JPH0557183A - Method for producing hydrocarbon adsorbent - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a method for producing a hydrocarbon adsorbent having excellent adsorption performance for hydrocarbons in exhaust gas of an internal combustion engine, especially at low temperatures. [Composition] ZSM-5 zeolite powder ion-exchanged with Pd as a metal for improving the adsorption performance of hydrocarbons in exhaust gas is coated on a monolith carrier and then calcined at a high temperature of 600 to 1000 ° C, or After firing the mixed powder of the above zeolite at a high temperature, the monolith carrier is coated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrocarbon (HC) used in a device for purifying exhaust gas from an internal combustion engine such as an automobile.
The present invention relates to a method for manufacturing an adsorbent.

[0002]

2. Description of the Related Art Pellet or monolith type catalysts are currently used to purify exhaust gas from internal combustion engines of automobiles and the like. Hydrocarbons that are harmful components in exhaust gas
Of the (HC), carbon monoxide (CO), and nitrogen oxides (NO _X ), the catalytic purification capacity of HC is particularly affected by the exhaust gas temperature, and is generally purified by a precious metal catalyst at temperatures above 300 ° C. ..

Therefore, when the exhaust gas temperature is low, such as immediately after the engine is started, the HC is difficult to be purified by the catalyst. Moreover, a large amount of HC is discharged immediately after the engine starts,
HC (hereinafter referred to as cold HC) accounts for a large proportion of the total HC emissions, and the challenge was to suppress the emission of cold HC.

An example of such an exhaust gas purifying apparatus for reducing HC at the time of cold start is disclosed in Japanese Patent Laid-Open No. Heisei 2-
There is one disclosed in Japanese Patent No. 135126.

[0005]

However, in the catalyst having the HC adsorbing ability at the time of cold start used in the exhaust gas purifying apparatus disclosed in the above-mentioned JP-A-2-135126, the zeolite is coated. After that, since the catalyst metal is supported, the ion exchange is not sufficiently performed, and since the Y-type zeolite or mordenite is used as the zeolite, the adsorption capacity is not sufficient. Furthermore, zeolite has a high temperature dependence, and from room temperature to about 100 ° C.
Since the water in the exhaust gas is preferentially adsorbed up to the rank, the HC adsorption capacity during cold is not sufficient.

Therefore, an object of the present invention is to provide a method for producing a hydrocarbon adsorbent used in an exhaust gas purifying apparatus, which has an improved adsorption capacity for adsorbing hydrocarbons, particularly an adsorption capacity at low temperature of exhaust gas. To do.

[0007]

The present invention, as an adsorbent for adsorbing hydrocarbons, uses Pd burned at a high temperature in an air atmosphere.
Adsorption performance is improved by using a mixed powder of ZSM-5 zeolite that has been ion-exchanged, and by arranging this adsorbent in front of the exhaust gas purifying catalyst that supports the catalyst components, it is possible to obtain sufficient temperature It is based on the finding that an exhaust gas purifying device having a high HC adsorption capacity can be obtained.

That is, the present invention relates to a method for producing a hydrocarbon adsorbent used in a device for purifying exhaust gas from an internal combustion engine of an automobile or the like. In the first method, a metal for modifying adsorption characteristics is used. After coating ZSM-5 zeolite powder ion-exchanged with Pd on a monolith carrier, 600 ℃ -10
Bake at a temperature of 00 ° C.

In the second method, the ZSM-5 zeolite powder ion-exchanged with Pd as a metal for modifying the adsorption property is fired at a high temperature and then coated on the monolith support.

[0010]

Next, the operation will be described. Zeolites are crystalline porous substances having uniform pore inlets, and have the property of selectively adsorbing only molecules having a size that can pass through the pore inlets from the mixture into the pores. Due to this characteristic, the HC discharged at the time of engine start is adsorbed, and the increase of HC emission due to the release of HC in the temperature range where the catalytic reaction does not occur is prevented. Further, the HC adsorption capacity of zeolite varies depending on the exhaust gas temperature, but the present inventors can change the adsorption characteristics of HC by using ZSM-5 zeolite with different firing temperature and firing time after ion exchange of Pd. I found it. Among them, 600 ℃ or more (preferably 600 ℃ ~ 750
(° C) at a temperature of 2 hours or more (preferably 2 to 4 hours) in an air atmosphere at a high temperature, a suitable dealumination of the zeolite occurs to improve the hydrophobicity, and the ion-exchanged noble metal is uniform. As a complex oxide, it is kept in a more stable state in the active site of zeolite. Therefore, it is less likely to be affected by water when cold, and the HC adsorption capacity improves from room temperature. Zeolite has hydrophilicity and is easily affected by water at low firing temperatures. Further, if the temperature is higher than 1000 ° C., dealumination of the zeolite progresses remarkably and the crystal structure is broken, which is not preferable.

[0011]

EXAMPLES The present invention will be described below with reference to Examples, Comparative Examples and Test Examples. In addition, "part" in the examples means "part by weight" unless otherwise specified.

Example 1 First, 100 parts of H-type ZSM-5 zeolite (hereinafter referred to as Pd / HZSM-5) ion-exchanged with Pd, silica sol (solid content 20
%) 65 parts and 65 parts of water are charged into a magnetic pot for 40 minutes with a vibration mill device or with a universal ball mill device.
A washcoat slurry was manufactured by mixing and grinding for 5 hours. After the cordierite monolith carrier was subjected to water absorption treatment by a suction coating method, the slurry produced above was uniformly added to the entire cross section of the carrier, and the excess slurry was removed by a suction coating method. After that, it was dried and calcined at 400 ° C. for about 1 hour.

