JPH06327978A - Catalyst for purifying waste gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purifying a waste gas having excellent high temp. durability by using a mixture of a modified crystalline aluminosilicate having specific crystal structure with a catalyst element. CONSTITUTION:The properties of the modified crystalline aluminosilcate used is such that alphax-ray reflecting intensity of at least one crystal plane (f) in plural crystal planes CF1<=2 in Miller index of (h), (k), (l) in a 1st crystal surface group >=40Angstrom in spacing of lattice plane is increased by >=4% than the X-ray reflecting intensity of the same crystal plane (f) in the unmodified one. The catalytic element is composed of a ceramic made carrier, a metal for catalyst carried on the carrier and/or a metal oxide for catalyst and the metal is selected from group Ib, group VII a, iron group and platinum group in periodical table. The heat resistance due to the crystal structure of the crystalline aluminosilicate is improved by producing the catalyst by mixing the aliminosilicate with the catalytic element or laminating both.

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 reformed modified crystalline aluminosilicate and a catalytic element.

[0002]

2. Description of the Related Art In the past, an exhaust gas component adsorber having zeolite was disposed upstream of an exhaust gas purification catalyst in an exhaust system in order to improve the purification rate of low-temperature exhaust gas immediately after engine startup. A gas purification device is known (see Japanese Patent Laid-Open No. 2-75327).

[0003]

The heat resistance of 900 to 1000 ° C. is required for the constituent elements of the exhaust gas purifying catalyst in the engine, but since the heat resistance temperature of zeolite in the conventional device is about 700 ° C., There is a problem that the high temperature durability of the adsorber is poor and the performance is deteriorated in a short time. Further, the conventional device requires an exhaust gas purifying catalyst and an adsorber, which complicates the configuration of the device.
There is also a problem.

In view of the above, the present invention has a function of adsorbing a low-temperature exhaust gas component immediately after the engine is started, and immediately purifies the adsorbed exhaust gas component and new exhaust gas as the temperature of the catalytic element rises due to the exhaust gas. It is an object of the present invention to provide the above exhaust gas purifying catalyst that is capable of achieving high temperature durability and has a simplified structure.

[0005]

An exhaust gas purifying catalyst according to the present invention comprises a mixture of a modified crystalline aluminosilicate and a catalyst element, and the modified crystalline aluminosilicate has a lattice spacing. In the first crystal plane group having a mirror index of 4.0 Å or more, at least one crystal plane f of a plurality of crystal planes CF ₁ having Miller indices h, k, and 1 of 2 or less.
Is subjected to a modification treatment so that the X-ray reflection intensity thereof is 4% or more than the X-ray reflection intensity of the same crystal plane f as the crystal plane f in the unmodified crystalline aluminosilicate,
The catalyst element comprises a ceramic carrier and at least one of a catalyst metal and a catalyst metal oxide supported on the carrier, and the metal constituting the catalyst metal and the metal oxide is a Group Ib group in the periodic table. , Group VIIa of the periodic table, at least one metal selected from the group consisting of the iron group and the platinum group.

The exhaust gas purifying catalyst according to the present invention comprises a lower layer made of a modified crystalline aluminosilicate and an upper layer made of a catalyst element laminated on the lower layer, and the modified crystalline aluminosilicate is used. In the first crystal plane group having a lattice spacing of 4.0 Å or more, Miller indices h, k,
The X-ray reflection intensity of at least one crystal plane f out of the plurality of crystal planes CF ₁ in which l is 2 or less is the same as that of the crystal plane f in the unmodified crystalline aluminosilicate. The catalyst element is subjected to a modification treatment so as to increase the line reflection intensity by 4% or more, and the catalyst element comprises a ceramic carrier and at least one of a catalyst metal and a catalyst metal oxide carried on the carrier. The metal for the catalyst and the metal constituting the metal oxide are Ib of the periodic table.
It is characterized in that it is at least one metal selected from at least one group selected from Group VIIa, Periodic Table Group VIIa, Iron Group and Platinum Group.

[0007]

When the crystal structure of the crystalline aluminosilicate is specified 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.

The reason why the heat resistance is improved is considered as follows. That is, the crystal face CF ₁ is a crystal plane due to the periodicity of the crystalline aluminosilicate unique cavity structure having a molecular micropores, the crystal plane CF ₁
The increase in the X-ray reflection intensity as described above means that the crystallinity of the crystal plane CF ₁ thereof is improved, which is a factor for improving the heat resistance.

