JP2003326137A - Exhaust gas purification method and catalyst for exhaust gas purification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress reduction of HC adsorption capacity by using zeolite with a large Si/Al ratio and secure the same high cracking capacity as that of zeolite having a small Si/Al ratio. <P>SOLUTION: A catalyst for exhaust gas comprises a support layer containing zeolite selected from mordenite, ZSM-5 and Y-type zeolite, a noble metal and a solid superacid which are carried by the support layer. The support layer is composed of zeolite which has a molar ratio (Si/Al) of 150 or more and is subjected to superacidification, a porous support body, and an oxygen releasing material in a rich atmosphere. The noble metal is carried by at least either the porous support body or the oxygen releasing material. Al removal is hardly caused, thus reduction of HC adsorption capacity with the passage of time is prevented. Characteristic to crack SOF is secured by superacidification and reduction purification rate of NO<SB>x</SB>is highly improved by HC produced through cracking. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purification method and
The present invention relates to an exhaust gas purifying catalyst. This method and catalyst is
The carbon monoxide (CO) and hydrocarbons (HC) contained in the
If it contains more oxygen than is needed to convert
At that time, the nitrogen oxides (NO _x)
It is suitable when

[0002]

2. Description of the Related Art A three-way catalyst for purifying exhaust gas by simultaneously oxidizing CO and HC and reducing NO _x is used as an exhaust gas purification catalyst for automobiles. As such a catalyst, for example, a porous carrier layer made of γ-alumina is formed on a heat-resistant carrier substrate such as cordierite, and the carrier layer is formed on the carrier layer.
Those carrying a noble metal such as Pt, Pd, and Rh are widely known.

By the way, the purification performance of such an exhaust gas purifying catalyst greatly differs depending on the air-fuel ratio (A / F) of the engine. That is, on the lean side where the air-fuel ratio is large, that is, the fuel concentration is lean, the amount of oxygen in the exhaust gas increases,
While the oxidation reaction that purifies CO and HC is active, the reduction reaction that purifies NO _x becomes inactive. On the contrary, on the rich side where the air-fuel ratio is small, that is, the fuel concentration is high, the amount of oxygen in the exhaust gas is small and the oxidation reaction becomes inactive, but the reduction reaction becomes active.

On the other hand, when driving an automobile, acceleration and deceleration are frequently performed in urban areas, and the air-fuel ratio frequently changes within the range from near stoichiometric (theoretical air-fuel ratio) to the rich state. In order to meet the demand for low fuel consumption in such traveling, lean burn control for supplying an oxygen-rich mixture as much as possible is necessary. However, the exhaust gas from the lean burn engine has a large amount of oxygen, and the reduction reaction for purifying NO _x is inactive. Therefore, there is a demand for the development of an exhaust gas purifying catalyst that can sufficiently purify NO _x in exhaust gas from a lean burn engine that contains a large amount of oxygen.

Therefore, conventionally, a catalyst for purifying exhaust gas has been proposed which employs a zeolite such as mordenite having HC adsorbing ability as a catalyst supporting layer (see, for example, JP-A-04-11).
8030 publication). In this exhaust gas purifying catalyst, HC in the exhaust gas is adsorbed while the temperature of the exhaust gas is low, and the adsorbed HC is released when the temperature of the exhaust gas rises, whereby NO _x in the exhaust gas is reduced and NO _x. The purification rate can be improved.

[0006] Zeolites have a large number of acid points and are acidic in nature, so that they have an excellent ability to adsorb HC and adsorb HC in exhaust gas. Therefore, even in the case of exhaust gas in an oxygen excess atmosphere,
HC becomes large stoichiometric-rich atmosphere, NO _x is reduced and purified by reacting with HC which is adsorbed by the catalytic action of supported precious metal.

Further, zeolite has a cracking action, and zeolites such as mordenite, ZSM-5 and ultra-stable Y type zeolite (US-Y) show a particularly high cracking action. Therefore, by using these zeolites as a catalyst carrier, SOF in diesel exhaust gas is cracked and becomes a low molecular weight HC that is more easily reacted, and thereby NO _x can be reduced and purified more efficiently.

For example, Japanese Patent Laid-Open No. 06-165918 proposes an exhaust gas purification method in which a specific catalyst is provided and liquid HC having 5 or more carbon atoms is added upstream thereof. In this method, HC is supplied from the upstream side while the downstream catalyst is in a low active state, NO _x is reduced by this HC, and the NO _x purification rate is improved. Here, HC having 5 or more carbon atoms, that is, high-grade HC, is gradually cracked by heat in the exhaust gas, so when the downstream catalyst is in an active state of 300 to 500 ° C, the carbon number is high due to cracking. It is considered that it becomes a low-grade HC of less than 5 and can certainly reduce NO _x .

Zeolites are chemically tectoaluminosilicates, and zeolites having various Si / Al ratios are known. It has been found that the catalytic properties of zeolite vary greatly depending on the value of this Si / Al ratio.

Zeolites with a small Si / Al ratio have many acid sites, exhibit high cracking ability and high HC adsorption ability, and therefore NO _x
Excellent in purification ability. However, in a zeolite with a small Si / Al ratio and a large number of acid points, HC such as soluble organic components (SOF) adsorbed in the pores is carbonized and easily coked, resulting in clogging of the pores with the result that HC adsorption capacity is high. There is a problem that it decreases over time.

Further, in the case of a zeolite having a small Si / Al ratio and a large number of acid points, acid points easily disappear due to de-Al (4 coordination in the zeolite structure becomes 6 coordination) when hydrothermal durability is applied, and cracking occurs. There is a problem that performance is reduced. Further, such a catalyst in which a noble metal is supported on zeolite also has a problem that the noble metal particles grow due to de-Al removal due to hydrothermal durability, resulting in a decrease in activity.

On the other hand, zeolite having a high Si / Al ratio has a low cracking ability because it has few acid points. However, since coking does not occur, the HC adsorption capacity does not decrease over time, and
Since the grain growth of the noble metal due to Al is also suppressed, it has the advantage of excellent durability.

[0013]

[Patent Document 1] JP-A-04-118030

[Patent Document 2] Japanese Patent Laid-Open No. 06-165918

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and NO _x, even if it is exhaust gas containing a large amount of SOF, such as exhaust gas from a diesel engine.
Is intended to be removed more efficiently. Another object of the present invention is to suppress the decrease in HC adsorption capacity by using zeolite with a large Si / Al ratio, and to secure the same high cracking capacity as zeolite with a small Si / Al ratio. _The purpose is to remove _x more efficiently.

[0015]

The feature of the exhaust gas purification method of the present invention is that in an exhaust gas purification method for reducing and purifying nitrogen oxides in exhaust gas in an oxygen excess atmosphere, it has HC adsorbing ability, mordenite, and ZSM-5. And a carrier layer containing an HC adsorbent composed of zeolite selected from Y-type zeolite, and a precious metal and a solid superacid supported on the carrier layer, wherein the carrier layer has a molar ratio of silicon to aluminum (Si / Al) of 1
It consists of zeolite that has been super strongly oxidized at 50 or more, and an oxygen-releasing material that releases oxygen in a porous carrier and a rich atmosphere,
The precious metal uses an exhaust gas purifying catalyst supported on at least one of a porous carrier and an oxygen releasing material, adsorbs and holds HC by the HC adsorbing material, and cracks the HC released from the HC adsorbing material with a solid superacid, HC generated by this
Is used to reduce and purify nitrogen oxides in exhaust gas.

