JPH06142520A - Hydrocarbon adsorptive catalyst - Google Patents

Abstract

PURPOSE:To provide a hydrocarbon(HC) adsorptive catalyst which is put in the upper stream side of an exhaust gas purifying catalyst in a gas discharging system to purify the exhaust gas from an automotive internal combustion engine and purifies HC removed from an adsorptive layer. CONSTITUTION:Regarding a hydrocarbon adsorptive catalyst to be placed in the upper stream side, it is provided with a first catalytic layer and a second layer, wherein the first layer is provided with an adsorbent consisting of ZSM-5 zeolite ion-exchanged with copper and/or palladium to adsorb hydrocarbons in the front part of a monolithic carrier and at least one of platinum and palladium carried on an activated ceria and/or alumina in the rear part and the second layer contains rhodium as a catalytic component carried on activated ceria and/or alumina and is formed on the first layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrocarbon (HC) adsorption catalyst arranged upstream of an exhaust gas purifying catalyst of an exhaust gas purifying apparatus for an automobile exhaust system.

[0002]

2. Description of the Related Art Carbon monoxide (CO) and hydrocarbon (HC) are used as exhaust gas purifying catalysts for internal combustion engines of automobiles and the like.
A catalyst that simultaneously performs oxidation of nitrogen and reduction of nitrogen oxides (NO _x ) is widely used. Such a catalyst is disclosed in, for example, Japanese Examined Patent Publication No. 58-20307, for example, a noble metal such as Pd, Pt, and Rh is contained in an alumina coating layer on a refractory carrier, and optionally Ce, La, or the like as a promoter component. In most cases, a rare earth metal or a base metal oxide such as Ni is added.

Such a catalyst is strongly influenced by the exhaust gas temperature and the set air-fuel ratio of the engine. The exhaust gas temperature at which an automobile catalyst exerts its purifying ability is generally required to be 300 ° C. or higher, and the air-fuel ratio is a theoretical air-fuel ratio (A / F = 14.6) which can balance the oxidation of HC and CO and the reduction of NO _x. The catalyst works most effectively in the vicinity. Therefore, a conventional automobile equipped with an exhaust gas purification device that uses a three-way catalyst is installed at a position where the three-way catalyst works effectively, and the oxygen concentration in the exhaust system is detected to create a theoretical air-fuel mixture. Feedback control is performed so as to keep the fuel ratio close to.

Even if a conventional three-way catalyst is installed immediately after the exhaust manifold, the exhaust gas temperature is low (300 ° C or lower).
There is a problem that the catalyst activity is low immediately after the engine is started, and a large amount of HC discharged immediately after the engine is started (at the time of cold start) is not purified but is discharged as it is.

As an exhaust gas purifying apparatus for solving the above problems, cold HC is provided on the upstream side of the exhaust of a catalytic converter.
There has been proposed one in which an HC trapper containing an adsorbent for adsorbing is disposed (JP-A-2-135126).

[0006]

However, in the adsorbent used in the exhaust gas purifying apparatus disclosed in Japanese Patent Laid-Open No. 2-135126, 1) Cu, Pd, etc. are used as the HC purifying catalyst metal. Since the zeolite is partially supported and the zeolite is H-type model night or H-type zeolite, the HC adsorption capacity of the zeolite is not sufficient. 2) Since the catalyst metal is impregnated and supported after the zeolite and alumina are coated together, the durability of the catalyst component is not sufficient. There is a problem.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an HC adsorbing catalyst which is used upstream of an exhaust gas purifying catalyst of an exhaust system and which purifies HC desorbed from an adsorbing layer. Especially.

[0008]

The present invention is directed to H in exhaust gas.
An HC adsorption catalyst for purifying C, wherein the front portion of the monolith carrier is coated with ZSM-5 zeolite ion-exchanged with at least one metal of Cu and Pd effective for HC adsorption, and the rear portion is activated ceria. And / or a catalyst first layer containing at least one or more of Pt and Pd supported on a powder containing alumina as a main component, and activated ceria and / or alumina supported on the first layer as a catalyst component. It is an HC adsorption catalyst comprising a second layer containing Rh.

[0009]

In the HC adsorbing catalyst used in the automobile exhaust gas purifying apparatus of the present invention, the catalytically active component carried on the rear part of the carrier is heated faster than the catalyst arranged on the downstream side of the adsorbent, so that the front part of the carrier is From the adsorbent coated on H
Even when C begins to be desorbed and the catalyst in the catalytic converter from the downstream side is not sufficiently activated, the catalytically active component coated on the rear portion of the adsorbent is sufficiently activated and HC is satisfactorily purified. It Moreover, reaction heat is generated when HC is purified by the metal catalyst, so that the catalyst in the catalytic converter is heated and activation is promoted.