Further, in a high temperature environment containing water, unmodified crystalline aluminosilicate causes structural destruction due to highly active high temperature water, but the modified crystalline aluminosilicate has excellent heat resistance. It is stable even under the harsh environment described above.

Generally, when the X-ray reflection intensity of a specific crystal plane is improved, it can be regarded as a change in orientation of the crystal (change in morphology), but in the case of the modified crystalline aluminosilicate, SEM observation, etc. Does not cause any change in morphology, and does not cause a decrease in the X-ray reflection intensity of the other complementary crystal faces that is observed when the orientation changes. Therefore, the modified crystalline aluminosilicate The change in the X-ray reflection intensity on the crystal plane is not due to the change in orientation, but is due to the periodicity of the cavity structure peculiar to the crystalline aluminosilicate.

Such a modified crystalline aluminosilicate has a function of adsorbing a low temperature exhaust gas component immediately after the engine is started with a high collection rate. Then, since the adsorbed exhaust gas component is released as the temperature of the exhaust gas rises, the exhaust gas component and new exhaust gas are immediately purified by the heated catalyst element.

In this case, if the catalytic metal or the like is directly supported on the modified crystalline aluminosilicate, most of the catalytic metal or the like will be present in the fine pores, so that in the activated atmosphere in the fine pores. However, the catalyst metal or the like may sinter to cause thermal deterioration of the catalyst, but as described above, the catalyst metal or the like is supported on the ceramic carrier and mixed with the modified crystalline aluminosilicate, or With the laminated structure, the problem of heat deterioration can be avoided.

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

[0014]

EXAMPLES A. About modified crystalline aluminosilicate Modified crystalline aluminosilicate is a modified crystalline aluminosilicate produced by subjecting unmodified mordenite as unmodified zeolite, unmodified ZSM-5 zeolite and the like to a predetermined modification treatment. Mordenite, modified ZSM-5 zeolite, and the like are applicable, and the modified mordenite and the like form fine particles.

The reforming process is performed in the following procedure.
(A) The fine granular unmodified zeolite was put into a treatment tank containing water, 12N HCl was gradually added, and the mixture was heated at a heating rate of 1.5 ° C / min for 1 hour. 90 ° C
And a HCl solution having a predetermined normality. (B) The unmodified zeolite is kept at this temperature for a predetermined time, and at the same time HC
l Stir the solution. In this case, a cooling tower is attached to the treatment tank to maintain the concentration of the HCl solution at the specified level. (C) Cool the HCl solution having a predetermined normality to room temperature under the condition of the temperature decreasing rate of 3 ° C./min. (D) The modified zeolite is taken out of the treatment tank, washed with pure water until pH 5 or more, and then dried. Impurities are removed during this modification process, and de-Alization occurs. [Example-I] In this example, unmodified ZSM-5 zeolite manufactured by the following method was used as the unmodified zeolite.

First, colloidal silica and aluminum nitrate are mixed so as to have a SiO ₂ / Al ₂ O ₃ molar ratio of 35.2, and tetrapropylammonium (TPA) is added to the mixed solution in a SiO ₂ / TPA molar ratio. To obtain an aqueous gel. Next, hydrothermal synthesis was carried out using an aqueous gel under the conditions of 10 atm, 150 ° C. and 350 hours, and then the synthetic product was subjected to a calcination treatment to remove TPA to obtain fine granular ZSM-5 zeolite. This ZSM
-5 zeolite SiO ₂ / Al ₂ O ₃ molar ratio is 35.
It was 2.

The unmodified ZSM-5 zeolite was treated as follows to obtain the modified ZSM-5 zeolites of Examples 1 and 2.

The modified ZSM-5 zeolite of Example 1 was prepared by adding the same amount of pure water to the unmodified ZSM-5 zeolite and maintaining the wet ZSM-5 zeolite in an atmosphere of 800 ° C. for 3 hours. Then 90 ° C HCl solution normality
The modification treatment was performed under the conditions of a 5 N, 90 ° C. constant temperature holding time of 20 hours. The particle size of Example 1 is 1-3 μm.

The modified ZSM-5 zeolite of Example 2 was prepared by adding the same amount of pure water to the unmodified ZSM-5 zeolite and maintaining the wet ZSM-5 zeolite in an atmosphere of 500 ° C. for 3 hours. Then, the same modification treatment as in Example 1 was performed, and then the atmosphere holding and the modification treatment were repeated twice. The particle size of Example 2 is 4-7 μm.

