to 60.
A method of raising the temperature to 0 ° C. and holding it in the high temperature atmosphere for about 4 hours is adopted.

Further, for steam treatment, low activity ZS
M-5 zeolite containing about 10% water content 600-
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.

Next, a specific example will be described.

A. For high activity ZSM-5 zeolites Table 1 shows low activity ZSM-5 zeolites and
Related Examples 1-5 of Highly Active ZSM-5 Zeolites
Crystal lattice constants a, b, c and single lattice volume V ₁, V₂
Table 2 shows low activity ZSM-5 Zeola.
Ito Example 1 to 5 shows the activation treatment conditions,
Table 3 shows low activity ZSM-5 zeolite and high activity ZS.
Alkali metal Na in Examples 1-5 of M-5 zeolite
Content C₁, Impurity Fe content C₂And heat resistant temperature
And Examples 1 to 5 of highly active ZSM-5 zeolite
SiO₂/ Al₂O₃The molar ratios are shown.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]FIG. 3 shows the results of measurement by Si solid state NMR (nuclear magnetic resonance) method,
Example 1 of low activity and high activity ZSM-5 zeolite
Si chemical shift, δ (ppm) is shown. Highly active ZSM-
Si chemical shift of Example 1 of 5 zeolite, δ₁Is δ₁=-
112.43 ppm and low activity ZSM-5 Zeora
Si chemical shift of Example 1, δ₂Is δ ₂= -112.
31.

Here, Jay. M. Thomas (JM
Thomas' formula, α (or β) = (− 25.44)
-Δ) /0.5793, low and high activity ZSM
-5 Si-O-Si bond angle α in Example 1 of zeolite
And β were found, α = 149.96 °, β = 1
It was found to be 50.16 ° and therefore β> α. Therefore, V is between the two single lattice volumes V ₁ and V _2.
The relationship of ₁ <V ₂ is established. In this case, the removed element E is Al.

The heat resistant temperature measurements of Examples 1 to 5 of low activity and high activity ZSM-5 zeolites were carried out by the method described below. First, the BET specific surface area of each of Examples 1 to 5, that is, the initial BET specific surface area was measured, and then each of Examples 1 to 5 was measured to be 10
The sample was heated and heated in an air atmosphere containing 10% of water for 20 hours, and the BET specific surface area after heating was measured at every 25 ° C.
Then, the temperature when the BET specific surface area after heating maintains 95% of the initial BET specific surface area is set in each of Examples 1 to 5
The heat resistant temperature of

Highly active ZSM measured by such a method
The heat-resistant temperature in Examples 1 to 5 of -5 zeolite is 1000
° C, while low activity ZSM measured in a similar manner
-5 Zeolites Examples 1-5 (however, Examples 1 and 4 and 2
And 5 are the same), the heat resistant temperature was 725 ° C, and an improvement of 275 ° C was observed.

B. Catalyst 1 ₁ having a single-layer structure shown in FIG. 4 for an exhaust gas purifying catalyst, the fine particulate high activity ZS
A mixture of M-5 zeolite and a fine granular catalyst element, the catalyst _{11 of which} is supported on the honeycomb body 2.

The catalyst element comprises a fine granular ceramics carrier and at least one of a catalyst metal and a catalyst metal oxide supported on the carrier. As a ceramic carrier, chemically active γ-Al ₂ O ₃ , ZrO ₂ ,
Fine particles such as TiO ₂ , SiO ₂ , MgO and CeO ₂ are used. Further, the metal in the catalyst metal and the metal oxide for catalyst corresponds to at least one metal selected from at least one group selected from the group Ib of the periodic table, the group VIIa of the periodic table, the iron group and the platinum group. C in Ib group of the periodic table
u, Ag, Au are included, and M is included in Group VIIa of the periodic table.
n, Te, Re are included, and Fe, Co,
Ni is included, and the platinum group includes Ru, Rh, and P.
d, Os, Ir, Pt are included. C as required
e, Ba, La, Y, Nd, Sm, Gd, Nb, Zr,
Co-catalysts such as Ni, Fe and their oxides are used together.