As a result, Pd H-type ZSM-5 zeolite was coated on the carrier at a coating amount of about 90 g / L. The above washcoating, drying and calcination were repeated two more times to coat a total of 200 g / L of Pd / HZSM-5 zeolite and calcination was performed at 650 ° C for 4 hours in an air atmosphere to obtain (Adsorbent 1). It was

Example 2 A washcoat slurry was prepared in the same manner as in Example 1,
The monolithic carrier was coated with Pd / HZSM-5 zeolite by the same coating method and calcined at 750 ° C. for 4 hours in an air atmosphere (adsorbent 2).

Example 3 A washcoat slurry was prepared in the same manner as in Example 1,
The monolithic carrier was coated with Pd / HZSM-5 zeolite by the same coating method and calcined in an air atmosphere at 850 ° C. for 4 hours (adsorbent 3).

Comparative Example 1 A washcoat slurry was prepared in the same manner as in Example 1,
The monolithic carrier was coated with Pd / HZSM-5 zeolite by the same coating method and calcined at 1050 ° C. for 4 hours in an air atmosphere (adsorbent 4).

Example 4 100 parts of Pd ion-exchanged H-type ZSM-5 zeolite (Pd / HZSM-5) calcined at 650 ° C. for 4 hours in an air atmosphere, 65 parts of silica sol (solid content 20%), and 65 parts of water was charged into a magnetic pot to prepare a washcoat slurry in the same manner as in Example 1, and Pd / HZ was added to the monolith carrier by the same coating method.
Coated with SM-5 zeolite, 1 at 600 ℃ in air atmosphere
Firing was carried out for an hour to obtain (Adsorbent 5).

Example 5 100 parts of Pd ion-exchanged H-type ZSM-5 zeolite (Pd / HZSM-5) calcined at 750 ° C. for 4 hours in an air atmosphere, 65 parts of silica sol (solid content 20%), and 65 parts of water was charged into a magnetic pot to prepare a wash coat slurry in the same manner as in Example 1, and the monolith carrier was coated with Pd /
HZSM-5 zeolite was coated and calcined in an air atmosphere at 600 ° C. for 1 hour to obtain (adsorbent 6).

Comparative Example 2 100 parts of H-type ZSM-5 zeolite (Pt / HZSM-5) ion-exchanged with dinitrodiamine platinum, 65 parts of silica sol, and
65 parts of water was charged into a magnetic pot, a washcoat slurry was produced in the same manner as in Example 1, and the coating amount of Pt / HZSM-5 zeolite was 200 g / L by the same coating method.
(Adsorbent 7) was obtained. It was

Comparative Example 3 H-type ZSM-5 zeolite (Rh
/ HZSM-5), 100 parts of silica sol, 65 parts of silica sol, and 65 parts of water are charged into a magnetic pot to prepare a washcoat slurry by the same method as in Example 1, and Rh / HZ is prepared by the same coating method.
The amount of SM-5 zeolite coated is 200 g / L (Adsorbent 8)
Got

Any carrier such as a monolith carrier or a metal carrier can be used as the carrier in the above embodiments.

Test Examples Adsorbents (1-8) of Examples 1-5 and Comparative Examples 1-3
The model gas was evaluated under the following conditions to measure the amount of adsorbed HC. Table 1 shows the results of evaluation of the obtained HC adsorption characteristics. Adsorbent capacity 60 cc NO amount 1000 ppm Total gas flow rate 50 L / min CO amount 6000 ppm HC amount 1000 ppm O ₂ amount 1000 ppm H ₂ O 10% H ₂ amount 2000 ppm

[0023]

[Table 1]

[0024]

As described above, according to the method for producing a hydrocarbon adsorbent of the present invention, after Pd is ion-exchanged, a mixed powder of ZSM-5 zeolite which is calcined at a high temperature in an air atmosphere is used, After coating the monolith carrier, 600-1
Since the monolithic carrier is coated after high-temperature calcination at 000 ° C or high-temperature calcination of the above zeolite mixed powder, the adsorbent obtained has improved adsorbability especially at low temperature of exhaust gas. ..

Furthermore, when the adsorbent is placed in front of the exhaust gas purifying catalyst supporting the catalyst component in the exhaust gas purifying apparatus, it can purify the exhaust gas effectively from low temperature to high temperature. The effect is obtained.

Claims (2)

[Claims] 1. When manufacturing an adsorbent for adsorbing hydrocarbons in exhaust gas, a monolithic carrier is coated with ZSM-5 zeolite powder ion-exchanged with Pd as a metal for modifying the adsorption property of hydrocarbons. Then, a method for producing a hydrocarbon adsorbent, which comprises firing at a temperature of 600 to 1000 ° C. 2. In producing an adsorbent which adsorbs hydrocarbons in exhaust gas, 60 ZSM-5 zeolite powders, which are ion-exchanged with Pd as a metal for modifying adsorption characteristics of hydrocarbons, are produced.
A method for producing a hydrocarbon adsorbent, which comprises coating a monolithic carrier after high-temperature calcination at a temperature of 0 to 1000 ° C.