FIG. 1 shows the X of unmodified ZSM-5 zeolite.
The line diffraction result is shown.

Each peak of the first crystal plane group having a lattice spacing of 4.0 Å or more appears at an angle 2θ of 2θ ≦ 22 °. Therefore, in the first crystal plane group, (101) plane / (01
1) plane, (200) plane / (020) plane, (102) plane,
The (301) plane, the (202) plane, and the (232) plane are included. Here, a plurality of crystal planes CF ₁ having Miller indices h, k, and 1 of 2 or less are (101) plane / (011)
Plane, (200) plane / (020) plane, (102) plane, (2
02) surface is applicable. These crystal planes CF ₁ are ZSM-
5 This is a crystal plane due to the periodicity of the cavity structure peculiar to zeolite.

Each peak of the second crystal plane group having a lattice plane spacing of 3 Å or more and less than 4 Å has an angle 2θ of 22 ° <2θ ≦ 30.
Appearing in °, and therefore the second crystallographic group is (501)
Planes, (303) planes, and (133) planes are included. This second
Out of the crystal plane group, the crystal plane CF showing the maximum X-ray reflection intensity
_The (501) plane corresponds to 2. This (501) plane is Z
It is a crystal plane resulting from the basic skeleton structure of SM-5 zeolite.

FIGS. 2 and 3 show the modified ZSM-5 Ze of Examples 1 and 2.
The X-ray diffraction results of olite are shown respectively. 1 and 2
3 and FIG. 3, the crystal plane CF₁X-ray reflection
The strength I (cps) is the binding of unmodified ZSM-5 zeolite.
Crystal face CF₁X-ray reflection intensity I ₀More than (cps)
You can see that

Table 1 shows the crystal plane CF ₁ of the modified ZSM-5 zeolites of Examples 1 and 2, thus (101) / (01
1) Increasing rate of X-ray reflection intensity on crystal planes and crystal plane C
The change rate of the X-ray reflection intensity of F ₂ and thus the (501) plane is shown. The rate of increase and the rate of change are {(I−I ₀ ) ×
It was calculated | required as _I0 } * 100 (%).

[0025]

[Table 1] Modified ZSM-5 zeolites of Examples 1 and 2 and unmodified ZS
Regarding M-5 zeolite, heating temperature 600 in air
The heat deterioration test was conducted under the conditions of ˜1100 ° C. and heating time of 18 hours, and then powder X-ray diffraction by Cu—Kα ray was carried out for Example 1 and the like to observe the state of crystal destruction by heat. Got

In Table 2, "○" indicates that the X-ray reflection intensity did not change even after the test, and "△" indicates that the decrease rate of the X-ray reflection intensity after the test was 1.
It shows the case where it is less than 0%, and the mark "x" shows the case where the reduction rate of the X-ray reflection intensity after the test is 10% or more.

[0027]

[Table 2] As is clear from Tables 1 and 2, the modified ZSM-of Examples 1 and 2
In 5 zeolite, at least one crystal face f of the plurality of crystal faces CF ₁ , in these examples all crystal faces, that is,
(101) plane, (200) plane, (102) plane and (2
Due to the fact that the increase rate of the X-ray reflection intensity on the (02) plane is 4% or more, the heat resistant temperature is improved to 1000 ° C.

Further, in the modified ZSM-5 zeolites of Examples 1 and ₂ , the change rate of the X-ray reflection intensity on the crystal plane CF ₂ and hence on the (501) plane was small, and the X-ray reflection intensity was not modified. Quality ZSM-5 zeolite. As a result, 100
It can be seen that the basic skeleton structure of ZSM-5 zeolite is hardly destroyed in the temperature range of 0 ° C or lower.

From the above facts, the heat-resistant modified zeolites of Examples 1 and 2 were caused by the periodicity of the cavity structure peculiar to zeolite, without affecting the ZSM-5 zeolite and therefore the basic skeleton structure of the zeolite. It can be said that only the crystal plane CF ₁ is changed. Therefore, even if the X-ray reflection intensity of the crystal plane CF ₁ is improved by the modification treatment, if the X-ray reflection intensity of the crystal plane CF ₂ is decreased, the heat resistance of the modified zeolite is decreased. EXAMPLE -II] In this example, as the non-modified zeolite, a commercially available powdered Na-type unmodified mordenite (SiO ₂ / Al ₂
O ₃ molar ratio = 16.6) was used. Table 3 shows the normality of the 90 ° C. HCl solution and the 90 ° C. constant temperature holding time in the modifying treatment of the modified mordenites of Examples 3 and 4. Examples 3, 4
Has a particle size of 4 to 7 μm.