[0033] The hitting the preparation of the catalyst 1 _1, first, for example a ceramic support was placed in a solution that dissolves the catalytic metal, produce a catalyst element by loading a catalyst metal on the support surface To do. Then, the highly active ZSM-5 zeolite and the catalyst element are mixed to prepare a slurry-like mixture,
The honeycomb body 2 is immersed in the slurry-like mixture, pulled up, and then the slurry-like mixture adhering to the honeycomb body 2 is dried to obtain the catalyst 11 ₁ .

FIG. Multilayer structure shown in 5, the catalyst 1 ₂ having a two-layer structure in the illustrated example, at least one layer made of a high activity ZSM-5 zeolite, that is the lower layer 3 _1, at least consisting of the same catalyst element It is composed of _two layers, that is, the upper layer 3 _2, and the catalyst 1 ₂ is supported on the honeycomb body 2.

[0035] The hitting the preparation of such catalysts 1 _2, first, a slurry-like material containing a highly active ZSM-5 zeolite was prepared, the honeycomb body 2 was immersed into the slurry-like material, honeycomb After pulled up The slurry attached to the body 2 is dried to form the lower layer 3 ₁ . Then, the honeycomb body 2 is dipped in the same slurry-like material containing a catalyst element and pulled up, and then the lower layer 3
_The slurry attached to ₁ is dried to form the upper layer 3 ₂ . When the upper layer 3 ₂ is composed of highly active ZSM-5 zeolite and the lower layer 3 ₁ is composed of a catalyst element, the dipping order of the honeycomb body 2 may be reversed in the above operation.

In the catalysts 1 ₁ and 1 ₂ , the particle size of the catalyst element is 0.05 μm or more and 50 μm or less. If the particle size is less than 0.05 μm, the flowability of exhaust gas deteriorates because the particle size of the catalyst element is too small. On the other hand, if the particle size exceeds 50 μm, the particle size of the carrier becomes large. The specific surface area of is reduced, the amount of the catalyst metal supported and the like is reduced, and the catalytic activity is reduced. Preferably,
The particle size of the catalyst element is 0.1 μm or more and 25 μm or less.

[I] HC Purifying Catalyst Using Highly Active ZSM-5 Zeolite Table 4 shows the structures of the catalysts of Examples 1 and 2 and Comparative Examples 1 to 6. In the table, zeolite means high activity ZSM-5 zeolite, and low activity means low activity ZSM-5 zeolite. CeO, BaO, ZrO as the co-catalyst
₂ was used. In addition, Examples 1 and 2 and Comparative Examples 1 and 3
A honeycomb body carrying up to 6 catalysts has a diameter of 25 m.
A cylindrical shape having a length of m and a length of 60 mm and having 300 cells / in ² was used.

[0038]

[Table 4] The catalyst of Example 1 was composed of a mixture of highly active ZSM-5 zeolite and a catalytic element in a single layer structure, and Example 2
The catalyst of (1) has a two-layer structure composed of a lower layer made of highly active ZSM-5 zeolite and an upper layer made of a catalytic element. The catalyst of Comparative Example 1 is composed of a highly active ZSM-5 zeolite carrying a catalytic metal by an ion exchange method,
Further, the catalysts of Comparative Examples 3 and 4 were composed of only catalytic elements,
Furthermore, the catalyst of Comparative Example 5 is composed of a mixture of low activity ZSM-5 zeolite and a catalytic element in a single layer structure, and further, the catalyst of Comparative Example 6 is composed of a lower layer of low activity ZSM-5 zeolite and a catalytic element. It has a two-layer structure consisting of the upper layer and the upper layer.

The catalyst of Comparative Example 2 is composed of highly active ZSM-5 zeolite supported on the first honeycomb body and catalyst elements supported on the second honeycomb body, and the first honeycomb body is located on the upstream side of the exhaust system. And the second honeycomb body is arranged on the downstream side thereof. The spacing between both honeycomb bodies was set to 5 mm. The honeycomb bodies have the same structure as described above, except that the length is 30 mm.

In order to investigate the initial performance of the catalysts of Example 1 and Comparative Examples 1 to 4, the following HC purification test was conducted and the HC purification rate by each catalyst was measured. Obtained.