[0010]

EXAMPLES The present invention will be described in more detail with reference to Examples, Comparative Examples and Test Examples. In the examples, "parts" means "parts by weight" unless otherwise specified. Example 1 ZSM-5 zeolite ion-exchanged with Pd (hereinafter referred to as PSM
d / ZSM-5) 100 parts, silica sol (solid content 20
%) 65 parts and 65 parts of water are charged into a magnetic pot and the vibration mill device is used for 40 minutes or the universal ball mill device is 6.5
A washcoat slurry was produced by time-mixing and grinding. After impregnating only the front part of the cordierite monolith carrier with the slurry produced above, excess slurry was removed by air-blowing, followed by drying and calcination at 400 ° C. for about 1 hour. As a result, Pd / ZSM-5 zeolite was coated on the carrier at a coating amount of about 100 g / L. The above wash coating, drying and calcination were further repeated to coat a total of 180 g / L of Pd / ZSM-5 zeolite, and calcination was carried out at 650 ° C. for 2 to 6 hours (preferably 4 hours) in an air atmosphere.

Next, 100 parts of activated ceria powder carrying Pt (hereinafter referred to as Pt / CeO ₂ ), 50 parts of alumina, 2
% Of 150% acetic acid was charged into a magnetic pot to prepare a washcoat slurry in the same manner as described above, and a Pt catalyst layer of 150 g / L was coated only on the rear part of the carrier by the same method, and after drying, 400 wt. Firing was carried out at a temperature of 1 to 4 hours (preferably 1 hour).

Further, 100 parts of Rh-supported alumina powder (hereinafter referred to as Rh / Al ₂ O ₃ ), 50 parts of alumina,
150 parts of 2% acetic acid was charged into a magnetic pot, a washcoat slurry was prepared in the same manner as above, and 50 g / L of Rh / A was formed on the Pt / CeO ₂ layer in the rear part of the carrier in the same manner.
l ₂ O ₃ catalyst layer was coated and dried, then 400
Calcination is performed for 1 to 4 hours (preferably 1 hour) at
(Adsorption catalyst-1) was obtained.

Example 2 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts of water and 65 parts of water were charged into a magnetic pot, a washcoat slurry was produced by the same method as in Example 1, and Pd / ZSM-5 was added to the front part of the monolith carrier by the same coating method.
It was coated with 80 g / L, dried and baked.

Next, 100 parts of activated ceria powder carrying Pd (hereinafter referred to as Pd / CeO ₂ ), 50 parts of alumina, 2
% Of 150% nitric acid was charged in a magnetic pot, a washcoat slurry was produced in the same manner as in Example 1, 150 g / L of Pd catalyst layer was coated on the rear part of the carrier by the same coating method, dried and calcined. I did.

Further, in the same manner as in Example 1, Rh / A
An l ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-2).

Example 3 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts of water and 65 parts of water were charged into a magnetic pot, a washcoat slurry was produced by the same method as in Example 1, and Pd / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with 0 g / L, dried and baked.

Next, an alumina powder carrying Pt (hereinafter, referred to as
Pt / Al ₂ O ₃ ) 100 parts, alumina 50 parts, 2%
150 parts of acetic acid was charged into a magnetic pot, a washcoat slurry was produced in the same manner as in Example 1, and 150 g / L of Pt catalyst layer was coated on the rear part of the carrier by the same coating method, followed by drying and firing. It was

Further, in the same manner as in Example 1, Rh / A
An l ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-3).

Example 4 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts of water and 65 parts of water were charged into a magnetic pot, a washcoat slurry was produced by the same method as in Example 1, and Pd / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with 0 g / L, dried and baked.

Next, an alumina powder carrying Pd (hereinafter referred to as
Pd / Al ₂ O ₃ ) 100 parts, alumina 50 parts, 2%
150 parts of acetic acid was charged into a magnetic pot, a washcoat slurry was produced in the same manner as in Example 1, 150 g / L of Pd catalyst layer was coated on the rear part of the carrier by the same coating method, dried and calcined. It was

Further, in the same manner as in Example 1, Rh / A
An l ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-4).

Example 5 ZSM-5 zeolite ion-exchanged with Cu (hereinafter referred to as C
u / ZSM-5) 100 parts, silica sol (solid content 20
%) 65 parts and 65 parts of water were charged in a magnetic pot, a washcoat slurry was produced in the same manner as in Example 1, and Cu / ZSM-5 was applied to the front portion of the monolith carrier by the same coating method.
Was coated at 180 g / L, dried, and then baked in an air atmosphere at 400 ° C. for 1 to 4 hours (preferably 1 hour).