The characteristics of the exhaust gas purifying catalyst of the present invention are as follows:
In an exhaust gas purifying catalyst for reducing and purifying nitrogen oxides in exhaust gas under an oxygen-excess atmosphere, a carrier layer containing an HC adsorbent composed of zeolite selected from mordenite having HC adsorbing ability, ZSM-5 and Y-type zeolite, The support layer comprises a noble metal and a solid superacid supported on the support layer, and the support layer contains a zeolite that has been superstrongly oxidized at a molar ratio of silicon to aluminum (Si / Al) of 150 or more, and oxygen in a porous carrier and in a rich atmosphere. It consists of an oxygen-releasing material that releases, and the noble metal is supported on at least one of the porous carrier and the oxygen-releasing material.

Zeolite has a coat layer made of at least one of titania, silica and zirconia, and it is desirable that the coat layer be super-strongly oxidized.

The oxygen-releasing material is composed of a ceria-zirconia composite oxide having a molar ratio Zr / Ce of 1 or less, titania,
It is desirable to have a coat layer made of at least one of silica and zirconia, and it is desirable that the coat layer be super-strongly oxidized.

Further, the porous carrier includes titania, silica,
It is preferable that at least one selected from the group consisting of zirconia and alumina coated with at least one of titania, silica and zirconia is super-strongly oxidized.

Further, Ir, Pd, Rh, In, Mn and Fe are contained in the supporting layer.
It is preferable that at least one NO _x oxidant selected from the group consisting of: is supported, and it is preferable that the NO _x storage material is further included.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purification method of the present invention, HC is cracked by a dehydrogenation reaction with a solid superacid supported on a catalyst support layer, thereby producing lower HC highly reactive with NO _x. To do. This low-grade HC is definitely NO
Reacts with _x to obtain a high NO _x purification rate improvement.

At this time, since the cracking of HC occurs in the catalyst, even a lower HC which is hard to be adsorbed by the noble metal when cracked on the upstream side of the catalyst is easily adsorbed by the noble metal in the present invention. Further, HC in the exhaust gas or the supplied HC is adsorbed and held by the HC adsorbent, so that the residence time of HC in the catalyst becomes long, and cracking by solid superacid and reactivity of lower HC with NO _x . Is improved.

Furthermore, since the adsorption of HC by the HC adsorbent is performed in a temperature range where HC is not oxidized, it is
In addition to suppressing the emission of HC, the HC is released from the HC adsorbent in the high temperature range due to temperature rise and
It is used in the cracking of HC and, in turn, in the reaction between low-grade HC and NO _x .

Therefore, according to the exhaust gas purification method of the present invention, a high NO _x purification rate can be reliably exhibited even with exhaust gas in an oxygen excess atmosphere.

In the exhaust gas purifying catalyst of the present invention, a heat resistant honeycomb body made of cordierite or the like can be used as a base material. In this case, it is possible to form a carrier layer containing the HC adsorbent on the honeycomb body and further carry a noble metal on the carrier layer. Further, the HC adsorbent itself may be formed into a honeycomb shape or a pellet shape, and a precious metal may be supported on the HC adsorbent.

A porous carrier such as alumina, silica, zirconia, titania or silica-alumina can be used for the supporting layer. Although the carrier layer contains the HC adsorbent, the carrier layer may be composed of only the HC adsorbent.

As the HC adsorbent, mordenite, ZSM-5
And a zeolite selected from Y-type zeolite can be adopted.

When zeolite is used in combination with another porous carrier, the content of zeolite is preferably 20% by weight or more. If the content of zeolite is less than 20% by weight, the HC adsorbing ability becomes small, and the effect of the present invention is difficult to be achieved.

Noble metals include gold, silver and platinum group (Ru, Rh, Pd,
Os, Ir, Pt). Pt, Rh as practical precious metals
One or more of Pd and Pd can be adopted. The amount of noble metal supported on the entire catalyst is 0.5 to 1 liter of the catalyst.
A range of 10 g is suitable. If it is less than this range, almost no activity is obtained, and if it is supported more than this range, the activity is saturated and the cost rises.

As the solid strong acid, a strong acid such as zirconia, alumina and titania is treated with a strong acid such as sulfuric acid, tungstic acid and molybdic acid to adhere the strong acid to the oxide. Solid acid can be employed. This solid superacid is obtained by adsorbing an aqueous solution of a water-soluble metal salt on the above-mentioned supporting layer, and then subjecting the water-soluble metal salt to an alkali treatment to expose a metal hydroxide on the supporting layer, and then acidifying the metal hydroxide. It is desirable to treat and carry it on the carrier layer. In this way, the solid superacid can be chemically supported on the carrier layer, so that the fine solid superacid diffuses evenly around the pores of the HC adsorbent. Therefore, the HC surely contacts the solid superacid and is easily cracked.

Solid superacids are defined as acidity functions (Hammett acid strength) Ho <-11.0 to -11.9.

It is more preferable to employ a cerium sulfate-zirconium composite oxide as the solid superacid. Cerium sulfate-zirconium composite oxide is Ce-Zr-Y sulfate
It may be a complex oxide, a Ce—Zr—Ca sulfate complex oxide, or the like. The ceria-based oxide has an oxygen storage capacity of releasing oxygen when rich and storing oxygen when lean. The ceria-based solid strong acid is an acid carrier of ceria-based oxide and also has an oxygen storage capacity. Therefore, in the first catalyst that employs the cerium sulfate-zirconium composite oxide as the solid superacid, the oxygen released by the ceria-based solid superacid oxidizes NO in the exhaust gas into NO ₂ .
Makes it easier to adsorb to the precious metal of the catalyst. Therefore, NO _x is concentrated on the noble metal and efficiently reduced and purified by the cracked low-grade HC.

Further, the exhaust gas contains SO ₂ produced by combustion of sulfur (S) contained in the fuel, which is further oxidized by a noble metal in an oxygen excess atmosphere to become SO ₃ . That is, these sulphates are also contained in the exhaust gas. Therefore, in the catalyst containing the ceria-based oxide, the sulfate is likely to be adsorbed on the ceria-based oxide, and the oxygen storage capacity is deteriorated. However, with a catalyst that employs a cerium sulfate-zirconium complex oxide as a solid superacid, it is difficult to adsorb sulfate because the cerium sulfate-zirconium complex oxide has an acid property.
The oxygen storage capacity of the cerium sulfate-zirconium composite oxide is not reduced.

In the exhaust gas purifying catalyst of the present invention, the supporting layer has a molar ratio of silicon to aluminum (Si / Al) of 1
It consists of zeolite that is super-strongly oxidized at 50 or more, a porous carrier and an oxygen releasing material, and the noble metal is supported on at least one of the porous carrier and the oxygen releasing material. Of zeolite
By setting the Si / Al ratio to 150 or more, almost no Al removal occurs, so that the decrease in HC adsorption capacity over time is prevented. In addition, coking is also suppressed because there are few acid points.

However, zeolite having a Si / Al ratio of 150 or more has a low cracking ability due to the small number of acid points, and
There is a problem that cracking of OF becomes insufficient and reduction purification of NO _x by HC becomes insufficient. Therefore, in the present invention, the zeolite is used after being subjected to super strong oxidation. The property of cracking SOF is secured by super strong oxidation, and the reduction purification rate of NO _x is remarkably improved by the HC generated by cracking.

On the other hand, when a precious metal is loaded on the zeolite,
Adsorption of HC to zeolite is inhibited by the reaction heat of the oxidation reaction of HC. In addition, the noble metal supported in the pores of zeolite has its active sites lowered due to the blockage of the pores due to coking.

Therefore, the precious metal is not supported on the zeolite,
It is desirable that it is supported on at least one of the porous carrier and the oxygen releasing material. As a result, HC is smoothly adsorbed on the zeolite and the activity of the noble metal is suppressed from decreasing, so that the NO _x purification capacity is improved.