[0030]

[Table 3] FIG. 4 shows the X-ray diffraction results of unmodified mordenite.

Each peak of the first crystal plane group having a lattice spacing of 4.0 Å or more appears at an angle 2θ of 2θ ≦ 22 °. Therefore, the first crystal plane group has a Miller index (hereinafter the same). And (110) plane, (020) plane, (200) plane,
(111) plane, (130) plane, (310) plane, (33
0) plane / (400) plane are included. Here, a plurality of crystal planes CF ₁ whose Miller indices h, k, and l are 2 or less, respectively.
Has (110) plane, (020) plane, (200) plane, (1
11) Face is applicable. These crystal planes CF ₁ are crystal planes due to the periodicity of the cavity structure peculiar to mordenite.

Each peak of the second crystal plane group having a lattice plane spacing of 3 Å or more and less than 4 Å has an angle 2θ of 22 ° <2θ ≦ 30.
Appear in °, and therefore the second group of crystal planes is (150)
Plane, (241) plane, (002) plane, (202) plane, (3
The (50) plane and the (132) plane / (511) plane / (530) plane are included. The (202) plane corresponds to the crystal plane CF ₂ showing the maximum X-ray reflection intensity in the second crystal plane group. The (202) plane is a crystal plane mainly due to the basic skeleton structure of mordenite composed of SiO ₄ tetrahedra.

5 and 6 show the X-ray diffraction results of the modified mordenites of Examples 3 and 4, respectively. 4 and 5 and 6
When compared with, the X-ray reflection intensity I of the crystal plane CF ₁
(Cps) is X of the crystal plane CF ₁ of unmodified mordenite
It can be seen that the line reflection intensity is higher than I ₀ (cps).

Table 4 shows the crystal planes CF ₁ of the modified mordenites of Examples 3 and 4, and thus the (110) plane, the (020) plane,
The rate of increase in X-ray reflection intensity on the (200) plane and the like, and the rate of change in crystal plane CF ₂ , and thus the X-ray reflection intensity of the (202) plane, are shown. These rate of increase and rate of change are {(II
₀ ) / I ₀ } × 100 (%).

[0035]

[Table 4] The modified mordenite and the unmodified mordenite of Examples 3 and 4 were heated in the air at a heating temperature of 600 to 1100 ° C.
A heat deterioration test was performed under the condition of heating time of 18 hours, and then powder X-ray diffraction by Cu-Kα ray was performed on Example 3 and the like to observe the state of crystal breakdown by heat, and the results in Table 5 were obtained.

In Table 5, “◯” indicates that the X-ray reflection intensity did not change after the test, and “Δ” indicates that the decrease rate of the X-ray reflection intensity after the test was 1.
It shows the case where it is less than 0%, and the mark "x" shows the case where the reduction rate of the X-ray reflection intensity after the test is 10% or more.

[0037]

[Table 5] As is clear from Tables 4 and 5, in the modified mordenites of Examples 3 and 4, at least one crystal plane f of the plurality of crystal planes CF ₁ , and in all of these examples, (11)
0) plane, (020) plane, (200) plane and (111) plane
Due to the fact that the increase rate of the X-ray reflection intensity on the surface is 4% or more, the heat resistant temperature is improved to 900 to 1000 ° C.

In the modified mordenites of Examples 3 and 4, the crystal plane CF ₂ and therefore the X in the (202) plane were used.
The change rate of the line reflection intensity is small, and the X-ray reflection intensity is almost equal to that of the unmodified mordenite. This allows
The thermal deterioration test also shows that the basic skeleton structure of mordenite is hardly destroyed in the temperature range of 900 to 1000 ° C. or less.

B. Catalyst 1 ₁ having a single-layer structure shown in FIG. 7 for the exhaust gas purifying catalyst, the fine particulate modified ZSM
-5 Zeolite or modified mordenite is mixed with fine granular catalyst elements, and the catalyst ₁₁ is supported on the honeycomb body 2.

The catalyst element comprises a fine granular ceramic carrier and at least one of a catalyst metal and a catalyst metal oxide carried on the carrier.