Then, in the same manner as in Example 1, a Pt / CeO ₂ catalyst layer was coated at 150 g / L on the rear portion of the carrier, and dried,
Firing was performed. Further, in the same manner as in Example 1, Rh
/ Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-5).

Example 6 100 parts of Cu / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and Cu / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with 0 g / L, dried and baked.

Then, in the same manner as in Example 2, a Pd / CeO ₂ catalyst layer was coated at 150 g / L on the rear portion of the carrier, and dried,
Firing was performed. Further, in the same manner as in Example 1, Rh
/ Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-6).

Example 7 100 parts of Cu / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and Cu / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with 0 g / L, dried and baked.

Then, in the same manner as in Example 3, a Pt / Al ₂ O ₃ catalyst layer was coated at 150 g / L on the rear portion of the carrier, dried and fired. Further, 50 g / L of Rh / Al ₂ O ₃ catalyst layer was coated by the same method as in Example 1, dried and calcined to obtain (Adsorption catalyst-7).

Example 8 100 parts of Cu / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and Cu / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with 0 g / L, dried and baked.

Then, in the same manner as in Example 4, a Pd / Al ₂ O ₃ catalyst layer was coated at 150 g / L on the rear portion of the carrier, dried and calcined. Further, 50 g / L of Rh / Al ₂ O ₃ catalyst layer was coated in the same manner as in Example 1, dried and calcined to obtain (Adsorption catalyst-8).

Example 9 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 1, and Pd / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with g / L, dried and baked. Then Cu / Z
100 parts of SM-5, 65 parts of silica sol (solid content 20%), water
65 parts were placed in a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and 90 g / L of Cu / ZSM-5 was formed on the Pd / ZSM-5 layer by the same coating method.
It was coated, dried and baked.

Then, in the same manner as in Example 1, a Pt / CeO ₂ catalyst layer was coated at 150 g / L on the rear portion of the support, and dried,
Firing was performed. Further, in the same manner as in Example 1, Rh
/ Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-9).

Example 10 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 1, and Pd / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with g / L, dried and baked. Then Cu / Z
100 parts of SM-5, 65 parts of silica sol (solid content 20%), water
65 parts were placed in a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and 90 g / L of Cu / ZSM-5 was formed on the Pd / ZSM-5 layer by the same coating method.
It was coated, dried and baked.

Then, in the same manner as in Example 2, a Pd / CeO ₂ catalyst layer was coated at 150 g / L on the rear portion of the support and dried,
Firing was performed. Further, in the same manner as in Example 1, Rh
/ Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-9).

Example 11 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 1, and Pd / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with g / L, dried and baked. Then Cu / Z
100 parts of SM-5, 65 parts of silica sol (solid content 20%), water
65 parts were placed in a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and 90 g / L of Cu / ZSM-5 was formed on the Pd / ZSM-5 layer by the same coating method.
It was coated, dried and baked.

Then, in the same manner as in Example 3, a Pt / Al ₂ O ₃ catalyst layer was coated at 150 g / L on the rear portion of the carrier, dried and baked. Further, 50 g / L of Rh / Al ₂ O ₃ catalyst layer was coated in the same manner as in Example 1, dried and calcined to obtain (Adsorption catalyst-11).

Example 12 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 1, and Pd / ZSM-5 was added to the front portion of the monolith carrier by the same coating method.
It was coated with g / L, dried and baked. Then Cu / Z
100 parts of SM-5, 65 parts of silica sol (solid content 20%), water
65 parts were placed in a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and 90 g / L of Cu / ZSM-5 was formed on the Pd / ZSM-5 layer by the same coating method.
It was coated, dried and baked.

Next, in the same manner as in Example 4, 150 g / L of Pd / Al ₂ O ₃ catalyst layer was coated on the rear portion of the carrier, dried and calcined. Further, 50 g / L of Rh / Al ₂ O ₃ catalyst layer was coated by the same method as in Example 1, dried and calcined to obtain (Adsorption catalyst-12).

Example 13 25 parts of Pd / ZSM-5, 75 parts of Cu / ZSM-5, 65 parts of silica sol, and 65 parts of water were charged in a pot, and a washcoat slurry was produced in the same manner as in Example 1. Then
By the same coating method, 180 g / L of PSM and Cu-mixed ZSM-5 zeolite was coated on the front part of the carrier, dried and calcined.

Then, in the same manner as in Example 1, a Pt / CeO ₂ catalyst layer was coated at 150 g / L on the rear portion of the support, and dried,
Firing was performed. Further, in the same manner as in Example 1, Rh
/ Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-13).