The porous carrier is mainly used for supporting a noble metal. This porous carrier is preferably selected from at least one of titania, zirconia and silica. Alumina is not preferable because it tends to adsorb SO _x and its activity may decrease due to sulfur poisoning.

Further, not only NO but also oxygen existing in a large amount in the atmosphere is adsorbed by the noble metal, so that the surface of the noble metal is covered with oxygen, and the activity is reduced, resulting in oxygen poisoning. However, it has been clarified that supporting a noble metal on a porous carrier made of at least one of titania, silica and zirconia has the effect of suppressing oxygen poisoning as compared with the case of supporting it on alumina. Therefore, by supporting a noble metal on a porous carrier made of at least one of titania, silica, and zirconia, the decrease in activity due to oxygen poisoning is suppressed, and high durability is exhibited.

The porous carrier is alumina, titania,
It is also preferable that at least one of zirconia and silica is coated and a noble metal is supported on the coating layer. By doing so, since an oxide layer having a high acid property is formed on the outermost surface, it is possible to prevent the sulfur oxide in the exhaust gas from coming close to the supported precious metal, and the sulfur poisoning of the precious metal is prevented. Suppressed. Further, the influence of alumina having a high specific surface area is greatly exerted, and the growth of precious metal particles is suppressed.

Furthermore, it is also preferable to super-strongly oxidize at least one coat layer of titania, zirconia and silica formed on the surface of alumina. By doing so, the acidity of the surface is further enhanced, and sulfur poisoning is further suppressed. Further, by forming the super strong oxide layer, the oxygen poisoning of the noble metal is further suppressed. Therefore, by adopting a structure in which the noble metal is supported on the outermost superoxide layer, the durability of NO _x purification activity is further improved.

The oxygen-releasing material is the release of HC from the zeolite.
The surface of the catalyst that has become rich due to
The NO on the surface of the precious metal
NO ₂ NO by promoting oxidation to
_x It has the function of improving the purification capacity.

Therefore, if a precious metal is supported on the surface of the oxygen-releasing material, the above-described action is smoothly performed, and the NO _x purification capacity is further improved. In addition, the loading of the noble metal also has the effect of improving the oxygen release rate.

Ceria can be used as the oxygen-releasing material. It is also preferable to use ceria stabilized by solid solution of zirconia. in this case,
The composition ratio of the ceria-zirconia composite oxide is not particularly limited, but those having a molar ratio of Zr / Ce ≦ 1 have a high oxygen-releasing ability but are easily poisoned by sulfur, and Zr / Ce> 1 is resistant to sulfur poisoning. However, it has a characteristic of low oxygen releasing ability.

Therefore, it is preferable to form a coat layer made of at least one of titania, zirconia and silica on the surface of the ceria-zirconia composite oxide having Zr / Ce ≦ 1. By doing so, sulfur poisoning can be suppressed while ensuring a high oxygen releasing ability. Further, if the coat layer is further strongly oxidized, the oxygen releasing material can also have a cracking action.

To obtain a super-strongly oxidized zeolite, the zeolite may be directly super-strongly oxidized, but the Si / Al ratio is 150.
On the surface of the above zeolite, it is desirable to form a super strong acid oxide layer made of at least one of titania, zirconia, and silica, which has been subjected to acid treatment to undergo super strong oxidation. If a noble metal is supported on the super-strong oxide layer formed on the zeolite surface, the reaction of NO _x and HC on the noble metal occurs reliably when the HC adsorbed on the zeolite is released, and cracking results in low molecular weight. Since the probability of reaction between the converted HC and NO _x is increased, the purification rate of NO _x is further improved.

The super strong acid oxide layer can be formed by forming an oxide layer of at least one of titania, zirconia and silica on the surface of zeolite and subjecting it to a super strong acid treatment. To form the oxide layer, for example, the zeolite is dispersed in an aqueous nitrate solution of at least one of titanium, zirconium and silicon, and an aqueous ammonia solution is added dropwise to coprecipitate it, followed by filtration, drying and firing. be able to. The super strong acid treatment can be carried out by treating zeolite having an oxide layer with a super strong acid aqueous solution of sulfuric acid, molybdic acid, tungstic acid or the like, and filtering, drying and firing.

It is preferable that the super-strong acid oxide layer is formed so that the weight ratio of the zeolite to the super-strong acid oxide is 10 to 20. If the amount of super strong oxide is less than this range, the effect of forming a super strong oxide layer cannot be obtained, and if it is more than this range, the pores of the zeolite are blocked, so that HC
The adsorption capacity is reduced and the NO _x purification activity is also reduced.

The noble metal may be supported on either the zeolite or the super strong acid oxide layer, but it is desirable to support it on the super strong acid oxide layer. As a result, the probability of reaction between HC and NO _x , which have been reduced to a low molecular weight due to cracking, is increased, and the NO _x purification rate is further improved.

It is also preferable to support the noble metal on an oxide such as silica, titania or zirconia, and mix it with a zeolite having a super strong oxide layer. In this way, NO in the exhaust gas is more likely to be adsorbed by the noble metal than when the noble metal is supported on the super-strong oxide layer, and NO is released by HC released through the super-strong oxide layer.
_x can be reduced and purified more reliably. in this case,
It is not preferable to use alumina as the carrier for supporting the noble metal. This is because alumina easily adsorbs SO _x, and its activity may decrease due to sulfur poisoning.

That is, in the exhaust gas purifying catalyst of the present invention,
By using zeolite with Si / Al ratio of 150 or more,
Sufficient cracking ability is secured by suppressing the decrease in HC adsorption ability and forming a super strong oxide layer on the surface.
Therefore, SOF in the exhaust gas is cracked by the super-strong oxide layer, and the generated HC and HC in the exhaust gas are adsorbed by the zeolite.

On the other hand, although NO _x in the exhaust gas is partially oxidized on the surface of the precious metal by oxygen existing in the exhaust gas, it reacts with HC released from the zeolite on the surface of the precious metal and is reduced and purified to N _2. To be done.

The carrier layer preferably carries at least one NO _x oxidant selected from the group consisting of Ir, Pd, Rh, In, Mn and Fe. By supporting such a NO _x oxidant, the reaction of NO → NO ₂ is promoted and the NOx oxidant is easily adsorbed on the noble metal of the catalyst. Therefore, NO _x is concentrated in the vicinity of the noble metal and efficiently reduced by the low-grade HC formed by cracking, and the NO _x purification rate is further improved.
The supported Mn and Fe become oxides by firing in the catalyst production step.

The amount of the NO _x oxidant supported is appropriately in the range of 0.01 to 1.5 mol per liter of catalyst. If the loading amount is less than this range, the above effect is not exerted, and if the loading amount is more than this range, the NO _x reduction reaction is inhibited and the NO _x purification rate decreases.

Further, it is desirable that the carrier layer further contains a NO _x storage material. The NO _x generated by the promotion of the reaction of NO → NO ₂ by the oxygen releasing material is stored in the NO _x storage material, so that the emission of NO _x in the oxygen excess atmosphere is suppressed. The NO _x released from _the NO _x storage material is reduced by reacting with HC released from the HC adsorbent. Therefore NO _x
Since the storage / reduction of NOx is promoted, the NO _x purification rate is further improved. Furthermore, since the SOF adsorbed on the catalyst is oxidized by the oxygen released from the oxygen-releasing material, the desorption of SOF is promoted.

The type of oxygen releasing material used may be the same as that described above. Also NO _x
The storage material refers to oxides, carbonates, etc. of metals selected from alkali metals, alkaline earth metals and rare earth elements,
The catalyst may be contained in an amount of 0.01 to 1.0 mol per 1 liter.