As the ceramic carrier, chemically active γ-Al ₂ O ₃ , ZrO ₂ , TiO ₂ , SiO ₂ and M are used.
Fine particles such as gO and CeO ₂ are used, and the metal in the catalyst metal and the metal oxide for the catalyst is Ib of the periodic table.
At least one metal selected from the group, at least one group from Group VIIa of the Periodic Table, the iron group and the platinum group is applicable. The group Ib of the periodic table contains Cu, Ag and Au, the group VIIa of the periodic table contains Mn, Te and Re, and the iron group contains Fe, Co and Ni, and also platinum. The group includes Ru, Rh, Pd, Os, Ir and Pt. If necessary, Ce, B, La, Y, Nd, Sm,
A cocatalyst such as Gd, Nb, Zr, Ni, Fe and their oxides is used in combination.

The hitting the preparation of the catalyst 1 _1, first, for example, by dissolving a catalyst metal to ceramic carrier was introduced into the solution and, on the carrier surface, by supporting the catalyst metal mainly by ionic bonds To produce a catalytic element. Then, for example, the modified 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, and the slurry-like mixture adhered to the honeycomb body 2 after being pulled up is removed. The catalyst 1 ₁ is obtained by drying.

[0043] Catalyst 1 ₂ having a two-layer structure shown in FIG. 8, for example, the lower layer 3 ₁ made of modified ZSM-5 zeolite, the upper layer 3 made of the same catalyst element are stacked on the lower layer 3 _1
2 and the catalyst 1 ₂ is supported on the honeycomb body 2.

Such a catalyst 1₂When manufacturing
First, a slurry-like material containing modified ZSM-5 zeolite was prepared.
Then, immerse the honeycomb body 2 in the slurry and pull it up.
After that, the slurry-like material adhered to the honeycomb body 2 is dried to form a lower layer.
Three₁To form. Then, a catalyst containing a catalyst element similar to the above.
After immersing the honeycomb body 2 in the slurry and pulling it up, the lower layer 3 ₁
The slurry-like material adhered to is dried to form the upper layer 3₂To form.

In the catalysts 1 ₁ and 1 ₂ , the catalyst element has a particle size of 0.05 μm or more and 5 μm or less. If the particle size is less than 0.05 μm, the particle size of the catalyst element is too small, so that the flowability of exhaust gas deteriorates, while if it exceeds 5 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 2 μm or less.

[I] Regarding HC Purifying Catalyst Using Modified ZSM-5 Zeolite Table 6 shows the structures of the catalysts of Examples 1 and 2 and Comparative Examples 1 to 6. In the table, modified zeolite means modified ZSM-5 zeolite, and unmodified means unmodified ZSM-5 zeolite. CeO, BaO, Zr as a co-catalyst
O ₂ was used. In addition, Examples 1 and 2 and Comparative Example 1,
A honeycomb body carrying 3 to 6 catalysts has a diameter of 25.
A cylindrical shape having a length of 60 mm and a size of 300 cells / in ³ was used.

[0047]

[Table 6] The catalyst of Example 1 is composed of a mixture of modified ZSM-5 zeolite and a catalytic element in a single layer structure, and the catalyst of Example 2 is a lower layer of modified ZSM-5 zeolite and an upper layer of catalytic element. It is composed of two layers. The catalyst of Comparative Example 1 is constituted by supporting a modified ZSM-5 zeolite with a metal for catalyst by an ion exchange method, and the catalysts of Comparative Examples 3 and 4 are constituted by only catalytic elements. Is composed of a mixture of unmodified ZSM-5 zeolite and a catalytic element in a single layer structure, and the catalyst of Comparative Example 6 is composed of a lower layer composed of unmodified ZSM-5 zeolite and an upper layer composed of a catalytic element. It has a two-layer structure.

The catalyst of Comparative Example 2 is composed of the modified ZSM-5 zeolite supported on the first honeycomb body and the catalyst element supported on the second honeycomb body, and the first honeycomb body is 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 above 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 each honeycomb body (first and second honeycomb bodies in Comparative Example 2) at a space velocity (S.V.) of 20000 h ⁻¹ . 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. 9, 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. 9, 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 because the reformed ZS is used in the region where the gas temperature is low.
This is because the M-5 zeolite exhibits a function of adsorbing low-temperature HC with a high collection rate, and that the catalyst element exhibits a high HC purification ability in a region where the gas temperature is high.