The test shows that the composition is 0.5% by volume.
O ₂ , 400 ppm HC (C ₃ H ₆ ), 500 ppm NO,
5000ppm CO, 14vol% CO ₂ , 1700ppm H
₂ , 10% by volume H ₂ O and the balance N ₂ were passed through the test gas at a space velocity (SV) of 20000 h ⁻¹ in each honeycomb body (first and second honeycomb bodies in Comparative Example 2). The temperature of the test gas was raised to 50 to 350 ° C. at a heating rate of 3 to 15 ° C./sec, and the HC purification rate was measured during this period.

In FIG. 6, the line a indicates the catalyst of Example 1,
Lines b to e correspond to the catalysts of Comparative Examples 1 to 4, respectively. Line f shows the gas temperature. From FIG. 6, it can be seen that both the catalysts of Example 1 shown by line a and Comparative example 1 shown by line b have a high HC purification rate from a low gas temperature region to a high gas temperature region. This is due to the high activity Z in the region where the gas temperature is low.
This is because the SM-5 zeolite exerts a function of adsorbing low-temperature HC with a high collection rate, and the catalytic element exerts high HC purifying ability in a region where the gas temperature is high.

In the case of the catalyst of Comparative Example 2 shown by the line c, the HC purification rate is high in the region where the gas temperature is low, but in the region where the gas temperature is high, the temperature rise of the catalyst element carried by the second honeycomb body is the first. Since it is hindered by the honeycomb body, the HC purification rate is low. Since the catalysts of Comparative Examples 3 and 4 indicated by the lines d and e have no HC adsorption ability in the region where the gas temperature is low,
The purification rate is low.

Next, Examples 1 and 2 and Comparative Examples 1 and 3 to
The catalyst No. 6 was placed in the exhaust system of the engine and kept at a high temperature of 900 ° C. for 20 hours, and thereafter, in order to examine the performance after the durability test of each catalyst, the same HC purification test as described above was conducted. When the HC purification rate was measured by the method, the results shown in FIG. 7 were obtained.

The relationship between each line in FIG. 7 and each catalyst is shown in Table 5.
It is as follows. The line f shows the gas temperature as described above.

[0046]

[Table 5]From FIG. 7, line a₁, G₁The catalyst of Examples 1 and 2 shown in
b₁, E₁, D₁, H ₁, K₁Comparative Examples 1, 3 to 6
The HC purification rate after the durability test is higher than that of the above catalyst. this
Is a highly active ZSM-5 zeolite in Examples 1 and 2.
Both catalysts have excellent high temperature resistance
It has nothing to do with longevity. Especially the line g₁Shown by
The double-layered catalyst of Example 2 has a line a₁Of Example 1 shown in
It has a higher catalytic activity than the single layer structure catalyst.

In the case of the catalyst of Comparative Example 1 shown by the line b ₁ , since the highly active ZSM-5 zeolite exhibits heat resistance in the durability test, the highly active ZS-5 is used in the low gas temperature region.
The HC adsorption capacity of M-5 zeolite is obtained to show a high HC purification rate, but in the durability test, Pd which is a metal for a catalyst is used.
Due to the occurrence of sintering, the HC purification rate is low in a region where the gas temperature is high. In the case of the catalyst of Comparative Example 3 shown by the line d ₁ , the amount of Pt and Rh, which are the metal for the catalyst, was originally small, and since it was thermally deteriorated by the durability test, the HC purification rate was higher than that before the durability test. Drastically reduced. In the case of the catalyst of Comparative Example 4 shown by the line e ₁ , the degree of heat deterioration due to the durability test is relatively small, and therefore the decrease in the HC purification rate is small. Comparative Examples 5 and 6 indicated by lines h ₁ and k ₁
In the case of the above catalyst, low activity ZSM-
5 Zeolite is thermally deteriorated, so the HC purification rate is low.

FIG. 8 shows the elapsed time and H after the engine (displacement of 2000 cc) is started in the FTP LA-4 mode.
The relationship with the emission level of C is shown. In the figure, lines m, a ₂ , d
₂ shows the change of the HC component discharged from the engine. When the line m does not use a catalyst, the line a ₂ uses the catalyst of Example 1 after the durability test, and the line d ₂ shows the above. This is the case when the catalyst of Comparative Example 3 after the durability test was used.

As is apparent from FIG. 8, when the catalyst of Example 1 is used as shown by the line a ₂ , Comparative Example 3 shown by the line d ₂ is obtained.
Compared with the case where the catalyst of
% Or more.