[0057]

[Examples] Table 1 shows the compositions of the catalysts of Examples and Comparative Examples described below.

[0058]

[Table 1]

Example 1 <Zeolite> A commercially available mordenite powder (“HSZ690HO
A ”Tosoh Co., Ltd., Si / Al ratio = 200) was prepared in 1000 parts, mixed with an aqueous solution of 145 parts of zirconium oxynitrate dissolved in 5000 parts of pure water, and stirred for 30 minutes. Then, 200 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes.
After aging for 12 hours, filter and wash with water, and then in the air at 110 ° C for 2
Dried for hours.

The total amount of the obtained powder is 50 with a 1N aqueous sulfuric acid solution.
Mix in 00 parts, stir for 1 hour, then filter to remove 1
It was dried at 10 ° C. for 2 hours and further calcined in air at 700 ° C. for 3 hours. As a result, a super strong oxide zirconia layer was formed on the surface of the mordenite powder.

<Porous carrier> 100 parts of titania powder and 4
100 parts by weight of an aqueous solution of hexaammineplatinum hydrochloride and 200 parts of pure water were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then bake at 300 ° C for 2 hours to make Pt-supported titania (Pt /
TiO ₂ ) powder was prepared. The supported amount of Pt supported is 2% by weight.

<Oxygen-releasing material> 100 parts of a ceria-zirconia composite oxide (Zr / Ce = 1/4) powder, 100 parts of a 4 wt% hexaammineplatinum hydrate solution and 200 parts of pure water were mixed. Stir for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, then 300
Pt-supported CZS (Pt / CZS) powder was prepared by firing at 2 ° C. for 2 hours. The supported amount of Pt supported is 2% by weight.

<Coating> 90 parts of mordenite powder having a super strong oxide zirconia layer, 60 parts of Pt / TiO ₂ powder, and Pt
30 parts of / CZS powder, 200 parts of pure water and 55 parts of titania sol (solid content 35%) were mixed and stirred to prepare a slurry. And the cordierite honeycomb carrier substrate (400
(Cell / in ² , volume 1.7 L) was prepared, immersed in the slurry, pulled up to blow off excess slurry, dried at 100 ° C. for 2 hours, and then calcined at 500 ° C. for 2 hours to obtain the catalyst of Example 1. . The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 2) <Zeolite> The same as in Example 1.

<Porous carrier> In the same manner as in Example 1 except that 100 parts of silica powder was used in place of the titania powder,
Pt-supported silica (Pt / SiO ₂ ) powder was prepared.

<Oxygen-releasing material> The same as in Example 1.

<Coating> Same as Example 1 except that 60 parts of Pt / SiO ₂ powder was used in place of the Pt-supported titania powder, and 55 parts of silica sol (solid content 35%) was used in place of the titania sol. Then, the catalyst of Example 2 was prepared. The coating amount is 180 g per 1 L of the carrier substrate, and Pt
The supported amount is 1.8 g per 1 L of the carrier substrate.

(Example 3) <Zeolite> The same as in Example 1.

<Porous Carrier> A Pt-supporting zirconia (Pt / ZrO ₂ ) powder was prepared in the same manner as in Example 1 except that 100 parts of zirconia powder was used instead of the titania powder.

<Oxygen-releasing material> The same as in Example 1.

<Coating> Example 1 except that 60 parts of Pt / ZrO ₂ powder was used in place of the Pt-supported titania powder, and 55 parts of zirconia sol (solid content 35%) was used in place of the titania sol. Similarly, the catalyst of Example 3 was prepared. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 4) <Zeolite> Y-type zeolite powder (“HSZ390HUA” manufactured by Tosoh Corp., Si / Al ratio =) instead of mordenite powder
400) was used in the same manner as in Example 1 except that the same amount was used.
A super strong oxide zirconia layer was formed on the surface of the Y-type zeolite powder.

<Porous carrier> The same as in Example 1.

<Oxygen-releasing material> The same as in Example 1.

<Coating> The catalyst of Example 4 was used in the same manner as in Example 1 except that 90 parts of Y-type zeolite powder having a super strong oxide zirconia layer was used in place of the mordenite powder having a super strong oxide zirconia layer. Was prepared. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

Example 5 <Zeolite> ZSM-5 type zeolite powder (“HSZ890HOA” manufactured by Tosoh Corporation, Si / Al instead of mordenite powder)
A super strong zirconia layer was formed on the surface of the ZSM-5 type zeolite powder in the same manner as in Example 1 except that the same amount (ratio = 2000) was used.

<Porous carrier> The same as in Example 1.

<Oxygen releasing material> The same as in Example 1.

<Coating> Example 5 was carried out in the same manner as in Example 1 except that 90 parts of ZSM-5 type zeolite powder having a super strong oxide zirconia layer was used in place of the mordenite powder having a super strong oxide zirconia layer. Was prepared. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 6) <Zeolite> The same as in Example 1.

<Porous carrier> The same as in Example 1.

<Oxygen-releasing material> 500 parts of a ceria-zirconia composite oxide (Zr / Ce = 1/4) powder was mixed with an aqueous solution of 2000 parts of pure water and 300 parts of zirconium oxynitrate and stirred for 30 minutes. . Then, 300 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes. The mixture was aged for 12 hours, filtered, washed with water, and dried in the atmosphere at 110 ° C for 2 hours. Then, it was fired in the air at 500 ° C for 3 hours to prepare CZS (Zr-CZS) powder having a zirconia layer.

Next, 100 parts of Zr-CZS powder, 100 parts of a 4 wt% hexaammineplatinum hydroxide aqueous solution and 200 parts of pure water were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then
Pt-supported Zr-CZS (Pt / Zr-CZS) powder was prepared by firing at 00 ° C for 2 hours. The supported amount of Pt supported is 2% by weight.

<Coating> 90 parts of mordenite powder having a super strong zirconia layer similar to that of Example 1, 60 parts of Pt / TiO ₂ powder similar to that of Example 3, and 30 parts of Pt / Zr-CZS powder, 200 parts of pure water and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Example 6. The coating amount is 180 g per 1 L of the carrier substrate, and the amount of Pt carried is the carrier substrate 1
It is 1.8 g per L.

(Example 7) <Zeolite> The same as in Example 1.

<Porous carrier> The same as in Example 3.

<Oxygen-releasing material> 500 parts of ceria-zirconia composite oxide (Zr / Ce = 1/4) powder was mixed with 2000 parts of pure water and 300 parts of zirconium oxynitrate and stirred for 30 minutes. . Then, 300 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes. The mixture was aged for 12 hours, filtered, washed with water, and dried in the atmosphere at 110 ° C for 2 hours.

Next, the total amount of the obtained Zr-CZS powder was mixed with 5000 parts of 1N sulfuric acid aqueous solution, stirred for 1 hour, filtered, dried in the atmosphere at 110 ° C. for 2 hours, and further in the atmosphere. 700 ° C
Ultra-strongly oxidized Zr-CZS powder was prepared by firing for 3 hours.

Next, 100 parts of super-strong oxidized Zr-CZS powder, 100 parts of a 4 wt% hexaammineplatinum hydroxide aqueous solution and pure water.
200 parts were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then bake at 300 ° C for 2 hours to carry out Pt-supported super strong oxidation Zr-CZS.
(Pt / super-strong oxidized Zr-CZS) powder was prepared. Supported Pt
Is 2% by weight.