Example 14 25 parts of Pd / ZSM-5, 75 parts of Cu / ZSM-5, 65 parts of silica sol, and 65 parts of water were charged in a pot, and a washcoat slurry was produced in the same manner as in Example 1. Then
By the same coating method, 180 g / L of ZSM-5 zeolite containing Pd and Cu was coated on the front part of the carrier, and dried.
Firing was performed.

Then, in the same manner as in Example 2, a Pd / CeO ₂ catalyst layer was coated at 150 g / L on the rear portion of the support, dried and
Firing was performed. Further, in the same manner as in Example 1, Rh
/ Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-14).

Example 15 25 parts of Pd / ZSM-5, 75 parts of Cu / ZSM-5, 65 parts of silica sol, and 65 parts of water were charged in a pot, and a washcoat slurry was produced in the same manner as in Example 1. Then
By the same coating method, 180 g / L of PSM and Cu-mixed ZSM-5 zeolite was coated on the front part of the carrier, dried and calcined.

Then, in the same manner as in Example 3, a Pt / Al ₂ O ₃ catalyst layer was coated at 150 g / L on the rear portion of the support, dried and baked. Further, in the same manner as in Example 1, a Rh / Al ₂ O ₃ catalyst layer was coated at 50 g / L, dried and calcined to obtain (Adsorption catalyst-15).

Example 16 25 parts of Pd / ZSM-5, 75 parts of Cu / ZSM-5, 65 parts of silica sol, and 65 parts of water were charged in a pot, and a washcoat slurry was produced in the same manner as in Example 1. Then
By the same coating method, 180 g / L of ZSM-5 zeolite containing Pd and Cu was coated on the front part of the carrier, and dried.
Firing was performed.

Then, in the same manner as in Example 4, 150 g / L of Pd / Al ₂ O ₃ catalyst layer was coated on the rear portion of the carrier, dried and calcined. Further, 50 g / L of Rh / Al ₂ O ₃ catalyst layer was coated in the same manner as in Example 1, dried and calcined to obtain (Adsorption catalyst-16).

Comparative Example 1 100 parts of Pd / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 1, and 180 g / L of Pd / ZSM-5 was added to a monolith carrier by the same coating method.
After coating, drying and baking, (adsorption catalyst-17) was obtained.

Comparative Example 2 100 parts of Cu / ZSM-5, silica sol (solid content 20%)
65 parts and 65 parts of water were charged into a porcelain pot, a washcoat slurry was produced in the same manner as in Example 5, and 180 g / L of Cu / ZSM-5 was added to the monolith carrier by the same coating method.
It was coated, dried and calcined to obtain (Adsorption catalyst-18). Any carrier such as a monolith carrier or a metal carrier can be used as the carrier in the above embodiments.

Test Example The adsorbed catalysts of Examples 1 to 16 and Comparative Examples 1 and 2 were evaluated under the following conditions to measure the HC adsorption purification rate. The results obtained are shown in Table 1. Catalyst capacity 120 cm ³ (SV: 40,000 / h) Evaluation engine 2000cc engine (using EGI)

Evaluation mode is cold (water temperature 25 ° C.)
Engine started from 20 to idle state (700 rpm)
Hold for 2 seconds (Fig. 1), then 2000 rpm, -200 mmHg
Accelerate and hold. The adsorption rate was calculated from the integrated value (1-adsorption catalyst outlet / adsorption catalyst inlet) for 100 seconds after gas flow.
FIG. 1 shows changes with time in the engine inlet temperature and accompanying changes in the reference temperature of hydrocarbons.

[0050]

[Table 1]

[0051]

EFFECT OF THE INVENTION In the exhaust gas purifying catalyst of the present invention,
Since the exhaust gas purifying catalyst is carried in the rear portion of the adsorbent, the desorbed HC is favorably purified even at the temperature at which the HC begins to desorb from the HC adsorbent, and the HC in the rear portion of the adsorbent purifies the HC. Depending on the heat of reaction when
Since the activation of the catalyst in the catalytic converter is promoted,
The purification performance of HC at a relatively low temperature at which HC starts to separate from the adsorbent is significantly improved.

[Brief description of drawings]

FIG. 1 is a graph showing changes with time in engine inlet temperature and accompanying changes in reference concentration of hydrocarbons in a test example.

Claims (1)

[Claims] 1. An adsorbent for adsorbing a hydrocarbon composed of ZSM-5 zeolite ion-exchanged with at least one metal of copper and palladium in a hydrocarbon adsorbing catalyst arranged upstream of an exhaust gas purifying catalyst of an exhaust system. Is provided in the front part of the monolithic carrier, and the rear part thereof comprises a catalyst first layer containing at least one or more of platinum and palladium supported on active ceria and / or alumina, and further active as a catalyst component on the first layer. A hydrocarbon adsorption catalyst comprising a second layer containing rhodium supported on ceria and / or alumina.