In the case of the catalyst of Comparative Example 2 indicated 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
Got the result.

Table 7 shows the relationship between each line in FIG. 10 and each catalyst. The line f shows the gas temperature as described above.

[0055]

[Table 7] From FIG. 10, the catalysts of Examples 1 and 2 shown by lines a ₁ and g ₁ are comparative examples ₁ and 3 shown by lines b ₁ , e ₁ , d ₁ , h ₁ and k ₁ respectively.
The HC purification rate after the durability test is higher than that of the catalyst of No. 6. This is nothing but that both catalysts have excellent high-temperature durability because the modified ZSM-5 zeolites of Examples 1 and 2 have good heat resistance. In particular, the two-layer structure catalyst of Example 2 shown by the line g ₁ has higher catalytic activity than the single-layer structure catalyst of Example 1 shown by the line a ₁ .

In the case of the catalyst of Comparative Example 1 shown by the line b ₁ , the modified ZSM-5 zeolite exhibits heat resistance in the above durability test, so that the modified ZSM-zeolite is used in the low gas temperature region.
5 shows high HC purification rate by obtaining HC adsorption capacity of zeolite, but due to sintering of Pd, which is a metal for catalyst, in the durability test, HC purification rate in high gas temperature region Is low. In the case of the catalyst of Comparative Example 3 shown by the line d ₁ , the amount of Pt and Rh that are catalyst metals was originally small, and the HC purification rate was higher than that before the durability test because it was thermally deteriorated by 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. In the case of the catalysts of Comparative Examples 5 and 6 indicated by the lines h ₁ and k ₁ , the unmodified ZSM-5 zeolite is thermally deteriorated by the heat resistance test, so that the HC purification rate is low.

FIG. 11 shows the relationship between the elapsed time after starting the engine (displacement of 2000 cc) and the emission level of HC in the FTP LA-4 mode. In the figure, lines m, a ₂ ,
d ₂ represents the change of the HC component discharged from the engine,
When the line a ₂ uses the catalyst of Example 1 after the durability test, the line m ₂ does not use the catalyst, and the line d ₂ uses the catalyst of Comparative Example 3 after the durability test. Applicable to each

As is apparent from FIG. 11, when the catalyst of Example 1 shown by line a ₂ is used, the emission level of HC is higher than that when the catalyst of Comparative Example 3 shown by line d ₂ is used. 5
It can be reduced by 0% or more.

[II] NOx Purifying Catalyst Using Modified Zeolite Table 8 shows the structures of the catalysts of Examples 3 to 7 and Comparative Examples 7 and 8. In the table, modified zeolite means modified ZSM-5 zeolite (Example 1) or modified mordenite (Example 3), and unmodified means unmodified ZSM-5 zeolite. As a honeycomb body supporting each catalyst, a cylindrical shape having a diameter of 25 mm and a length of 60 mm was formed in the same manner as described above, and 300 cells /
in ³ was used.

[0060]

[Table 8] The catalysts of Examples 3 to 5 are composed of a mixture of the modified ZSM-5 zeolite and the catalyst element in a single layer structure, and the catalyst of Example 6 is the lower layer of ZSM-5 zeolite and the upper layer of the catalyst element. And a two-layer structure, and the catalyst of Example 7 has a single-layer structure of a mixture of modified mordenite and a catalytic element.

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

In order to examine the initial performance of the catalysts of Examples 5 and 6 and Comparative Examples 7 and 8, the following lean NOx purification test was conducted, and the relationship between the gas temperature and the NOx purification rate of each catalyst was determined. Upon examination, the results shown in FIG. 12 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. 12, lines n and o represent the fifth and sixth embodiments.
And the lines p and q correspond to Comparative Examples 7 and 8, respectively.
Of the catalysts. As is apparent from FIG. 12, each catalyst has 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. 13 were obtained.

Table 9 shows the relationship between each line in FIG. 13 and each catalyst.

[0067]

[Table 9] As is clear from FIG. 13, the lines r ₁ , s ₁ , n ₁ ,
The catalysts of Examples 3 to 7 indicated by o ₁ and t 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 the modified Z in Examples 3-7.
Since the SM-5 zeolite and the modified mordenite have good heat resistance, each catalyst has excellent high temperature durability. Further, similarly to the above, the two-layer structure catalyst of Example 6 shown by the line o ₁ has higher catalytic activity than the single-layer structure catalyst of Example 3 shown by the line r ₁ etc.

