JPH0714463B2 - Automotive exhaust gas purification device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an automobile exhaust gas purification apparatus.

(Prior Art) A pellet-shaped or monolith-type catalyst is used for purifying exhaust gas of an automobile. Of the harmful components (HC, CO, NOx) in the exhaust gas, the purification of HC, especially with a catalyst,
Exhaust gas temperature has a strong effect, and a temperature of 300 ° C or higher is generally required even when a precious metal catalyst is used. Therefore, when the exhaust gas temperature is low, such as immediately after the engine is started, the HC
Is hard to be purified by a catalyst. Moreover, since a large amount of HC is discharged immediately after the engine is started, the emission of HC (hereinafter referred to as cold HC) when the temperature of the exhaust gas is low accounts for a large proportion of the total. Therefore, it has been an issue to suppress the emission of cold HC.

As an automobile exhaust gas purifying device for solving the above problems, an exhaust system of an engine, a catalytic converter containing a purifying catalyst for harmful components in exhaust gas is disposed, and a cold HC is provided upstream of the catalytic converter. It is proposed that an HC trapper containing an adsorbent for adsorbing is arranged (Japanese Patent Application No. 63-226070). In the exhaust gas purification device, HC is trapped in the adsorbent at low temperatures, and HC is desorbed from the adsorbent at high temperatures and purified by a catalyst. As an adsorbent,
Since zeolite has excellent adsorptivity, for example, a monolith carrier coated with zeolite has been proposed.

(Problems to be Solved by the Invention) However, in the exhaust gas purifying apparatus of Japanese Patent Application No. 63-226070, when the exhaust gas temperature is a temperature at which HC starts to desorb from the adsorbent (about 170 ° C.), the catalytic converter The catalyst therein is not sufficiently heated and activated, and it takes time from that temperature to a temperature (300 ° C. or higher) at which the catalyst in the catalytic converter is sufficiently heated and activated. Therefore, the HC desorbed from the adsorbent during this period is exhausted without being sufficiently purified, which poses a problem that the purification performance of the exhaust gas purification device deteriorates.

Therefore, the present invention provides a vehicle exhaust gas purification system that purifies HC even after the exhaust gas temperature rises and HC begins to desorb from the adsorbent until the catalyst in the catalytic converter is sufficiently heated. The purpose is to provide a device.

(Means for Solving the Problems) An automobile exhaust gas purification apparatus of the present invention for achieving the above object is provided with an exhaust gas purification catalyst in an exhaust system, and an H-type mordenite as zeolite is provided upstream of the catalyst. Alternatively, an automobile exhaust gas purification apparatus comprising an adsorbent comprising one or more kinds of catalytic metals supported on a monolithic carrier coated with HY zeolite, wherein the exhaust gas flow section of the monolithic carrier has a length of The catalyst metal is supported on one-third or more of the exhaust gas inflow end.

The catalytic metal supported on the predetermined portion of the monolith carrier is a metal usually used as an exhaust gas purifying catalyst, for example, Cu,
It is possible to select from Pd, Pt, Rh, Fe, Cr, V, etc., and it is particularly preferable to use one that is effective for purification of HC.

As described above, the catalyst metal is supported on one third or more of the length of the exhaust gas flowing portion of the monolith carrier from the exhaust gas inflow end, in other words, of the length of the exhaust gas flowing portion of the monolith carrier. The catalyst metal is not supported at all in the portion from the exhaust gas inflow end to one third. The method of supporting the catalytic metal is
For example, of the length of the exhaust gas flow portion of the monolith carrier, it may be carried on the whole one-third or more from the exhaust gas inflow end, or by further dividing one-third or more from the exhaust gas inflow end. Alternatively, it may be supported on a part thereof.

Further, the catalyst metal to be supported may be one kind or two or more kinds. When supporting two or more kinds, two or more kinds of catalyst metals may be carried together in the same place, or two or more kinds. Each of the above catalytic metals may be supported at different locations.

As the zeolite, H-type mordenite or HY type zeolite is used in terms of adsorption performance.

The zeolite coating can be carried out by repeating the operation of immersing the carrier in a washcoat slurry containing zeolite, drying and firing once or several times, but more preferably coating Na-type zeolite, Na
After changing the ⁺ ions to NH ₄ ⁺ ions, they are heated to form H ⁺ ions to form an H-type zeolite. In the case of mordenite, hydrochloric acid may be used to directly convert Na ⁺ ions into H ⁺ ions.

The catalyst metal can be supported on the zeolite-coated monolithic carrier by immersing a part of the carrier in a solution containing the catalyst metal.