<Coating> 90 parts of super strong oxide zirconia layer forming mordenite powder as in Example 1 and Example 3
60 parts of Pt / ZrO ₂ powder similar to the above, and Pt / super strong oxidation Zr-CZS powder
30 parts, pure water 200 parts and zirconia sol (solid content 35%)
55 parts were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared, and Example 1
The catalyst of Example 7 was obtained by coating in the same manner as in. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 8) <Zeolite> The same as in Example 1.

<Porous carrier> Activated alumina (specific surface area 2
500 parts of 00m ² / g) powder was mixed with an aqueous solution of 300 parts of zirconium oxynitrate dissolved in 2000 parts of pure water and stirred for 30 minutes. Then, 300 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes. After aging for 12 hours, filter and wash with water,
It was dried in air at 110 ° C. for 2 hours. Then in the atmosphere
By firing at 500 ° C. for 3 hours, an alumina (Zr-Al ₂ O ₃ ) powder having a zirconia layer was prepared.

Next, 100 parts of Zr-Al ₂ O ₃ powder, 100 parts of a 4% by weight hexaammine platinum hydroxide aqueous solution and 200 parts of pure water were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness and dry at 120 ° C for 2 hours.
Pt-supported Zr-alumina (Pt / Zr-A
l ₂ O ₃ ) powder was prepared. The supported amount of Pt supported is 2% by weight.

<Oxygen releasing material> The same as in Example 1.

<Coating> 90 parts of mordenite powder having a super strong oxide zirconia layer similar to that in Example 1 and the above Pt
/ Zr-Al ₂ O ₃ powder 60 parts and the same Pt / CZS powder as in Example 1
30 parts, pure water 200 parts and zirconia sol (solid content 35%)
55 parts were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared, and Example 1
The catalyst of Example 8 was obtained by coating in the same manner as in. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 9) <Zeolite> The same as in Example 1.

<Porous carrier> Activated alumina (specific surface area 2
500 parts of 00m ² / g) powder was mixed with an aqueous solution of 300 parts of zirconium oxynitrate dissolved in 2000 parts of pure water and stirred for 30 minutes. Then, 300 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes. After aging for 12 hours, filter and wash with water,
It was dried in air at 110 ° C. for 2 hours.

Next, the total amount of the obtained Zr-Al ₂ O ₃ powder was mixed with 5000 parts of a 1N sulfuric acid aqueous solution, stirred for 1 hour, filtered, dried in the atmosphere at 110 ° C. for 2 hours, and further dried in the atmosphere. Inside 700
The powder was calcined at ℃ for 3 hours to prepare a super-strong oxide zirconia layer-forming alumina (super-strong oxide Zr-Al ₂ O ₃ ) powder.

Next, 100 parts of super-strong oxidized Zr-Al ₂ O ₃ powder and 4 parts were added.
100 parts by weight of an aqueous solution of hexaammineplatinum hydrochloride and 200 parts of pure water were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then bake at 300 ° C for 2 hours, and carry out Pt-supported super-strong oxidized Zr-alumina powder (Pt / super-strong oxidized Zr-Al ₂ O ₃ ) was prepared. The supported amount of Pt supported is 2% by weight.

<Oxygen-releasing material> The same as in Example 1.

<Coating> 90 parts of mordenite powder having a super strong oxide zirconia layer similar to that of Example 1 and the above Pt
/ 60 parts of super strong oxide Zr-Al ₂ O ₃ powder and Pt / same as in Example 1 /
30 parts of CZS powder, 200 parts of pure water and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Example 9. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 10) <Zeolite> The same as in Example 1.

<Porous carrier> Activated alumina (specific surface area 2
00 m ² / g) 500 parts of powder was mixed with 3000 parts of 1N aqueous sulfuric acid solution, stirred for 3 hours, filtered, and dried in air at 110 ° C. for 2 hours. Then, it was fired in the air at 700 ° C. for 3 hours to prepare a super-strong oxide alumina (super-strong oxide Al ₂ O ₃ ) powder.

Next, 100 parts of super-strongly oxidized Al ₂ O ₃ powder, 100 parts of a 4 wt% hexaammineplatinum hydroxide aqueous solution and pure water were added.
200 parts were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then bake at 300 ° C for 2 hours to obtain Pt-supported ultra-strong oxidized alumina (Pt / ultra-strong oxidized Al ₂ O ₃ ) powder. Prepared. Supported Pt
Is 2% by weight.

<Oxygen-releasing material> The same as in Example 1.

<Coating> 90 parts of mordenite powder having the same super-strong oxidized zirconia layer as in Example 1 and the above Pt
/ 60 parts of super strong oxide Al ₂ O ₃ powder and Pt / CZ as in Example 1
30 parts S powder, 200 parts pure water and zirconia sol (solid content
(35%) 55 parts were mixed and stirred to prepare a slurry.
Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Example 10. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 11) 100 parts of titania powder, 100 parts of 6 wt% hexaammineplatinum hydroxide aqueous solution and pure water
200 parts were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then bake at 300 ° C for 2 hours to carry Pt-supported titania () Pt /
A TiO ₂ powder was prepared. The supported amount of Pt supported is 3% by weight.

90 parts of mordenite powder having a super strong oxide zirconia layer similar to that of Example 1 and the obtained Pt / TiO ₂ powder 60
Parts and ceria-zirconia composite oxide (CZS, Zr / Ce =
1/4) 30 parts of powder, 200 parts of pure water and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Example 11. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Example 12) Activated alumina (specific surface area 200
100 parts of m ² / g) powder, 100 parts of a 4 wt% hexaammineplatinum hydroxide aqueous solution and 200 parts of pure water were mixed and stirred for 1 hour. After that, heating was continued at 100 ° C. to evaporate water to dryness, dried at 120 ° C. for 2 hours, and further calcined at 300 ° C. for 2 hours to prepare Pt / Al ₂ O ₃ powder. The supported amount of Pt supported is 2% by weight.

90 parts of mordenite powder having the same super-strong oxidized zirconia layer as in Example 1 and the obtained Pt / Al ₂ O ₃ powder
60 parts, 30 parts of Pt / CZS powder similar to that of Example 1, and pure water 2
00 parts and zirconia sol (solid content 35%) 55 parts were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Example 12. Coat amount is 1L of carrier substrate
180g per 1g, Pt loading amount per 1L of carrier substrate
It is 1.8 g.

Comparative Example 1 Commercially available mordenite powder (“HSZ690HOA” manufactured by Tosoh Corporation, Si / Al ratio = 200) 90
Parts, 60 parts of Pt / TiO ₂ powder similar to that of Example 1, and Example 1
30 parts of the same Pt / CZS powder as described above, 200 parts of pure water and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Comparative Example 1. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Comparative Example 2) A commercially available mordenite powder (“HSZ660HOA” manufactured by Tosoh Corp., Si / Al ratio = 30) was used as 10 parts.
Prepare 00 parts and add 5000 parts of pure water to zirconium oxynitrate 145
Parts were mixed with the dissolved aqueous solution and stirred for 30 minutes. afterwards
200 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes. Aged for 12 hours, filtered and washed with water, and then in air 1
It was dried at 10 ° C for 2 hours.

The total amount of the obtained powder is 50 with 1N aqueous sulfuric acid solution.
Mix in 00 parts, stir for 1 hour, then filter to remove 1
It was dried at 10 ° C. for 2 hours and further calcined in air at 700 ° C. for 3 hours. As a result, a super strong oxide zirconia layer was formed on the surface of the mordenite powder.

90 parts of the obtained mordenite powder having a super-strong oxide zirconia layer, 60 parts of Pt / TiO ₂ powder as in Example 1, 30 parts of Pt / CZS powder as in Example 1, and pure water 200 parts and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Comparative Example 2. Coating amount per 1L of carrier substrate
180g, and the amount of Pt supported is 1.8g per liter of carrier substrate
Is.