[II] NOx Purifying Catalyst Using Highly Active ZSM-5 Zeolite Table 6 shows the structures of the catalysts of Examples 3 to 7 and Comparative Examples 7 and 8. In the table, zeolite means high activity ZSM-5 zeolite, and low activity means low activity ZSM-5 zeolite. As a honeycomb body carrying each catalyst,
A cylindrical shape with a diameter of 25 mm and a length of 60 mm is formed in the same manner as above.
A cell of 00 cells / in ² was used.

[0051]

[Table 6] The catalysts of Examples 3 to 5 were composed of a mixture of high activity ZSM-5 zeolite and a catalytic element in a single layer structure, and the catalyst of Example 6 was composed of a lower layer of high activity ZSM-5 zeolite and a catalytic element. Consists of a two-layer structure consisting of
Furthermore, the catalyst of Example 7 has a two-layer structure composed of a lower layer made of a catalytic element and an upper layer made of highly active ZSM-5 zeolite.

The catalyst of Comparative Example 7 is constituted by supporting a metal for catalyst on the low activity ZSM-5 zeolite by the ion exchange method, and the catalyst of Comparative Example 8 is composed of the low activity ZSM-5 zeolite and the catalyst element. It is composed of a mixture into a single layer structure.

In order to examine the initial performance of the catalysts of Examples 5 to 7 and Comparative Examples 7 and 8, the following NOx purification test assuming combustion of a lean air-fuel mixture was conducted. When the relationship with the NOx purification rate was investigated, the results shown in FIG. 9 were obtained.

The above test was conducted with the composition of 10% by volume O ₂ .
_{800ppm HC (C 3 H 6)} , 800ppm NO, 0.1
Volume% CO, 10 volume% CO ₂ , 500 ppm H ₂ , 10
A test gas of volume% H ₂ O and the balance of N ₂ was passed through each honeycomb body at a space velocity (SV) of 20000 h ⁻¹ and the temperature of the test gas was 25 to 400 ° C.
The temperature was raised at a heating rate of 10 to 40 ° C./min and the NOx purification rate was measured during this period.

In FIG. 9, lines n, o, and u represent the fifth embodiment.
6 and 7, respectively, and lines p and q correspond to the catalysts of Comparative Examples 7 and 8, respectively. As is clear from FIG. 9, each catalyst has a relatively good initial performance.

Next, the catalysts of Examples 3 to 7 and Comparative Examples 7 and 8 were placed in the exhaust system of the engine and kept at a high temperature of 700 ° C. for 20 hours, after which the performance of each catalyst after a durability test. In order to investigate the above, a NOx purification test similar to the above was conducted, and the NOx purification rate by each catalyst was measured, and the results in FIG. 10 were obtained.

Table 7 shows the relationship between each line in FIG. 10 and each catalyst.

[0058]

[Table 7] As is clear from FIG. 10, the lines r ₁ , s ₁ , n ₁ ,
The catalysts of Examples 3 to 7 indicated by o ₁ and u ₁ have the lines p ₁ and q _1.
NO after the durability test compared with the catalysts of Comparative Examples 7 and 8 shown in
x High purification rate. This is because the heat resistance of the highly active ZSM-5 zeolite in Examples 3 to 7 is good,
Each catalyst has excellent high temperature durability.
Further, similarly to the above, the two-layer structure catalysts of Examples 6 and 7 indicated by lines o ₁ and u ₁ have higher catalytic activity than the single-layer structure catalysts of Example 3 and the like indicated by lines r _{1 and the} like. In this case, the catalytic activities of both Examples 6 and 7 are almost the same.

The catalyst may be provided with two or more layers, such as a layer made of highly active ZSM-5 zeolite and a layer made of a catalyst element, which are alternately laminated.

[0060]

According to the first aspect of the present invention, a high HC purifying ability is exhibited immediately after the engine is started, and the NOx purifying ability due to the combustion of the lean air-fuel mixture in the oxygen excess state is also high, which is further excellent. It is possible to provide an exhaust gas purifying catalyst that has high temperature durability and has a simplified structure.

According to the second aspect of the present invention, it is possible to provide an exhaust gas purifying catalyst having a higher catalytic activity than the above case.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a regular ZSM-5 type crystal structure.