[0068]

According to the invention described in claim 1, there is provided an exhaust gas purifying catalyst which exhibits a high exhaust gas purifying ability immediately after the engine is started, has an excellent high temperature durability and has a simplified structure. Can be provided.

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 X-ray diffraction pattern of unmodified ZSM-5 zeolite.

2 is an X-ray diffractogram of the modified ZSM-5 zeolite of Example 1. FIG.

FIG. 3 is an X-ray diffraction pattern of the modified ZSM-5 zeolite of Example 2.

FIG. 4 is an X-ray diffraction pattern of unmodified mordenite.

5 is an X-ray diffraction diagram of modified mordenite of Example 3. FIG.

6 is an X-ray diffraction pattern of modified mordenite of Example 4. FIG.

FIG. 7 is a cross-sectional view showing a catalyst having a single layer structure.

FIG. 8 is a cross-sectional view showing a catalyst having a two-layer structure.

FIG. 9 is a graph showing the relationship between the elapsed time after the start of gas distribution and the HC purification rate in the initial performance test of each catalyst.

FIG. 10 is a graph showing the relationship between the elapsed time after the start of gas distribution and the HC purification rate after the durability test of each catalyst.

FIG. 11 is a graph showing the relationship between the elapsed time after the engine is started and the HC emission level in the FTP LA-4 mode.

FIG. 12 is a graph showing the relationship between the gas temperature and the NOx purification rate in the initial performance test of each catalyst.

FIG. 13: 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 the front page (72) Inventor Kazuhide Terada 1-4-1, Chuo, Wako-shi, Saitama, Honda R & D Co., Ltd. (72) Inventor Yoshikazu Fujisawa 1-4-1, Chuo, Wako-shi, Saitama No. Stock Company Honda Technical Research Institute

Claims (5)

[Claims] 1. A mixture of a modified crystalline aluminosilicate and a catalytic element, wherein the modified crystalline aluminosilicate has a lattice spacing of 4.0 Å or more in a first crystal plane group, The X-ray reflection intensity of at least one crystal plane f of the plurality of crystal planes CF ₁ having Miller indices h, k, and 1 of 2 or less is the same as the crystal plane f of the unmodified crystalline aluminosilicate. Is subjected to a modification treatment so as to increase by 4% or more than the X-ray reflection intensity of the crystal plane f of the catalyst element, and the catalyst element is a ceramic carrier, and the catalyst metal and the catalyst metal carried on the carrier. The metal for at least one of the oxides, which constitutes the metal for the catalyst and the metal oxide, is Group Ib of the Periodic Table, 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 lower layer made of a modified crystalline aluminosilicate and an upper layer made of a catalyst element laminated on the lower layer, wherein the modified crystalline aluminosilicate has a lattice spacing of 4.0Å. In the above first crystal plane group,
The X-ray reflection intensity of at least one crystal plane f of the plurality of crystal planes CF ₁ having Miller indices h, k, and 1 of 2 or less is the same as the crystal plane f of the unmodified crystalline aluminosilicate. Is subjected to a modification treatment so as to increase by 4% or more than the X-ray reflection intensity of the crystal plane f of the catalyst element, and the catalyst element is a ceramic carrier, and the catalyst metal and the catalyst metal carried on the carrier. The metal for the catalyst and the metal constituting the metal oxide, which is composed of at least one of oxides, is at least one selected from at least one group of Ib group, VIIa group, iron group and platinum group of the periodic table. An exhaust gas purifying catalyst characterized by being a metal of 3. As the modified crystalline aluminosilicate, a second crystal plane group having a lattice spacing of 3 Å or more and less than 4 Å has a maximum X-ray reflection intensity of X ₂ of a crystal plane CF ₂ .
Line reflection intensity is used substantially equal to the X-ray reflection intensity of crystal face CF ₂ identical to the crystal plane CF ₂ in the crystalline aluminosilicate unmodified, for purifying exhaust gases according to claim 1 or 2, wherein catalyst. 4. The exhaust gas purifying catalyst according to claim 1, wherein the modified crystalline aluminosilicate is one of modified mordenite and modified ZSM-5 zeolite. 5. The catalyst element is in the form of fine particles, and the particle size is 0.05 μm or more and 5 μm or less.
The exhaust gas purifying catalyst according to 2, 3, or 4.