Comparative Example 3 100 parts of mordenite powder having the same super-strong oxidized zirconia layer as in Example 1 and 2% by weight
Hexaammine platinum hydroxide aqueous solution 100 parts and pure water 200
And the mixture were stirred for 1 hour. Then, continue heating at 100 ° C to evaporate the water to dryness, dry at 120 ° C for 2 hours, and then bake at 300 ° C for 2 hours to form mordenite (Pt / super-strong oxidized ZrO ₂ layer) with Pt-supported super strong zirconia layer. Formed-mordenite) powder was prepared. The amount of Pt carried is 1
% By weight.

Further, 100 parts of titania powder, 100 parts of a 2 wt% hexaammineplatinum hydroxide aqueous solution and 200 parts of pure water were mixed and stirred for 1 hour. After that, continue heating at 100 ° C to evaporate the water to dryness and dry at 120 ° C for 2 hours.
Pt / TiO ₂ powder was prepared by firing at 300 ° C. for 2 hours. The supported amount of Pt supported is 1% by weight.

Further, 100 parts of a ceria-zirconia composite oxide (Zr / Ce = 1/4) powder, 100 parts of a 2 wt% hexaammineplatinum hydroxide aqueous solution and 200 parts of pure water were mixed, and the mixture was mixed for 1 hour. It was stirred. After that, heating was continued at 100 ° C. to evaporate water to dryness, dried at 120 ° C. for 2 hours and further baked at 300 ° C. for 2 hours to prepare Pt / CZS powder. Supported Pt
The supported amount is 1% by weight.

Pt / super-strong oxidation ZrO ₂ layer formation-90 parts mordenite powder, 60 parts Pt / TiO ₂ powder, 30 parts Pt / CZS powder,
200 parts of pure water and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. And Example 1
A honeycomb carrier base material similar to the above was prepared and coated in the same manner as in Example 1 to obtain a catalyst of Comparative Example 3. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

Comparative Example 4 90 parts of commercially available mordenite powder (“HSZ660HOA” manufactured by Tosoh Corp., Si / Al ratio = 30), 60 parts of Pt / TiO ₂ powder similar to that of Example 1, and 30 parts of the same Pt / CZS powder as in Example 1, 200 parts of pure water and 55 parts of zirconia sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Comparative Example 4. The coating amount is 180 g per liter of carrier substrate, and P
The supported amount of t is 1.8 g per 1 L of the carrier substrate.

Comparative Example 5 60 parts of the same Pt / TiO ₂ powder as in Example 1 was mixed with 200 parts of pure water and 55 parts of zirconia sol (solid content 35%) without using zeolite, and the mixture was stirred. To prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Comparative Example 5. The amount of coating is 180 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

Comparative Example 6 90 parts of mordenite powder having a super strong zirconia layer similar to that of Example 1, 60 parts of Pt / TiO ₂ powder similar to that of Example 1, 200 parts of pure water and zirconia sol ( 55 parts (solid content 35%) were mixed and stirred to prepare a slurry. Then, the same honeycomb carrier substrate as in Example 1 was prepared and coated in the same manner as in Example 1 to obtain the catalyst of Comparative Example 6. The coating amount is 180 g per 1 L of the carrier substrate,
The amount of Pt supported is 1.8 g per 1 L of the carrier substrate.

(Evaluation test)
It was installed in the exhaust system of a 00cc in-line 4-cylinder diesel engine, and the temperature was kept constant at 3600 rpm, and the temperature of the gas containing the catalyst was adjusted to 600 ° C depending on the load, and a 25-hour durability test was conducted.

Each catalyst after the durability test was mounted on the exhaust system of the engine similar to that of the durability test, and the load was changed so that the rotation speed changed in the range of 1000 to 2500 rpm as shown in FIG. The purification rates of HC and NO were measured while adding light oil in the range of 300-1200ppmC. The results are shown in Figure 2.

From FIG. 2, it can be seen that the catalysts of the respective examples have higher NO purification rate and HC purification rate after endurance and are superior in durability as compared with the catalyst of the comparative example.

When analyzed in more detail, the purification rate of the catalyst of Example 11 is lower than that of Example 1. This difference is due to the difference in the presence or absence of Pt supported on the oxygen-releasing material, and it is understood that it is preferable to support Pt also on the oxygen-releasing material.

The catalyst of Example 8 has a lower purification rate than that of Example 1. This difference is due to the difference in the type of porous oxide,
It can be seen that titania is preferred over alumina with a zirconia layer.

Comparing Example 3 with Example 7, the purification rate of the catalyst of Example 7 is higher. That is, it is preferable to super-oxidize the coat layer of the oxygen-releasing material. In addition, comparison between Example 8 and Example 9 reveals that it is also preferable to strongly oxidize the porous carrier.

In Comparative Example 1, the purification rate was lower than that in Example 1 because the zeolite was not subjected to super strong oxidation.
In Comparative Examples 2 and 4, since the Si / Al ratio of zeolite is as small as 30, the purification rate is low. Further, in Comparative Example 3, since Pt is supported on zeolite, the purification rate is low. In Comparative Example 2 and Comparative Example 4, Comparative Example 2 has a higher purification rate, but this is due to the difference in the presence / absence of the super strong oxide zirconia layer of the zeolite, and even if the Si / Al ratio is small, the super strong oxide zirconia is It can be seen that it is preferable to form the layers.

Further, in Comparative Example 5, the purification rate was extremely low because neither zeolite nor oxygen-releasing material was present, and in Comparative Example 6, the purification rate was lower than in Example 1 because there was no oxygen-releasing material. There is.

That is, the difference in these effects is due to the difference in the constitution of the carrier, and it is clear that the durability of the NO _x purifying ability is improved by the constitution of the catalyst of the present invention.

Reference Example 1 <Formation of Super Strong Oxide Layer> A commercially available mordenite powder (“HSZ690HOA” manufactured by Tosoh Corporation, Si / Al ratio = 200) was used.
Prepare 1000 parts, and add 5000 parts of pure water to zirconium oxynitrate 1
45 parts was mixed with the dissolved aqueous solution and stirred for 30 minutes. Then, 200 parts of 25% aqueous ammonia solution was mixed, and further mixed for 30 minutes. After aging for 12 hours, filter, wash with water, and in the air
It was dried at 110 ° C. for 2 hours.

The total amount of the obtained powder is 50 with 1N aqueous sulfuric acid solution.
Mix in 00 parts, stir for 1 hour, then filter to remove 1
It was dried at 10 ° C. for 2 hours and further calcined in air at 700 ° C. for 3 hours. As a result, a super strong oxide zirconia layer was formed on the surface of the mordenite powder.

<Supporting noble metal> 100 parts of mordenite powder having a super-strong oxidized zirconia layer obtained above and 1
The mixture was mixed with 100 parts by weight of an aqueous solution of hexaammine platinum hydrochloride and 200 parts of pure water, and the mixture was stirred for 1 hour. After that, heating was continued at 100 ° C. to evaporate water to dryness, followed by drying at 120 ° C. for 2 hours and then baking at 300 ° C. for 2 hours. Carried by this
The loading amount of Pt is 1% by weight.

<Coating> Pt-supported mordenite powder having a super strong zirconia layer 150 parts and pure water 200
Parts and 55 parts of silica sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, a honeycomb carrier base material (volume: 1.5 L) made of cordierite was prepared, soaked in the slurry, pulled up to blow off excess slurry, dried at 100 ° C. for 2 hours, and then calcined at 500 ° C. for 2 hours to prepare a reference example 1. The catalyst was obtained. The coating amount is 150 g per liter of carrier substrate, and Pt
The supported amount is 1.5 g per 1 L of the carrier substrate.