(Operation) In the automobile exhaust gas purification apparatus of the present invention, in the adsorbent using H-type mordenite or HY-type zeolite as the zeolite, from the exhaust gas inflow end of the length of the exhaust gas flowing portion of the monolith carrier Since the catalytic metal is supported after one-third, relatively low temperature, especially 20
The HC purification performance is not lost even at 0 ° C or lower (200 ° C to 150 ° C). Further, since the catalytic metal supported on the adsorbent is heated faster than the catalyst arranged on the downstream side of the adsorbent,
Even when HC starts to desorb from the adsorbent and the catalyst in the catalytic converter is not sufficiently activated, the catalytic metal supported on the adsorbent is sufficiently activated and HC is satisfactorily purified. Moreover, reaction heat is generated when the HC is purified by the metal catalyst, so that the catalyst in the catalytic converter is heated and activation is promoted.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples. In the examples, "parts" means "parts by weight".

Example: An exhaust gas purifying apparatus is manufactured by the following method.

Manufacture of HC adsorbent Cordierite monolith carrier (volume 1.3l, cell number 400 / i
Immerse n ² ) in water, pull it up, and then blow off the water. This was stirred with 100 parts of Na-type mordenite powder, 140 parts of alumina sol (10% by weight) and 30 parts of water, and the pH was adjusted with an Al (NO ₃ ) aqueous solution.
It is immersed in an adjusted Na-type mordenite slurry having a viscosity of about 150 cps, pulled up, the excess slurry is blown off, dried at 100 ° C. for 1 hour, and then calcined at 500 ° C. for 3 hours. The above operation, that is, the immersion in the slurry, the drying, and the calcination are repeated twice more. As a result, Na-type mordenite is coated in a total amount of 140 g / l (value with respect to a carrier volume of 1 l, hereinafter, the amount of mordenite adhered is the same).

Next, the obtained Na-type mordenite-coated monolith carrier is immersed in a 1N ammonium oxide aqueous solution to convert Na ⁺ ions into NH ₄ ⁺ ions. Then, by heating at 300 ° C. for 1 hour, NH ₄ ⁺ ions are further converted into H ⁺ ions. As a result, an HC adsorbent coated with H-type mordenite at a deposition amount of 140 g / l is obtained.

The H-type mordenite coated monolith carrier thus obtained was immersed in 1.0 l of a 0.01 mol / l copper acetate aqueous solution (pH 4.8) at a portion of one-third of the exhaust outflow side, and after pulling up,
After washing with water and drying at 100 ° C for 1 hour, heat at 300 ° C for 1 hour. As a result, 1.0g / l is added to the one-third of the exhaust outlet side.
(Value for the volume of the copper-supported part of the carrier (1.3 × 1/3 l),
Hereinafter, the deposition amount of the catalyst metal is similarly expressed) and copper is supported.

The copper-supported mordenite-coated monolithic carrier thus obtained was supported on a copper-supported portion by immersing it in 1.0 l of an aqueous solution containing 5 g / l of a platinum solution (8p) 45.9 ml and pyromellitic vinegar (2 g / l) 354 ml, to remove platinum. After loading, wash with water in the same manner as loading copper, 100
Drying was performed at ℃ × 1 hour, and heating was performed at 300 ℃ × 1 hour. As a result, 0.5 g / l of platinum is supported on one-third of the exhaust-outflow side, and as shown in FIG. 1, copper and platinum are deposited on the part 2 of the exhaust-outflow-side one-third of the H-type mordenite coat monolith carrier. Thus, the adsorbent 1 carrying is obtained.

Preparation of catalyst In a washcoat slurry prepared by ball milling 100 parts of alumina, 140 parts of alumina sol (10 wt%) and 14 parts of a commercially available aqueous solution of aluminum nitrate together with water and nitric acid, a cordierite monolith carrier (volume:
Soak 1.7l, cell number 40 / in ² ). After pulling up the monolith carrier from the slurry, the excess liquid in the cell of the monolith type carrier is blown off with compressed air, the free water is removed by drying the monolith carrier, and the monolith carrier is dried at 500 ° C. for 1 hour, A carrier in which alumina is coated on a mold carrier is obtained.

Next, this carrier is immersed in an aqueous nitric acid solution of dinitrodiammineplatinum, dried, and calcined at 200 ° C for 1 hour to obtain 1.35 g / l.
Of platinum. Subsequently, the platinum catalyst is immersed in an aqueous rhodium chloride solution, dried, and calcined at 200 ° C. for 1 hour to support 0.15 g / l of rhodium on the carrier to prepare a platinum-rhodium catalyst 5.

As shown in FIG. 2, the HC trapper 3 containing the HC adsorbent 1 produced above is arranged on the upstream side of the engine exhaust system, and the catalytic converter 4 containing the catalyst 5 is arranged on the downstream side. The exhaust gas purification device 6 is obtained.