FIG. 2 is an explanatory diagram showing an anomalous ZSM-5 type crystal structure.

FIG. 3 is a graph showing Si chemical shifts for high activity and low activity ZSM-5 zeolites.

FIG. 4 is a cross-sectional view showing a catalyst having a single layer structure.

FIG. 5 is a cross-sectional view showing a catalyst having a two-layer structure.

FIG. 6 is a graph showing the relationship between the elapsed time after the start of gas flow and the HC purification rate in the initial performance test of each catalyst.

FIG. 7 is a graph showing the relationship between the elapsed time after the start of gas flow and the HC purification rate after the durability test of each catalyst.

FIG. 8 is a graph showing the relationship between the elapsed time after engine start and the HC emission level in the FTP LA-4 mode.

FIG. 9: Gas temperature and N in initial performance test of each catalyst
It is a graph which shows the relationship with Ox purification rate.

FIG. 10: Gas temperature and N after durability test of each catalyst
It is a graph which shows the relationship with Ox purification rate.

[Explanation of symbols]

1 ₁ , 1 ₂ catalyst 2 honeycomb body 3 ₁ lower layer 3 ₂ upper layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takahiro Naka Naka, 1-4-1 Chuo, Wako-shi, Saitama, Ltd., Honda R & D Co., Ltd. (72) Kaoru Fukuda 1-4-1 Chuo, Wako, Saitama Incorporated in Honda R & D Co., Ltd. (72) Inventor Tetsuo Endo 1-4-1 Chuo, Wako, Saitama Incorporated in R & D Co., Ltd.

Claims (7)

[Claims] 1. A mixture of a crystalline aluminosilicate and a catalytic element, wherein the crystalline aluminosilicate comprises:
A crystalline aluminosilicate having a regular crystal structure has an irregular crystal structure in which some of the constituent elements are absent, and the single lattice volume V ₁ obtained from the crystal lattice constant by the X-ray diffraction method in the irregular crystal structure Is set to be smaller than the single lattice volume V ₂ (V ₁ <V ₂ ) obtained from the crystal lattice constant by the X-ray diffraction method in the regular crystal structure, and the catalyst element is a ceramic carrier and The catalyst metal and the metal oxide, which are composed of at least one of a catalyst metal and a catalyst metal oxide supported on a carrier, are metals of Group Ib and VIIa of the Periodic Table.
An exhaust gas purifying catalyst comprising at least one metal selected from at least one group selected from the group consisting of iron, iron and platinum. 2. A multi-layer structure comprising at least one layer made of crystalline aluminosilicate and at least one layer made of catalyst element, wherein the crystalline aluminosilicate has a regular crystalline structure. The aluminosilicate has an anomalous crystal structure lacking some of the constituent elements, and the single lattice volume V ₁ obtained from the crystal lattice constant by the X-ray diffraction method in the anomalous crystal structure is expressed as X The catalyst element is set to be smaller than the single lattice volume V ₂ (V ₁ <V ₂ ) determined from the crystal lattice constant by the line diffraction method, and the catalyst element is a ceramic carrier and a catalyst metal supported on the carrier. And at least one of the metal oxide for catalyst, and the metal constituting the metal for catalyst and the metal oxide are Group Ib and Group V of the Periodic Table.
An exhaust gas purifying catalyst, which is at least one metal selected from at least one group of the IIa group, the iron group, and the platinum group. 3. The exhaust gas purifying catalyst according to claim 2, wherein an upper layer is made of the catalyst element and a lower layer is made of the crystalline aluminosilicate. 4. The exhaust gas purifying catalyst according to claim 2, wherein the upper layer is made of the crystalline aluminosilicate and the lower layer is made of the catalyst element. 5. The single lattice volume V ₁ in the irregular crystal structure is V ₁ ≦ 5373Å ³ ,
The exhaust gas purifying catalyst as described in 3 or 4. 6. At least one metal selected from the group consisting of one or more metals selected from alkali metals and one or more metals selected from alkaline earth metals, wherein the content C _{1 of the} metals is C ₁ ≦ 450 ppm. There are claims 1, 2, 3,
The exhaust gas purifying catalyst according to 4 or 5. 7. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst element is in the form of fine particles, and the particle size is 0.05 μm or more and 50 μm or less.