Reference Example 2 An ultra strong titania oxide layer was formed on the surface of mordenite powder in the same manner as in Reference Example 1 except that 145 parts of titanium oxynitrate was used instead of zirconium oxynitrate.

Using this mordenite powder having a super strong acid titania layer, a noble metal was supported and coating was carried out in the same manner as in Reference Example 1 to prepare a catalyst of Reference Example 2. The amount of coating is 150 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.5 g per 1 L of the carrier substrate.

Reference Example 3 <Formation of Super Strong Oxide Layer> Commercially available mordenite powder (“HSZ690HOA” manufactured by Tosoh Corporation, Si / Al ratio = 200) 15
0 parts and 33 parts of zirconia sol having a solid content of 30% by weight were mixed and stirred for 30 minutes. Thereafter, heating was continued at 100 ° C. to evaporate the water to dryness, followed by drying at 120 ° C. for 2 hours and then baking at 300 ° C. for 2 hours.

1000 parts of the obtained powder was added to a 1N aqueous solution of sulfuric acid.
Mix in 5,000 parts, stir for 1 hour, then filter and put in air
It was dried at 110 ° C. for 2 hours and then calcined in air at 700 ° C. for 3 hours. As a result, a super strong oxide zirconia layer was formed on the surface of the mordenite powder.

Using this mordenite powder having a super-strong oxidized zirconia layer, a noble metal was supported and coating was performed in the same manner as in Reference Example 1 to prepare a catalyst of Reference Example 3. The coating amount is 150 g per liter of carrier substrate, and Pt
The supported amount is 1.5 g per 1 L of the carrier substrate.

Reference Example 4 <Formation of Super Strong Oxide Layer> Commercially available mordenite powder (“HSZ690HOA” manufactured by Tosoh Corporation, Si / Al ratio = 200) 15
0 parts and 33 parts of titania sol having a solid content of 30% by weight were mixed and stirred for 30 minutes. After that, heating was continued at 100 ° C. to evaporate water to dryness, followed by drying at 120 ° C. for 2 hours and then baking at 300 ° C. for 2 hours.

1000 parts of the obtained powder was mixed with 1N sulfuric acid aqueous solution.
Mix in 5,000 parts, stir for 1 hour, then filter and put in air
It was dried at 110 ° C. for 2 hours and then calcined in air at 700 ° C. for 3 hours. As a result, a super strong titania oxide layer was formed on the surface of the mordenite powder.

A catalyst of Reference Example 4 was prepared by using this mordenite powder having a super strong titania layer and carrying a noble metal and coating in the same manner as in Reference Example 1. The amount of coating is 150 g per liter of the carrier substrate, and the amount of Pt supported is 1.5 g per liter of the carrier substrate.

Reference Example 5 <Formation of Super Strong Oxide Layer> Commercially available mordenite powder (“HSZ690HOA” manufactured by Tosoh Corporation, Si / Al ratio = 200) 15
0 parts and 33 parts of silica sol having a solid content of 30% by weight are mixed,
Stir for 0 minutes. After that, heating was continued at 100 ° C. to evaporate water to dryness, followed by drying at 120 ° C. for 2 hours and then baking at 300 ° C. for 2 hours.

1000 parts of the obtained powder was mixed with 1N sulfuric acid aqueous solution.
Mix in 5,000 parts, stir for 1 hour, then filter and put in air
It was dried at 110 ° C. for 2 hours and then calcined in air at 700 ° C. for 3 hours. As a result, a super strong oxide silica layer was formed on the surface of the mordenite powder.

A catalyst of Reference Example 5 was prepared by using this mordenite powder having a super-strong oxidized silica layer, carrying a noble metal and coating in the same manner as in Reference Example 1. The amount of coating is 150 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.5 g per 1 L of the carrier substrate.

Reference Example 6 Y-type zeolite powder (“HSZ390HUA” manufactured by Tosoh Corp., instead of mordenite powder,
A super strong oxide zirconia layer was formed on the surface of the Y-type zeolite powder in the same manner as in Reference Example 1 except that the same amount of Si / Al ratio = 400) was used.

A catalyst of Reference Example 6 was prepared by using this Y-type zeolite powder having a super-strong oxidized zirconia layer, carrying a noble metal and coating the same as in Reference Example 1. The coating amount is 150 g per 1 L of the carrier substrate,
The amount of Pt supported is 1.5 g per 1 L of the carrier substrate.

Reference Example 7 Instead of the mordenite powder
ZSM-5 type zeolite powder (“HSZ890HOA” Tosoh Corporation)
Example 1 except that the same amount of Si / Al ratio = 2000) was used.
In the same manner as described above, a super strong oxide zirconia layer was formed on the surface of ZSM-5 type zeolite powder.

Using this ZSM-5 type zeolite powder having a super-strong oxidized zirconia layer, a noble metal was supported and coating was performed in the same manner as in Reference Example 1 to prepare a catalyst of Reference Example 7. The amount of coating is 150 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.5 g per 1 L of the carrier substrate.

Reference Example 8 100 parts of the same mordenite powder as in Reference Example 1, 100 parts of a 1 wt% hexaammineplatinum hydroxide aqueous solution, and 200 parts of pure water were mixed and stirred for 1 hour. Continue to heat at ℃ to evaporate the water to dryness, 120 ℃
After being dried for 2 hours, it was further baked at 300 ° C. for 2 hours. Thus, a Pt-supported mordenite powder was prepared.

Next, 150 parts of Pt-supporting mordenite powder,
200 parts of pure water and 55 parts of silica sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, prepare a cordierite honeycomb carrier base material (volume: 1.5 L), soak it in the slurry and then pull it up to blow off the excess slurry,
Reference Example 8 after drying at 100 ° C for 2 hours and baking at 500 ° C for 2 hours
The catalyst was obtained. The amount of coating is 150 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.5 g per 1 L of the carrier substrate.

Reference Example 9 Commercially available mordenite powder (“HSZ660HOA” manufactured by Tosoh Corporation, Si / Al ratio = 30) 100
Parts and 1% by weight aqueous solution of hexaammineplatinum hydrate 100
Parts and 200 parts of pure water were mixed, stirred for 1 hour, and then continuously heated at 100 ° C. to evaporate water to dryness, dried at 120 ° C. for 2 hours, and further calcined at 300 ° C. for 2 hours. Thus, a Pt-supported mordenite powder was prepared.

Next, 150 parts of Pt-supporting mordenite powder,
200 parts of pure water and 55 parts of silica sol (solid content 35%) were mixed and stirred to prepare a slurry. Then, prepare a cordierite honeycomb carrier base material (volume: 1.5 L), soak it in the slurry and then pull it up to blow off the excess slurry,
Reference Example 9 after drying at 100 ° C for 2 hours and baking at 500 ° C for 2 hours
The catalyst was obtained. The amount of coating is 150 g per 1 L of the carrier substrate, and the amount of Pt supported is 1.5 g per 1 L of the carrier substrate.

Reference Example 10 As zeolite powder, mordenite powder (“HSZ660HOA” manufactured by Tosoh Corporation, Si / Al) was used.
A super strong oxide zirconia layer was formed on the surface of the mordenite powder in the same manner as in Reference Example 1 except that the same amount of (Ratio = 30) was used.

Using this mordenite powder having a super-strong oxidized zirconia layer, a noble metal was loaded and coating was performed in the same manner as in Reference Example 1 to prepare a catalyst of Reference Example 10. The coating amount is 150 g per liter of carrier substrate, and Pt
The supported amount is 1.5 g per 1 L of the carrier substrate.