In addition to the adsorbent according to the present embodiment, as shown in FIG. 3, platinum is loaded on the exhaust gas outflow side one-third portion 7 of the monolith carrier and copper is loaded on the central one-third portion 8 of the monolith carrier. The adsorbent 1'supported may be used as well.

Comparative Example: An exhaust gas purifying apparatus is manufactured by the same method as in the example except that the adsorbent does not support copper and platinum.

Test Example 1 On an engine bench, the HC purification performances of the exhaust gas purification devices of the example and the comparative example were compared. The evaluation was performed by cold start evaluation (starting → idling → acceleration → 60 km / Hr steady running). As a result, the HC reduction rate of Example was 45%, and the HC reduction rate of Comparative Example 1 was 35%.

Test Example 2: As an example product, in the same manner as in the example, a volume of 35c
c, using a cordierite-based monolith carrier having a cell number of 400 / in ² , 140 g / l of H-type mordenite is coated, 1.0 g / l of copper is supported, and 0.5 g / l of platinum is supported, Produce test adsorbent.

As a comparative example product 1, a test adsorbent is manufactured by using the monolith carrier having the same specifications as the example product and by the same method as the comparative example.

As Comparative Example Product 2, a monolith carrier having the same specifications as those of the Example product was used, and the same procedure as in the Example was carried out except that only copper (support amount 1.0 g / l) was supported on the entire carrier as the metal catalyst.
Produce test adsorbent.

As Comparative Example Product 3, a monolith carrier having the same specifications as those of the Example product was used, and a test was conducted in the same manner as in the Example except that only platinum (loading amount: 0.5 g / l) was loaded on the entire carrier as a metal catalyst. Manufacture adsorbents for automobiles.

Using the example product, the comparative example product 1, the comparative example product 2, and the comparative example product 3, the HC purification rate at each exhaust gas temperature is examined. The results are shown in the graph of FIG.

Comparative Examples 2 and 3 (adsorbents in which the catalytic metal is supported on the entire monolith carrier) have no HC purification performance at 200 ° C or lower (Comparative Example 3) or have extremely low HC purification performance ( Comparative example product 2). Contrary to Comparative Examples 2 and 3, Comparative Example 1
(Adsorbent in which the catalytic metal is not supported on the entire monolith carrier) has a slight H at approximately 200 ° C or lower (230 ° C to 150 ° C).
It has only C purification performance (effect of adsorption).

From the graph, it is clear that the example product exhibits the same HC purification rate at each temperature as the comparative product showing the best HC purification rate at that temperature, and has the advantages of each comparative example product.

(Effects of the Invention) In the above-mentioned device for exhaust gas of automobiles of the present invention, in the adsorbent comprising one or more kinds of catalytic metals supported on a monolith carrier coated with H-type mordenite or HY-type zeolite as zeolite, the monolith Of the length of the exhaust gas flow portion of the carrier, since the catalyst metal is supported on one third or more from the exhaust gas inflow end, the catalyst metal is also supported on the part from the exhaust gas inflow end to one third. When the adsorbent used is below 200 ° C, it has no HC purification performance at all, or the HC purification performance is extremely low, whereas it is below 200 ° C (2
It has HC purification performance even at 00 ℃ to 150 ℃. In addition, even at the temperature at which HC begins to desorb from the HC adsorbent, the desorbed HC is satisfactorily purified, and the heat of reaction when the HC is purified by the catalyst on the adsorbent is used to activate the catalyst in the catalytic converter. As a result, the purification performance of HC at a relatively low temperature at which HC starts to desorb from the adsorbent is significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an HC adsorbent manufactured in one embodiment of the present invention, FIG. 2 is a schematic view showing an exhaust gas purifying device manufactured in the embodiment, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a schematic diagram showing the adsorbents produced in the example of FIG. 4, and FIG. 4 is a graph showing the HC purification rates of the HC adsorbents of the present invention and the HC adsorbents of the comparative examples. 1 ... Adsorbent, 5 ... Catalyst 6 ... Exhaust gas purification device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F01N 3/24 ZAB E

Claims (1)

[Claims] 1. A monolith carrier comprising an exhaust gas purifying catalyst in the exhaust system, and H type mordenite or HY type zeolite as a zeolite coated on the upstream side of the catalyst.
An exhaust gas purifying apparatus for an automobile, comprising an adsorbent carrying at least one kind of catalytic metal, wherein the catalyst is provided after one third of the exhaust gas inflow end of the length of the exhaust gas flowing portion of the monolith carrier. An automobile exhaust gas purification apparatus, which is characterized in that a metal is carried.