(Evaluation test) Each of the above-mentioned catalysts
It was installed in the exhaust system of a 00cc in-line 4-cylinder diesel engine, and the temperature was kept constant at 3600 rpm, and the temperature of the gas containing the catalyst was adjusted to 600 ° C depending on the load, and a 25-hour durability test was conducted.

[0157] Each catalyst after the durability test was mounted on the exhaust system of the engine similar to that in the durability test, and the load was changed so that the rotation speed was changed in the range of 1000 to 2500 rpm as shown in Fig. 1, and the exhaust gas was changed. The maximum purification rates of HC and NO were measured while adding light oil in the range of 300-1200ppmC. The results are shown in Fig. 3.

From FIG. 3, the catalysts of Reference Examples 1 to 7 are the same as those of Reference Example 8
Compared to the catalysts of ~ 10, both HC purification rate and NO purification rate show excellent results. Then, the catalysts of Reference Examples 1 to 3 show a markedly higher purification rate than that of Reference Example 8, and it can be seen that the presence of the super strong oxide layer significantly contributes to the improvement of the purification rate. In addition, the catalysts of Reference Examples 1 to 7 showed almost no difference in purification performance before and after the durability test and were excellent in durability.

On the other hand, the catalyst of Reference Example 10 has a higher purification rate than that of Reference Examples 8 and 9 because it has a super strong oxide layer, but the purification rate is lower than that of Reference Examples 1-7. Considering that the catalyst of Reference Example 10 showed a slightly higher purification rate than that of Reference Example 1 before the durability test, the catalyst of Reference Example 10 had a small Si / Al ratio of the zeolite, and therefore the durability test It is considered that coking occurred in the inside and grain growth occurred in Pt due to Al removal, resulting in a significant decrease in purification performance.

[0160]

[Effects of the Invention] That is, according to the exhaust gas purification method and the exhaust gas purification catalyst of the present invention, NO _x in exhaust gas with excess oxygen can be efficiently purified, and the NO _x purification performance is extremely excellent in durability. Therefore, it becomes possible to stably purify NO _x for a long period of time.

HC and NO _x can be efficiently removed even when the exhaust gas temperature is low immediately after the start of operation or during deceleration.
NO _x in exhaust gas containing a large amount of OF can be reduced and removed more efficiently.

Therefore, when the present invention is used in an automobile exhaust gas purification system, NO _x emissions can be suppressed and air pollution due to automobile exhaust gas can be suppressed.

[Brief description of drawings]

FIG. 1 is a graph showing operating conditions of an engine when measuring a purification rate.

FIG. 2 is a bar graph showing the NO purification rate and the HC purification rate after the durability test of the exhaust gas purifying catalysts of Examples 1-12 and Comparative Examples 1-6.

FIG. 3 is a bar graph showing NO purification rate and HC purification rate after an endurance test of exhaust gas purifying catalysts of Reference Examples 1 to 10.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/10 F01N 3/28 301C 3/28 301 301P B01D 53/36 102B (31) Priority claim number Special Japanese Patent Application No. 9-225218 (32) Priority Date August 21, 1997 (August 21, 1997) (33) Priority claim country Japan (JP) (31) Priority claim number Japanese Patent Application No. 9-225224 (32) ) Priority date August 21, 1997 (August 21, 1997) (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 9-225229 (32) Priority date August 1997 21st (August 21, 1997) (33) Priority claiming country Japan (JP) (72) Inventor Katsu Ishii 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Saeko Kurachi Aichi 1 Toyota-cho, Toyota-shi, F (Reference) 3G091 AA02 AA12 AA18 AB05 AB06 AB09 AB10 BA11 BA14 FB10 GA01 GA06 GA16 GB01X GB02Y GB03Y GB04Y GB05W GB06W GB07W GB09W GB10W GB16X 4D048 AA06 AB02 BA06ABAYBA06ABAYBA06ABAYB06YBA30ABAYBA30XBA17YBA30X BA07A BA07B BC18A BC43B BC62A BC66A BC71A BC72A BC74A BC75A BC75B CA03 CA08 CA13 FA02 FA03 FB14 ZA04B ZA06B ZA11B ZC04

Claims (12)

[Claims] 1. In an exhaust gas purification method for reducing and purifying nitrogen oxides in exhaust gas in an oxygen-excess atmosphere, an HC adsorbent having a hydrocarbon adsorbing ability and comprising zeolite selected from mordenite, ZSM-5 and Y-type zeolite. A supporting layer containing, and a noble metal and a solid superacid supported on the supporting layer,
The supporting layer comprises a zeolite that is super-strongly oxidized with a molar ratio of silicon to aluminum (Si / Al) of 150 or more,
The precious metal comprises a porous carrier and an oxygen-releasing material that releases oxygen in a rich atmosphere, and the precious metal uses an exhaust gas-purifying catalyst supported on at least one of the porous carrier and the oxygen-releasing material. To adsorb and retain hydrocarbons, to crack the hydrocarbons released from the HC adsorbent by the solid superacid, and to reduce and purify nitrogen oxides in the exhaust gas by using the hydrocarbons produced thereby as reducing agents. A characteristic exhaust gas purification method. 2. The zeolite has a coat layer composed of at least one of titania, silica and zirconia,
The exhaust gas purification method according to claim 1, wherein the coating layer is super-strongly oxidized. 3. The oxygen-releasing material comprises a ceria-zirconia composite oxide having a molar ratio Zr / Ce of 1 or less, titania,
The exhaust gas purification method according to claim 1, having a coat layer made of at least one of silica and zirconia. 4. The exhaust gas purification method according to claim 3, wherein the coat layer is super-strongly oxidized. 5. The porous carrier is titania, silica,
A super strong oxidation of at least one selected from the group consisting of zirconia and alumina coated with at least one of titania, silica and zirconia.
The exhaust gas purification method described in. 6. An exhaust gas purifying catalyst for reducing and purifying nitrogen oxides in exhaust gas in an oxygen-excess atmosphere, an HC adsorbent comprising a zeolite selected from mordenite having a hydrocarbon adsorbing ability, ZSM-5 and Y-type zeolite. And a noble metal and a solid superacid supported on the supporting layer, wherein the supporting layer has a molar ratio of silicon to aluminum (Si / A).
l) is 150 or more and is super strongly oxidized, and a porous carrier and an oxygen-releasing material that releases oxygen in a rich atmosphere. The precious metal is supported on at least one of the porous carrier and the oxygen-releasing material. A catalyst for purifying exhaust gas, which is characterized in that 7. The zeolite has a coat layer composed of at least one of titania, silica and zirconia,
The exhaust gas-purifying catalyst according to claim 6, wherein the coat layer is super-strongly oxidized. 8. The oxygen-releasing material comprises a ceria-zirconia composite oxide having a molar ratio Zr / Ce of 1 or less, and titania,
The exhaust gas-purifying catalyst according to claim 7, which has a coat layer made of at least one of silica and zirconia. 9. The exhaust gas-purifying catalyst according to claim 8, wherein the coating layer is super-strongly oxidized. 10. The porous carrier is titania, silica,
7. A super strong oxidation of at least one selected from the group consisting of zirconia and alumina coated with at least one of titania, silica and zirconia.
The exhaust gas purifying catalyst according to 1. 11. The carrier layer comprises Ir, Pd, Rh, In, Mn and
The exhaust gas-purifying catalyst according to claim 6, which carries at least one NO _x oxidizing agent selected from the group consisting of Fe. 12. The exhaust gas-purifying catalyst according to claim 6, further comprising a NO _x storage material.